diff --git a/shared/tree-sitter-extractor/src/extractor/mod.rs b/shared/tree-sitter-extractor/src/extractor/mod.rs
index 436ff9f65a15..b066fbc85b30 100644
--- a/shared/tree-sitter-extractor/src/extractor/mod.rs
+++ b/shared/tree-sitter-extractor/src/extractor/mod.rs
@@ -280,10 +280,11 @@ pub fn location_label(writer: &mut trap::Writer, location: trap::Location) -> tr
 }
 
 /// Extracts the source file at `path`, which is assumed to be canonicalized.
-/// When `yeast_runner` is `Some`, the parsed tree is first transformed
-/// through the supplied yeast `Runner` before TRAP extraction. Building the
-/// `Runner` (which parses YAML and constructs the schema) is the caller's
-/// responsibility, allowing it to be done once and shared across files.
+/// When `desugarer` is `Some`, the parsed tree is first transformed
+/// through the supplied yeast desugarer before TRAP extraction. Building
+/// the desugarer (which parses YAML and constructs the schema) is the
+/// caller's responsibility, allowing it to be done once and shared across
+/// files.
 #[allow(clippy::too_many_arguments)]
 pub fn extract(
     language: &Language,
@@ -295,7 +296,7 @@ pub fn extract(
     path: &Path,
     source: &[u8],
     ranges: &[Range],
-    yeast_runner: Option<&yeast::Runner<'_>>,
+    desugarer: Option<&dyn yeast::Desugarer>,
 ) {
     let path_str = file_paths::normalize_and_transform_path(path, transformer);
     let source_root = std::env::current_dir()
@@ -328,8 +329,8 @@ pub fn extract(
         schema,
     );
 
-    if let Some(yeast_runner) = yeast_runner {
-        let ast = yeast_runner
+    if let Some(desugarer) = desugarer {
+        let ast = desugarer
             .run_from_tree(&tree, source)
             .unwrap_or_else(|e| panic!("Desugaring failed for {path_str}: {e}"));
         traverse_yeast(&ast, &mut visitor);
diff --git a/shared/tree-sitter-extractor/src/extractor/simple.rs b/shared/tree-sitter-extractor/src/extractor/simple.rs
index 6fcd29b03443..9ba6f21778cf 100644
--- a/shared/tree-sitter-extractor/src/extractor/simple.rs
+++ b/shared/tree-sitter-extractor/src/extractor/simple.rs
@@ -13,11 +13,14 @@ pub struct LanguageSpec {
     pub prefix: &'static str,
     pub ts_language: tree_sitter::Language,
     pub node_types: &'static str,
-    /// Optional yeast desugaring configuration. When set, the parsed
-    /// tree is rewritten through yeast before TRAP extraction. The
-    /// config's `output_node_types_yaml` (if set) provides the schema
-    /// used both at runtime (for the rewriter) and for TRAP validation.
-    pub desugar: Option<yeast::DesugaringConfig>,
+    /// Optional desugarer. When set, the parsed tree is rewritten through
+    /// the desugarer before TRAP extraction. The desugarer's
+    /// `output_node_types_yaml()` (if set) provides the schema used both
+    /// at runtime (for the rewriter) and for TRAP validation.
+    ///
+    /// `Box<dyn yeast::Desugarer>` so the shared extractor is agnostic to
+    /// the user-defined context type the desugarer uses internally.
+    pub desugar: Option<Box<dyn yeast::Desugarer>>,
     pub file_globs: Vec<String>,
 }
 
@@ -91,35 +94,22 @@ impl Extractor {
             .collect();
 
         let mut schemas = vec![];
-        let mut yeast_runners = Vec::new();
         for lang in &self.languages {
-            let effective_node_types: String =
-                match lang.desugar.as_ref().and_then(|c| c.output_node_types_yaml) {
-                    Some(yaml) => yeast::node_types_yaml::convert(yaml).map_err(|e| {
-                        std::io::Error::other(format!(
-                            "Failed to convert YAML node-types to JSON for {}: {e}",
-                            lang.prefix
-                        ))
-                    })?,
-                    None => lang.node_types.to_string(),
-                };
-            let schema = node_types::read_node_types_str(lang.prefix, &effective_node_types)?;
-            schemas.push(schema);
-
-            // Build the yeast runner once per language so the YAML schema
-            // isn't re-parsed for every file.
-            let yeast_runner = lang
+            let effective_node_types: String = match lang
                 .desugar
                 .as_ref()
-                .map(|config| yeast::Runner::from_config(lang.ts_language.clone(), config))
-                .transpose()
-                .map_err(|e| {
+                .and_then(|d| d.output_node_types_yaml())
+            {
+                Some(yaml) => yeast::node_types_yaml::convert(yaml).map_err(|e| {
                     std::io::Error::other(format!(
-                        "Failed to build desugaring runner for {}: {e}",
+                        "Failed to convert YAML node-types to JSON for {}: {e}",
                         lang.prefix
                     ))
-                })?;
-            yeast_runners.push(yeast_runner);
+                })?,
+                None => lang.node_types.to_string(),
+            };
+            let schema = node_types::read_node_types_str(lang.prefix, &effective_node_types)?;
+            schemas.push(schema);
         }
 
         // Construct a single globset containing all language globs,
@@ -194,7 +184,7 @@ impl Extractor {
                                     &path,
                                     &source,
                                     &[],
-                                    yeast_runners[i].as_ref(),
+                                    lang.desugar.as_deref(),
                                 );
                                 std::fs::create_dir_all(src_archive_file.parent().unwrap())?;
                                 std::fs::copy(&path, &src_archive_file)?;
diff --git a/shared/yeast-macros/src/lib.rs b/shared/yeast-macros/src/lib.rs
index 07077be51f04..7153cf306443 100644
--- a/shared/yeast-macros/src/lib.rs
+++ b/shared/yeast-macros/src/lib.rs
@@ -121,3 +121,37 @@ pub fn rule(input: TokenStream) -> TokenStream {
         Err(err) => err.to_compile_error().into(),
     }
 }
+
+/// Define a desugaring rule whose transform is a hand-written Rust block.
+///
+/// Use `manual_rule!` when the transform needs control over capture
+/// translation timing — for example, when an outer rule needs to set
+/// state in `ctx` (the `BuildCtx`'s user context) before recursive
+/// translation reaches inner rules that read that state.
+///
+/// ```text
+/// manual_rule!(
+///     (query_pattern field: (_) @name)
+///     {
+///         // `ctx` is a `&mut BuildCtx<'_, C>`; capture variables
+///         // (`name: NodeRef`, etc.) are bound from the query.
+///         let translated = ctx.translate(name)?;
+///         Ok(translated)
+///     }
+/// )
+/// ```
+///
+/// Differences from [`rule!`]:
+/// - Captures are **not** auto-translated before the body runs; they
+///   refer to raw input-schema nodes. Use [`BuildCtx::translate`] (or
+///   [`BuildCtx::translate_opt`]) to translate them when you choose.
+/// - The body is plain Rust returning `Result<Vec<Id>, String>` — no
+///   tree template, no `Ok(...)` wrap.
+#[proc_macro]
+pub fn manual_rule(input: TokenStream) -> TokenStream {
+    let input2: TokenStream2 = input.into();
+    match parse::parse_manual_rule_top(input2) {
+        Ok(output) => output.into(),
+        Err(err) => err.to_compile_error().into(),
+    }
+}
diff --git a/shared/yeast-macros/src/parse.rs b/shared/yeast-macros/src/parse.rs
index 4b27b9804392..fc6031eb39d2 100644
--- a/shared/yeast-macros/src/parse.rs
+++ b/shared/yeast-macros/src/parse.rs
@@ -121,9 +121,9 @@ fn parse_query_fields(tokens: &mut Tokens) -> Result<Vec<TokenStream>> {
         std::collections::HashMap::new();
     let mut bare_children: Vec<TokenStream> = Vec::new();
     let push_field_elem = |order: &mut Vec<String>,
-                               map: &mut std::collections::HashMap<String, Vec<TokenStream>>,
-                               name: String,
-                               elem: TokenStream| {
+                           map: &mut std::collections::HashMap<String, Vec<TokenStream>>,
+                           name: String,
+                           elem: TokenStream| {
         if !map.contains_key(&name) {
             order.push(name.clone());
             map.insert(name, vec![elem]);
@@ -160,8 +160,7 @@ fn parse_query_fields(tokens: &mut Tokens) -> Result<Vec<TokenStream>> {
             } else {
                 let child = if peek_is_at(tokens) {
                     tokens.next();
-                    let capture_name =
-                        expect_ident(tokens, "expected capture name after @")?;
+                    let capture_name = expect_ident(tokens, "expected capture name after @")?;
                     let name_str = capture_name.to_string();
                     quote! {
                         yeast::query::QueryNode::Capture {
@@ -296,10 +295,10 @@ fn parse_query_list(tokens: &mut Tokens) -> Result<Vec<TokenStream>> {
 // tree! / trees! parsing — direct code generation against BuildCtx
 // ---------------------------------------------------------------------------
 
-const IMPLICIT_CTX: &str = "__yeast_ctx";
+const IMPLICIT_CTX: &str = "ctx";
 
 /// Determine the context identifier: either explicit `ctx,` or the implicit
-/// `__yeast_ctx` from an enclosing `rule!`.
+/// `ctx` from an enclosing `rule!`.
 fn parse_ctx_or_implicit(tokens: &mut Tokens) -> Ident {
     // Check if first token is an ident followed by a comma
     let mut lookahead = tokens.clone();
@@ -359,7 +358,7 @@ fn parse_direct_node(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStream> {
         Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Brace => {
             let group = expect_group(tokens, Delimiter::Brace)?;
             let expr = group.stream();
-            Ok(quote! { ::std::convert::Into::<usize>::into(#expr) })
+            Ok(quote! { ::std::convert::Into::<usize>::into({ #expr }) })
         }
         Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Parenthesis => {
             let group = expect_group(tokens, Delimiter::Parenthesis)?;
@@ -396,7 +395,7 @@ fn parse_direct_node_inner(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStre
         let expr = group.stream();
         return Ok(quote! {
             {
-                let __expr = (#expr);
+                let __expr = { #expr };
                 let __value = yeast::YeastDisplay::yeast_to_string(&__expr, &*#ctx.ast);
                 let __source_range = yeast::YeastSourceRange::yeast_source_range(&__expr, &*#ctx.ast);
                 #ctx.literal_with_source_range(#kind_str, &__value, __source_range)
@@ -420,7 +419,11 @@ fn parse_direct_node_inner(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStre
     // Named fields — compute each value into a temp, then reference it
     while peek_is_field(tokens) {
         let field_name = expect_ident(tokens, "expected field name")?;
-        let field_str = field_name.to_string().strip_prefix("r#").unwrap_or(&field_name.to_string()).to_string();
+        let field_str = field_name
+            .to_string()
+            .strip_prefix("r#")
+            .unwrap_or(&field_name.to_string())
+            .to_string();
         expect_punct(tokens, ':', "expected `:` after field name")?;
         let temp = Ident::new(
             &format!("__field_{field_str}_{field_counter}"),
@@ -438,7 +441,8 @@ fn parse_direct_node_inner(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStre
                 // Determine if a chain (.map(..)) follows the `{}` group.
                 let mut after = tokens.clone();
                 after.next(); // skip the brace group
-                let has_chain = matches!(after.peek(), Some(TokenTree::Punct(p)) if p.as_char() == '.');
+                let has_chain =
+                    matches!(after.peek(), Some(TokenTree::Punct(p)) if p.as_char() == '.');
 
                 if is_splice || has_chain {
                     let group = expect_group(tokens, Delimiter::Brace)?;
@@ -448,11 +452,11 @@ fn parse_direct_node_inner(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStre
                         inner.next(); // consume second .
                         let expr: TokenStream = inner.collect();
                         quote! {
-                            (#expr).into_iter().map(::std::convert::Into::<usize>::into)
+                            { #expr }.into_iter().map(::std::convert::Into::<usize>::into)
                         }
                     } else {
                         let expr = group.stream();
-                        quote! { (#expr).into_iter() }
+                        quote! { { #expr }.into_iter() }
                     };
                     let chained = parse_chain_suffix(tokens, ctx, base)?;
                     stmts.push(quote! {
@@ -506,11 +510,7 @@ fn parse_direct_node_inner(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStre
 /// Each call expects the receiver to be an iterator. The `base` argument
 /// should therefore already be an iterator (use `.into_iter()` on it before
 /// calling this function).
-fn parse_chain_suffix(
-    tokens: &mut Tokens,
-    ctx: &Ident,
-    base: TokenStream,
-) -> Result<TokenStream> {
+fn parse_chain_suffix(tokens: &mut Tokens, ctx: &Ident, base: TokenStream) -> Result<TokenStream> {
     let mut current = base;
     while matches!(tokens.peek(), Some(TokenTree::Punct(p)) if p.as_char() == '.') {
         tokens.next(); // consume .
@@ -608,7 +608,8 @@ fn parse_direct_list(tokens: &mut Tokens, ctx: &Ident) -> Result<Vec<TokenStream
         // {expr} or {..expr} (with optional .chain) — single node or splice
         if peek_is_group(tokens, Delimiter::Brace) {
             let group = expect_group(tokens, Delimiter::Brace)?;
-            let has_chain = matches!(tokens.peek(), Some(TokenTree::Punct(p)) if p.as_char() == '.');
+            let has_chain =
+                matches!(tokens.peek(), Some(TokenTree::Punct(p)) if p.as_char() == '.');
             let mut inner = group.stream().into_iter().peekable();
             let is_splice = peek_is_dotdot(&inner);
             if is_splice || has_chain {
@@ -617,11 +618,11 @@ fn parse_direct_list(tokens: &mut Tokens, ctx: &Ident) -> Result<Vec<TokenStream
                     inner.next(); // consume second .
                     let expr: TokenStream = inner.collect();
                     quote! {
-                        (#expr).into_iter().map(::std::convert::Into::<usize>::into)
+                        { #expr }.into_iter().map(::std::convert::Into::<usize>::into)
                     }
                 } else {
                     let expr = group.stream();
-                    quote! { (#expr).into_iter() }
+                    quote! { { #expr }.into_iter() }
                 };
                 let chained = parse_chain_suffix(tokens, ctx, base)?;
                 items.push(quote! {
@@ -630,7 +631,7 @@ fn parse_direct_list(tokens: &mut Tokens, ctx: &Ident) -> Result<Vec<TokenStream
             } else {
                 let expr = group.stream();
                 items.push(quote! {
-                    __nodes.push(::std::convert::Into::<usize>::into(#expr));
+                    __nodes.push(::std::convert::Into::<usize>::into({ #expr }));
                 });
             }
             continue;
@@ -888,10 +889,117 @@ pub fn parse_rule_top(input: TokenStream) -> Result<TokenStream> {
     Ok(quote! {
         {
             let __query = #query_code;
-            yeast::Rule::new(__query, Box::new(|__ast: &mut yeast::Ast, __captures: yeast::captures::Captures, __fresh: &yeast::tree_builder::FreshScope, __source_range: Option<tree_sitter::Range>| {
+            yeast::Rule::new(__query, Box::new(|__ast: &mut yeast::Ast, mut __captures: yeast::captures::Captures, __fresh: &yeast::tree_builder::FreshScope, __source_range: Option<tree_sitter::Range>, __user_ctx: &mut _, __translator: yeast::TranslatorHandle<'_, _>| {
+                // Auto-translation prefix: recursively translate every
+                // captured node before invoking the user's transform body.
+                // For OneShot rules this preserves the legacy behaviour
+                // (input-schema captures translated to output-schema
+                // nodes); for Repeating rules it is a no-op.
+                __translator.auto_translate_captures(&mut __captures, __ast, __user_ctx)?;
+                #(#bindings)*
+                let mut #ctx_ident = yeast::build::BuildCtx::with_translator(__ast, &__captures, __fresh, __source_range, __user_ctx, __translator);
+                let __result: Vec<usize> = { #transform_body };
+                Ok(__result)
+            }))
+        }
+    })
+}
+
+/// Parse `manual_rule!( query { body } )`.
+///
+/// Like [`parse_rule_top`] but:
+/// - Expects a Rust block `{ ... }` after the query (no `=>` arrow).
+/// - Generates code that does NOT auto-translate captures before
+///   running the body. Capture variables refer to raw (input-schema)
+///   nodes; the body is responsible for explicit translation via
+///   `ctx.translate(...)`.
+/// - The body is included verbatim and must evaluate to
+///   `Result<Vec<usize>, String>`.
+pub fn parse_manual_rule_top(input: TokenStream) -> Result<TokenStream> {
+    let mut tokens = input.into_iter().peekable();
+
+    // Collect query tokens up to the body block `{ ... }`.
+    let mut query_tokens = Vec::new();
+    loop {
+        match tokens.peek() {
+            None => {
+                return Err(syn::Error::new(
+                    Span::call_site(),
+                    "expected a Rust block `{ ... }` after the query in manual_rule!",
+                ))
+            }
+            Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Brace => break,
+            _ => {
+                query_tokens.push(tokens.next().unwrap());
+            }
+        }
+    }
+
+    let query_stream: TokenStream = query_tokens.into_iter().collect();
+
+    // Extract captures from the query (same as in `rule!`).
+    let captures = extract_captures(&query_stream);
+
+    // Parse the query into the QueryNode-building expression.
+    let query_code = parse_query_top(query_stream)?;
+
+    // Generate capture bindings (same as in `rule!`).
+    let ctx_ident = Ident::new(IMPLICIT_CTX, Span::call_site());
+    let bindings: Vec<TokenStream> = captures
+        .iter()
+        .map(|cap| {
+            let name = Ident::new(&cap.name, Span::call_site());
+            let name_str = &cap.name;
+            match cap.multiplicity {
+                CaptureMultiplicity::Repeated => quote! {
+                    let #name: Vec<yeast::NodeRef> = __captures.get_all(#name_str)
+                        .into_iter()
+                        .map(yeast::NodeRef)
+                        .collect();
+                },
+                CaptureMultiplicity::Optional => quote! {
+                    let #name: Option<yeast::NodeRef> =
+                        __captures.get_opt(#name_str).map(yeast::NodeRef);
+                },
+                CaptureMultiplicity::Single => quote! {
+                    let #name: yeast::NodeRef =
+                        yeast::NodeRef(__captures.get_var(#name_str).unwrap());
+                },
+            }
+        })
+        .collect();
+
+    // Consume the body block.
+    let body_group = match tokens.next() {
+        Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Brace => g,
+        other => {
+            return Err(syn::Error::new(
+                Span::call_site(),
+                format!(
+                    "expected a Rust block `{{ ... }}` after the query in manual_rule!, found: {other:?}"
+                ),
+            ))
+        }
+    };
+    let body_stream = body_group.stream();
+
+    // No tokens should follow the body.
+    if let Some(tok) = tokens.next() {
+        return Err(syn::Error::new_spanned(
+            tok,
+            "unexpected token after manual_rule! body",
+        ));
+    }
+
+    Ok(quote! {
+        {
+            let __query = #query_code;
+            yeast::Rule::new(__query, Box::new(|__ast: &mut yeast::Ast, __captures: yeast::captures::Captures, __fresh: &yeast::tree_builder::FreshScope, __source_range: Option<tree_sitter::Range>, __user_ctx: &mut _, __translator: yeast::TranslatorHandle<'_, _>| {
+                // No auto-translate prefix for manual rules — the body
+                // is responsible for translating captures explicitly.
                 #(#bindings)*
-                let mut #ctx_ident = yeast::build::BuildCtx::with_source_range(__ast, &__captures, __fresh, __source_range);
-                #transform_body
+                let mut #ctx_ident = yeast::build::BuildCtx::with_translator(__ast, &__captures, __fresh, __source_range, __user_ctx, __translator);
+                #body_stream
             }))
         }
     })
diff --git a/shared/yeast/doc/yeast.md b/shared/yeast/doc/yeast.md
index 823bf1c19425..1700029b43c0 100644
--- a/shared/yeast/doc/yeast.md
+++ b/shared/yeast/doc/yeast.md
@@ -265,7 +265,21 @@ occurrences of the same `$name` within one `BuildCtx` share the same value:
 )
 ```
 
-`{..expr}` splices a `Vec<Id>` (or any iterable of `Id`):
+The contents of `{…}` are treated as a Rust block, so multi-statement
+expressions (with `let` bindings) work too:
+
+```rust
+(assignment
+    left: {tmp}
+    right: {
+        let lit = ctx.literal("integer", "0");
+        tree!((binary_expr op: (operator "+") left: {tmp} right: {lit}))
+    })
+```
+
+`{..expr}` splices a `Vec<Id>` (or any iterable of `Id`); the contents
+are likewise a Rust block, so the splice can be the result of arbitrary
+computation:
 
 ```rust
 yeast::trees!(ctx,
diff --git a/shared/yeast/src/bin/main.rs b/shared/yeast/src/bin/main.rs
index 975c8e8b25f5..978be21cc003 100644
--- a/shared/yeast/src/bin/main.rs
+++ b/shared/yeast/src/bin/main.rs
@@ -20,7 +20,7 @@ fn main() {
     let args = Cli::parse();
     let language = get_language(&args.language);
     let source = std::fs::read_to_string(&args.file).unwrap();
-    let runner = yeast::Runner::new(language, &[]);
+    let runner: yeast::Runner = yeast::Runner::new(language, &[]);
     let ast = runner.run(&source).unwrap();
     println!("{}", ast.print(&source, ast.get_root()));
 }
diff --git a/shared/yeast/src/build.rs b/shared/yeast/src/build.rs
index d0f1394ca6d9..c7c605305994 100644
--- a/shared/yeast/src/build.rs
+++ b/shared/yeast/src/build.rs
@@ -2,28 +2,60 @@ use std::collections::BTreeMap;
 
 use crate::captures::Captures;
 use crate::tree_builder::FreshScope;
-use crate::{Ast, FieldId, Id, NodeContent};
+use crate::{Ast, FieldId, Id, NodeContent, TranslatorHandle};
 
 /// Context for building new AST nodes during a transformation.
 ///
 /// Used by the `tree!` and `trees!` macros. Holds a mutable reference to the
-/// AST, a reference to the captures from a query match, and a `FreshScope` for
-/// generating unique identifiers.
-pub struct BuildCtx<'a> {
+/// AST, a reference to the captures from a query match, a `FreshScope` for
+/// generating unique identifiers, and a mutable reference to a user-defined
+/// context of type `C`.
+///
+/// The user context `C` is shared across rules via the framework's driver:
+/// outer rules can write to it before recursive translation, and inner rules
+/// can read (or further mutate) it during their transforms. The framework
+/// snapshots and restores the user context around each rule application, so
+/// mutations made by a rule are visible to its descendants (via recursive
+/// translation) but not to its parent's siblings.
+///
+/// `BuildCtx` implements [`Deref`] and [`DerefMut`] targeting `C`, so user
+/// context fields are accessible as `ctx.my_field` directly (provided they
+/// don't collide with `BuildCtx`'s own fields like `ast`, `captures`, etc.).
+///
+/// The default `C = ()` means rules that don't need any user context don't
+/// pay any cost.
+///
+/// When constructed by the framework (via the rule! macro), `BuildCtx` also
+/// carries a [`TranslatorHandle`] that the [`translate`] method delegates
+/// to. When constructed by hand (e.g. in tests), the translator is `None`
+/// and [`translate`] returns an error.
+pub struct BuildCtx<'a, C: 'a = ()> {
     pub ast: &'a mut Ast,
     pub captures: &'a Captures,
     pub fresh: &'a FreshScope,
     /// Source range of the matched node, inherited by synthetic nodes.
     pub source_range: Option<tree_sitter::Range>,
+    /// User-supplied context, accessible directly via `ctx.field` (via Deref).
+    pub user_ctx: &'a mut C,
+    /// Optional translator handle, populated when the context is built by
+    /// the framework's rule driver. None when the context is built by hand.
+    pub(crate) translator: Option<TranslatorHandle<'a, C>>,
 }
 
-impl<'a> BuildCtx<'a> {
-    pub fn new(ast: &'a mut Ast, captures: &'a Captures, fresh: &'a FreshScope) -> Self {
+impl<'a, C> BuildCtx<'a, C> {
+    pub fn new(
+        ast: &'a mut Ast,
+        captures: &'a Captures,
+        fresh: &'a FreshScope,
+        user_ctx: &'a mut C,
+    ) -> Self {
         Self {
             ast,
             captures,
             fresh,
             source_range: None,
+            user_ctx,
+            translator: None,
         }
     }
 
@@ -32,12 +64,35 @@ impl<'a> BuildCtx<'a> {
         captures: &'a Captures,
         fresh: &'a FreshScope,
         source_range: Option<tree_sitter::Range>,
+        user_ctx: &'a mut C,
+    ) -> Self {
+        Self {
+            ast,
+            captures,
+            fresh,
+            source_range,
+            user_ctx,
+            translator: None,
+        }
+    }
+
+    /// Construct a `BuildCtx` carrying a translator handle. Used by the
+    /// `rule!` macro to enable [`translate`] inside rule transforms.
+    pub fn with_translator(
+        ast: &'a mut Ast,
+        captures: &'a Captures,
+        fresh: &'a FreshScope,
+        source_range: Option<tree_sitter::Range>,
+        user_ctx: &'a mut C,
+        translator: TranslatorHandle<'a, C>,
     ) -> Self {
         Self {
             ast,
             captures,
             fresh,
             source_range,
+            user_ctx,
+            translator: Some(translator),
         }
     }
 
@@ -113,3 +168,52 @@ impl<'a> BuildCtx<'a> {
         self.ast.prepend_field_child(node_id, field_id, value_id);
     }
 }
+
+impl<C: Clone> BuildCtx<'_, C> {
+    /// Recursively translate a node via the framework's rule machinery.
+    /// In a OneShot phase, applies OneShot rules to the given node and
+    /// returns the resulting node ids. In a Repeating phase, errors
+    /// (translation is not meaningful when input and output share a
+    /// schema).
+    ///
+    /// Accepts any value convertible to [`Id`] (including [`crate::NodeRef`]),
+    /// so manual rules can pass capture bindings directly without unwrapping.
+    ///
+    /// Errors if this `BuildCtx` was constructed by hand (without a
+    /// translator handle) — for example, in unit tests that don't go
+    /// through the rule driver.
+    pub fn translate<I: Into<Id>>(&mut self, id: I) -> Result<Vec<Id>, String> {
+        let id = id.into();
+        match &self.translator {
+            Some(t) => t.translate(self.ast, self.user_ctx, id),
+            None => Err("translate() called on a BuildCtx without a translator handle".into()),
+        }
+    }
+
+    /// Translate an optional capture, returning the first translated id or
+    /// `None`. Convenience for `?`-quantifier captures (`Option<NodeRef>`).
+    ///
+    /// If the underlying translation produces multiple ids for a single
+    /// input, only the first is returned. For most use cases (e.g.
+    /// translating a single type annotation) this is what you want; if
+    /// you need all ids, use [`translate`] directly.
+    pub fn translate_opt<I: Into<Id>>(&mut self, id: Option<I>) -> Result<Option<Id>, String> {
+        match id {
+            Some(id) => Ok(self.translate(id)?.into_iter().next()),
+            None => Ok(None),
+        }
+    }
+}
+
+impl<C> std::ops::Deref for BuildCtx<'_, C> {
+    type Target = C;
+    fn deref(&self) -> &C {
+        &*self.user_ctx
+    }
+}
+
+impl<C> std::ops::DerefMut for BuildCtx<'_, C> {
+    fn deref_mut(&mut self) -> &mut C {
+        &mut *self.user_ctx
+    }
+}
diff --git a/shared/yeast/src/dump.rs b/shared/yeast/src/dump.rs
index d046c192053d..be496d40bd5b 100644
--- a/shared/yeast/src/dump.rs
+++ b/shared/yeast/src/dump.rs
@@ -53,12 +53,7 @@ pub fn dump_ast_with_options(
 ///
 /// Any node that does not match the expected type set for its parent field is
 /// rendered with a trailing `" <-- ERROR: ..."` annotation on the same line.
-pub fn dump_ast_with_type_errors(
-    ast: &Ast,
-    root: usize,
-    source: &str,
-    schema: &Schema,
-) -> String {
+pub fn dump_ast_with_type_errors(ast: &Ast, root: usize, source: &str, schema: &Schema) -> String {
     dump_ast_with_type_errors_and_options(ast, root, source, schema, &DumpOptions::default())
 }
 
@@ -74,7 +69,15 @@ pub fn dump_ast_with_type_errors_and_options(
     options: &DumpOptions,
 ) -> String {
     let mut out = String::new();
-    dump_node(ast, root, source, options, 0, Some((schema, None, None)), &mut out);
+    dump_node(
+        ast,
+        root,
+        source,
+        options,
+        0,
+        Some((schema, None, None)),
+        &mut out,
+    );
     out
 }
 
@@ -232,8 +235,8 @@ fn dump_node(
         }
         let field_name = ast.field_name_for_id(field_id).unwrap_or("?");
         let child_type_check = type_check.map(|(schema, _, _)| {
-            let expected = expected_for_field(schema, node.kind_name(), field_id)
-                .or(Some(EMPTY_NODE_TYPES));
+            let expected =
+                expected_for_field(schema, node.kind_name(), field_id).or(Some(EMPTY_NODE_TYPES));
             let parent_field = Some((node.kind_name(), field_name));
             (schema, expected, parent_field)
         });
diff --git a/shared/yeast/src/lib.rs b/shared/yeast/src/lib.rs
index 9c3a4ad41141..e0fffc551f34 100644
--- a/shared/yeast/src/lib.rs
+++ b/shared/yeast/src/lib.rs
@@ -16,7 +16,7 @@ pub mod schema;
 pub mod tree_builder;
 mod visitor;
 
-pub use yeast_macros::{query, rule, tree, trees};
+pub use yeast_macros::{manual_rule, query, rule, tree, trees};
 
 use captures::Captures;
 pub use cursor::Cursor;
@@ -297,7 +297,9 @@ impl Ast {
     /// Returns the source text for `id`, resolving `NodeContent::Range`
     /// against the stored source bytes when available.
     pub fn source_text(&self, id: Id) -> String {
-        let Some(node) = self.get_node(id) else { return String::new(); };
+        let Some(node) = self.get_node(id) else {
+            return String::new();
+        };
         let read_range = |range: &tree_sitter::Range| {
             let start = range.start_byte;
             let end = range.end_byte;
@@ -488,7 +490,10 @@ impl Ast {
 
     /// Prepend a child id to the given field of the given node.
     pub fn prepend_field_child(&mut self, node_id: Id, field_id: FieldId, value_id: Id) {
-        let node = self.nodes.get_mut(node_id).expect("prepend_field_child: invalid node id");
+        let node = self
+            .nodes
+            .get_mut(node_id)
+            .expect("prepend_field_child: invalid node id");
         node.fields.entry(field_id).or_default().insert(0, value_id);
     }
 
@@ -700,18 +705,118 @@ impl From<tree_sitter::Range> for NodeContent {
     }
 }
 
-/// The transform function for a rule: takes the AST, captured variables, a
-/// fresh-name scope, and the source range of the matched node, and returns
-/// the IDs of the replacement nodes.
-pub type Transform = Box<
-    dyn Fn(&mut Ast, Captures, &tree_builder::FreshScope, Option<tree_sitter::Range>) -> Vec<Id>
+/// A handle that lets a rule transform recursively translate AST nodes via
+/// the framework's rule machinery. Constructed by the driver and passed as
+/// the last argument of every [`Transform`] invocation.
+///
+/// The `rule!` macro uses [`TranslatorHandle::auto_translate_captures`] in
+/// its generated prefix to translate captures before running the user's
+/// transform body. Manually-written transforms (using [`Rule::new`]
+/// directly) can call [`TranslatorHandle::translate`] selectively on
+/// specific node ids to control when translation happens.
+pub struct TranslatorHandle<'a, C> {
+    inner: TranslatorImpl<'a, C>,
+}
+
+/// Internal phase-specific translation state. Kept private — callers
+/// interact with [`TranslatorHandle`] only.
+enum TranslatorImpl<'a, C> {
+    /// OneShot phase translator: recursively applies OneShot rules.
+    OneShot {
+        index: &'a RuleIndex<'a, C>,
+        fresh: &'a tree_builder::FreshScope,
+        rewrite_depth: usize,
+        /// The id of the node the current rule is matching. Used by
+        /// [`auto_translate_captures`] to avoid infinite recursion when a
+        /// rule captures its own match root (e.g. via `(_) @_`).
+        matched_root: Id,
+    },
+    /// Repeating phase translator: translation is not meaningful here
+    /// (input and output schemas are the same). [`translate`] errors;
+    /// [`auto_translate_captures`] is a no-op so the macro's auto-prefix
+    /// works unchanged for Repeating rules.
+    Repeating,
+}
+
+impl<'a, C: Clone> TranslatorHandle<'a, C> {
+    /// Recursively apply OneShot rules to `id` and return the resulting
+    /// node ids. Errors in a Repeating phase (where translation is not
+    /// meaningful).
+    pub fn translate(&self, ast: &mut Ast, user_ctx: &mut C, id: Id) -> Result<Vec<Id>, String> {
+        match &self.inner {
+            TranslatorImpl::OneShot {
+                index,
+                fresh,
+                rewrite_depth,
+                ..
+            } => apply_one_shot_rules_inner(index, ast, user_ctx, id, fresh, rewrite_depth + 1),
+            TranslatorImpl::Repeating => {
+                Err("translate() is not available in a Repeating phase".into())
+            }
+        }
+    }
+
+    /// Translate every captured node in `captures` in place (OneShot phase
+    /// only). In a Repeating phase this is a no-op — Repeating rules
+    /// receive raw captures.
+    ///
+    /// Used by the `rule!` macro's generated prefix to preserve the
+    /// pre-existing "auto-translate captures before running the transform
+    /// body" behavior. Manually-written transforms typically translate
+    /// captures selectively via [`translate`] instead.
+    ///
+    /// To avoid infinite recursion, a capture whose id matches the rule's
+    /// matched root (e.g. from a `(_) @_` pattern) is left unchanged.
+    pub fn auto_translate_captures(
+        &self,
+        captures: &mut Captures,
+        ast: &mut Ast,
+        user_ctx: &mut C,
+    ) -> Result<(), String> {
+        match &self.inner {
+            TranslatorImpl::OneShot { matched_root, .. } => {
+                let root = *matched_root;
+                captures.try_map_all_captures(|cid| {
+                    if cid == root {
+                        Ok(vec![cid])
+                    } else {
+                        self.translate(ast, user_ctx, cid)
+                    }
+                })
+            }
+            TranslatorImpl::Repeating => Ok(()),
+        }
+    }
+}
+
+/// The transform function for a rule.
+///
+/// Takes the AST, the (raw, untranslated) captured variables, a fresh-name
+/// scope, the source range of the matched node, a mutable reference to the
+/// user context of type `C`, and a [`TranslatorHandle`] for recursively
+/// translating nodes. Returns the IDs of the replacement nodes, or an
+/// error message if the transform could not be completed.
+///
+/// Transforms produced by [`Rule::new`] receive **raw** captures and must
+/// translate them themselves (via the handle). Transforms produced by the
+/// `rule!` macro have an auto-translation prefix injected for backward
+/// compatibility.
+pub type Transform<C = ()> = Box<
+    dyn Fn(
+            &mut Ast,
+            Captures,
+            &tree_builder::FreshScope,
+            Option<tree_sitter::Range>,
+            &mut C,
+            TranslatorHandle<'_, C>,
+        ) -> Result<Vec<Id>, String>
         + Send
         + Sync,
 >;
 
-pub struct Rule {
+pub struct Rule<C = ()> {
     query: QueryNode,
-    transform: Transform,
+    transform: Transform<C>,
     /// If true, after this rule fires on a node the engine will try to
     /// re-apply this same rule on the result root. Defaults to false:
     /// each rule fires at most once on a given node, which prevents
@@ -719,8 +824,8 @@ pub struct Rule {
     repeated: bool,
 }
 
-impl Rule {
-    pub fn new(query: QueryNode, transform: Transform) -> Self {
+impl<C> Rule<C> {
+    pub fn new(query: QueryNode, transform: Transform<C>) -> Self {
         Self {
             query,
             transform,
@@ -742,9 +847,13 @@ impl Rule {
         ast: &mut Ast,
         node: Id,
         fresh: &tree_builder::FreshScope,
+        user_ctx: &mut C,
+        translator: TranslatorHandle<'_, C>,
     ) -> Result<Option<Vec<Id>>, String> {
         match self.try_match(ast, node)? {
-            Some(captures) => Ok(Some(self.run_transform(ast, captures, node, fresh))),
+            Some(captures) => Ok(Some(
+                self.run_transform(ast, captures, node, fresh, user_ctx, translator)?,
+            )),
             None => Ok(None),
         }
     }
@@ -768,29 +877,31 @@ impl Rule {
         captures: Captures,
         node: Id,
         fresh: &tree_builder::FreshScope,
-    ) -> Vec<Id> {
+        user_ctx: &mut C,
+        translator: TranslatorHandle<'_, C>,
+    ) -> Result<Vec<Id>, String> {
         fresh.next_scope();
         let source_range = ast.get_node(node).and_then(|n| match n.content {
             NodeContent::Range(r) => Some(r),
             _ => n.source_range,
         });
-        (self.transform)(ast, captures, fresh, source_range)
+        (self.transform)(ast, captures, fresh, source_range, user_ctx, translator)
     }
 }
 
 const MAX_REWRITE_DEPTH: usize = 100;
 
 /// Index of rules by their root query kind for fast lookup.
-struct RuleIndex<'a> {
+struct RuleIndex<'a, C> {
     /// Rules indexed by root node kind name.
-    by_kind: BTreeMap<&'static str, Vec<&'a Rule>>,
+    by_kind: BTreeMap<&'static str, Vec<&'a Rule<C>>>,
     /// Rules with wildcard queries (Any) that apply to all nodes.
-    wildcard: Vec<&'a Rule>,
+    wildcard: Vec<&'a Rule<C>>,
 }
 
-impl<'a> RuleIndex<'a> {
-    fn new(rules: &'a [Rule]) -> Self {
-        let mut by_kind: BTreeMap<&'static str, Vec<&'a Rule>> = BTreeMap::new();
+impl<'a, C> RuleIndex<'a, C> {
+    fn new(rules: &'a [Rule<C>]) -> Self {
+        let mut by_kind: BTreeMap<&'static str, Vec<&'a Rule<C>>> = BTreeMap::new();
         let mut wildcard = Vec::new();
         for rule in rules {
             match rule.query.root_kind() {
@@ -801,7 +912,7 @@ impl<'a> RuleIndex<'a> {
         Self { by_kind, wildcard }
     }
 
-    fn rules_for_kind(&self, kind: &str) -> impl Iterator<Item = &&'a Rule> {
+    fn rules_for_kind(&self, kind: &str) -> impl Iterator<Item = &&'a Rule<C>> {
         self.by_kind
             .get(kind)
             .into_iter()
@@ -810,23 +921,25 @@ impl<'a> RuleIndex<'a> {
     }
 }
 
-fn apply_repeating_rules(
-    rules: &[Rule],
+fn apply_repeating_rules<C: Clone>(
+    rules: &[Rule<C>],
     ast: &mut Ast,
+    user_ctx: &mut C,
     id: Id,
     fresh: &tree_builder::FreshScope,
 ) -> Result<Vec<Id>, String> {
     let index = RuleIndex::new(rules);
-    apply_repeating_rules_inner(&index, ast, id, fresh, 0, None)
+    apply_repeating_rules_inner(&index, ast, user_ctx, id, fresh, 0, None)
 }
 
-fn apply_repeating_rules_inner(
-    index: &RuleIndex,
+fn apply_repeating_rules_inner<C: Clone>(
+    index: &RuleIndex<C>,
     ast: &mut Ast,
+    user_ctx: &mut C,
     id: Id,
     fresh: &tree_builder::FreshScope,
     rewrite_depth: usize,
-    skip_rule: Option<*const Rule>,
+    skip_rule: Option<*const Rule<C>>,
 ) -> Result<Vec<Id>, String> {
     if rewrite_depth > MAX_REWRITE_DEPTH {
         return Err(format!(
@@ -837,11 +950,23 @@ fn apply_repeating_rules_inner(
 
     let node_kind = ast.get_node(id).map(|n| n.kind()).unwrap_or("");
     for rule in index.rules_for_kind(node_kind) {
-        let rule_ptr = *rule as *const Rule;
+        let rule_ptr = *rule as *const Rule<C>;
         if Some(rule_ptr) == skip_rule {
             continue;
         }
-        if let Some(result_node) = rule.try_rule(ast, id, fresh)? {
+        // Snapshot the user context before invoking the rule so that any
+        // mutations the rule makes are visible during recursive translation
+        // of its result, but not leaked to the parent's siblings.
+        let snapshot = user_ctx.clone();
+        // Repeating rules don't need a real translator: their captures
+        // aren't auto-translated (Repeating preserves the input schema),
+        // and `ctx.translate(id)` errors if invoked from a Repeating
+        // transform.
+        let translator = TranslatorHandle {
+            inner: TranslatorImpl::Repeating,
+        };
+        let try_result = rule.try_rule(ast, id, fresh, user_ctx, translator)?;
+        if let Some(result_node) = try_result {
             // For non-repeated rules, suppress further application of *this*
             // rule on the result root, so a rule whose output matches its own
             // query doesn't loop. Other rules and child traversal are
@@ -852,14 +977,19 @@ fn apply_repeating_rules_inner(
                 results.extend(apply_repeating_rules_inner(
                     index,
                     ast,
+                    user_ctx,
                     node,
                     fresh,
                     rewrite_depth + 1,
                     next_skip,
                 )?);
             }
+            *user_ctx = snapshot;
             return Ok(results);
         }
+        // Rule didn't match; restore any speculative changes (none expected
+        // since try_rule only mutates on match, but be defensive).
+        *user_ctx = snapshot;
     }
 
     // Take the parent's fields by ownership: the recursion will rewrite
@@ -874,7 +1004,15 @@ fn apply_repeating_rules_inner(
     for children in fields.values_mut() {
         let mut new_children: Option<Vec<Id>> = None;
         for (i, &child_id) in children.iter().enumerate() {
-            let result = apply_repeating_rules_inner(index, ast, child_id, fresh, rewrite_depth, None)?;
+            let result = apply_repeating_rules_inner(
+                index,
+                ast,
+                user_ctx,
+                child_id,
+                fresh,
+                rewrite_depth,
+                None,
+            )?;
             let unchanged = result.len() == 1 && result[0] == child_id;
             match (&mut new_children, unchanged) {
                 (None, true) => {} // unchanged so far, no allocation needed
@@ -903,24 +1041,25 @@ fn apply_repeating_rules_inner(
 /// each visited node, recursion proceeds only through captured nodes (not
 /// through the input node's children directly), and an error is returned if
 /// no rule matches a visited node.
-fn apply_one_shot_rules(
-    rules: &[Rule],
+fn apply_one_shot_rules<C: Clone>(
+    rules: &[Rule<C>],
     ast: &mut Ast,
+    user_ctx: &mut C,
     id: Id,
     fresh: &tree_builder::FreshScope,
 ) -> Result<Vec<Id>, String> {
     let index = RuleIndex::new(rules);
-    apply_one_shot_rules_inner(&index, ast, id, fresh, 0)
+    apply_one_shot_rules_inner(&index, ast, user_ctx, id, fresh, 0)
 }
 
-fn apply_one_shot_rules_inner(
-    index: &RuleIndex,
+fn apply_one_shot_rules_inner<C: Clone>(
+    index: &RuleIndex<C>,
     ast: &mut Ast,
+    user_ctx: &mut C,
     id: Id,
     fresh: &tree_builder::FreshScope,
     rewrite_depth: usize,
 ) -> Result<Vec<Id>, String> {
-
     if rewrite_depth > MAX_REWRITE_DEPTH {
         return Err(format!(
             "Desugaring exceeded maximum rewrite depth ({MAX_REWRITE_DEPTH}). \
@@ -931,22 +1070,27 @@ fn apply_one_shot_rules_inner(
     let node_kind = ast.get_node(id).map(|n| n.kind()).unwrap_or("");
 
     for rule in index.rules_for_kind(node_kind) {
-        if let Some(mut captures) = rule.try_match(ast, id)? {
-            // Recursively translate every captured node before invoking the
-            // transform. The transform's output uses output-schema kinds, so
-            // we must translate captured input-schema nodes to their
-            // output-schema equivalents first.
-            captures.try_map_all_captures(|captured_id| {
-                // Avoid infinite recursion when a capture refers to the root
-                // node of the matched tree (e.g. an `@_` capture on the
-                // pattern root): re-analyzing it would match the same rule
-                // again indefinitely.
-                if captured_id == id {
-                    return Ok(vec![captured_id]);
-                }
-                apply_one_shot_rules_inner(index, ast, captured_id, fresh, rewrite_depth + 1)
-            })?;
-            return Ok(rule.run_transform(ast, captures, id, fresh));
+        if let Some(captures) = rule.try_match(ast, id)? {
+            // Snapshot the user context before invoking the rule so that any
+            // mutations the rule (or its transitively-translated captures)
+            // make are visible during this rule's transform, but not leaked
+            // to the parent's siblings.
+            let snapshot = user_ctx.clone();
+            // Build the translator handle the transform will use to
+            // recursively translate captures (or, for macro-generated
+            // rules, the auto-translate prefix uses it to translate every
+            // capture up front, preserving the legacy behavior).
+            let translator = TranslatorHandle {
+                inner: TranslatorImpl::OneShot {
+                    index,
+                    fresh,
+                    rewrite_depth,
+                    matched_root: id,
+                },
+            };
+            let result = rule.run_transform(ast, captures, id, fresh, user_ctx, translator)?;
+            *user_ctx = snapshot;
+            return Ok(result);
         }
     }
 
@@ -974,15 +1118,15 @@ pub enum PhaseKind {
 /// starts. Rules within a phase compete for matches as usual; rules in
 /// different phases never compete because each traversal only considers the
 /// current phase's rules.
-pub struct Phase {
+pub struct Phase<C = ()> {
     /// Name used in error messages.
     pub name: String,
-    pub rules: Vec<Rule>,
+    pub rules: Vec<Rule<C>>,
     pub kind: PhaseKind,
 }
 
-impl Phase {
-    pub fn new(name: impl Into<String>, kind: PhaseKind, rules: Vec<Rule>) -> Self {
+impl<C> Phase<C> {
+    pub fn new(name: impl Into<String>, kind: PhaseKind, rules: Vec<Rule<C>>) -> Self {
         Self {
             name: name.into(),
             rules,
@@ -1008,17 +1152,30 @@ impl Phase {
 ///     .add_phase("desugar", PhaseKind::Repeating, desugar_rules)
 ///     .with_output_node_types_yaml(yaml);
 /// ```
-#[derive(Default)]
-pub struct DesugaringConfig {
+///
+/// The optional type parameter `C` is the user context type threaded through
+/// rule transforms. Defaults to `()` (no user context).
+pub struct DesugaringConfig<C = ()> {
     /// Phases of rule application, applied in order.
-    pub phases: Vec<Phase>,
+    pub phases: Vec<Phase<C>>,
     /// Output node-types in YAML format. If `None`, the input grammar's
     /// node types are used (i.e. the desugared AST has the same node types
     /// as the tree-sitter grammar).
     pub output_node_types_yaml: Option<&'static str>,
 }
 
-impl DesugaringConfig {
+// Manual `Default` impl so users with a custom `C` that doesn't implement
+// `Default` can still construct an empty config.
+impl<C> Default for DesugaringConfig<C> {
+    fn default() -> Self {
+        Self {
+            phases: Vec::new(),
+            output_node_types_yaml: None,
+        }
+    }
+}
+
+impl<C> DesugaringConfig<C> {
     /// Create an empty configuration. Add phases via [`add_phase`] and an
     /// optional output schema via [`with_output_node_types_yaml`].
     pub fn new() -> Self {
@@ -1030,7 +1187,7 @@ impl DesugaringConfig {
         mut self,
         name: impl Into<String>,
         kind: PhaseKind,
-        rules: Vec<Rule>,
+        rules: Vec<Rule<C>>,
     ) -> Self {
         self.phases.push(Phase::new(name, kind, rules));
         self
@@ -1052,15 +1209,15 @@ impl DesugaringConfig {
     }
 }
 
-pub struct Runner<'a> {
+pub struct Runner<'a, C = ()> {
     language: tree_sitter::Language,
     schema: schema::Schema,
-    phases: &'a [Phase],
+    phases: &'a [Phase<C>],
 }
 
-impl<'a> Runner<'a> {
+impl<'a, C> Runner<'a, C> {
     /// Create a runner using the input grammar's schema for output.
-    pub fn new(language: tree_sitter::Language, phases: &'a [Phase]) -> Self {
+    pub fn new(language: tree_sitter::Language, phases: &'a [Phase<C>]) -> Self {
         let schema = schema::Schema::from_language(&language);
         Self {
             language,
@@ -1073,7 +1230,7 @@ impl<'a> Runner<'a> {
     pub fn with_schema(
         language: tree_sitter::Language,
         schema: &schema::Schema,
-        phases: &'a [Phase],
+        phases: &'a [Phase<C>],
     ) -> Self {
         Self {
             language,
@@ -1085,7 +1242,7 @@ impl<'a> Runner<'a> {
     /// Create a runner from a [`DesugaringConfig`].
     pub fn from_config(
         language: tree_sitter::Language,
-        config: &'a DesugaringConfig,
+        config: &'a DesugaringConfig<C>,
     ) -> Result<Self, String> {
         let schema = config.build_schema(&language)?;
         Ok(Self {
@@ -1094,11 +1251,17 @@ impl<'a> Runner<'a> {
             phases: &config.phases,
         })
     }
+}
 
-    pub fn run_from_tree(
+impl<'a, C: Clone> Runner<'a, C> {
+    /// Parse `tree` against `source` and run all phases, threading
+    /// `user_ctx` through every rule transform. The caller owns the
+    /// initial context state.
+    pub fn run_from_tree_with_ctx(
         &self,
         tree: &tree_sitter::Tree,
         source: &[u8],
+        user_ctx: &mut C,
     ) -> Result<Ast, String> {
         let mut ast = Ast::from_tree_with_schema_and_source(
             self.schema.clone(),
@@ -1106,11 +1269,13 @@ impl<'a> Runner<'a> {
             &self.language,
             source.to_vec(),
         );
-        self.run_phases(&mut ast)?;
+        self.run_phases(&mut ast, user_ctx)?;
         Ok(ast)
     }
 
-    pub fn run(&self, input: &str) -> Result<Ast, String> {
+    /// Parse `input` and run all phases, threading `user_ctx` through
+    /// every rule transform. The caller owns the initial context state.
+    pub fn run_with_ctx(&self, input: &str, user_ctx: &mut C) -> Result<Ast, String> {
         let mut parser = tree_sitter::Parser::new();
         parser
             .set_language(&self.language)
@@ -1124,20 +1289,24 @@ impl<'a> Runner<'a> {
             &self.language,
             input.as_bytes().to_vec(),
         );
-        self.run_phases(&mut ast)?;
+        self.run_phases(&mut ast, user_ctx)?;
         Ok(ast)
     }
 
     /// Apply each phase in turn to the AST, threading the root through.
     /// A single `FreshScope` is shared across phases so that fresh
     /// identifiers generated in different phases don't collide.
-    fn run_phases(&self, ast: &mut Ast) -> Result<(), String> {
+    fn run_phases(&self, ast: &mut Ast, user_ctx: &mut C) -> Result<(), String> {
         let fresh = tree_builder::FreshScope::new();
         let mut root = ast.get_root();
         for phase in self.phases {
             let res = match phase.kind {
-                PhaseKind::Repeating => apply_repeating_rules(&phase.rules, ast, root, &fresh),
-                PhaseKind::OneShot => apply_one_shot_rules(&phase.rules, ast, root, &fresh),
+                PhaseKind::Repeating => {
+                    apply_repeating_rules(&phase.rules, ast, user_ctx, root, &fresh)
+                }
+                PhaseKind::OneShot => {
+                    apply_one_shot_rules(&phase.rules, ast, user_ctx, root, &fresh)
+                }
             }
             .map_err(|e| format!("Phase `{}`: {e}", phase.name))?;
             if res.len() != 1 {
@@ -1153,3 +1322,78 @@ impl<'a> Runner<'a> {
         Ok(())
     }
 }
+
+impl<'a, C: Clone + Default> Runner<'a, C> {
+    /// Parse `tree` against `source` and run all phases, using the
+    /// default context (`C::default()`) as the initial context state.
+    pub fn run_from_tree(&self, tree: &tree_sitter::Tree, source: &[u8]) -> Result<Ast, String> {
+        let mut user_ctx = C::default();
+        self.run_from_tree_with_ctx(tree, source, &mut user_ctx)
+    }
+
+    /// Parse `input` and run all phases, using the default context
+    /// (`C::default()`) as the initial context state.
+    pub fn run(&self, input: &str) -> Result<Ast, String> {
+        let mut user_ctx = C::default();
+        self.run_with_ctx(input, &mut user_ctx)
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Desugarer: type-erased view of a DesugaringConfig + Runner
+// ---------------------------------------------------------------------------
+
+/// Type-erased interface to a desugaring pipeline for a single language.
+///
+/// Consumers (e.g. a generic tree-sitter extractor) hold
+/// `Box<dyn Desugarer>` so they can dispatch through the trait without
+/// knowing the user context type `C` that's internal to yeast.
+///
+/// Construct one via [`ConcreteDesugarer::new`] from a
+/// [`DesugaringConfig<C>`] and a [`tree_sitter::Language`].
+pub trait Desugarer: Send + Sync {
+    /// The output AST schema (in YAML format), or `None` if the input
+    /// grammar's schema should be used.
+    fn output_node_types_yaml(&self) -> Option<&'static str>;
+
+    /// Parse `tree` against `source` and run the desugaring pipeline.
+    /// Each call constructs a fresh default user context internally.
+    fn run_from_tree(&self, tree: &tree_sitter::Tree, source: &[u8]) -> Result<Ast, String>;
+}
+
+/// A concrete [`Desugarer`] backed by a [`DesugaringConfig<C>`] for a
+/// specific user context type `C`. Stores the language and a pre-built
+/// schema so that per-call cost is bounded to constructing a transient
+/// [`Runner`] and cloning the schema (no YAML re-parsing).
+pub struct ConcreteDesugarer<C: Default + Clone + Send + Sync + 'static> {
+    language: tree_sitter::Language,
+    schema: schema::Schema,
+    config: DesugaringConfig<C>,
+}
+
+impl<C: Default + Clone + Send + Sync + 'static> ConcreteDesugarer<C> {
+    /// Build a desugarer for `language` from `config`. Parses the output
+    /// schema YAML once (if set) and stores it for reuse across files.
+    pub fn new(
+        language: tree_sitter::Language,
+        config: DesugaringConfig<C>,
+    ) -> Result<Self, String> {
+        let schema = config.build_schema(&language)?;
+        Ok(Self {
+            language,
+            schema,
+            config,
+        })
+    }
+}
+
+impl<C: Default + Clone + Send + Sync + 'static> Desugarer for ConcreteDesugarer<C> {
+    fn output_node_types_yaml(&self) -> Option<&'static str> {
+        self.config.output_node_types_yaml
+    }
+
+    fn run_from_tree(&self, tree: &tree_sitter::Tree, source: &[u8]) -> Result<Ast, String> {
+        let runner = Runner::with_schema(self.language.clone(), &self.schema, &self.config.phases);
+        runner.run_from_tree(tree, source)
+    }
+}
diff --git a/shared/yeast/src/node_types_yaml.rs b/shared/yeast/src/node_types_yaml.rs
index 797f14cba720..f4d9f2a1c427 100644
--- a/shared/yeast/src/node_types_yaml.rs
+++ b/shared/yeast/src/node_types_yaml.rs
@@ -242,10 +242,7 @@ pub fn convert(yaml_input: &str) -> Result<String, String> {
 
 /// Apply YAML node-type definitions to a mutable Schema.
 /// Registers all types, fields, and allowed types from the YAML into the schema.
-fn apply_yaml_to_schema(
-    yaml: &YamlNodeTypes,
-    schema: &mut crate::schema::Schema,
-) {
+fn apply_yaml_to_schema(yaml: &YamlNodeTypes, schema: &mut crate::schema::Schema) {
     // Register all supertypes as node kinds
     for name in yaml.supertypes.keys() {
         schema.register_kind(name);
@@ -307,7 +304,8 @@ fn apply_yaml_to_schema(
                 .into_vec()
                 .into_iter()
                 .map(|type_ref| {
-                    let (kind, named) = resolve_type_ref_pair(&type_ref, &named_types, &unnamed_types);
+                    let (kind, named) =
+                        resolve_type_ref_pair(&type_ref, &named_types, &unnamed_types);
                     crate::schema::NodeType { kind, named }
                 })
                 .collect::<Vec<_>>();
diff --git a/shared/yeast/src/schema.rs b/shared/yeast/src/schema.rs
index bbd425f15a2c..da13bb8b6b70 100644
--- a/shared/yeast/src/schema.rs
+++ b/shared/yeast/src/schema.rs
@@ -198,13 +198,8 @@ impl Schema {
             .insert((parent_kind.to_string(), field_id), node_types);
     }
 
-    pub fn field_types(
-        &self,
-        parent_kind: &str,
-        field_id: FieldId,
-    ) -> Option<&Vec<NodeType>> {
-        self.field_types
-            .get(&(parent_kind.to_string(), field_id))
+    pub fn field_types(&self, parent_kind: &str, field_id: FieldId) -> Option<&Vec<NodeType>> {
+        self.field_types.get(&(parent_kind.to_string(), field_id))
     }
 
     pub fn set_field_cardinality(
diff --git a/shared/yeast/tests/test.rs b/shared/yeast/tests/test.rs
index 069132d09237..99471f129abf 100644
--- a/shared/yeast/tests/test.rs
+++ b/shared/yeast/tests/test.rs
@@ -7,7 +7,7 @@ const OUTPUT_SCHEMA_YAML: &str = include_str!("node-types.yml");
 
 /// Helper: parse Ruby source with no rules, return dump.
 fn parse_and_dump(input: &str) -> String {
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run(input).unwrap();
     dump_ast(&ast, ast.get_root(), input)
 }
@@ -24,7 +24,7 @@ fn run_and_ast(input: &str, rules: Vec<Rule>) -> Ast {
     let schema =
         yeast::node_types_yaml::schema_from_yaml_with_language(OUTPUT_SCHEMA_YAML, &lang).unwrap();
     let phases = vec![Phase::new("test", PhaseKind::Repeating, rules)];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
     runner.run(input).unwrap()
 }
 
@@ -34,7 +34,7 @@ fn run_phased_and_dump(input: &str, phases: Vec<Phase>) -> String {
     let lang: tree_sitter::Language = tree_sitter_ruby::LANGUAGE.into();
     let schema =
         yeast::node_types_yaml::schema_from_yaml_with_language(OUTPUT_SCHEMA_YAML, &lang).unwrap();
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
     let ast = runner.run(input).unwrap();
     dump_ast(&ast, ast.get_root(), input)
 }
@@ -46,7 +46,7 @@ fn run_and_get_error(input: &str, rules: Vec<Rule>) -> String {
     let schema =
         yeast::node_types_yaml::schema_from_yaml_with_language(OUTPUT_SCHEMA_YAML, &lang).unwrap();
     let phases = vec![Phase::new("test", PhaseKind::Repeating, rules)];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
     runner
         .run(input)
         .expect_err("expected runner to return an error")
@@ -54,7 +54,7 @@ fn run_and_get_error(input: &str, rules: Vec<Rule>) -> String {
 
 /// Helper: parse Ruby source with no rules and dump with schema type errors.
 fn parse_and_dump_typed(input: &str, schema_yaml: &str) -> String {
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run(input).unwrap();
     let schema = yeast::node_types_yaml::schema_from_yaml(schema_yaml).unwrap();
     dump_ast_with_type_errors(&ast, ast.get_root(), input, &schema)
@@ -64,10 +64,10 @@ fn parse_and_dump_typed(input: &str, schema_yaml: &str) -> String {
 /// building schema with language IDs so field checks align with parser fields.
 fn parse_and_dump_typed_with_language(input: &str, schema_yaml: &str) -> String {
     let lang: tree_sitter::Language = tree_sitter_ruby::LANGUAGE.into();
-    let runner = Runner::new(lang.clone(), &[]);
+    let runner: Runner = Runner::new(lang.clone(), &[]);
     let ast = runner.run(input).unwrap();
-    let schema = yeast::node_types_yaml::schema_from_yaml_with_language(schema_yaml, &lang)
-        .unwrap();
+    let schema =
+        yeast::node_types_yaml::schema_from_yaml_with_language(schema_yaml, &lang).unwrap();
     dump_ast_with_type_errors(&ast, ast.get_root(), input, &schema)
 }
 
@@ -76,7 +76,7 @@ fn run_and_dump_typed(input: &str, rules: Vec<Rule>, schema_yaml: &str) -> Strin
     let lang: tree_sitter::Language = tree_sitter_ruby::LANGUAGE.into();
     let schema = yeast::node_types_yaml::schema_from_yaml(schema_yaml).unwrap();
     let phases = vec![Phase::new("test", PhaseKind::Repeating, rules)];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
     let ast = runner.run(input).unwrap();
     dump_ast_with_type_errors(&ast, ast.get_root(), input, &schema)
 }
@@ -166,7 +166,7 @@ fn test_parse_for_loop() {
 
 #[test]
 fn test_dump_highlights_type_errors_inline() {
-        let schema_yaml = r#"
+    let schema_yaml = r#"
 named:
     program:
         $children*: assignment
@@ -176,13 +176,13 @@ named:
     identifier:
 "#;
 
-        let dump = parse_and_dump_typed("x = 1", schema_yaml);
-        assert!(dump.contains("integer \"1\" <-- ERROR:"));
+    let dump = parse_and_dump_typed("x = 1", schema_yaml);
+    assert!(dump.contains("integer \"1\" <-- ERROR:"));
 }
 
 #[test]
 fn test_dump_reports_preserved_unknown_kind_after_transformation() {
-        let schema_yaml = r#"
+    let schema_yaml = r#"
 named:
     program:
         $children*: assignment
@@ -192,25 +192,25 @@ named:
     identifier:
 "#;
 
-        // This rewrite runs and preserves the RHS node kind via capture.
-        // With schema above, preserving `integer` should be reported inline.
-        let rules = vec![yeast::rule!(
-                (assignment left: (_) @left right: (_) @right)
-                =>
-                (assignment
-                        left: {left}
-                        right: {right}
-                )
-        )];
+    // This rewrite runs and preserves the RHS node kind via capture.
+    // With schema above, preserving `integer` should be reported inline.
+    let rules: Vec<Rule> = vec![yeast::rule!(
+            (assignment left: (_) @left right: (_) @right)
+            =>
+            (assignment
+                    left: {left}
+                    right: {right}
+            )
+    )];
 
-        let dump = run_and_dump_typed("x = 1", rules, schema_yaml);
-        assert!(dump.contains("integer \"1\" <-- ERROR:"));
-        assert!(dump.contains("node kind 'integer' not in schema"));
+    let dump = run_and_dump_typed("x = 1", rules, schema_yaml);
+    assert!(dump.contains("integer \"1\" <-- ERROR:"));
+    assert!(dump.contains("node kind 'integer' not in schema"));
 }
 
 #[test]
 fn test_dump_reports_undeclared_field_on_node() {
-        let schema_yaml = r#"
+    let schema_yaml = r#"
 named:
     program:
         $children*: assignment
@@ -219,14 +219,14 @@ named:
     identifier:
 "#;
 
-        let dump = parse_and_dump_typed_with_language("x = y", schema_yaml);
-        assert!(dump.contains("right: identifier \"y\" <-- ERROR:"));
-        assert!(dump.contains("the node 'assignment' has no field 'right'"));
+    let dump = parse_and_dump_typed_with_language("x = y", schema_yaml);
+    assert!(dump.contains("right: identifier \"y\" <-- ERROR:"));
+    assert!(dump.contains("the node 'assignment' has no field 'right'"));
 }
 
 #[test]
 fn test_dump_reports_disallowed_kind_in_field_type() {
-        let schema_yaml = r#"
+    let schema_yaml = r#"
 named:
     program:
         $children*: assignment
@@ -237,17 +237,17 @@ named:
     integer:
 "#;
 
-        let dump = parse_and_dump_typed_with_language("x = 1", schema_yaml);
-        assert!(dump.contains("right: integer \"1\" <-- ERROR:"));
-        assert!(dump.contains("should contain"));
-        assert!(dump.contains("but got integer"));
+    let dump = parse_and_dump_typed_with_language("x = 1", schema_yaml);
+    assert!(dump.contains("right: integer \"1\" <-- ERROR:"));
+    assert!(dump.contains("should contain"));
+    assert!(dump.contains("but got integer"));
 }
 
 // ---- Query tests ----
 
 #[test]
 fn test_query_match() {
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x = 1").unwrap();
 
     let query = yeast::query!(
@@ -268,7 +268,7 @@ fn test_query_match() {
 
 #[test]
 fn test_query_no_match() {
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x = 1").unwrap();
 
     let query = yeast::query!(
@@ -293,7 +293,7 @@ fn test_query_skips_extras_in_positional_match() {
     // captured comment to nothing (a common idiom, e.g.
     // `(comment) => ()` in Swift) leaves the capture's match-list empty
     // and causes the transform to fail with "Variable X has 0 matches".
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("[1, # comment\n2]").unwrap();
 
     // Navigate to the `array` node: program -> array.
@@ -309,15 +309,11 @@ fn test_query_skips_extras_in_positional_match() {
     let matched = query.do_match(&ast, array_id, &mut captures).unwrap();
     assert!(matched);
     assert_eq!(
-        ast.get_node(captures.get_var("a").unwrap())
-            .unwrap()
-            .kind(),
+        ast.get_node(captures.get_var("a").unwrap()).unwrap().kind(),
         "integer"
     );
     assert_eq!(
-        ast.get_node(captures.get_var("b").unwrap())
-            .unwrap()
-            .kind(),
+        ast.get_node(captures.get_var("b").unwrap()).unwrap().kind(),
         "integer"
     );
 }
@@ -325,14 +321,14 @@ fn test_query_skips_extras_in_positional_match() {
 #[test]
 fn test_reachable_nodes_excludes_orphaned_rewrite_nodes() {
     let lang: tree_sitter::Language = tree_sitter_ruby::LANGUAGE.into();
-    let schema = yeast::node_types_yaml::schema_from_yaml_with_language(OUTPUT_SCHEMA_YAML, &lang)
-        .unwrap();
-    let phases = vec![Phase::new(
+    let schema =
+        yeast::node_types_yaml::schema_from_yaml_with_language(OUTPUT_SCHEMA_YAML, &lang).unwrap();
+    let phases: Vec<Phase> = vec![Phase::new(
         "test",
         PhaseKind::Repeating,
         vec![yeast::rule!((integer) => (identifier "replaced"))],
     )];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
 
     let input = "x = 1";
     let ast = runner.run(input).unwrap();
@@ -350,7 +346,7 @@ fn test_reachable_nodes_excludes_orphaned_rewrite_nodes() {
 
 #[test]
 fn test_query_repeated_capture() {
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x, y, z = 1").unwrap();
 
     let query = yeast::query!(
@@ -375,7 +371,7 @@ fn test_query_repeated_capture() {
 #[test]
 fn test_capture_unnamed_node_parenthesized() {
     // `("=") @op` captures the unnamed `=` token between left and right.
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x = 1").unwrap();
 
     let query = yeast::query!(
@@ -403,7 +399,7 @@ fn test_capture_unnamed_node_parenthesized() {
 fn test_capture_bare_underscore_repeated() {
     // `_` matches named and unnamed nodes in bare-child position. On this
     // assignment shape, bare children correspond to unnamed tokens (the `=`).
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x = 1").unwrap();
 
     let query = yeast::query!((assignment _* @all));
@@ -425,7 +421,7 @@ fn test_capture_bare_underscore_repeated() {
 #[test]
 fn test_capture_unnamed_node_bare_literal() {
     // `"=" @op` (without surrounding parens) is the same as `("=") @op`.
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x = 1").unwrap();
 
     let query = yeast::query!(
@@ -454,7 +450,7 @@ fn test_bare_underscore_matches_unnamed() {
     // Bare `_` matches any node, including unnamed tokens, while `(_)`
     // matches only named nodes. Demonstrate by matching the unnamed `=`
     // token in the implicit `child` field of an `assignment`.
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x = 1").unwrap();
 
     let mut cursor = AstCursor::new(&ast);
@@ -493,7 +489,7 @@ fn test_bare_forms_in_field_position() {
     // field's value, not just in the bare-children position. This is
     // syntactic sugar for `(_)` / `("…")` and goes through the same
     // code paths.
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x = 1").unwrap();
 
     let mut cursor = AstCursor::new(&ast);
@@ -532,7 +528,7 @@ fn test_forward_scan_finds_unnamed_token_late() {
     // query for `("end")` skip past the first two and match the third.
     // Without forward-scan, the matcher took the first child unconditionally
     // and failed.
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("for x in list do\n  y\nend").unwrap();
 
     // Navigate: program > for > do (the body wrapper).
@@ -559,7 +555,7 @@ fn test_forward_scan_preserves_order() {
     // order. A query for ("end") then ("do") should fail because `do`
     // appears before `end` in the source order; once forward-scan has
     // consumed `end`, the iterator is exhausted.
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("for x in list do\n  y\nend").unwrap();
 
     let mut cursor = AstCursor::new(&ast);
@@ -580,7 +576,7 @@ fn test_forward_scan_preserves_order() {
 
 #[test]
 fn test_tree_builder() {
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let mut ast = runner.run("x = 1").unwrap();
     let input = "x = 1";
 
@@ -598,7 +594,8 @@ fn test_tree_builder() {
 
     // Swap left and right
     let fresh = yeast::tree_builder::FreshScope::new();
-    let mut ctx = yeast::build::BuildCtx::new(&mut ast, &captures, &fresh);
+    let mut user_ctx = ();
+    let mut ctx = yeast::build::BuildCtx::new(&mut ast, &captures, &fresh, &mut user_ctx);
     let new_id = yeast::tree!(ctx,
         (program
             child: (assignment
@@ -626,7 +623,7 @@ fn test_tree_builder() {
 // tree-sitter-ruby grammar with named fields for nodes that only have
 // unnamed children in tree-sitter (e.g. block_body.stmt, block_parameters.parameter).
 fn ruby_rules() -> Vec<Rule> {
-    let assign_rule = yeast::rule!(
+    let assign_rule: Rule = yeast::rule!(
         (assignment
             left: (left_assignment_list
                 (identifier)* @left
@@ -651,7 +648,7 @@ fn ruby_rules() -> Vec<Rule> {
         )}
     );
 
-    let for_rule = yeast::rule!(
+    let for_rule: Rule = yeast::rule!(
         (for
             pattern: (_) @pat
             value: (in (_) @val)
@@ -733,7 +730,7 @@ fn test_desugar_for_loop() {
 
 #[test]
 fn test_shorthand_rule() {
-    let rule = yeast::rule!(
+    let rule: Rule = yeast::rule!(
         (assignment
             left: (_) @method
             right: (_) @receiver
@@ -885,7 +882,7 @@ fn test_phase_error_includes_phase_name() {
         PhaseKind::Repeating,
         vec![swap_assignment_rule().repeated()],
     )];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
     let err = runner
         .run("x = 1")
         .expect_err("expected runner to return an error");
@@ -928,7 +925,7 @@ fn test_one_shot_phase() {
         PhaseKind::OneShot,
         one_shot_xeq1_rules(),
     )];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
 
     let input = "x = 1";
     let ast = runner.run(input).unwrap();
@@ -954,7 +951,7 @@ fn test_one_shot_phase_errors_when_no_rule_matches() {
     let mut rules = one_shot_xeq1_rules();
     rules.pop();
     let phases = vec![Phase::new("translate", PhaseKind::OneShot, rules)];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
 
     let err = runner
         .run("x = 1")
@@ -978,7 +975,7 @@ fn test_one_shot_recurses_into_returned_capture() {
     let lang: tree_sitter::Language = tree_sitter_ruby::LANGUAGE.into();
     let schema =
         yeast::node_types_yaml::schema_from_yaml_with_language(OUTPUT_SCHEMA_YAML, &lang).unwrap();
-    let rules = vec![
+    let rules: Vec<Rule> = vec![
         yeast::rule!(
             (program (_)* @stmts)
             =>
@@ -994,7 +991,7 @@ fn test_one_shot_recurses_into_returned_capture() {
         yeast::rule!((integer) => (integer "INT")),
     ];
     let phases = vec![Phase::new("translate", PhaseKind::OneShot, rules)];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
 
     let input = "x = 1";
     let ast = runner.run(input).unwrap();
@@ -1020,7 +1017,7 @@ fn test_one_shot_does_not_recurse_into_wrapper_output() {
     let lang: tree_sitter::Language = tree_sitter_ruby::LANGUAGE.into();
     let schema =
         yeast::node_types_yaml::schema_from_yaml_with_language(OUTPUT_SCHEMA_YAML, &lang).unwrap();
-    let rules = vec![
+    let rules: Vec<Rule> = vec![
         yeast::rule!(
             (program (_)* @stmts)
             =>
@@ -1041,7 +1038,7 @@ fn test_one_shot_does_not_recurse_into_wrapper_output() {
         yeast::rule!((integer) => (integer "INT")),
     ];
     let phases = vec![Phase::new("translate", PhaseKind::OneShot, rules)];
-    let runner = Runner::with_schema(lang, &schema, &phases);
+    let runner: Runner = Runner::with_schema(lang, &schema, &phases);
 
     let input = "x = 1";
     let ast = runner.run(input).unwrap();
@@ -1065,7 +1062,7 @@ fn test_one_shot_does_not_recurse_into_wrapper_output() {
 
 #[test]
 fn test_cursor_navigation() {
-    let runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
+    let runner: Runner = Runner::new(tree_sitter_ruby::LANGUAGE.into(), &[]);
     let ast = runner.run("x = 1").unwrap();
     let mut cursor = AstCursor::new(&ast);
 
@@ -1139,7 +1136,7 @@ fn test_desugar_for_with_multiple_assignment() {
 /// resolves to the captured node's source text via `YeastDisplay`.
 #[test]
 fn test_hash_brace_renders_capture_source_text() {
-    let rule = rule!(
+    let rule: Rule = rule!(
         (call
             method: (identifier) @name
             receiver: (identifier) @recv
@@ -1168,7 +1165,7 @@ fn test_hash_brace_renders_capture_source_text() {
 /// `Display` impl (covered by `YeastDisplay`'s blanket impls for primitives).
 #[test]
 fn test_hash_brace_renders_integer_expression() {
-    let rule = rule!(
+    let rule: Rule = rule!(
         (identifier) @_
         =>
         (identifier #{1 + 2})
@@ -1187,7 +1184,7 @@ fn test_hash_brace_renders_integer_expression() {
 /// source location, not the full source range of the matched rule root.
 #[test]
 fn test_hash_brace_uses_capture_location_for_leaf() {
-    let rule = rule!(
+    let rule: Rule = rule!(
         (call
             method: (identifier) @name
             receiver: (identifier) @recv
@@ -1204,7 +1201,9 @@ fn test_hash_brace_uses_capture_location_for_leaf() {
 
     let mut bar_ids: Vec<usize> = Vec::new();
     for id in ast.reachable_node_ids() {
-        let Some(node) = ast.get_node(id) else { continue; };
+        let Some(node) = ast.get_node(id) else {
+            continue;
+        };
         if node.kind() == "identifier" && ast.source_text(id) == "bar" {
             bar_ids.push(id);
         }
diff --git a/unified/extractor/src/extractor.rs b/unified/extractor/src/extractor.rs
index 7601fa8addbe..301c6cf533f4 100644
--- a/unified/extractor/src/extractor.rs
+++ b/unified/extractor/src/extractor.rs
@@ -1,9 +1,9 @@
 use clap::Args;
 use std::path::PathBuf;
 
+use crate::languages;
 use codeql_extractor::extractor::simple;
 use codeql_extractor::trap;
-use crate::languages;
 
 #[derive(Args)]
 pub struct Options {
@@ -35,7 +35,9 @@ pub fn run(options: Options) -> std::io::Result<()> {
         prefix: "unified".to_string(),
         languages,
         trap_dir: options.output_dir,
-        trap_compression: trap::Compression::from_env("CODEQL_EXTRACTOR_UNIFIED_OPTION_TRAP_COMPRESSION"),
+        trap_compression: trap::Compression::from_env(
+            "CODEQL_EXTRACTOR_UNIFIED_OPTION_TRAP_COMPRESSION",
+        ),
         source_archive_dir: options.source_archive_dir,
         file_lists: vec![options.file_list],
     };
diff --git a/unified/extractor/src/generator.rs b/unified/extractor/src/generator.rs
index cbf971a8ff25..974de5dbca97 100644
--- a/unified/extractor/src/generator.rs
+++ b/unified/extractor/src/generator.rs
@@ -22,14 +22,19 @@ pub fn run(options: Options) -> std::io::Result<()> {
     // The QL-visible schema is the unified output AST, not the per-language
     // input grammars. Pass it via `desugar.output_node_types_yaml` so the
     // generator converts the YAML to JSON node-types.
-    let desugar = yeast::DesugaringConfig::new()
-        .with_output_node_types_yaml(languages::OUTPUT_AST_SCHEMA);
+    let desugar =
+        yeast::DesugaringConfig::new().with_output_node_types_yaml(languages::OUTPUT_AST_SCHEMA);
 
     let languages = vec![Language {
         name: "Unified".to_owned(),
-        node_types: "",   // unused: generator picks up output_node_types_yaml above
+        node_types: "", // unused: generator picks up output_node_types_yaml above
         desugar: Some(desugar),
     }];
 
-    generate(languages, options.dbscheme, options.library, "run unified/scripts/create-extractor-pack.sh")
+    generate(
+        languages,
+        options.dbscheme,
+        options.library,
+        "run unified/scripts/create-extractor-pack.sh",
+    )
 }
diff --git a/unified/extractor/src/languages/swift/swift.rs b/unified/extractor/src/languages/swift/swift.rs
index 79f0e65b02f5..c84e3cf38676 100644
--- a/unified/extractor/src/languages/swift/swift.rs
+++ b/unified/extractor/src/languages/swift/swift.rs
@@ -1,7 +1,98 @@
 use codeql_extractor::extractor::simple;
-use yeast::{rule, DesugaringConfig, PhaseKind};
+use yeast::{ConcreteDesugarer, DesugaringConfig, PhaseKind, Rule, manual_rule, rule, tree};
 
-fn translation_rules() -> Vec<yeast::Rule> {
+/// User context propagated from outer rules down to the inner rules that
+/// emit the corresponding output declarations, so that each emitted node
+/// is born with the outer information (name, type, modifiers, etc.)
+/// already set — no schema-invalid intermediate state requiring
+/// post-hoc mutation.
+#[derive(Clone, Default)]
+struct SwiftContext {
+    /// Identifier node for the property name. Set by the outer
+    /// `property_binding` (computed accessors / willSet-didSet) and
+    /// `protocol_property_declaration` rules before translating accessor
+    /// children; read by the accessor inner rules
+    /// (`computed_getter`/`computed_setter`/`computed_modify`/
+    /// `willset_clause`/`didset_clause`/`getter_specifier`/
+    /// `setter_specifier`).
+    property_name: Option<yeast::Id>,
+    /// Translated type node for the property type. Set by the outer
+    /// `property_binding` rule (computed accessors variant) and
+    /// `protocol_property_declaration` when present; read by the
+    /// accessor inner rules.
+    property_type: Option<yeast::Id>,
+    /// Default-value expression for the next translated `parameter`. Set
+    /// by the outer `function_parameter` rule; read by the `parameter`
+    /// rules.
+    default_value: Option<yeast::Id>,
+    /// Translated outer modifiers (e.g. visibility, attributes) to
+    /// attach to each child of a flattening outer rule. Set by
+    /// `property_declaration`, `enum_entry`, and
+    /// `protocol_property_declaration`.
+    outer_modifiers: Vec<yeast::Id>,
+    /// The `let`/`var` binding modifier for a `property_declaration`.
+    /// Set by `property_declaration`; read by the inner declaration
+    /// rules (`property_binding` variants, accessor rules) so they
+    /// emit it as part of the output node's `modifier:` field.
+    binding_modifier: Option<yeast::Id>,
+    /// True when the current child of a flattening outer rule is not
+    /// the first one — its inner rule should emit a
+    /// `chained_declaration` modifier so the original grouping can be
+    /// recovered downstream.
+    is_chained: bool,
+}
+
+/// Build a freshly-created `chained_declaration` modifier node if
+/// `ctx.is_chained`, else `None`. Used by inner declaration rules to
+/// emit the chained tag for non-first children of a flattening outer
+/// rule. Returns `Option<Id>` so it splices via `{..…}` to 0 or 1 ids.
+fn chained_modifier(ctx: &mut yeast::build::BuildCtx<'_, SwiftContext>) -> Option<yeast::Id> {
+    if ctx.is_chained {
+        Some(ctx.literal("modifier", "chained_declaration"))
+    } else {
+        None
+    }
+}
+
+/// Combine a list of boolean sub-conditions into a single expression by
+/// left-folding with the infix `&&` operator. Used by control-flow
+/// rules (`if`, `guard`, `while`, `repeat-while`) whose tree-sitter
+/// nodes carry one or more comma-separated conditions that the target
+/// AST represents as a single `condition:` field. Panics on an empty
+/// input because every caller's grammar guarantees at least one
+/// condition.
+fn and_chain(
+    ctx: &mut yeast::build::BuildCtx<'_, SwiftContext>,
+    conds: Vec<yeast::NodeRef>,
+) -> yeast::Id {
+    conds.into_iter()
+        .map(yeast::Id::from)
+        .reduce(|acc, elem| {
+            tree!((binary_expr operator: (infix_operator "&&") left: {acc} right: {elem}))
+        })
+        .expect("control-flow statement must have at least one condition")
+}
+
+/// Translate a multi-part identifier (for example `Foo.Bar.Baz`) into a
+/// `member_access_expr` chain rooted at a `name_expr` over the first
+/// part. Panics on an empty input because the grammar's `_+` quantifier
+/// guarantees at least one part.
+fn member_chain(
+    ctx: &mut yeast::build::BuildCtx<'_, SwiftContext>,
+    parts: Vec<yeast::NodeRef>,
+) -> yeast::Id {
+    let mut iter = parts.into_iter();
+    let first = iter
+        .next()
+        .expect("identifier with `part:` must have at least one part");
+    let init = tree!((name_expr identifier: (identifier #{first})));
+    iter.fold(
+        init,
+        |acc, elem| tree!((member_access_expr base: {acc} member: (identifier #{elem}))),
+    )
+}
+
+fn translation_rules() -> Vec<Rule<SwiftContext>> {
     vec![
         // ---- Top-level ----
         // Capture all top-level statements, including unnamed tokens like `nil`.
@@ -88,32 +179,49 @@ fn translation_rules() -> Vec<yeast::Rule> {
         // nodes for individual declarators. The outer property_declaration rule splices these out
         // and attaches binding/modifiers from the parent.
 
-        // Computed property with explicit accessors (get/set/modify) →
-        // a sequence of accessor_declaration nodes, each with the property name
-        // attached. Subsequent accessors will be tagged chained_declaration by
-        // the outer property_declaration rule.
-        rule!(
+        // Computed property with explicit accessors (get/set/modify) → a
+        // sequence of `accessor_declaration` nodes. The outer rule
+        // publishes the property's name and type into `ctx` so that each
+        // inner accessor rule
+        // (`computed_getter`/`computed_setter`/`computed_modify`) builds
+        // its `accessor_declaration` with `name` and `type` set from the
+        // start — no schema-invalid intermediate state.
+        //
+        // Toggles `ctx.is_chained` per accessor iteration: the first
+        // accessor inherits the outer rule's chained state (i.e. whether
+        // this whole property_binding is itself a non-first declarator
+        // of a containing property_declaration); subsequent accessors
+        // always emit `chained_declaration`.
+        manual_rule!(
             (property_binding
                 name: @pattern
                 type: _? @ty
                 computed_value: (computed_property accessor: _+ @accessors))
-            =>
-            {..{
-                let name_text = __yeast_ctx.ast.source_text(pattern.into());
-                let ty_ids: Vec<usize> = ty.iter().map(|&t| t.into()).collect();
-                let acc_ids: Vec<usize> = accessors.iter().map(|&a| a.into()).collect();
-                for &acc_id in &acc_ids {
-                    let ident = __yeast_ctx.literal("identifier", &name_text);
-                    __yeast_ctx.prepend_field(acc_id, "name", ident);
-                    for &ty_id in ty_ids.iter().rev() {
-                        __yeast_ctx.prepend_field(acc_id, "type", ty_id);
+            {
+                // Translate `ty` first so the context holds an
+                // output-schema node id.
+                let translated_ty = ctx.translate_opt(ty)?;
+                // Build the property-name identifier from the
+                // (untranslated) pattern leaf.
+                let name_id = tree!((identifier #{pattern}));
+
+                ctx.property_name = Some(name_id);
+                ctx.property_type = translated_ty;
+
+                let mut result = Vec::new();
+                for (i, acc) in accessors.into_iter().enumerate() {
+                    if i > 0 {
+                        ctx.is_chained = true;
                     }
+                    result.extend(ctx.translate(acc)?);
                 }
-                acc_ids
-            }}
+                Ok(result)
+            }
         ),
-        // Computed property: shorthand getter (no explicit get/set, just statements) →
-        // a single accessor_declaration with kind "get".
+        // Computed property: shorthand getter (no explicit get/set, just
+        // statements) → a single accessor_declaration with kind "get".
+        // Reads outer modifiers / chained tag from `ctx` (set by the
+        // outer `property_declaration` rule).
         rule!(
             (property_binding
                 name: (pattern bound_identifier: @name)
@@ -121,49 +229,62 @@ fn translation_rules() -> Vec<yeast::Rule> {
                 computed_value: (computed_property statement: _* @body))
             =>
             (accessor_declaration
+                modifier: {..ctx.binding_modifier}
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
                 name: (identifier #{name})
                 type: {..ty}
                 accessor_kind: (accessor_kind "get")
                 body: (block stmt: {..body}))
         ),
-        // Stored property with willSet/didSet observers (initializer optional) →
-        // variable_declaration followed by one accessor_declaration per observer,
-        // each carrying the property name. Subsequent items are tagged
-        // chained_declaration by the outer property_declaration rule.
-        rule!(
+        // Stored property with willSet/didSet observers (initializer
+        // optional) → a `variable_declaration` followed by one
+        // `accessor_declaration` per observer, each born with the
+        // property name set. Manual rule: we publish the property name
+        // into `ctx` before translating the observer children so the
+        // inner `willset_clause` / `didset_clause` rules construct
+        // valid `accessor_declaration` nodes from the start.
+        //
+        // The `variable_declaration` itself inherits the outer rule's
+        // chained state; observers always get `chained_declaration`
+        // because they're subsequent outputs of this flattening rule.
+        manual_rule!(
             (property_binding
                 name: (pattern bound_identifier: @name)
                 type: _? @ty
                 value: _? @val
                 observers: (willset_didset_block willset: _? @ws didset: _? @ds))
-            =>
-            {..{
-                let name_text = __yeast_ctx.ast.source_text(name.into());
-                let val_ids: Vec<usize> = val.iter().map(|&v| v.into()).collect();
-                let ty_ids: Vec<usize> = ty.iter().map(|&t| t.into()).collect();
-                let mut obs_ids: Vec<usize> = Vec::new();
-                obs_ids.extend(ws.iter().map(|&o| { let id: usize = o.into(); id }));
-                obs_ids.extend(ds.iter().map(|&o| { let id: usize = o.into(); id }));
-                let ident_for_var = __yeast_ctx.literal("identifier", &name_text);
-                let pat = __yeast_ctx.node("name_pattern", vec![("identifier", vec![ident_for_var])]);
-                let mut var_fields: Vec<(&str, Vec<usize>)> = vec![("pattern", vec![pat])];
-                if !ty_ids.is_empty() {
-                    var_fields.push(("type", ty_ids));
-                }
-                if !val_ids.is_empty() {
-                    var_fields.push(("value", val_ids));
-                }
-                let var_id = __yeast_ctx.node("variable_declaration", var_fields);
-                let mut result = vec![var_id];
-                for obs_id in obs_ids {
-                    let ident = __yeast_ctx.literal("identifier", &name_text);
-                    __yeast_ctx.prepend_field(obs_id, "name", ident);
-                    result.push(obs_id);
+            {
+                // Translate ty and val so the variable_declaration
+                // below contains output-schema nodes.
+                let translated_ty = ctx.translate_opt(ty)?;
+                let translated_val = ctx.translate_opt(val)?;
+
+                let var_decl = tree!(
+                    (variable_declaration
+                        modifier: {..ctx.binding_modifier}
+                        modifier: {..ctx.outer_modifiers.clone()}
+                        modifier: {..chained_modifier(&mut ctx)}
+                        pattern: (name_pattern identifier: (identifier #{name}))
+                        type: {..translated_ty}
+                        value: {..translated_val})
+                );
+
+                // Publish the property name for the observer rules.
+                ctx.property_name = Some(tree!((identifier #{name})));
+                // Observers are subsequent outputs of this flattening
+                // rule, so they always get `chained_declaration`.
+                ctx.is_chained = true;
+
+                let mut result = vec![var_decl];
+                for obs in ws.into_iter().chain(ds) {
+                    result.extend(ctx.translate(obs)?);
                 }
-                result
-            }}
+                Ok(result)
+            }
         ),
-        // property_binding with any pattern name (identifier or destructuring)
+        // property_binding with any pattern name (identifier or
+        // destructuring). Reads outer modifiers / chained tag from `ctx`.
         rule!(
             (property_binding
                 name: @pattern
@@ -171,37 +292,44 @@ fn translation_rules() -> Vec<yeast::Rule> {
                 value: _? @val)
             =>
             (variable_declaration
+                modifier: {..ctx.binding_modifier}
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
                 pattern: {pattern}
                 type: {..ty}
                 value: {..val})
         ),
-        // property_declaration: splice declarators (each may translate to multiple nodes —
-        // variable_declaration and/or accessor_declaration), and attach the binding modifier
-        // (let/var) and any outer modifiers to each. All children after the first additionally
-        // get a synthetic chained_declaration modifier so the grouping can be recovered.
-        rule!(
+        // property_declaration: flatten declarators (each may translate
+        // to multiple nodes — variable_declaration and/or
+        // accessor_declaration) and attach the binding modifier
+        // (let/var), outer modifiers, and `chained_declaration` for
+        // non-first declarations. Manual rule: publishes
+        // binding/outer modifiers into `ctx` and translates each
+        // declarator with `ctx.is_chained` toggled per iteration. The
+        // inner declaration rules (`property_binding` variants,
+        // accessor inner rules) read these fields and emit complete
+        // `modifier:` lists from the start.
+        manual_rule!(
             (property_declaration
                 binding: (value_binding_pattern mutability: @binding_kind)
                 declarator: _* @decls
                 (modifiers)* @mods)
-            =>
-            {..{
-                let binding_text = __yeast_ctx.ast.source_text(binding_kind.into());
-                let mod_ids: Vec<usize> = mods.iter().map(|&m| m.into()).collect();
-                let decl_ids: Vec<usize> = decls.iter().map(|&d| d.into()).collect();
-                for (i, &decl_id) in decl_ids.iter().enumerate() {
-                    if i > 0 {
-                        let chained = __yeast_ctx.literal("modifier", "chained_declaration");
-                        __yeast_ctx.prepend_field(decl_id, "modifier", chained);
-                    }
-                    for &mod_id in mod_ids.iter().rev() {
-                        __yeast_ctx.prepend_field(decl_id, "modifier", mod_id);
-                    }
-                    let binding_mod = __yeast_ctx.literal("modifier", &binding_text);
-                    __yeast_ctx.prepend_field(decl_id, "modifier", binding_mod);
+            {
+                let binding_text = ctx.ast.source_text(binding_kind.0);
+                ctx.binding_modifier = Some(ctx.literal("modifier", &binding_text));
+                let mut modifiers = Vec::new();
+                for m in mods {
+                    modifiers.extend(ctx.translate(m)?);
+                }
+                ctx.outer_modifiers = modifiers;
+
+                let mut result = Vec::new();
+                for (i, decl) in decls.into_iter().enumerate() {
+                    ctx.is_chained = i > 0;
+                    result.extend(ctx.translate(decl)?);
                 }
-                decl_ids
-            }}
+                Ok(result)
+            }
         ),
         // ---- Enums ----
         // enum_type_parameter → parameter (with optional name as pattern).
@@ -217,14 +345,18 @@ fn translation_rules() -> Vec<yeast::Rule> {
             =>
             (parameter type: {ty})
         ),
-        // enum_case_entry with associated values → class_like_declaration containing
-        // a constructor whose parameters are the data parameters.
+        // enum_case_entry with associated values → class_like_declaration
+        // containing a constructor whose parameters are the data
+        // parameters. Reads outer modifiers / chained tag from `ctx`
+        // (set by the outer `enum_entry` rule).
         rule!(
             (enum_case_entry
                 name: @name
                 data_contents: (enum_type_parameters parameter: _* @params))
             =>
             (class_like_declaration
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
                 modifier: (modifier "enum_case")
                 name: (identifier #{name})
                 member: (constructor_declaration parameter: {..params} body: (block)))
@@ -234,6 +366,8 @@ fn translation_rules() -> Vec<yeast::Rule> {
             (enum_case_entry name: @name raw_value: @val)
             =>
             (variable_declaration
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
                 modifier: (modifier "enum_case")
                 pattern: (name_pattern identifier: (identifier #{name}))
                 value: {val})
@@ -243,28 +377,31 @@ fn translation_rules() -> Vec<yeast::Rule> {
             (enum_case_entry name: @name)
             =>
             (variable_declaration
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
                 modifier: (modifier "enum_case")
                 pattern: (name_pattern identifier: (identifier #{name})))
         ),
-        // enum_entry: flatten case entries; attach outer modifiers to each, and
-        // chained_declaration on every entry after the first.
-        rule!(
+        // enum_entry: flatten case entries; publish outer modifiers
+        // into `ctx` and translate each case with `ctx.is_chained`
+        // toggled per iteration so the inner `enum_case_entry` rules
+        // emit complete `modifier:` lists from the start.
+        manual_rule!(
             (enum_entry case: _+ @cases (modifiers)* @mods)
-            =>
-            {..{
-                let mod_ids: Vec<usize> = mods.iter().map(|&m| m.into()).collect();
-                let case_ids: Vec<usize> = cases.iter().map(|&c| c.into()).collect();
-                for (i, &case_id) in case_ids.iter().enumerate() {
-                    if i > 0 {
-                        let chained = __yeast_ctx.literal("modifier", "chained_declaration");
-                        __yeast_ctx.prepend_field(case_id, "modifier", chained);
-                    }
-                    for &mod_id in mod_ids.iter().rev() {
-                        __yeast_ctx.prepend_field(case_id, "modifier", mod_id);
-                    }
+            {
+                let mut modifiers = Vec::new();
+                for m in mods {
+                    modifiers.extend(ctx.translate(m)?);
                 }
-                case_ids
-            }}
+                ctx.outer_modifiers = modifiers;
+
+                let mut result = Vec::new();
+                for (i, case) in cases.into_iter().enumerate() {
+                    ctx.is_chained = i > 0;
+                    result.extend(ctx.translate(case)?);
+                }
+                Ok(result)
+            }
         ),
         // Plain assignment: `x = expr`
         rule!(
@@ -336,17 +473,15 @@ fn translation_rules() -> Vec<yeast::Rule> {
                 body: (block stmt: {..body_stmts}))
         ),
         // Parameters are wrapped in function_parameter, which also carries
-        // optional default values.
-        rule!(
+        // optional default values. Publishes the default value into `ctx`
+        // before translating the inner `parameter` so the `parameter`
+        // rules can include it as a `default:` field directly.
+        manual_rule!(
             (function_parameter parameter: @p default_value: _? @def)
-            =>
-            {..{
-                let p_id: usize = p.into();
-                for &d in def.iter().rev() {
-                    __yeast_ctx.prepend_field(p_id, "default", d.into());
-                }
-                vec![p_id]
-            }}
+            {
+                ctx.default_value = ctx.translate_opt(def)?;
+                ctx.translate(p)
+            }
         ),
         // Parameter with external name and type
         rule!(
@@ -354,7 +489,8 @@ fn translation_rules() -> Vec<yeast::Rule> {
             =>
             (parameter
                 external_name: (identifier #{ext})
-                pattern: (name_pattern identifier: (identifier #{name})))
+                pattern: (name_pattern identifier: (identifier #{name}))
+                default: {..ctx.default_value})
         ),
         rule!(
             (parameter external_name: @ext name: @name type: @ty)
@@ -362,21 +498,24 @@ fn translation_rules() -> Vec<yeast::Rule> {
             (parameter
                 external_name: (identifier #{ext})
                 pattern: (name_pattern identifier: (identifier #{name}))
-                type: {ty})
+                type: {ty}
+                default: {..ctx.default_value})
         ),
         // Parameter with just name and type (no external name)
         rule!(
             (parameter name: @name)
             =>
             (parameter
-                pattern: (name_pattern identifier: (identifier #{name})))
+                pattern: (name_pattern identifier: (identifier #{name}))
+                default: {..ctx.default_value})
         ),
         rule!(
             (parameter name: @name type: @ty)
             =>
             (parameter
                 pattern: (name_pattern identifier: (identifier #{name}))
-                type: {ty})
+                type: {ty}
+                default: {..ctx.default_value})
         ),
         // Reference to a function, f(x:y:z:). This is parsed as a call with a single argument with multiple reference_specifier labels.
         // We don't want downstream QL to try to handle this as a call_expr with a weird argument, so explicitly mark it as unsupported for now.
@@ -484,11 +623,12 @@ fn translation_rules() -> Vec<yeast::Rule> {
                 argument: (argument value: {closure}))
         ),
         // ---- Control flow ----
+        // If statement
         rule!(
             (if_statement condition: _* @cond body: @then_body else_branch: _? @else_stmts)
             =>
             (if_expr
-                condition: {..cond}.reduce_left(first -> {first}, acc, elem -> (binary_expr operator: (infix_operator "&&") left: {acc} right: {elem}))
+                condition: {and_chain(&mut ctx, cond)}
                 then: {then_body}
                 else: {..else_stmts})
         ),
@@ -497,7 +637,7 @@ fn translation_rules() -> Vec<yeast::Rule> {
             (guard_statement condition: _* @cond body: (block statement: _* @else_stmts))
             =>
             (guard_if_stmt
-                condition: {..cond}.reduce_left(first -> {first}, acc, elem -> (binary_expr operator: (infix_operator "&&") left: {acc} right: {elem}))
+                condition: {and_chain(&mut ctx, cond)}
                 else: (block stmt: {..else_stmts}))
         ),
         // Ternary expression → if_expr
@@ -575,20 +715,24 @@ fn translation_rules() -> Vec<yeast::Rule> {
         rule!(
             (while_statement condition: _* @cond body: (block statement: _* @body))
             =>
-            (while_stmt condition: {..cond}.reduce_left(first -> {first}, acc, elem -> (binary_expr operator: (infix_operator "&&") left: {acc} right: {elem})) body: (block stmt: {..body}))
+            (while_stmt
+                condition: {and_chain(&mut ctx, cond)}
+                body: (block stmt: {..body}))
         ),
         // Repeat-while loop
         rule!(
             (repeat_while_statement condition: _* @cond body: (block statement: _* @body))
             =>
-            (do_while_stmt condition: {..cond}.reduce_left(first -> {first}, acc, elem -> (binary_expr operator: (infix_operator "&&") left: {acc} right: {elem})) body: (block stmt: {..body}))
+            (do_while_stmt
+                condition: {and_chain(&mut ctx, cond)}
+                body: (block stmt: {..body}))
         ),
         // Labeled statement (e.g. `outer: for ...`). Strip the trailing ':' from the label token.
-        rule!((labeled_statement label: (statement_label) @lbl statement: @stmt) => {..{
-            let text = __yeast_ctx.ast.source_text(lbl.into());
-            let name = __yeast_ctx.literal("identifier", &text[..text.len() - 1]);
-            vec![__yeast_ctx.node("labeled_stmt", vec![("label", vec![name]), ("stmt", vec![stmt.into()])])]
-        }}),
+        rule!((labeled_statement label: (statement_label) @lbl statement: @stmt) => {
+            let text = ctx.ast.source_text(lbl.into());
+            let name = &text[..text.len() - 1];
+            tree!((labeled_stmt label: (identifier #{name}) stmt: {stmt}))
+        }),
         // ---- Collections ----
         // Array literal
         rule!((array_literal element: _* @elems) => (array_literal element: {..elems})),
@@ -598,16 +742,9 @@ fn translation_rules() -> Vec<yeast::Rule> {
         rule!(
             (dictionary_literal key: _* @keys value: _* @vals)
             =>
-            (map_literal element: {..{
-                keys.iter().zip(vals.iter()).map(|(&k, &v)| {
-                    let k_id: usize = k.into();
-                    let v_id: usize = v.into();
-                    __yeast_ctx.node("key_value_pair", vec![
-                        ("key", vec![k_id]),
-                        ("value", vec![v_id]),
-                    ])
-                }).collect::<Vec<_>>()
-            }})
+            (map_literal element: {..keys.into_iter().zip(vals).map(|(k, v)|
+                tree!((key_value_pair key: {k} value: {v}))
+            )})
         ),
         rule!((dictionary_literal element: _* @elems) => (map_literal element: {..elems})),
         rule!((dictionary_literal_item key: @k value: @v) => (key_value_pair key: {k} value: {v})),
@@ -669,9 +806,7 @@ fn translation_rules() -> Vec<yeast::Rule> {
         rule!(
             (identifier part: _+ @parts)
             =>
-            {parts}.reduce_left(
-                first -> (name_expr identifier: (identifier #{first})),
-                acc, elem -> (member_access_expr base: {acc} member: (identifier #{elem})))
+            {member_chain(&mut ctx, parts)}
         ),
         // Scoped import declaration (for example `import struct Foo.Bar`):
         // flatten the identifier parts into a member_access_expr and bind the
@@ -874,48 +1009,76 @@ fn translation_rules() -> Vec<yeast::Rule> {
                 name: (identifier #{name})
                 bound: {..bound})
         ),
-        // Protocol property declaration: translate each accessor requirement to an
-        // accessor_declaration without a body, carrying the property name and type.
-        // Subsequent accessors get chained_declaration (same flattening as computed properties).
-        rule!(
+        // Protocol property declaration: translate each accessor
+        // requirement to an `accessor_declaration` carrying the property
+        // name, type, and outer modifiers. Manual rule: we publish the
+        // property's name/type/modifiers into `ctx` and translate each
+        // accessor with `ctx.is_chained` toggled per iteration so the
+        // inner `getter_specifier`/`setter_specifier` rules emit
+        // complete nodes from the start (including the
+        // `chained_declaration` tag for non-first accessors).
+        manual_rule!(
             (protocol_property_declaration
-                name: @pattern
+                name: (pattern bound_identifier: @name)
                 requirements: (protocol_property_requirements accessor: _+ @accessors)
                 type: _? @ty
                 (modifiers)* @mods)
-            =>
-            {..{
-                let name_text = __yeast_ctx.ast.source_text(pattern.into());
-                let mod_ids: Vec<usize> = mods.iter().map(|&m| m.into()).collect();
-                let ty_ids: Vec<usize> = ty.iter().map(|&t| t.into()).collect();
-                let acc_ids: Vec<usize> = accessors.iter().map(|&a| a.into()).collect();
-                for (i, &acc_id) in acc_ids.iter().enumerate() {
-                    if i > 0 {
-                        let chained = __yeast_ctx.literal("modifier", "chained_declaration");
-                        __yeast_ctx.prepend_field(acc_id, "modifier", chained);
-                    }
-                    for &mod_id in mod_ids.iter().rev() {
-                        __yeast_ctx.prepend_field(acc_id, "modifier", mod_id);
-                    }
-                    for &ty_id in ty_ids.iter().rev() {
-                        __yeast_ctx.prepend_field(acc_id, "type", ty_id);
-                    }
-                    let ident = __yeast_ctx.literal("identifier", &name_text);
-                    __yeast_ctx.prepend_field(acc_id, "name", ident);
+            {
+                ctx.property_name = Some(tree!((identifier #{name})));
+                ctx.property_type = ctx.translate_opt(ty)?;
+                let mut modifiers = Vec::new();
+                for m in mods {
+                    modifiers.extend(ctx.translate(m)?);
                 }
-                acc_ids
-            }}
+                ctx.outer_modifiers = modifiers;
+
+                let mut result = Vec::new();
+                for (i, acc) in accessors.into_iter().enumerate() {
+                    ctx.is_chained = i > 0;
+                    result.extend(ctx.translate(acc)?);
+                }
+                Ok(result)
+            }
         ),
         // getter_specifier / setter_specifier → bodyless accessor_declaration
-        rule!((getter_specifier) => (accessor_declaration accessor_kind: (accessor_kind "get"))),
-        rule!((setter_specifier) => (accessor_declaration accessor_kind: (accessor_kind "set"))),
+        // getter_specifier / setter_specifier → bodyless
+        // accessor_declaration. Reads property name/type/modifiers from
+        // `ctx` set by the outer `protocol_property_declaration` rule.
+        rule!(
+            (getter_specifier)
+            =>
+            (accessor_declaration
+                name: {ctx.property_name.ok_or("getter_specifier outside protocol_property_declaration context")?}
+                type: {..ctx.property_type}
+                accessor_kind: (accessor_kind "get")
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)})
+        ),
+        rule!(
+            (setter_specifier)
+            =>
+            (accessor_declaration
+                name: {ctx.property_name.ok_or("setter_specifier outside protocol_property_declaration context")?}
+                type: {..ctx.property_type}
+                accessor_kind: (accessor_kind "set")
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)})
+        ),
         // protocol_property_requirements wrapper — should be consumed by above; fallback
         rule!((protocol_property_requirements accessor: _* @accs) => {..accs}),
         // Computed getter → accessor_declaration (body optional).
+        // Reads property name/type from the outer property_binding rule
+        // and binding/outer modifiers + chained tag from the outer
+        // property_declaration rule.
         rule!(
             (computed_getter body: (block statement: _* @body)?)
             =>
             (accessor_declaration
+                modifier: {..ctx.binding_modifier}
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
+                name: {ctx.property_name.ok_or("computed_getter outside property_binding context")?}
+                type: {..ctx.property_type}
                 accessor_kind: (accessor_kind "get")
                 body: (block stmt: {..body}))
         ),
@@ -924,6 +1087,11 @@ fn translation_rules() -> Vec<yeast::Rule> {
             (computed_setter parameter: @param body: (block statement: _* @body))
             =>
             (accessor_declaration
+                modifier: {..ctx.binding_modifier}
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
+                name: {ctx.property_name.ok_or("computed_setter outside property_binding context")?}
+                type: {..ctx.property_type}
                 accessor_kind: (accessor_kind "set")
                 parameter: (parameter pattern: (name_pattern identifier: (identifier #{param})))
                 body: (block stmt: {..body}))
@@ -933,6 +1101,11 @@ fn translation_rules() -> Vec<yeast::Rule> {
             (computed_setter body: (block statement: _* @body)?)
             =>
             (accessor_declaration
+                modifier: {..ctx.binding_modifier}
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
+                name: {ctx.property_name.ok_or("computed_setter outside property_binding context")?}
+                type: {..ctx.property_type}
                 accessor_kind: (accessor_kind "set")
                 body: (block stmt: {..body}))
         ),
@@ -941,16 +1114,30 @@ fn translation_rules() -> Vec<yeast::Rule> {
             (computed_modify body: (block statement: _* @body))
             =>
             (accessor_declaration
+                modifier: {..ctx.binding_modifier}
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
+                name: {ctx.property_name.ok_or("computed_modify outside property_binding context")?}
+                type: {..ctx.property_type}
                 accessor_kind: (accessor_kind "modify")
                 body: (block stmt: {..body}))
         ),
-        // willset/didset block — spread to children
+        // willset/didset block — spread to children (only reachable as a
+        // fallback; the outer property_binding manual rule normally
+        // captures the willset/didset clauses directly).
         rule!((willset_didset_block _* @clauses) => {..clauses}),
-        // willset clause → accessor_declaration (body optional).
+        // willset clause → accessor_declaration (body optional). Reads
+        // `ctx.property_name` set by the outer property_binding rule and
+        // binding/outer modifiers + chained tag from the outer
+        // property_declaration rule.
         rule!(
             (willset_clause body: (block statement: _* @body)?)
             =>
             (accessor_declaration
+                modifier: {..ctx.binding_modifier}
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
+                name: {ctx.property_name.ok_or("willset_clause outside property_binding context")?}
                 accessor_kind: (accessor_kind "willSet")
                 body: (block stmt: {..body}))
         ),
@@ -959,6 +1146,10 @@ fn translation_rules() -> Vec<yeast::Rule> {
             (didset_clause body: (block statement: _* @body)?)
             =>
             (accessor_declaration
+                modifier: {..ctx.binding_modifier}
+                modifier: {..ctx.outer_modifiers.clone()}
+                modifier: {..chained_modifier(&mut ctx)}
+                name: {ctx.property_name.ok_or("didset_clause outside property_binding context")?}
                 accessor_kind: (accessor_kind "didSet")
                 body: (block stmt: {..body}))
         ),
@@ -979,14 +1170,17 @@ fn translation_rules() -> Vec<yeast::Rule> {
 }
 
 pub fn language_spec(desugared_ast_schema: &'static str) -> simple::LanguageSpec {
-    let desugar = DesugaringConfig::new()
+    let ts_language: tree_sitter::Language = tree_sitter_swift::LANGUAGE.into();
+    let config = DesugaringConfig::<SwiftContext>::new()
         .add_phase("translate", PhaseKind::OneShot, translation_rules())
         .with_output_node_types_yaml(desugared_ast_schema);
+    let desugarer = ConcreteDesugarer::new(ts_language.clone(), config)
+        .expect("failed to build Swift desugarer");
     simple::LanguageSpec {
         prefix: "swift",
-        ts_language: tree_sitter_swift::LANGUAGE.into(),
+        ts_language,
         node_types: tree_sitter_swift::NODE_TYPES,
         file_globs: vec!["*.swift".into(), "*.swiftinterface".into()],
-        desugar: Some(desugar),
+        desugar: Some(Box::new(desugarer)),
     }
 }
diff --git a/unified/extractor/tests/corpus/swift/types.txt b/unified/extractor/tests/corpus/swift/types.txt
index ef15ad87f594..9c22ae74798b 100644
--- a/unified/extractor/tests/corpus/swift/types.txt
+++ b/unified/extractor/tests/corpus/swift/types.txt
@@ -924,3 +924,159 @@ top_level
               accessor_kind: accessor_kind "set"
           modifier: modifier "class"
           name: identifier "Box"
+
+===
+Protocol with read-only and read-write property requirements
+===
+
+protocol P {
+  var foo: Int { get }
+  var bar: String { get set }
+}
+
+---
+
+source_file
+  statement:
+    protocol_declaration
+      body:
+        protocol_body
+          member:
+            protocol_property_declaration
+              name:
+                pattern
+                  binding:
+                    value_binding_pattern
+                      mutability: var
+                  bound_identifier: simple_identifier "foo"
+              requirements:
+                protocol_property_requirements
+                  accessor:
+                    getter_specifier
+              type:
+                type_annotation
+                  type:
+                    type
+                      name:
+                        user_type
+                          part:
+                            simple_user_type
+                              name: type_identifier "Int"
+            protocol_property_declaration
+              name:
+                pattern
+                  binding:
+                    value_binding_pattern
+                      mutability: var
+                  bound_identifier: simple_identifier "bar"
+              requirements:
+                protocol_property_requirements
+                  accessor:
+                    getter_specifier
+                    setter_specifier
+              type:
+                type_annotation
+                  type:
+                    type
+                      name:
+                        user_type
+                          part:
+                            simple_user_type
+                              name: type_identifier "String"
+      name: type_identifier "P"
+
+---
+
+top_level
+  body:
+    block
+      stmt:
+        class_like_declaration
+          member:
+            accessor_declaration
+              name: identifier "foo"
+              type:
+                named_type_expr
+                  name: identifier "Int"
+              accessor_kind: accessor_kind "get"
+            accessor_declaration
+              name: identifier "bar"
+              type:
+                named_type_expr
+                  name: identifier "String"
+              accessor_kind: accessor_kind "get"
+            accessor_declaration
+              modifier: modifier "chained_declaration"
+              name: identifier "bar"
+              type:
+                named_type_expr
+                  name: identifier "String"
+              accessor_kind: accessor_kind "set"
+          modifier: modifier "protocol"
+          name: identifier "P"
+
+===
+Enum with comma-separated cases (chained_declaration)
+===
+
+enum Suit {
+  case clubs, diamonds, hearts, spades
+}
+
+---
+
+source_file
+  statement:
+    class_declaration
+      body:
+        enum_class_body
+          member:
+            enum_entry
+              case:
+                enum_case_entry
+                  name: simple_identifier "clubs"
+                enum_case_entry
+                  name: simple_identifier "diamonds"
+                enum_case_entry
+                  name: simple_identifier "hearts"
+                enum_case_entry
+                  name: simple_identifier "spades"
+      declaration_kind: enum
+      name: type_identifier "Suit"
+
+---
+
+top_level
+  body:
+    block
+      stmt:
+        class_like_declaration
+          member:
+            variable_declaration
+              modifier: modifier "enum_case"
+              pattern:
+                name_pattern
+                  identifier: identifier "clubs"
+            variable_declaration
+              modifier:
+                modifier "chained_declaration"
+                modifier "enum_case"
+              pattern:
+                name_pattern
+                  identifier: identifier "diamonds"
+            variable_declaration
+              modifier:
+                modifier "chained_declaration"
+                modifier "enum_case"
+              pattern:
+                name_pattern
+                  identifier: identifier "hearts"
+            variable_declaration
+              modifier:
+                modifier "chained_declaration"
+                modifier "enum_case"
+              pattern:
+                name_pattern
+                  identifier: identifier "spades"
+          modifier: modifier "enum"
+          name: identifier "Suit"
diff --git a/unified/extractor/tests/corpus/swift/variables.txt b/unified/extractor/tests/corpus/swift/variables.txt
index f1da058eef2e..78b80d9a5098 100644
--- a/unified/extractor/tests/corpus/swift/variables.txt
+++ b/unified/extractor/tests/corpus/swift/variables.txt
@@ -319,3 +319,130 @@ top_level
             name_expr
               identifier: identifier "x"
           value: int_literal "1"
+
+===
+Property with willSet and didSet observers
+===
+
+class C {
+  var x: Int = 0 {
+    willSet { print(newValue) }
+    didSet { print(oldValue) }
+  }
+}
+
+---
+
+source_file
+  statement:
+    class_declaration
+      body:
+        class_body
+          member:
+            property_declaration
+              binding:
+                value_binding_pattern
+                  mutability: var
+              declarator:
+                property_binding
+                  name:
+                    pattern
+                      bound_identifier: simple_identifier "x"
+                  observers:
+                    willset_didset_block
+                      didset:
+                        didset_clause
+                          body:
+                            block
+                              statement:
+                                call_expression
+                                  function: simple_identifier "print"
+                                  suffix:
+                                    call_suffix
+                                      arguments:
+                                        value_arguments
+                                          argument:
+                                            value_argument
+                                              value: simple_identifier "oldValue"
+                      willset:
+                        willset_clause
+                          body:
+                            block
+                              statement:
+                                call_expression
+                                  function: simple_identifier "print"
+                                  suffix:
+                                    call_suffix
+                                      arguments:
+                                        value_arguments
+                                          argument:
+                                            value_argument
+                                              value: simple_identifier "newValue"
+                  type:
+                    type_annotation
+                      type:
+                        type
+                          name:
+                            user_type
+                              part:
+                                simple_user_type
+                                  name: type_identifier "Int"
+                  value: integer_literal "0"
+      declaration_kind: class
+      name: type_identifier "C"
+
+---
+
+top_level
+  body:
+    block
+      stmt:
+        class_like_declaration
+          member:
+            variable_declaration
+              modifier: modifier "var"
+              pattern:
+                name_pattern
+                  identifier: identifier "x"
+              type:
+                named_type_expr
+                  name: identifier "Int"
+              value: int_literal "0"
+            accessor_declaration
+              body:
+                block
+                  stmt:
+                    call_expr
+                      argument:
+                        argument
+                          value:
+                            name_expr
+                              identifier: identifier "newValue"
+                      callee:
+                        name_expr
+                          identifier: identifier "print"
+              modifier:
+                modifier "var"
+                modifier "chained_declaration"
+              name: identifier "x"
+              accessor_kind: accessor_kind "willSet"
+            accessor_declaration
+              body:
+                block
+                  stmt:
+                    call_expr
+                      argument:
+                        argument
+                          value:
+                            name_expr
+                              identifier: identifier "oldValue"
+                      callee:
+                        name_expr
+                          identifier: identifier "print"
+              modifier:
+                modifier "var"
+                modifier "chained_declaration"
+              name: identifier "x"
+              accessor_kind: accessor_kind "didSet"
+          modifier: modifier "class"
+          name: identifier "C"
diff --git a/unified/extractor/tests/corpus_tests.rs b/unified/extractor/tests/corpus_tests.rs
index 0f1057a8e5b9..6c859c2f6cf0 100644
--- a/unified/extractor/tests/corpus_tests.rs
+++ b/unified/extractor/tests/corpus_tests.rs
@@ -2,7 +2,7 @@ use std::fs;
 use std::path::Path;
 
 use codeql_extractor::extractor::simple;
-use yeast::{dump::dump_ast, dump::dump_ast_with_type_errors, Runner};
+use yeast::{Runner, dump::dump_ast, dump::dump_ast_with_type_errors};
 
 #[path = "../src/languages/mod.rs"]
 mod languages;
@@ -146,29 +146,36 @@ fn render_corpus(cases: &[CorpusCase]) -> String {
     out
 }
 
-fn run_desugaring(
-    lang: &simple::LanguageSpec,
-    input: &str,
-) -> Result<yeast::Ast, String> {
-    let runner = match lang.desugar.as_ref() {
-        Some(config) => Runner::from_config(lang.ts_language.clone(), config)
-            .map_err(|e| format!("Failed to create yeast runner: {e}"))?,
-        None => Runner::new(lang.ts_language.clone(), &[]),
-    };
-
-    runner
-        .run(input)
-        .map_err(|e| format!("Failed to parse input: {e}"))
+fn run_desugaring(lang: &simple::LanguageSpec, input: &str) -> Result<yeast::Ast, String> {
+    match lang.desugar.as_deref() {
+        Some(desugarer) => {
+            // Parse the input ourselves so we don't depend on the desugarer
+            // knowing about the language.
+            let mut parser = tree_sitter::Parser::new();
+            parser
+                .set_language(&lang.ts_language)
+                .map_err(|e| format!("Failed to set language: {e}"))?;
+            let tree = parser
+                .parse(input, None)
+                .ok_or_else(|| "Failed to parse input".to_string())?;
+            desugarer
+                .run_from_tree(&tree, input.as_bytes())
+                .map_err(|e| format!("Desugaring failed: {e}"))
+        }
+        None => {
+            let runner: Runner = Runner::new(lang.ts_language.clone(), &[]);
+            runner
+                .run(input)
+                .map_err(|e| format!("Failed to parse input: {e}"))
+        }
+    }
 }
 
 /// Produce the raw tree-sitter parse tree dump for `input`, with no
 /// desugaring rules applied. Uses a `Runner` with an empty phase list and
 /// the input grammar's own schema.
-fn dump_raw_parse(
-    lang: &simple::LanguageSpec,
-    input: &str,
-) -> Result<String, String> {
-    let runner = Runner::new(lang.ts_language.clone(), &[]);
+fn dump_raw_parse(lang: &simple::LanguageSpec, input: &str) -> Result<String, String> {
+    let runner: Runner = Runner::new(lang.ts_language.clone(), &[]);
     let ast = runner
         .run(input)
         .map_err(|e| format!("Failed to parse input: {e}"))?;
@@ -272,11 +279,7 @@ fn test_corpus() {
                 }
             }
 
-            assert!(
-                failures.is_empty(),
-                "{}",
-                failures.join("\n\n") + "\n\n"
-            );
+            assert!(failures.is_empty(), "{}", failures.join("\n\n") + "\n\n");
 
             if update_mode {
                 let updated = render_corpus(&cases);
@@ -285,7 +288,9 @@ fn test_corpus() {
                     write_result.is_ok(),
                     "Failed to update corpus file {}: {}",
                     corpus_path.display(),
-                    write_result.err().map_or_else(String::new, |e| e.to_string())
+                    write_result
+                        .err()
+                        .map_or_else(String::new, |e| e.to_string())
                 );
             }
         }