toolchain: batch example-case validation in precheck (~7x faster)

toolchain/bootstrap/precheck.sh

@@ -115,16 +115,15 @@ fi
 ) &
 PID_PARAM_DOCS=$!
 
-# Example case validation
+# Example case validation - validate ALL cases in ONE process (validate accepts multiple files) instead of a
+# per-case './mfc.sh validate' loop. Each invocation re-paid the mfc.sh/venv bootstrap (~2.4s), which dominated
+# (~90%) the ~6 min serial loop over 155 cases; batching drops it to well under a minute.
 (
-    failed=0
-    for case in examples/*/case.py; do
-        [ -f "$case" ] || continue
-        if ! ./mfc.sh validate "$case" > /dev/null 2>&1; then
-            failed=$((failed + 1))
-        fi
-    done
-    echo "$failed" > "$TMPDIR_PC/examples_exit"
+    if ./mfc.sh validate examples/*/case.py > /dev/null 2>&1; then
+        echo "0" > "$TMPDIR_PC/examples_exit"
+    else
+        echo "1" > "$TMPDIR_PC/examples_exit"
+    fi
 ) &
 PID_EXAMPLES=$!
 
@@ -194,7 +193,7 @@ EXAMPLES_FAILED=$(cat "$TMPDIR_PC/examples_exit" 2>/dev/null || echo "1")
 if [ "$EXAMPLES_FAILED" = "0" ]; then
     ok "All example cases are valid."
 else
-    error "$EXAMPLES_FAILED example case(s) failed validation. Run$MAGENTA ./mfc.sh validate examples/\*/case.py$COLOR_RESET for details."
+    error "Example case validation failed. Run$MAGENTA ./mfc.sh validate examples/\*/case.py$COLOR_RESET for the failing case(s)."
     FAILED=1
 fi
 

toolchain/mfc/args.py

@@ -175,6 +175,9 @@ def custom_error(message):
             continue
 
         if args.get(e) is not None:
-            args[e] = os.path.abspath(args[e])
+            if isinstance(args[e], list):  # validate accepts multiple case files (nargs="+")
+                args[e] = [os.path.abspath(p) for p in args[e]]
+            else:
+                args[e] = os.path.abspath(args[e])
 
     return args

toolchain/mfc/cli/commands.py

@@ -546,7 +546,8 @@
     positionals=[
         Positional(
             name="input",
-            help="Path to case file to validate.",
+            help="Path(s) to case file(s) to validate. Multiple files validate in one process (used by precheck).",
+            nargs="+",
             completion=Completion(type=CompletionType.FILES_PY),
         ),
     ],

toolchain/mfc/validate.py

@@ -12,9 +12,58 @@
 from .state import ARG
 
 
+def _validate_batch(inputs):
+    """Load + constraint-validate many case files in ONE process. Used by precheck to validate every example
+    case without re-paying the mfc.sh/venv bootstrap per case (the serial per-case './mfc.sh validate' loop
+    was ~90% bootstrap overhead). Only a load/parse failure fails the command - constraint issues are warnings -
+    matching the historical per-file exit behavior (a single './mfc.sh validate' exits non-zero only on load error).
+    Cases with constraint issues are still surfaced (listed in the summary) so the batched output is not misleading."""
+    failed = []
+    with_issues = []
+    for c in inputs:
+        if not os.path.isfile(c):
+            failed.append(c)
+            continue
+        try:
+            case = run_input.load(c, do_print=False)
+        except MFCException:
+            failed.append(c)
+            continue
+        had_issue = False
+        for stage in ("pre_process", "simulation", "post_process"):
+            try:
+                if CaseValidator(case.params).validate(stage):  # non-empty -> warnings
+                    had_issue = True
+            except CaseConstraintError:
+                had_issue = True  # constraint violation is a warning here, not a load failure
+        if had_issue:
+            with_issues.append(c)
+    n = len(inputs)
+    if failed:
+        cons.print(f"[bold red]✗ {len(failed)}/{n} case(s) failed to load:[/bold red]")
+        for c in failed:
+            cons.print(f"    {c}")
+        sys.exit(1)
+    if with_issues:
+        cons.print(f"[bold green]✓[/bold green] Validated {n} case(s): all loaded " f"([yellow]{len(with_issues)} with constraint issues[/yellow]; " f"run './mfc.sh validate <case>' for details):")
+        for c in with_issues:
+            cons.print(f"    [yellow]⚠[/yellow] {c}")
+    else:
+        cons.print(f"[bold green]✓[/bold green] Validated {n} case(s): all loaded, no constraint issues.")
+
+
 def validate():
-    """Validate a case file without building or running."""
-    input_file = ARG("input")
+    """Validate one or more case files without building or running."""
+    inputs = ARG("input")
+    if isinstance(inputs, str):
+        inputs = [inputs]
+    if len(inputs) > 1:
+        if ARG("migrate"):  # --migrate rewrites a file in place; only meaningful one case at a time
+            cons.print("[bold red]Error:[/bold red] --migrate operates on a single case file at a time.")
+            sys.exit(1)
+        _validate_batch(inputs)
+        return
+    input_file = inputs[0]
 
     if not os.path.isfile(input_file):
         cons.print(f"[bold red]Error:[/bold red] File not found: {input_file}")