diff --git a/.github/workflows/VersionCheck.yml b/.github/workflows/VersionCheck.yml
index 63396b0..ecedc3d 100644
--- a/.github/workflows/VersionCheck.yml
+++ b/.github/workflows/VersionCheck.yml
@@ -49,6 +49,45 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
+      # `[sources]` entries that must never reach `main`: an absolute `path` is a
+      # machine-specific `Pkg.develop` leak (it resolves the dep from a path that
+      # exists only on the author's machine, staying green on CI where it is
+      # absent), and a `url` is a cross-repo branch pin that is fine mid-review but
+      # resolves the dep from an unregistered branch once merged. A relative `path`
+      # (e.g. a subproject pointing at "..") is legitimate and allowed. Failing in
+      # draft PRs is intended: the point is to block these from reaching `main`.
+      - name: "Reject non-portable [sources] entries in Project.toml"
+        run: |
+          python3 - <<'PY'
+          import os, subprocess, sys, tomllib
+
+          files = subprocess.check_output(
+              ["git", "ls-files", "*Project.toml"], text=True
+          ).split()
+          bad = []
+          for f in files:
+              with open(f, "rb") as fh:
+                  data = tomllib.load(fh)
+              for name, spec in data.get("sources", {}).items():
+                  if not isinstance(spec, dict):
+                      continue
+                  path = spec.get("path")
+                  if path is not None and os.path.isabs(path):
+                      bad.append(f'{f}: [sources.{name}] has an absolute path = "{path}"')
+                  if "url" in spec:
+                      bad.append(f'{f}: [sources.{name}] has a url = "{spec["url"]}"')
+          if bad:
+              print(
+                  "::error::These [sources] entries must not be merged to main: an "
+                  "absolute path is machine-specific, and a url is a cross-repo "
+                  'branch pin. Use a relative path (e.g. "..") or drop the source.'
+              )
+              for b in bad:
+                  print(b)
+              sys.exit(1)
+          print(f"Checked {len(files)} Project.toml file(s); no non-portable [sources] entries.")
+          PY
+
       - uses: ITensor/ITensorActions/.github/actions/classify-pr@main
         id: classify
         with:
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..0970e9a
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,20 @@
+# ITensorActions
+
+Reusable GitHub Actions workflows shared across the ITensor Julia packages. Caller
+repos pin these workflows at the major-version tag (e.g.
+`ITensor/ITensorActions/.github/workflows/Tests.yml@v2`).
+
+## Releasing (required after any behavior change)
+
+Callers consume these workflows at the mutable `v2` tag, which does **not** follow
+`main`. A change merged to `main` therefore reaches no caller until a release moves
+`v2`. So after merging a PR that changes workflow behavior, cut a release:
+
+- Run `.scripts/release.sh vX.Y.Z` from a clean `main` checkout. It tags the new
+  version and moves the `v2` pointer to it (and pins the released commit's internal
+  `@main` action references to a fixed SHA so the release is a stable bundle).
+- Choose the bump per the SemVer rule in the README ("Versioning" section): patch
+  for fixes or internal hardening, minor for additive behavior or new inputs, major
+  for breaking caller-facing changes.
+- Docs-only PRs (including edits to this file) need no release and must not move
+  `v2`.
diff --git a/README.md b/README.md
index 8c97204..f7ab1f0 100644
--- a/README.md
+++ b/README.md
@@ -673,6 +673,15 @@ The suffix is freeform; any non-empty prerelease tag triggers the skip behavior.
 
 `VersionCheck` also validates the bump shape pre-merge (patch+1 for non-breaking, minor+1 with patch=0 for pre-1.0 breaking, major+1 with minor=patch=0 for post-1.0 breaking) so malformed bumps fail the PR check directly rather than only after merge in `Registrator`.
 
+### Project.toml `[sources]` check
+
+Independently of the version-bump check (it runs on every PR, regardless of scope or draft state), `VersionCheck` rejects `[sources]` entries in any tracked `Project.toml` that must not reach `main`:
+
+- an absolute `path`, which is a machine-specific `Pkg.develop` artifact: it resolves the dependency from a location that exists only on the author's machine, and stays green on CI, where the path is absent, so nothing else catches it;
+- a `url`, which is a cross-repo branch pin: legitimate while a dependent PR is in review, but once merged it resolves the dependency from an unregistered branch.
+
+A relative `path` (for example a subproject pointing at `".."`) is legitimate and allowed. Both the `[sources.Name]` table and the inline `Name = {path = "..."}` forms are checked. Because it runs regardless of draft state, a dependent PR that pins an upstream branch shows a failing check until it drops the pin before merge.
+
 ## Check Compat Bounds
 
 The `CheckCompatBounds` workflow instantiates the package and fails if any