feat(#1733): normalize-path-in-content production AST rule + fix Windows agent-skills content leak (Phase 5) (#1736)

* feat(#1733): normalize-path-in-content production AST rule (Phase 5)

ADR-1703 Phase 5 — the first production-code rule. local/normalize-path-in-content
(src/**/*.cts, @typescript-eslint/parser): flags a path-returning fn result
(path.basename excluded — returns a separator-less filename) interpolated into an
@-reference / config-dir markdown body without .replace(/\\/g,'/') normalization,
per RULESET.CONTENT-PATH-NORMALIZATION / DEFECT.WINDOWS-PATH-LEAK-IN-MARKDOWN-CONTENT.

Build-and-assess found the canonical defect site (computePathPrefix) already
compliant and only 1 src/ hit — a false positive (path.basename in a status
message) — eliminated by narrowing (exclude basename; require a real @-ref/
config-dir marker, not bare .md). 0 src/ violations: clean forward-prevention.

The out-of-band disable-ban now scans src/**/*.cts too (typescript-estree) so the
production rule also cannot be eslint-disabled. Registered (error) + PROTECTED_RULES;
CONTEXT.md predicates + how-to doc updated.

- RuleTester suite (26 cases)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* docs(#1733): add changeset for Windows agent-skills path-leak fix

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix: harden mutation-matrix.cjs stdin read against EAGAIN on non-blocking pipe

scripts/mutation-matrix.cjs read piped stdin via readFileSync(process.stdin.fd).
On macOS libuv marks the stdin pipe fd non-blocking, so a synchronous read can
throw EAGAIN before the writer fills the pipe — intermittently, under heavy CI
shard load — aborting the script (status 2) and flaking mutation-matrix-ratchet.
Replace with readStdinSync(): an fs.readSync loop that retries on EAGAIN (1ms
synchronous Atomics.wait yield), stops on 0-byte/EOF, and rethrows other errors.
Deterministic regression test injects EAGAIN via an fs.readSync monkeypatch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* ci: re-run golden-install-parity on src/lib + installer changes (close drift guard)

golden-install-parity hashes every installed bin/lib/*.cjs per runtime, so it
must re-run whenever the built lib could change. ci-test-scope selected it for
neither src/** nor installer changes, so a source-only edit (e.g. #1691's
milestone.cts/roadmap.cts) recompiled bin/lib and silently drifted the golden
fixtures past the scoped lane. Add golden-install-parity.test.cjs to both the
'TS runtime sources' and 'installer and package layout' selection rules, with
behavioral regression tests for each.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: review-bot <review-bot@gsd>

docs/contributing/cross-platform-portability-rules.md

@@ -21,8 +21,9 @@ running outside ESLint, fails the build if you try). Legitimately platform-speci
 | `local/no-unguarded-nonportable-exec` | A file that **both** sets a chmod exec-bit (`chmod`/`chmodSync` with `0oNNN & 0o111 !== 0`) **and** invokes `sh`/`bash` with a `-c` flag (`execFileSync`/`spawnSync`/`spawn`/`exec`/`execSync`) without a Windows platform guard — Windows Git Bash ignores the exec bit for extension-less PATH-executed scripts. | `tests/**/*.test.cjs` |
 | `local/no-crlf-fragile-split` | A `.split('\n')` or `.split("\n")` call on `readFileSync` content, **or** a regex literal containing a bare `\n` used against `readFileSync` content — Windows `git-autocrlf` yields `\r\n` line endings so a literal `\n` split or regex will mismatch. | `tests/**/*.test.cjs` |
 | `local/no-hardcoded-tmp` | A hardcoded `/tmp/` string passed as the first argument to an `fs.*` function or `path.join` — `/tmp` does not exist on Windows. Use `os.tmpdir()` instead. | `tests/**/*.test.cjs` |
-| `local/no-bare-npm-exec` | An `execFileSync`/`spawnSync`/`spawn`/`exec`/`execSync` call with `"npm"` as the command and no `{ shell: true }` option (or a platform-guarded equivalent) — `npm` is a `.cmd` batch wrapper on Windows and will not be found without a shell. | `tests/**/*.test.cjs` |
-| `local/require-userprofile-with-home` | A `process.env.HOME = <x>` assignment in a test file with no corresponding `process.env.USERPROFILE` reference anywhere in the file — Windows uses `USERPROFILE` as the home directory environment variable, not `HOME`. | `tests/**/*.test.cjs` |
+| `local/no-bare-npm-exec` | An `execFileSync`/`spawnSync`/`spawn` call with `"npm"` as the command and no `{ shell: true }` option (or a platform-guarded equivalent) — `npm` is a `.cmd` batch wrapper on Windows and is not found without a shell. (`execSync`/`exec` already run via a shell, so they are not flagged.) | `tests/**/*.test.cjs` |
+| `local/require-userprofile-with-home` | A `process.env.HOME = <x>` assignment in a test file with no corresponding `process.env.USERPROFILE` **assignment** — Windows uses `USERPROFILE` as the home directory environment variable, not `HOME`. | `tests/**/*.test.cjs` |
+| `local/normalize-path-in-content` | A path-returning fn result (excluding `path.basename`, which returns a separator-less filename) interpolated **directly** into content without `.replace(/\\/g,'/')` normalization — backslash paths leak into generated content on Windows (`RULESET.CONTENT-PATH-NORMALIZATION`). Two content shapes are detected: (a) the template/string contains an `@`-reference marker (`@~/`, `@$`, `@/`), `$HOME`, or `~/`; (b) the quasi immediately following the interpolation starts with `/…\.md` or `/…\.json`. **Indirect data-flow** (path stored in a variable/field then interpolated) is not detected — normalize at source. Fix: `String(resolvedTarget).replace(/\\/g, '/')`. | `src/**/*.cts` |
 
 (See ADR-1703's catalog and [epic #1702](https://github.com/open-gsd/gsd-core/issues/1702) for the full phase history.)
 
@@ -237,3 +238,14 @@ The rule matches by spelling and inspects the direct operand (or a `String(<path
   inspected; assert against the path call directly or its `String(...)` wrap.
 - For a genuine explicit-dir *pass-through* assertion (a resolver that returns its input
   verbatim), the `String(...).replace(/\\/g,'/')` remedy is a harmless no-op.
+- **The rule catches a path-returning call interpolated *directly* into `${ }`.** It does NOT
+  track **indirect data-flow** — a path stored in a variable or object field, then interpolated
+  (e.g. `${globalSkillDir}/SKILL.md` → `@${entry.ref}`). Indirect content-path-leaks rely on
+  `RULESET.CONTENT-PATH-NORMALIZATION` discipline (normalize at source) and code review.
+  The one known indirect leak (`src/init.cts` `cmdAgentSkills` `entry.ref` building) is fixed
+  by normalizing at the content-emit site: `- @${String(entry.ref).replace(/\\/g, '/')}`.
+- **Content detection shape (b)** fires when the quasi *immediately following* the interpolation
+  starts with `/…\.md` or `/…\.json`. A bare `.md` or `.json` token in the *middle* of prose
+  (e.g. `: see README.md`) does NOT qualify — the quasi must start with the forward slash.
+  Config-dir substrings (`/.claude`, `/commands`, `/skills`, etc.) are deliberately NOT content
+  markers — they caused false positives on log/error/diagnostic strings mentioning config dirs.