refactor(#870): extract ROADMAP.md parsing into roadmap-parser.cts (#876)

ADR-857 rollout phase 2b. Move the 6 ROADMAP.md-parsing functions
(stripShippedMilestones, extractCurrentMilestone, replaceInCurrentMilestone,
getRoadmapPhaseInternal, getMilestoneInfo, getMilestonePhaseFilter) + their
interfaces out of core.cts into a new leaf module src/roadmap-parser.cts.
core.cts re-exports them (behavior-preserving); ~9 external callers unchanged.

Resolves the parse/write straddle: roadmap.cts (ROADMAP.md mutation) now imports
its 3 parsing helpers from roadmap-parser.cjs directly instead of reaching
through core. roadmap-parser depends only on leaves (phase-id, planning-workspace,
shell-command-projection) — cycle-free, enabled by phase 2a.

New-CLI-module checklist done (.gitignore, eslint, INVENTORY 92->93 + row,
manifest, ARCHITECTURE, CONTEXT.md "Roadmap Parser Module"). Adds
tests/roadmap-parser.test.cjs (46 tests: behavioral + shim-identity +
adversarial ROADMAP.md fixtures).

Adversarial review surfaced a pre-existing fence-blindness bug in
getMilestonePhaseFilter (matches phase headings inside fenced code blocks);
filed as #875 and left for a separate fix (out of scope for this
behavior-preserving extraction). The two fenced-fixture tests characterize the
current behavior with a #875 reference and flip when it's fixed.

Gates: lint, code-review, security-review, codex adversarial-review (0
correctness findings). gsd-test: clean-build docker + Mac green; the full-suite
docker run's "X is not a function" errors on re-exported symbols were local
incremental-tsc staleness (verified: clean rebuild of the affected files = 195
pass, 0 fail; Mac = 4001 pass).

Closes #870

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

CONTEXT.md

@@ -112,6 +112,9 @@ Primary installer for all runtimes. Single production file: `bin/install.js` (ge
 ### I/O Module
 Module owning the tool's CLI I/O primitives: `output()` result emission (with large-payload temp-file spillover via `GSD_TEMP_DIR`/`ensureGsdTempDir`/`reapStaleTempFiles`), `error()` stderr emission with exit-code mapping, and the JSON-error-mode toggle (`setJsonErrorMode`/`getJsonErrorMode`, `ERROR_REASON`). Extracted from the Core module per ADR-857 rollout phase 1 (#859) so feature modules (`graphify`, `intel`, `audit`, `profile-pipeline`) depend on a small I/O seam instead of the core god-module; `core.cjs` re-exports the primitives for back-compat. Source of truth: `gsd-core/bin/lib/io.cjs` (generated from `src/io.cts`).
 
+### Roadmap Parser Module
+Module owning ROADMAP.md parsing: shipped-milestone slicing, current-milestone extraction, milestone/phase lookups, and milestone-phase filtering (`stripShippedMilestones`, `extractCurrentMilestone`, `replaceInCurrentMilestone`, `getRoadmapPhaseInternal`, `getMilestoneInfo`, `getMilestonePhaseFilter`). Depends only on leaf modules (`phase-id`, `planning-workspace`, `shell-command-projection`) — no `loadConfig`, no other core dependency. Extracted from the Core module per ADR-857 rollout phase 2b (#870), resolving the ROADMAP.md parse/write straddle so the Roadmap module (`roadmap.cjs`, which owns ROADMAP.md mutation) imports parsing directly instead of through Core; `core.cjs` re-exports the helpers for back-compat. Source of truth: `gsd-core/bin/lib/roadmap-parser.cjs` (generated from `src/roadmap-parser.cts`).
+
 ### Package Identity Module [Planned]
 Single seam owning GSD's published-package coordinates so a repoint/rename is a one-line change instead of a tree-wide sweep. Source of truth is `package.json`; values are *derived*, not re-typed: `packageName` (`.name` → `@opengsd/get-shit-done-redux`), `binName` (`Object.keys(.bin)[0]` → `get-shit-done-redux`), `repoSlug` (parsed from `.repository.url` → `open-gsd/get-shit-done-redux`), plus derived `changelogRawUrl` and `manualInstallCommand({ scope, runtime })`. Generated `.cjs` per ADR-457 (generated-single-source); shipped under `gsd-core/bin/lib/`. Three consumer worlds: **Node** consumers `require()` it at runtime (worker, `check-latest-version.cjs`, `bin/install.js`); the **bash launcher** snippet receives the literal injected by `scripts/sync-runtime-launcher.cjs` at sync time; **prose/help** literals (`update.md`, installer help) carry a committed copy. A drift-guard lint (`scripts/lint-package-identity-drift.cjs`, sibling to `check:alias-drift`) fails CI on any raw package/repo literal outside `package.json`, the generated module, and the value-checked materialization sites — this is what keeps the seam real (`two adapters`, not one). Replaces the contradictory pair it consolidates: the runtime-broken `require('../package.json').name` in `hooks/gsd-check-update-worker.js` (#378, resolves to `undefined` post-install) and the hardcoded constant in `check-latest-version.cjs` (#2992). _Avoid_: "package name string", "the npm name" (when you mean the seam). See ADR-457 and Installer Module.