docs: gate ECC progress sync readiness

Make the ECC 2.0 GitHub/Linear/handoff/roadmap progress-sync model part of the local observability readiness gate instead of leaving it as roadmap prose only.

- add `docs/architecture/progress-sync-contract.md` for GitHub, Linear, handoff, roadmap, and work-items sync
- add a `Tracker Sync` check to `scripts/observability-readiness.js`
- update observability tests with passing and missing-contract coverage
- update observability and GA roadmap docs so the local readiness gate is now 18/18 and records #1848 supply-chain hardening evidence

Validation:
- node tests/scripts/observability-readiness.test.js (9 passed, 0 failed)
- npm run observability:ready -- --format json (18/18, ready true)
- npx markdownlint-cli 'docs/architecture/progress-sync-contract.md' 'docs/architecture/observability-readiness.md' 'docs/ECC-2.0-GA-ROADMAP.md'
- git diff --check
- node tests/docs/ecc2-release-surface.test.js (18 passed)
- node tests/run-all.js (2378 passed, 0 failed)
- GitHub CI for #1849 green across Ubuntu, Windows, and macOS

No release, tag, npm publish, plugin tag, marketplace submission, or announcement was performed.

docs/architecture/progress-sync-contract.md

@@ -0,0 +1,67 @@
+# Progress Sync Contract
+
+ECC 2.0 tracks execution state across GitHub, Linear, local handoffs, and the
+repo roadmap. This contract defines the minimum evidence required before a
+status update can claim a lane is current.
+
+## Sources Of Truth
+
+| Surface | Role | Current rule |
+| --- | --- | --- |
+| GitHub PRs/issues/discussions | Public queue and review state | Recheck live counts before every significant merge batch and before release approval. |
+| Linear project | Executive roadmap and stakeholder status update | Post project status updates while issue capacity blocks issue creation. Create/reuse issues only when workspace capacity is available. |
+| Local handoff | Durable operator continuity | Update the active handoff after every merge batch, queue drain, skipped release gate, or blocked external action. |
+| Repo roadmap | Auditable planning mirror | Keep `docs/ECC-2.0-GA-ROADMAP.md` aligned to merged PR evidence and unresolved gates. |
+| `scripts/work-items.js` | Local tracker bridge | Sync GitHub PRs/issues into the SQLite work-items store for status snapshots and blocked follow-up. |
+
+## Flow Lanes
+
+The repo mirror uses these flow lanes so ECC work does not collapse into one
+undifferentiated backlog:
+
+- Queue hygiene and stale-work salvage
+- Release, naming, plugin publication, and announcements
+- Harness adapter compliance
+- Local observability, HUD/status, and session control
+- Evaluator/RAG and self-improving harness loops
+- AgentShield enterprise security platform
+- ECC Tools billing, PR-risk checks, deep analysis, and Linear sync
+- Legacy artifact audit and translator/manual-review tails
+
+Each flow lane needs one owner artifact, one current evidence source, and one
+next action. A lane is not current if any of those three fields are missing.
+
+## Significant Merge Batch Update
+
+After a significant merge batch, update Linear and the handoff with:
+
+1. Current public queue counts for tracked GitHub repos.
+2. Merged PR numbers, commit IDs, and validation evidence.
+3. Changed release gates, if any.
+4. Deferred or skipped work and the explicit reason.
+5. The next one or two implementation slices.
+
+When Linear issue capacity is unavailable, use a project status update instead
+of creating placeholder issues. When issue capacity is available, create or
+reuse exact-title issues and link them to the repo evidence.
+
+## Realtime Boundary
+
+The local realtime path is file-backed by default:
+
+- `node scripts/work-items.js sync-github --repo <owner/repo>` imports current
+  GitHub PR and issue state into the SQLite work-items store.
+- `node scripts/status.js --json` and `node scripts/work-items.js list --json`
+  expose local state for a HUD, handoff, or later Linear sync.
+- Linear remains the external status surface; the repo does not require hosted
+  telemetry to be release-ready.
+
+Hosted telemetry such as PostHog can be added later, but it must consume the
+same event model rather than becoming a second source of truth.
+
+## Release Gate
+
+Do not publish, tag, announce, submit marketplace packages, or claim plugin
+availability from this contract alone. Release readiness still requires the
+publication-readiness evidence documents, fresh queue checks, package checks,
+plugin checks, and explicit maintainer approval.