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.

tests/scripts/observability-readiness.test.js

@@ -57,11 +57,22 @@ function seedMinimalRepo(rootDir, overrides = {}) {
     'scripts/session-inspect.js': '--list-adapters --write inspectSessionTarget',
     'scripts/lib/session-adapters/registry.js': 'module.exports = {};',
     'scripts/harness-audit.js': 'Deterministic harness audit --format overall_score',
+    'scripts/work-items.js': 'sync-github github-pr github-issue sourceClosedAt ecc-work-items-sync-github',
     'scripts/hooks/session-activity-tracker.js': 'tool-usage.jsonl session_id tool_name',
     'ecc2/src/observability/mod.rs': 'ToolCallEvent RiskAssessment ToolLogger',
     'ecc2/src/session/store.rs': 'insert_tool_log query_tool_logs',
     'ecc2/src/session/manager.rs': 'sync_tool_activity_metrics tool-usage.jsonl',
     'docs/architecture/observability-readiness.md': 'node scripts/observability-readiness.js --format json',
+    'docs/architecture/progress-sync-contract.md': [
+      'Linear GitHub handoff work-items issue capacity status update',
+      'queue counts release gate flow lanes evidence'
+    ].join('\n'),
+    'docs/ECC-2.0-GA-ROADMAP.md': [
+      'Execution Lanes And Tracking Contract',
+      'docs/architecture/progress-sync-contract.md',
+      'Linear progress',
+      'Every significant merge batch'
+    ].join('\n'),
     'docs/architecture/hud-status-session-control.md': [
       'context toolCalls activeAgents todos checks cost risk queueState',
       'create resume status stop diff pr mergeQueue conflictQueue',
@@ -230,6 +241,23 @@ function runTests() {
     }
   })) passed++; else failed++;
 
+  if (test('missing progress sync contract fails without disturbing core tool checks', () => {
+    const projectRoot = createTempDir('observability-readiness-sync-fail-');
+
+    try {
+      seedMinimalRepo(projectRoot, {
+        'docs/architecture/progress-sync-contract.md': null
+      });
+      const report = buildReport(projectRoot);
+
+      assert.strictEqual(report.ready, false);
+      assert.ok(report.checks.some(check => check.id === 'progress-sync-contract' && !check.pass));
+      assert.ok(report.checks.some(check => check.id === 'loop-status-live-signal' && check.pass));
+    } finally {
+      cleanup(projectRoot);
+    }
+  })) passed++; else failed++;
+
   console.log('\nResults:');
   console.log(`  Passed: ${passed}`);
   console.log(`  Failed: ${failed}`);