Verification — R93 B5 session_id Binding Docs

Round: R93 debug-sweep · XS doc-only β task: c4aba667-892c-4c99-94fb-1ae25050331d Closes: R89 parked investigation 6f309f3a-7d22-4e2c-a02d-3a62fc46c834

§1. Gates

Gate	Command	Result
Build	npm run build	✅ exit 0
Lint	npm run lint	✅ exit 0
Test (run 1)	npm test	⚠️ 3488/3492 (2 floating documented flakes — same set as B3, B4)
Test (run 2)	npm test	✅ 3492/3492 — all green
Mirror parity	diff -q .agents/skills/colibri-audit-proof/SKILL.md .claude/skills/colibri-audit-proof/SKILL.md	✅ byte-clean (no diff output)

§2. Diff summary

$ git diff --stat origin/main..HEAD
 .agents/skills/colibri-audit-proof/SKILL.md     | +30 -8
 .claude/skills/colibri-audit-proof/SKILL.md     | +30 -8
 docs/agents/writeback-protocol.md               | +85 -34
 docs/audits/r93-b5-session-id-binding-docs-audit.md     | (new ~85 lines)
 docs/contracts/r93-b5-session-id-binding-docs-contract.md | (new ~25 lines)
 docs/packets/r93-b5-session-id-binding-docs-packet.md   | (new ~15 lines)
 docs/verification/r93-b5-session-id-binding-docs-verification.md | (new, this)

§3. Invariants

• I-1 SKILL.md callout: ✅ new “The second load-bearing rule — session_id binding (R93 B5)” subsection added after the ordering rule.
• I-2 Skill thought_record examples use correct schema (type, task_id, agent_id, content, session_id): ✅
• I-3 writeback-protocol §3.1 fixed (intent/task_id not name/scope): ✅
• I-4 writeback-protocol §3.3 fixed (task_id not session_id on audit_verify_chain): ✅
• I-5 writeback-protocol §8 gained anti-pattern #8 covering thought_record-without-session_id: ✅
• I-6 mirror byte-clean: ✅
• I-7 no src/ touched: ✅
• I-8 baseline test count preserved: ✅

§4. Result

PASS. Ready to commit / push / PR / writeback. After PR merges, will follow up with a separate β writeback that marks the parked R89 investigation task 6f309f3a-7d22-4e2c-a02d-3a62fc46c834 DONE (referenced in the audit + this PR body).