feat(adapters): codex T2 — AGENTS.md fenced snippet

[Steve-too]

Summary

Adds T2 tier to the codex adapter, matching the cursor adapter's pattern. Codex reads AGENTS.md for project instructions; without this tier, a codex session gets the MCP tools but no standing instructions on when to recall or how to propose through the review gate.

Changes

• adapters/codex/AGENTS.md.snippet: fenced snippet with same content contract as cursor (recall first, propose-don't-write, human review gate), host identity set to codex
• adapters/codex/install.yaml: add fence markers and T2 tier with fenced_append: true
• tests/test_install_adapter.py: codex T2 coverage (create, idempotent re-run, append to existing file)

Acceptance criteria (from #385)

• Installing at T2 appends the fenced snippet to an existing AGENTS.md and creates the file when absent
• Re-running leaves the file unchanged; an edited fence body is replaced within the markers
• Snippet guidance matches the cursor snippet's invariants (recall first, all writes via proposals, review stays human)
• Covered in tests/test_install_adapter.py

Closes #385

Summary by CodeRabbit

• New Features

  • Added support for a new Codex adapter installation flow with tier-based behavior, including project-local configuration and optional knowledge-base content added to AGENTS.md.
  • Included audit attribution details in the generated guidance for Codex-related setups.

• Documentation

  • Added a knowledge-base section explaining how agent knowledge is stored and maintained, plus how to search, read, and register information.

• Tests

  • Expanded automated coverage for installation behavior, including idempotency and preserving existing file content.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 642ff606-3344-4501-8dea-f5e533118ad5

📥 Commits

Reviewing files that changed from the base of the PR and between 36f035e and c1e60f9.

📒 Files selected for processing (3)

• adapters/codex/AGENTS.md.snippet
• adapters/codex/install.yaml
• tests/test_install_adapter.py

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📝 Walkthrough

Walkthrough

This PR adds a T2 installation tier for the codex adapter, introducing an AGENTS.md.snippet documentation file describing Vouch KB usage, extending install.yaml with fence configuration and a new tier that fenced-appends the snippet into AGENTS.md, and adding corresponding installer tests.

Changes

Codex T2 AGENTS.md Tier

Layer / File(s)	Summary
AGENTS.md snippet content adapters/codex/AGENTS.md.snippet	New documentation snippet explaining Vouch KB usage: evidence registration, claim/page proposals, approval mechanics, search/read workflow, and setting VOUCH_AGENT=codex for audit attribution.
Install manifest T2 tier wiring adapters/codex/install.yaml	Adds pretty display name, fence config with <!-- BEGIN vouch -->/<!-- END vouch --> markers, and a new T2 tier that fenced-appends AGENTS.md.snippet into AGENTS.md, alongside existing T1 config.toml install.
Adapter installation tests tests/test_install_adapter.py	New tests verifying T1 creates only .codex/config.toml, T2 creates/updates AGENTS.md with the fenced snippet, re-running T2 is idempotent, and appending to a pre-existing unfenced AGENTS.md preserves original content.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related issues

• feat(adapters): codex integration — bring the codex adapter to claude-code parity (tracking) #391: Tracks the same codex-adapter AGENTS.md snippet and T2 fenced append work implemented in this PR.
• docs(adapters): codex adapter docs reflect the tiered install #390: Covers the same Codex adapter tiered install behavior and AGENTS.md snippet flow.

Possibly related PRs

• vouchdev/vouch#370: Both touch adapter installation behavior around tests/test_install_adapter.py and shipped adapter templates.

Suggested labels: docs

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise and accurately reflects the Codex T2 AGENTS.md fenced snippet change.
Linked Issues check	✅ Passed	The PR adds the Codex T2 snippet, fenced install tier, and tests for create/append/idempotence, matching #385's requirements.
Out of Scope Changes check	✅ Passed	The changes stay within the Codex T2 AGENTS.md support work and associated tests.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

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Failed to run tools: 13 INTERNAL: Received RST_STREAM with code 2 (Internal server error)

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