herd: chat session file for daemon-signed-in sessions (RT-326)

[m4ttheweric]

Herd workers and shepherds that the daemon signs in to chat had no local chat session file, so every chat_* MCP tool refused them ("no signed-in chat session") while Bash rt chat still worked through the CLI's derived-handle fallback.

Herd handlers (lib/daemon/handlers/herd.ts)

• recordChatSession writes the session file after the daemon's chat:sign-in for a spawned worker, and for the shepherd on herd:start and herd:resume
• Keeps an existing file that names the same handle (the CLI's own sign-in)
• Rewrites a stale file that names another handle
• Logs a warning on a write failure

Verification: new tests in herd-handlers.test.ts for spawn, start, resume, stale handle and cleanup (RED first: no file after spawn); bun test lib/daemon lib/mcp 3055 pass; tsc --noEmit clean.

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Summary by CodeRabbit

• New Features
  • Herd sessions now save chat-session details when starting or resuming, and when workers sign in. This keeps session information available across those actions.
  • Matching session details are preserved; outdated handle information is refreshed without losing room details. A failure to save these details does not interrupt the herd operation.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: f8d5791d-5654-4f22-8cc7-bc7eb66beb08

📥 Commits

Reviewing files that changed from the base of the PR and between bf0c55f and 3587b93.

📒 Files selected for processing (2)

• lib/daemon/__tests__/herd-handlers.test.ts
• lib/daemon/handlers/herd.ts

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📝 Walkthrough

Walkthrough

Herd start and resume now record shepherd session identity. Successful worker sign-in records worker session identity. Existing session files for the same handle remain unchanged; files for a different handle are updated while retaining their room. Read and write errors are logged as warnings.

Changes

Herd session recording

Layer / File(s)	Summary
Record session identity lib/daemon/handlers/herd.ts, lib/daemon/__tests__/herd-handlers.test.ts	The handlers record session identity during shepherd start and resume, and after successful worker sign-in. Tests verify the session data, preserve files for the same handle, and check that updating a different handle retains the room. Test cleanup removes the session files.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 3587b

Daemon-signed-in Herd sessions will now have chat identity files, while persistence failures remain non-fatal. No concrete release-impacting regression is established, so the change appears ready to merge subject to normal checks.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to 3587b

Recording chat identity enables the intended tools, but the new files may remain usable for handle resolution after a session is signed out through the daemon. The downstream effect needs confirmation.

Retained concerns

• Medium · security · inferred: Daemon-created session files can continue to resolve a chat handle after daemon chat sign-out, because that sign-out does not remove the file and the MCP handle resolver checks the file rather than current presence. Downstream authorization impact is unverified.

Security review details

Security Blast Radius

• inferred — The directly affected scope is the local session IDs of shepherds and spawned workers for which herd handlers record chat handles. Evidence does not establish a cross-tenant, network, or infrastructure privilege change.

Security Findings and Attack Paths

• inferred — If a daemon-signed-in session is subsequently signed out through the daemon, its newly written file can still supply a handle to the MCP resolver. Whether a caller can use that handle for a chat operation after sign-out is not established.

Trust Boundaries and Controls

• observed — The MCP resolver takes its session ID from the process environment and accepts only a readable file with the same embedded ID and a string handle. It does not check the current presence row at handle-resolution time.

Resilience and Maintainability Implications

• inferred — A failed file write degrades MCP handle resolution without failing the herd operation. Existing tests cover matching and stale handles, but the available evidence does not establish write-failure or competing-writer outcomes end to end.

Hardening Proposals

• proposed — Define which component removes daemon-created session files at sign-out, and verify MCP behavior after daemon sign-out and handle reassignment before treating the file as a durable identity credential.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding chat session files for daemon-signed-in Herd sessions. It matches the pull request objectives and affected files.

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