fix(pty): don't leak an outer session id into session-less PTYs

[ThomasK33]

What

resolvePtyEnv (src/pty/createPty.ts) now treats a PTY spawned without a sessionId as session-less:

• Inherited AGENT_TTY_ACTIVE and AGENT_TTY_SESSION_ID are removed. Before, AGENT_TTY_ACTIVE=true was always set and an outer AGENT_TTY_SESSION_ID passed through unchanged.
• Caller env (--env) still wins, so precedence is unchanged.
• An empty sessionId now fails an invariant rather than being silently treated as "no session".

Sessions (hostMain, which always passes sessionId) behave exactly as before. The only session-less caller is the doctor PTY spawn probe. Run inside an agent-tty session, it no longer claims to be a managed session or reports the outer session's ID.

Why

Closes #177. The documented contract in docs/USAGE.md ("a session reports its own ID") didn't hold for PTYs without a session.

Changes

• src/pty/createPty.ts: drop inherited session vars when there's no sessionId; doc comment updated.
• test/unit/pty/createPty.test.ts: covers stripping inherited values with no session id, caller env still winning with no session id, no vars set with no session id, rejecting an empty session id. Existing session tests are kept.
• docs/USAGE.md: one sentence on session-less PTYs.

No CLI JSON, schema, or manifest changes.

Validation

mise run typecheck        # pass
mise run lint             # 0 warnings, 0 errors
mise run format-check     # pass
npx vitest run test/unit/pty test/unit/cli/commands/doctor*   # 3 files, 83 tests pass
mise run ci               # exit 0; 159 test files, 1645 tests pass

---

Generated with xum • Model: anthropic:claude-opus-5-5 • Thinking: high

[ThomasK33]

@codex review

[ThomasK33]

@codex security review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-24T10:57:38.047921Z	9e5590a	Manual request
🔒 Security Review	✅ Completed 2026-09-24T10:57:55.221003Z	9e5590a	Manual request

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🎉

Reviewed commit: 9e5590a81c

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🛡️ Codex Security Review

Security review completed. No security issues were found in this pull request.

Reviewed commit: 9e5590a81c

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