[SaulMoro]

Summary

Two session fixes.

• session migrate -t codex failed with "not installed" for anyone who had installed Codex but never run a session, because readiness required ~/.codex/sessions/. Codex is now a target when ~/.codex exists or codex is on PATH. The write already creates sessions/YYYY/MM/DD/.
• Every session pull rewrote sessions/repos/<repo>/_index.json, so the team checkout stayed modified, and the next pull that brought index changes failed with "Your local changes ... would be overwritten by merge". Three things differed from what push writes: a fresh top-level updatedAt, each entry's updatedAt (push records the session's own, the rebuild used pushedAt), and entry order (push appends, the rebuild used directory order). The rebuild now keeps each entry's updatedAt and order from the current index, and the index is not written when its content is unchanged.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature causing existing behavior to change)
• Documentation only
• Refactor / internal cleanup

Test Plan

• npx tsc --noEmit passes
• npm run lint passes
• npx vitest run: the session, sync and Codex files pass (27 files, 497 tests). The full run has two failures outside session code: mcp-reconcile (git EAGAIN under load; passes on its own) and gitlab-clone-realspawn (hangs locally).
• Added/updated tests for the change (both failed on main first)
  • session-codex-install.test.ts: migrate into Codex with only ~/.codex; Codex listed as installed with only the CLI on PATH; not listed with neither; listing with no sessions/ returns empty.
  • session-sync.test.ts: a bare remote and two clones; push, then pull twice, and git status is clean; a second push, then a pull merges and stays clean.

Real CLI after npm run build, isolated HOME:

Fix 1, HOME with only ~/.codex/, a planted Claude session, codex not on PATH:

main:   codex: ✗ not installed
        ✗ Migration failed: Target platform "codex" is not installed or its storage directory was not found. ... (available: claude-code).
branch: codex: ✓ installed
        ✓ Migration successful
        Target file: $HOME/.codex/sessions/2026/10/01/rollout-2026-10-01T10-00-00-aaaaaaaa-....jsonl

With codex-cli 0.162.1 on PATH, codex exec resume <id> opens the migrated session (session id: aaaaaaaa-...) and then stops at 401 Unauthorized, because the test HOME has no auth.

Fix 2, alice runs session push and git push, bob runs session pull twice:

main:   git status → M sessions/repos/github.com%2Forg%2Falpha/_index.json
        after alice pushes again: Error: git pull failed ...: Command failed: git pull origin main
branch: git status → clean
        after alice pushes again: ✓ Pulled and indexed 2 session(s), git status → clean

Not run locally: the other agents and the gitlab/github providers (left to CI).

Related Issues

Follow-up to #593. The _index.json problem showed up while working on #1139.

Notes for Reviewers

• Only Codex readiness changes. Claude Code, CodeBuddy, Cursor and WorkBuddy use the same "storage directory exists" check; whether those tools create it lazily is not verified here.
• The PATH check applies only to codex; codex-internal and tcodex still need their root directory.
• feat(session): safe session reads and copies for workflows, drivers, scorers, and benchmarks (#593 follow-up) #1135 and fix(session): merge a diverged session index on pull and retry push once (#1133) #1139 also change sync.ts. The edits here are two small blocks in writeIndex and rebuildIndex; whichever PR merges second rebases.

[github-actions]

No actionable findings in the specified diff.

The PR description satisfies the testing requirement: it records real-CLI verification after npm run build for both fixes. Deferring other agents and providers to CI is permitted.

Review was read-only; I did not run, build, or install anything from the PR.