Fix roborev fix discovering jobs from unrelated branches

[wesm]

Summary

• Switch job filtering from git reachability to branch matching. filterReachableJobs relied on git merge-base --is-ancestor to scope jobs to the current branch. On feature branches, all commits in the base branch's history are ancestors of HEAD, so jobs from main and other merged branches leaked through. After 45987ff removed the API branch filter, this became the sole filter and it was too permissive.
• Remove IsAncestor calls entirely. Jobs from squash-merged branches have SHAs that no longer exist in the local repo. git merge-base --is-ancestor returns exit 128 for unknown objects, triggering the fail-open path that included those jobs regardless of branch.
• Exclude branchless jobs from branch-filtered discovery. branchMatch previously returned true when a job had no branch set (fail-open from before branch tracking was added), causing old unrelated jobs to appear on every branch. Now both matchBranch and jobBranch must be non-empty and equal. Use --all-branches to include branchless jobs.

🤖 Generated with Claude Code

[roborev-ci]

roborev: Combined Review (11bf065)

Verdict: Changes introduce medium-severity regressions in roborev fix job discovery due to overly strict branch-based filtering.

Medium

• cmd/roborev/fix.go:533
  Strict branchMatch filtering now rejects jobs when the current checkout is in detached HEAD (matchBranch == ""), removing the prior SHA/range reachability fallback. This means roborev fix can no longer discover jobs for the currently checked out commit in detached-commit, tag, or bisect workflows.

• cmd/roborev/fix.go:533
  Jobs with an empty persisted Branch are now excluded from normal branch-filtered discovery. Because jobs are stored in SQLite, existing branchless rows (for example older jobs or jobs created from detached HEAD) become effectively undiscoverable unless users explicitly pass --all-branches.

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Synthesized from 3 reviews (agents: codex, gemini | types: default, security)

[wesm]

Intended behavior.