Create fix branch from PR branch, not main

[ejc3]

Summary

Fixes the Claude review agent getting lost trying to read files that don't exist locally.

Problem: The agent was wasting many turns doing:

[driver] Tool: Read  (file not found)
The files don't exist on my current branch. Let me check them out...
[driver] Tool: Bash  (git checkout)
Let me view these files from the origin branch directly...
[driver] Tool: Bash  (git show origin/...)

Root cause: Workflow checks out main, then setupFixBranch creates the fix branch from main. But the PR code is on origin/${headBranch}.

Fix: Create fix branch from origin/${headBranch}:

gitOrFail("checkout", "-b", ctx.fixBranch, `origin/${ctx.headBranch}`);

Now the PR code is checked out locally and the Read tool works directly.

Test plan

• Push to trigger Claude review on a PR
• Verify agent can Read files directly without workarounds
• Verify agent doesn't waste turns on git checkout/show commands

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Stacked on: ci-log-truncation-check (PR #109)

[claude-claude]

🔍 Claude Review

SEVERITY: medium

Findings

[MEDIUM] - Stale branch reuse: When the fix branch already exists (line 128), the code checks it out without updating it to the latest origin/. If the PR has new commits pushed since the last Claude run, the existing fix branch will point to an old commit, causing Claude to review/fix stale code instead of the current PR state.

Fix: After checking out an existing branch, reset it to origin/:

if (branchExists(ctx.fixBranch)) {
  log(`Branch ${ctx.fixBranch} already exists, checking out and updating`);
  gitOrFail("checkout", ctx.fixBranch);
  gitOrFail("reset", "--hard", `origin/${ctx.headBranch}`);
} else {
  // Create fix branch FROM the PR branch, not from main
  // This ensures Claude can read PR files locally with the Read tool
  log(`Creating new branch ${ctx.fixBranch} from origin/${ctx.headBranch}`);
  gitOrFail("checkout", "-b", ctx.fixBranch, `origin/${ctx.headBranch}`);
}

Summary

The core fix (creating branch from PR head instead of main) is correct and solves the immediate issue. However, there's a case where reusing an existing fix branch could leave Claude working on outdated code if the PR has been updated since the last run.

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Review by Claude | Run

[claude-claude]

🔧 Auto-Fix Created

I found issues and created a fix PR: #111

Please review and merge the fix PR first, then this PR.

View Claude Run

[claude-claude]

🔍 Claude Review

SEVERITY: medium

Findings

[MEDIUM] - Silent fetch failure: Line 125 uses git("fetch", ...) which returns a boolean but doesn't check or handle the result. If the fetch fails (network issues, invalid branch name, etc.), the code silently continues and may:

• Use a stale remote ref when checking out/resetting
• Fail later with confusing errors about missing refs
• Succeed with stale data if an old remote ref exists

Impact: Claude could review outdated code or encounter unclear failures during branch setup.

Fix: Use gitOrFail instead of git to ensure the fetch succeeds:

gitOrFail("fetch", "origin", ctx.headBranch);

Summary

The core fix and the stale branch issue (PR #111) are both properly addressed. However, the fetch operation should fail loudly rather than silently to prevent reviewing stale code.

---

Review by Claude | Run

[claude-claude]

🔧 Auto-Fix Created

I found issues and created a fix PR: #119

Please review and merge the fix PR first, then this PR.

View Claude Run

[claude-claude]

🔍 Claude Review

SEVERITY: none

Findings

No issues found. All previously identified issues have been addressed:

• ✅ Branch created from PR head instead of main (original fix)
• ✅ Existing branches reset to latest PR head to avoid stale code (PR fix: reset existing fix branch to latest PR head #111)
• ✅ Fetch operation uses gitOrFail to prevent silent failures (PR fix: ensure fetch succeeds before branch setup #119)

The code correctly:

1. Fetches the latest PR branch with error handling
2. Creates or updates the fix branch to point to the current PR state
3. Updates prompts to clarify that PR code is locally available

Summary

The PR successfully fixes the Claude review agent's workflow issues. All code changes are correct and complete.

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Review by Claude | Run