fix: handle PR comment fork branches safely

[captainsafia]

Summary

• Gate fork PR comment response runs on trusted trigger actors using author association or optional org membership checks.
• Route PR comment responses to the correct branch target for same-repo branches, modifiable fork heads, and fallback follow-up PRs into contributor forks.
• Clarify agent prompts and completion comments for fallback fork PR flows.
• Add coverage for trust gating, branch strategy payloads, prompts, and apply behavior.

Tests

• python3 -m pytest tests

Co-Authored-By: Oz oz-agent@warp.dev

[oz-for-oss]

@captainsafia

I'm starting a first review of this pull request.

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[oz-for-oss]

Overview

This PR adds trust gating and branch-target handling for respond-to-PR-comment runs on forked pull requests, including fallback follow-up PR creation when the fork head cannot be modified directly.

Concerns

• The fallback apply path always creates a new follow-up PR. Because the fallback branch name is deterministic per original PR, any later response run for the same PR will fail when GitHub reports an existing PR for that head/base pair, even though the branch was updated successfully.

Verdict

Found: 0 critical, 1 important, 0 suggestions

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[captainsafia]

/oz-review

[oz-for-oss]

@captainsafia

I'm re-reviewing this pull request in response to a review request.

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I completed the review and no human review was requested for this pull request.

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[oz-for-oss]

Overview

This PR adds trusted-actor gating for fork PR comment-response runs and expands branch handling for same-repo heads, directly modifiable fork heads, and follow-up PR fallback flows. It also updates prompts, apply behavior, documentation, and tests around those branch strategies.

Concerns

No blocking correctness, security, or error-handling concerns found in the reviewed diff.

Verdict

Found: 0 critical, 0 important, 0 suggestions

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[captainsafia]

@peicodes @vkodithala This sets us up so that at least Warpers can mention Oz to fix issues on PRs that come from forks. It includes some logic that let's us detect if the PR opener has allowed pushing changes to their fork (ref) or if we need to open a PR against it.

[peicodes]

Thanks for this!!