fix: preserve exact turn diffs after partial apply_patch failures

[jif-oai]

Why

Follow-up to #21180: turn diffs are operation-backed now, but a failed apply_patch can still leave exact filesystem mutations behind. For example, a move can write the destination file before failing to remove the source. Treating the whole call as unknowable then drops a change that Codex actually knows happened, so the emitted turn diff can drift from the workspace.

What changed

• apply-patch now returns ApplyPatchFailure with the exact committed prefix accumulated before an error. If a write failure may already have mutated the target, the delta is marked inexact instead of being reused blindly.
• Move handling now records the destination write before attempting source removal, so a partially failed move can still report the destination file that definitely landed (code).
• ApplyPatchRuntime now accumulates committed deltas across attempts and forwards them even when the visible tool result is failed or sandbox-denied (runtime path, event path).
• TurnDiffTracker now consumes committed exact deltas rather than only fully successful patches; exact-empty failures leave the aggregate unchanged, while inexact deltas still invalidate it.

Verification

• Added a regression test covering a failed move that still emits the committed destination diff: apply_patch_failed_move_preserves_committed_destination_diff.
• Kept explicit coverage that an inexact delta clears the aggregate instead of publishing a guessed diff: apply_patch_clears_aggregated_diff_after_inexact_delta.

[jif-oai]

@codex review

[chatgpt-codex-connector]

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Reviewed commit: f55724e027

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[jif-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Can't wait for the next one!

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
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• Comment "@codex review".

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[fcoury-oai]

I manually tested the happy path by creating a workspace where apply_patch could write the move destination but fail removing the locked source.

The file-change item failed, the locked file remained unchanged, but the destination file wwas updated with the proper contents.

It also still streamed a turn diff containing the committed destination change as expected.

Code looks good, approved! 👍