fix: preserve exact turn diffs after partial apply_patch failures (#21518)

## 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`](https://github.com/openai/codex/blob/f55724e0276a9b3213170daf2701ccfa0ce22646/codex-rs/apply-patch/src/lib.rs#L248-L345)
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](https://github.com/openai/codex/blob/f55724e0276a9b3213170daf2701ccfa0ce22646/codex-rs/apply-patch/src/lib.rs#L463-L521)).
-
[`ApplyPatchRuntime`](https://github.com/openai/codex/blob/f55724e0276a9b3213170daf2701ccfa0ce22646/codex-rs/core/src/tools/runtimes/apply_patch.rs#L49-L67)
now accumulates committed deltas across attempts and forwards them even
when the visible tool result is failed or sandbox-denied ([runtime
path](https://github.com/openai/codex/blob/f55724e0276a9b3213170daf2701ccfa0ce22646/codex-rs/core/src/tools/runtimes/apply_patch.rs#L223-L250),
[event
path](https://github.com/openai/codex/blob/f55724e0276a9b3213170daf2701ccfa0ce22646/codex-rs/core/src/tools/events.rs#L215-L225)).
- `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`](https://github.com/openai/codex/blob/f55724e0276a9b3213170daf2701ccfa0ce22646/codex-rs/core/tests/suite/apply_patch_cli.rs#L1517-L1586).
- Kept explicit coverage that an inexact delta clears the aggregate
instead of publishing a guessed diff:
[`apply_patch_clears_aggregated_diff_after_inexact_delta`](https://github.com/openai/codex/blob/f55724e0276a9b3213170daf2701ccfa0ce22646/codex-rs/core/tests/suite/apply_patch_cli.rs#L1589-L1655).

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/turn_diff_tracker.rs

@@ -13,8 +13,8 @@ const ZERO_OID: &str = "0000000000000000000000000000000000000000";
 const DEV_NULL: &str = "/dev/null";
 const REGULAR_FILE_MODE: &str = "100644";
 
-/// Tracks the net text diff for the current turn from successful apply_patch
-/// operations, without rereading the workspace filesystem.
+/// Tracks the net text diff for the current turn from committed apply_patch
+/// mutations, without rereading the workspace filesystem.
 pub struct TurnDiffTracker {
     valid: bool,
     display_root: Option<PathBuf>,
@@ -46,7 +46,7 @@ impl TurnDiffTracker {
         tracker
     }
 
-    pub fn track_successful_patch(&mut self, delta: &AppliedPatchDelta) {
+    pub fn track_delta(&mut self, delta: &AppliedPatchDelta) {
         if !delta.is_exact() {
             self.invalidate();
             return;