edit_prediction: Report patch apply failures (#60637)

# Objective

- Report V4 edit prediction patch apply failures as cloud rejection
events.
- Closes EP-210

## Solution

- Added `PatchApplyFailed` as an edit prediction rejection reason.
- Converted `prediction_edits_for_single_file_diff` errors into rejected
prediction results so the existing rejection pipeline posts them to
`/predict_edits/reject`.
- Kept interpolation failures reported as `InterpolateFailed`.

## Testing

- Ran `cargo fmt --check && cargo check -p edit_prediction`.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A

crates/cloud_llm_client/src/cloud_llm_client.rs

@@ -198,6 +198,8 @@ pub enum EditPredictionRejectReason {
     InterpolatedEmpty,
     /// Edits returned, but could not be interpolated after buffer changes
     InterpolateFailed,
+    /// A patch was returned, but could not be applied to the buffer
+    PatchApplyFailed,
     /// The new prediction was preferred over the current one
     Replaced,
     /// The current prediction was preferred over the new one

crates/edit_prediction/src/prediction.rs

@@ -104,6 +104,34 @@ impl EditPredictionResult {
             e2e_latency,
         }
     }
+
+    pub fn new_rejected(
+        id: EditPredictionId,
+        edited_buffer: &Entity<Buffer>,
+        edited_buffer_snapshot: &BufferSnapshot,
+        inputs: EditPredictionInputs,
+        model_version: Option<String>,
+        trigger: PredictEditsRequestTrigger,
+        e2e_latency: std::time::Duration,
+        reject_reason: EditPredictionRejectReason,
+    ) -> Self {
+        Self {
+            prediction: EditPrediction {
+                id,
+                edits: Arc::default(),
+                cursor_position: None,
+                editable_range: None,
+                snapshot: edited_buffer_snapshot.clone(),
+                edit_preview: EditPreview::unchanged(edited_buffer_snapshot),
+                inputs,
+                buffer: edited_buffer.clone(),
+                model_version,
+                trigger,
+            },
+            reject_reason: Some(reject_reason),
+            e2e_latency,
+        }
+    }
 }
 
 #[derive(Clone)]

crates/edit_prediction/src/zeta.rs

@@ -9,7 +9,9 @@ use crate::{
     udiff::prediction_edits_for_single_file_diff,
 };
 use anyhow::{Context as _, Result};
-use cloud_llm_client::{AcceptEditPredictionBody, predict_edits_v3::RawCompletionRequest};
+use cloud_llm_client::{
+    AcceptEditPredictionBody, EditPredictionRejectReason, predict_edits_v3::RawCompletionRequest,
+};
 use edit_prediction_types::PredictedCursorPosition;
 use gpui::{App, AppContext as _, Entity, Task, TaskExt, WeakEntity, prelude::*};
 use language::{
@@ -516,26 +518,41 @@ pub(crate) fn request_prediction_with_zeta(
                 snapshot: fallback_snapshot,
                 patch,
             } => {
-                let Some((buffer, snapshot, edits, cursor_position)) =
-                    prediction_edits_for_single_file_diff(&patch, &project, cx).await?
-                else {
-                    return Ok(Some(
-                        EditPredictionResult::new(
-                            id,
-                            &fallback_buffer,
-                            &fallback_snapshot,
-                            Arc::new([]),
-                            None,
-                            None,
-                            inputs,
-                            model_version,
-                            trigger,
-                            request_duration,
-                            cx,
-                        )
-                        .await,
-                    ));
-                };
+                let (buffer, snapshot, edits, cursor_position) =
+                    match prediction_edits_for_single_file_diff(&patch, &project, cx).await {
+                        Ok(Some(edits)) => edits,
+                        Ok(None) => {
+                            return Ok(Some(
+                                EditPredictionResult::new(
+                                    id,
+                                    &fallback_buffer,
+                                    &fallback_snapshot,
+                                    Arc::new([]),
+                                    None,
+                                    None,
+                                    inputs,
+                                    model_version,
+                                    trigger,
+                                    request_duration,
+                                    cx,
+                                )
+                                .await,
+                            ));
+                        }
+                        Err(error) => {
+                            log::error!("failed to apply edit prediction patch: {error:?}");
+                            return Ok(Some(EditPredictionResult::new_rejected(
+                                id,
+                                &fallback_buffer,
+                                &fallback_snapshot,
+                                inputs,
+                                model_version,
+                                trigger,
+                                request_duration,
+                                EditPredictionRejectReason::PatchApplyFailed,
+                            )));
+                        }
+                    };
                 let editable_range_in_buffer =
                     edits
                         .iter()