[app-server] feat: v2 apply_patch approval flow (#6760)

This PR adds the API V2 version of the apply_patch approval flow, which
centers around `ThreadItem::FileChange`.

This PR wires the new RPC (`item/fileChange/requestApproval`, V2 only)
and related events (`item/started`, `item/completed` for
`ThreadItem::FileChange`, which are emitted in both V1 and V2) through
the app-server
protocol. The new approval RPC is only sent when the user initiates a
turn with the new `turn/start` API so we don't break backwards
compatibility with VSCE.

Similar to https://github.com/openai/codex/pull/6758, the approach I
took was to make as few changes to the Codex core as possible,
leveraging existing `EventMsg` core events, and translating those in
app-server. I did have to add a few additional fields to
`EventMsg::PatchApplyBegin` and `EventMsg::PatchApplyEnd`, but those
were fairly lightweight.

However, the `EventMsg`s emitted by core are the following:
```
1) Auto-approved (no request for approval)

- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd

2) Approved by user
- EventMsg::ApplyPatchApprovalRequest
- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd

3) Declined by user
- EventMsg::ApplyPatchApprovalRequest
- EventMsg::PatchApplyBegin
- EventMsg::PatchApplyEnd
```

For a request triggering an approval, this would result in:
```
item/fileChange/requestApproval
item/started
item/completed
```

which is different from the `ThreadItem::CommandExecution` flow
introduced in https://github.com/openai/codex/pull/6758, which does the
below and is preferable:
```
item/started
item/commandExecution/requestApproval
item/completed
```

To fix this, we leverage `TurnSummaryStore` on codex_message_processor
to store a little bit of state, allowing us to fire `item/started` and
`item/fileChange/requestApproval` whenever we receive the underlying
`EventMsg::ApplyPatchApprovalRequest`, and no-oping when we receive the
`EventMsg::PatchApplyBegin` later.

This is much less invasive than modifying the order of EventMsg within
core (I tried).

The resulting payloads:
```
{
  "method": "item/started",
  "params": {
    "item": {
      "changes": [
        {
          "diff": "Hello from Codex!\n",
          "kind": "add",
          "path": "/Users/owen/repos/codex/codex-rs/APPROVAL_DEMO.txt"
        }
      ],
      "id": "call_Nxnwj7B3YXigfV6Mwh03d686",
      "status": "inProgress",
      "type": "fileChange"
    }
  }
}
```

```
{
  "id": 0,
  "method": "item/fileChange/requestApproval",
  "params": {
    "grantRoot": null,
    "itemId": "call_Nxnwj7B3YXigfV6Mwh03d686",
    "reason": null,
    "threadId": "019a9e11-8295-7883-a283-779e06502c6f",
    "turnId": "1"
  }
}
```

```
{
  "id": 0,
  "result": {
    "decision": "accept"
  }
}
```

```
{
  "method": "item/completed",
  "params": {
    "item": {
      "changes": [
        {
          "diff": "Hello from Codex!\n",
          "kind": "add",
          "path": "/Users/owen/repos/codex/codex-rs/APPROVAL_DEMO.txt"
        }
      ],
      "id": "call_Nxnwj7B3YXigfV6Mwh03d686",
      "status": "completed",
      "type": "fileChange"
    }
  }
}
```

codex-rs/core/src/codex.rs

@@ -919,6 +919,7 @@ impl Session {
 
         let event = EventMsg::ApplyPatchApprovalRequest(ApplyPatchApprovalRequestEvent {
             call_id,
+            turn_id: turn_context.sub_id.clone(),
             changes,
             reason,
             grant_root,

codex-rs/core/src/tools/events.rs

@@ -179,15 +179,17 @@ impl ToolEmitter {
                         ctx.turn,
                         EventMsg::PatchApplyBegin(PatchApplyBeginEvent {
                             call_id: ctx.call_id.to_string(),
+                            turn_id: ctx.turn.sub_id.clone(),
                             auto_approved: *auto_approved,
                             changes: changes.clone(),
                         }),
                     )
                     .await;
             }
-            (Self::ApplyPatch { .. }, ToolEventStage::Success(output)) => {
+            (Self::ApplyPatch { changes, .. }, ToolEventStage::Success(output)) => {
                 emit_patch_end(
                     ctx,
+                    changes.clone(),
                     output.stdout.text.clone(),
                     output.stderr.text.clone(),
                     output.exit_code == 0,
@@ -195,11 +197,12 @@ impl ToolEmitter {
                 .await;
             }
             (
-                Self::ApplyPatch { .. },
+                Self::ApplyPatch { changes, .. },
                 ToolEventStage::Failure(ToolEventFailure::Output(output)),
             ) => {
                 emit_patch_end(
                     ctx,
+                    changes.clone(),
                     output.stdout.text.clone(),
                     output.stderr.text.clone(),
                     output.exit_code == 0,
@@ -207,10 +210,17 @@ impl ToolEmitter {
                 .await;
             }
             (
-                Self::ApplyPatch { .. },
+                Self::ApplyPatch { changes, .. },
                 ToolEventStage::Failure(ToolEventFailure::Message(message)),
             ) => {
-                emit_patch_end(ctx, String::new(), (*message).to_string(), false).await;
+                emit_patch_end(
+                    ctx,
+                    changes.clone(),
+                    String::new(),
+                    (*message).to_string(),
+                    false,
+                )
+                .await;
             }
             (
                 Self::UnifiedExec {
@@ -409,15 +419,23 @@ async fn emit_exec_end(
         .await;
 }
 
-async fn emit_patch_end(ctx: ToolEventCtx<'_>, stdout: String, stderr: String, success: bool) {
+async fn emit_patch_end(
+    ctx: ToolEventCtx<'_>,
+    changes: HashMap<PathBuf, FileChange>,
+    stdout: String,
+    stderr: String,
+    success: bool,
+) {
     ctx.session
         .send_event(
             ctx.turn,
             EventMsg::PatchApplyEnd(PatchApplyEndEvent {
                 call_id: ctx.call_id.to_string(),
+                turn_id: ctx.turn.sub_id.clone(),
                 stdout,
                 stderr,
                 success,
+                changes,
             }),
         )
         .await;