Stop emitting item/fileChange/outputDelta output delta notifications (#20471)

## Why

`item/fileChange/outputDelta` text output was only the tool's summary or
error text and not used by client surfaces.

We keep `item/fileChange/outputDelta` in the app-server protocol as a
deprecated compatibility entry, but the server no longer emits it.

## What changed

- stop the `apply_patch` runtime from emitting `ExecCommandOutputDelta`
events
- simplify `item_event_to_server_notification` so command output deltas
always map to `item/commandExecution/outputDelta`
- remove the app-server bookkeeping that tried to detect whether an
output delta belonged to a file change
- mark `item/fileChange/outputDelta` as a deprecated legacy protocol
entry in the v2 types, schema, and README
- simplify the file-change approval tests so they only wait for
completion instead of expecting output-delta notifications

## Testing

- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-thread-manager-sample`
- `cargo test -p codex-app-server-protocol
protocol::event_mapping::tests::exec_command_output_delta_maps_to_command_execution_output_delta
-- --exact`
- `cargo test -p codex-app-server
turn_start_file_change_approval_accept_for_session_persists_v2 --
--exact` *(failed before the test assertions because the wiremock
`/responses` mock received 0 requests in setup)*

codex-rs/core/src/tools/runtimes/apply_patch.rs

@@ -25,10 +25,6 @@ use codex_protocol::exec_output::ExecToolCallOutput;
 use codex_protocol::exec_output::StreamOutput;
 use codex_protocol::models::AdditionalPermissionProfile;
 use codex_protocol::protocol::AskForApproval;
-use codex_protocol::protocol::Event;
-use codex_protocol::protocol::EventMsg;
-use codex_protocol::protocol::ExecCommandOutputDeltaEvent;
-use codex_protocol::protocol::ExecOutputStream;
 use codex_protocol::protocol::FileChange;
 use codex_protocol::protocol::ReviewDecision;
 use codex_sandboxing::SandboxType;
@@ -87,22 +83,6 @@ impl ApplyPatchRuntime {
             use_legacy_landlock: attempt.use_legacy_landlock,
         })
     }
-
-    async fn emit_output_delta(ctx: &ToolCtx, stream: ExecOutputStream, chunk: &[u8]) {
-        if chunk.is_empty() {
-            return;
-        }
-
-        let event = Event {
-            id: ctx.turn.sub_id.clone(),
-            msg: EventMsg::ExecCommandOutputDelta(ExecCommandOutputDeltaEvent {
-                call_id: ctx.call_id.clone(),
-                stream,
-                chunk: chunk.to_vec(),
-            }),
-        };
-        let _ = ctx.session.get_tx_event().send(event).await;
-    }
 }
 
 impl Sandboxable for ApplyPatchRuntime {
@@ -230,8 +210,6 @@ impl ToolRuntime<ApplyPatchRequest, ExecToolCallOutput> for ApplyPatchRuntime {
         .await;
         let stdout = String::from_utf8_lossy(&stdout).into_owned();
         let stderr = String::from_utf8_lossy(&stderr).into_owned();
-        Self::emit_output_delta(ctx, ExecOutputStream::Stdout, stdout.as_bytes()).await;
-        Self::emit_output_delta(ctx, ExecOutputStream::Stderr, stderr.as_bytes()).await;
         let exit_code = if result.is_ok() { 0 } else { 1 };
         let output = ExecToolCallOutput {
             exit_code,