fix(tui): conditionally restore status indicator using message phase (#10947)

TLDR: use new message phase field emitted by preamble-supported models
to determine whether an AgentMessage is mid-turn commentary. if so,
restore the status indicator afterwards to indicate the turn has not
completed.

### Problem
`commit_tick` hides the status indicator while streaming assistant text.
For preamble-capable models, that text can be commentary mid-turn, so
hiding was correct during streaming but restore timing mattered:
- restoring too aggressively caused jitter/flashing
- not restoring caused indicator to stay hidden before subsequent work
(tool calls, web search, etc.)

### Fix
- Add optional `phase` to `AgentMessageItem` and propagate it from
`ResponseItem::Message`
- Keep indicator hidden during streamed commit ticks, restore only when:
  - assistant item completes as `phase=commentary`, and
  - stream queues are idle + task is still running.
- Treat `phase=None` as final-answer behavior (no restore) to keep
existing behavior for non-preamble models

### Tests
Add/update tests for:
- no idle-tick restore without commentary completion
- commentary completion restoring status before tool begin
- snapshot coverage for preamble/status behavior

---------

Co-authored-by: Josh McKinney <joshka@openai.com>

codex-rs/app-server-protocol/schema/json/v1/ResumeConversationParams.json

@@ -271,11 +271,23 @@
       "type": "string"
     },
     "MessagePhase": {
-      "enum": [
-        "commentary",
-        "final_answer"
-      ],
-      "type": "string"
+      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "oneOf": [
+        {
+          "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
+          "enum": [
+            "commentary"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's terminal answer text for the current turn.",
+          "enum": [
+            "final_answer"
+          ],
+          "type": "string"
+        }
+      ]
     },
     "NewConversationParams": {
       "properties": {