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/core/src/event_mapping.rs

@@ -5,6 +5,7 @@ use codex_protocol::items::TurnItem;
 use codex_protocol::items::UserMessageItem;
 use codex_protocol::items::WebSearchItem;
 use codex_protocol::models::ContentItem;
+use codex_protocol::models::MessagePhase;
 use codex_protocol::models::ReasoningItemContent;
 use codex_protocol::models::ReasoningItemReasoningSummary;
 use codex_protocol::models::ResponseItem;
@@ -69,7 +70,11 @@ fn parse_user_message(message: &[ContentItem]) -> Option<UserMessageItem> {
     Some(UserMessageItem::new(&content))
 }
 
-fn parse_agent_message(id: Option<&String>, message: &[ContentItem]) -> AgentMessageItem {
+fn parse_agent_message(
+    id: Option<&String>,
+    message: &[ContentItem],
+    phase: Option<MessagePhase>,
+) -> AgentMessageItem {
     let mut content: Vec<AgentMessageContent> = Vec::new();
     for content_item in message.iter() {
         match content_item {
@@ -85,18 +90,23 @@ fn parse_agent_message(id: Option<&String>, message: &[ContentItem]) -> AgentMes
         }
     }
     let id = id.cloned().unwrap_or_else(|| Uuid::new_v4().to_string());
-    AgentMessageItem { id, content }
+    AgentMessageItem { id, content, phase }
 }
 
 pub fn parse_turn_item(item: &ResponseItem) -> Option<TurnItem> {
     match item {
         ResponseItem::Message {
-            role, content, id, ..
+            role,
+            content,
+            id,
+            phase,
+            ..
         } => match role.as_str() {
             "user" => parse_user_message(content).map(TurnItem::UserMessage),
             "assistant" => Some(TurnItem::AgentMessage(parse_agent_message(
                 id.as_ref(),
                 content,
+                phase.clone(),
             ))),
             "system" => None,
             _ => None,