Carry targeted moderation decisions on final-answer messages (#59842)

## What changed

Read `final_answer_moderation` metadata and attach `moderation: { moderated: boolean }` to the completed final-answer message only when its item ID matches. Apply this in both normal and plan modes, and reset the pending decision when a new response starts.

Preserve the answer's native item ID and moderation flag through legacy events and history reconstruction. Combine text parts into one legacy event when a moderation decision is present.

Expose nullable moderation data on app-server agent messages and update the JSON schemas, TypeScript types, and Python models.

## Testing

Add an integration test for moderation on completed answers and their legacy events. Extend protocol conversion tests to cover populated moderation data and serialization as `null` when absent.

GitOrigin-RevId: f286b67731a84b3daf5d10b7644f2e31b62f0e53

sdk/python/src/openai_codex/generated/v2_all.py

@@ -154,6 +154,13 @@ class AgentMessageInputContent(
     root: InputTextAgentMessageInputContent | EncryptedContentAgentMessageInputContent
 
 
+class AgentMessageModeration(BaseModel):
+    model_config = ConfigDict(
+        populate_by_name=True,
+    )
+    moderated: bool
+
+
 class AgentPath(RootModel[str]):
     root: str
 
@@ -10715,6 +10722,7 @@ class AgentMessageThreadItem(BaseModel):
     delivery: AgentMessageDelivery | None = None
     id: str
     memory_citation: Annotated[MemoryCitation | None, Field(alias="memoryCitation")] = None
+    moderation: AgentMessageModeration | None = None
     phase: MessagePhase | None = None
     questions: list[AsyncUserInputQuestion] | None = None
     started_at_ms: Annotated[