Support standalone tool outputs in turn/start (#41002)

## What changed

- Add an optional `toolOutput` to `turn/start` for starting or steering a turn with a named function-call output instead of user input.
- Emit standalone outputs as `functionCallOutput` thread items, persist them in durable history, and include them in resumed threads.
- Validate that tool outputs have a name, are not combined with nonempty `input`, satisfy the text-size limit, and use supported image URLs.

## Testing

- Cover standalone tool-output notifications, model input, and resumed history in both legacy and paginated history modes.
- Cover the text-size limit for structured tool output.

GitOrigin-RevId: a1eeec7b9b7de67b1a1c5e829a54552b85ec118b

codex-rs/tui/src/app/agent_status_feed.rs

@@ -192,7 +192,10 @@ fn activity_summary(item: &ThreadItem) -> Option<String> {
         ThreadItem::EnteredReviewMode { .. } => return Some("Entered review mode".to_string()),
         ThreadItem::ExitedReviewMode { .. } => return Some("Exited review mode".to_string()),
         ThreadItem::ContextCompaction { .. } => return Some("Compacted context".to_string()),
-        ThreadItem::UserMessage { .. } | ThreadItem::HookPrompt { .. } | ThreadItem::Sleep(_) => {
+        ThreadItem::UserMessage { .. }
+        | ThreadItem::HookPrompt { .. }
+        | ThreadItem::FunctionCallOutput { .. }
+        | ThreadItem::Sleep(_) => {
             return None;
         }
     };

codex-rs/tui/src/app_server_session.rs

@@ -1208,6 +1208,7 @@ impl AppServerSession {
                     turn_trigger: None,
                     client_user_message_id: None,
                     input: items,
+                    tool_output: None,
                     responsesapi_client_metadata: None,
                     additional_context: None,
                     environments: None,

codex-rs/tui/src/chatwidget/replay.rs

@@ -218,7 +218,7 @@ impl ChatWidget {
             ThreadItem::ContextCompaction { .. } => {
                 self.add_info_message("Context compacted".to_string(), /*hint*/ None);
             }
-            ThreadItem::HookPrompt { .. } => {}
+            ThreadItem::HookPrompt { .. } | ThreadItem::FunctionCallOutput { .. } => {}
             ThreadItem::CollabAgentToolCall {
                 id,
                 tool,

codex-rs/tui/src/dynamic_tools.rs

@@ -1061,6 +1061,7 @@ async fn execute_inner(
                                         "name": "webSearch", "status": null
                                     })),
                                     ThreadItem::UserMessage { .. }
+                                    | ThreadItem::FunctionCallOutput { .. }
                                     | ThreadItem::HookPrompt { .. }
                                     | ThreadItem::AgentMessage { .. }
                                     | ThreadItem::Plan { .. }
@@ -1316,6 +1317,23 @@ fn turn_summary(turn: &Turn, include_outputs: bool, output_chars: usize) -> Valu
             ThreadItem::HookPrompt { id, fragments } => json!({
                 "type": "hookPrompt", "id": id, "fragmentCount": fragments.len()
             }),
+            ThreadItem::FunctionCallOutput {
+                id,
+                name,
+                namespace,
+                output,
+            } => {
+                let mut item = json!({
+                    "type": "functionCallOutput", "id": id, "name": name, "namespace": namespace
+                });
+                if include_outputs {
+                    item["output"] = output_summary(
+                        output.to_text().as_deref().unwrap_or("[non-text output]"),
+                        output_chars,
+                    );
+                }
+                item
+            }
             ThreadItem::AgentMessage { id, text, phase, .. } => json!({
                 "type": "agentMessage", "id": id, "text": truncate(text, DEFAULT_OUTPUT_CHARS), "phase": phase
             }),

codex-rs/tui/src/thread_transcript.rs

@@ -281,6 +281,7 @@ fn fallback_transcript_cell(item: &ThreadItem) -> Option<PlainHistoryCell> {
         }
         ThreadItem::UserMessage { .. }
         | ThreadItem::AgentMessage { .. }
+        | ThreadItem::FunctionCallOutput { .. }
         | ThreadItem::Plan { .. }
         | ThreadItem::Reasoning { .. }
         | ThreadItem::Sleep(_) => return None,