Use goal preview metadata for goal-first threads (#21981)

Fixes #20792

## Why

`/goal`-first threads are valid resumable threads, but they can be
missing from `codex resume` and app recents because discovery depends on
metadata derived from a normal first user message.

PR #21489 attempted to fix this by using the goal objective as
`first_user_message`. Review feedback pointed out that
`first_user_message` does more than provide visible text today: it gates
listing, supplies preview text, and participates in deciding whether a
later title should surface as a distinct thread name. Reusing it for the
goal objective could leave a `/goal`-first thread with
`first_user_message=<goal>` and `title=<later prompt>`, even though the
goal should only provide the initial visible preview.

This PR follows that feedback by and keeps the `first_user_message` as
is but introduces a new `preview` field to separate concerns. The
`preview` field is populated from the first user message or the goal
objective. We can extend it in the future to include other sources.

## What Changed

- Added internal thread `preview` metadata in `codex-state`, including a
SQLite migration that backfills from `first_user_message` and from
existing `thread_goals` objectives when needed.
- Treated `ThreadGoalUpdated` as preview-bearing metadata so goal-first
threads can be listed and searched without mutating
`first_user_message`.
- Updated rollout listing, state queries, thread-store conversion, and
app-server mapping to use preview metadata while continuing to expose
the existing public `preview` field.
- Preserved title/name distinctness behavior around literal
`first_user_message`, so a later normal prompt after `/goal` does not
surface as a separate name just because the goal supplied the initial
preview.
- Preserved compatibility for older/internal metadata writes by deriving
preview from `first_user_message` when explicit preview metadata is
absent.

## Verification

- Manually verified that a thread that starts with a `/goal <objective>`
shows up in the resume picker.

codex-rs/state/src/extract.rs

@@ -33,7 +33,9 @@ pub fn apply_rollout_item(
 pub fn rollout_item_affects_thread_metadata(item: &RolloutItem) -> bool {
     match item {
         RolloutItem::SessionMeta(_) | RolloutItem::TurnContext(_) => true,
-        RolloutItem::EventMsg(EventMsg::TokenCount(_) | EventMsg::UserMessage(_)) => true,
+        RolloutItem::EventMsg(
+            EventMsg::TokenCount(_) | EventMsg::UserMessage(_) | EventMsg::ThreadGoalUpdated(_),
+        ) => true,
         RolloutItem::EventMsg(_) | RolloutItem::ResponseItem(_) | RolloutItem::Compacted(_) => {
             false
         }
@@ -86,9 +88,11 @@ fn apply_event_msg(metadata: &mut ThreadMetadata, event: &EventMsg) {
             }
         }
         EventMsg::UserMessage(user) => {
+            let preview = user_message_preview(user);
             if metadata.first_user_message.is_none() {
-                metadata.first_user_message = user_message_preview(user);
+                metadata.first_user_message = preview.clone();
             }
+            set_preview_if_empty(metadata, preview);
             if metadata.title.is_empty() {
                 let title = strip_user_message_prefix(user.message.as_str());
                 if !title.is_empty() {
@@ -96,12 +100,24 @@ fn apply_event_msg(metadata: &mut ThreadMetadata, event: &EventMsg) {
                 }
             }
         }
+        EventMsg::ThreadGoalUpdated(event) => {
+            let objective = event.goal.objective.trim();
+            if !objective.is_empty() {
+                set_preview_if_empty(metadata, Some(objective.to_string()));
+            }
+        }
         _ => {}
     }
 }
 
 fn apply_response_item(_metadata: &mut ThreadMetadata, _item: &ResponseItem) {}
 
+fn set_preview_if_empty(metadata: &mut ThreadMetadata, preview: Option<String>) {
+    if metadata.preview.is_none() {
+        metadata.preview = preview;
+    }
+}
+
 fn strip_user_message_prefix(text: &str) -> &str {
     match text.find(USER_MESSAGE_BEGIN) {
         Some(idx) => text[idx + USER_MESSAGE_BEGIN.len()..].trim(),
@@ -151,6 +167,9 @@ mod tests {
     use codex_protocol::protocol::SessionMeta;
     use codex_protocol::protocol::SessionMetaLine;
     use codex_protocol::protocol::SessionSource;
+    use codex_protocol::protocol::ThreadGoal;
+    use codex_protocol::protocol::ThreadGoalStatus;
+    use codex_protocol::protocol::ThreadGoalUpdatedEvent;
     use codex_protocol::protocol::TurnContextItem;
     use codex_protocol::protocol::USER_MESSAGE_BEGIN;
     use codex_protocol::protocol::UserMessageEvent;
@@ -174,6 +193,7 @@ mod tests {
         apply_rollout_item(&mut metadata, &item, "test-provider");
 
         assert_eq!(metadata.first_user_message, None);
+        assert_eq!(metadata.preview, None);
         assert_eq!(metadata.title, "");
     }
 
@@ -193,6 +213,7 @@ mod tests {
             metadata.first_user_message.as_deref(),
             Some("actual user request")
         );
+        assert_eq!(metadata.preview.as_deref(), Some("actual user request"));
         assert_eq!(metadata.title, "actual user request");
     }
 
@@ -212,6 +233,10 @@ mod tests {
             metadata.first_user_message.as_deref(),
             Some(super::IMAGE_ONLY_USER_MESSAGE_PLACEHOLDER)
         );
+        assert_eq!(
+            metadata.preview.as_deref(),
+            Some(super::IMAGE_ONLY_USER_MESSAGE_PLACEHOLDER)
+        );
         assert_eq!(metadata.title, "");
     }
 
@@ -228,9 +253,52 @@ mod tests {
         apply_rollout_item(&mut metadata, &item, "test-provider");
 
         assert_eq!(metadata.first_user_message, None);
+        assert_eq!(metadata.preview, None);
         assert_eq!(metadata.title, "");
     }
 
+    #[test]
+    fn event_msg_thread_goal_sets_preview_only_and_later_user_sets_message_title() {
+        let mut metadata = metadata_for_test();
+        let goal_item =
+            RolloutItem::EventMsg(EventMsg::ThreadGoalUpdated(ThreadGoalUpdatedEvent {
+                thread_id: metadata.id,
+                turn_id: None,
+                goal: ThreadGoal {
+                    thread_id: metadata.id,
+                    objective: "optimize the benchmark".to_string(),
+                    status: ThreadGoalStatus::Active,
+                    token_budget: None,
+                    tokens_used: 0,
+                    time_used_seconds: 0,
+                    created_at: 1,
+                    updated_at: 1,
+                },
+            }));
+
+        apply_rollout_item(&mut metadata, &goal_item, "test-provider");
+
+        assert_eq!(metadata.preview.as_deref(), Some("optimize the benchmark"));
+        assert_eq!(metadata.first_user_message, None);
+        assert_eq!(metadata.title, "");
+
+        let user_item = RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            message: format!("{USER_MESSAGE_BEGIN} next normal prompt"),
+            images: Some(vec![]),
+            local_images: vec![],
+            text_elements: vec![],
+        }));
+
+        apply_rollout_item(&mut metadata, &user_item, "test-provider");
+
+        assert_eq!(metadata.preview.as_deref(), Some("optimize the benchmark"));
+        assert_eq!(
+            metadata.first_user_message.as_deref(),
+            Some("next normal prompt")
+        );
+        assert_eq!(metadata.title, "next normal prompt");
+    }
+
     #[test]
     fn turn_context_does_not_override_session_cwd() {
         let mut metadata = metadata_for_test();
@@ -421,6 +489,7 @@ mod tests {
             cwd: PathBuf::from("/tmp"),
             cli_version: "0.0.0".to_string(),
             title: String::new(),
+            preview: None,
             sandbox_policy: "read-only".to_string(),
             approval_mode: "on-request".to_string(),
             tokens_used: 1,