[codex] Add rollout-backed thread content search (#23519)

## Summary
- add experimental `thread/search` for local rollout-backed thread
search using `rg` over JSONL rollouts
- return search-specific result rows with optional previews instead of
storing preview data on `StoredThread` or ordinary `Thread` responses
- keep `thread/list` separate from full-content search and document the
new app-server surface

## Testing
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server
thread_search_returns_content_and_title_matches -- --nocapture`

codex-rs/app-server-protocol/schema/json/ServerNotification.json

@@ -6546,4 +6546,4 @@
     }
   ],
   "title": "ServerNotification"
-}
+}

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -17440,6 +17440,21 @@
         "title": "ThreadRollbackResponse",
         "type": "object"
       },
+      "ThreadSearchResult": {
+        "properties": {
+          "snippet": {
+            "type": "string"
+          },
+          "thread": {
+            "$ref": "#/definitions/v2/Thread"
+          }
+        },
+        "required": [
+          "snippet",
+          "thread"
+        ],
+        "type": "object"
+      },
       "ThreadSetNameParams": {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "properties": {

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -15264,6 +15264,21 @@
       "title": "ThreadRollbackResponse",
       "type": "object"
     },
+    "ThreadSearchResult": {
+      "properties": {
+        "snippet": {
+          "type": "string"
+        },
+        "thread": {
+          "$ref": "#/definitions/Thread"
+        }
+      },
+      "required": [
+        "snippet",
+        "thread"
+      ],
+      "type": "object"
+    },
     "ThreadSetNameParams": {
       "$schema": "http://json-schema.org/draft-07/schema#",
       "properties": {

codex-rs/app-server-protocol/schema/typescript/v2/ThreadSearchResult.ts

@@ -0,0 +1,6 @@
+// GENERATED CODE! DO NOT MODIFY BY HAND!
+
+// This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+import type { Thread } from "./Thread";
+
+export type ThreadSearchResult = { thread: Thread, snippet: string, };

codex-rs/app-server-protocol/schema/typescript/v2/index.ts

@@ -401,6 +401,7 @@ export type { ThreadResumeParams } from "./ThreadResumeParams";
 export type { ThreadResumeResponse } from "./ThreadResumeResponse";
 export type { ThreadRollbackParams } from "./ThreadRollbackParams";
 export type { ThreadRollbackResponse } from "./ThreadRollbackResponse";
+export type { ThreadSearchResult } from "./ThreadSearchResult";
 export type { ThreadSetNameParams } from "./ThreadSetNameParams";
 export type { ThreadSetNameResponse } from "./ThreadSetNameResponse";
 export type { ThreadSettings } from "./ThreadSettings";