Deprecate full-history hydration for paginated threads (#40676)

## Why

Paginated thread history should be loaded incrementally through
`thread/turns/list` and `thread/items/list` instead of being fully reconstructed
in `thread.turns`.

## What changed

- Emit `deprecationNotice` when `thread/read`, `thread/resume`, or `thread/fork`
  requests full history for a paginated thread.
- Direct clients to omit `includeTurns` for reads or use `excludeTurns: true` for
  resumes and forks, then page history through the list APIs.
- Document the deprecation in the protocol schemas and app-server README.

## Testing

- Cover notices for paginated reads, cold and loaded resumes, and forks.
- Verify metadata-only requests, legacy threads, and rejected forks do not emit
  the notice.

GitOrigin-RevId: 0d387b46d73608f90b7960120a54af4ef332e510

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

@@ -20164,7 +20164,7 @@
             "type": "boolean"
           },
           "excludeTurns": {
-            "description": "When true, return only thread metadata and live fork state without populating `thread.turns`. This is useful when the client plans to call `thread/turns/list` immediately after forking.",
+            "description": "When true, return only thread metadata and live fork state without populating `thread.turns`. This is useful when the client plans to call `thread/turns/list` immediately after forking. Full-history hydration is deprecated for paginated threads; use this with `thread/turns/list` and `thread/items/list` instead.",
             "type": "boolean"
           },
           "lastTurnId": {
@@ -21739,7 +21739,7 @@
         "$schema": "http://json-schema.org/draft-07/schema#",
         "properties": {
           "includeTurns": {
-            "description": "When true, include turns and their items from rollout history.",
+            "description": "When true, include turns and their items from rollout history. Full-history hydration is deprecated for paginated threads; prefer a metadata-only read and page with `thread/turns/list` and `thread/items/list`.",
             "type": "boolean"
           },
           "threadId": {
@@ -22366,7 +22366,7 @@
             ]
           },
           "excludeTurns": {
-            "description": "When true, return only thread metadata and live-resume state without populating `thread.turns`. This is useful when the client plans to call `thread/turns/list` immediately after resuming.",
+            "description": "When true, return only thread metadata and live-resume state without populating `thread.turns`. This is useful when the client plans to call `thread/turns/list` immediately after resuming. Full-history hydration is deprecated for paginated threads; use this with `thread/turns/list` and `thread/items/list` instead.",
             "type": "boolean"
           },
           "model": {