Add excludeTurns parameter to thread/resume and thread/fork (#19014)

For callers who expect to be paginating the results for the UI, they can
now call thread/resume or thread/fork with excludeturns:true so it will
not fetch any pages of turns, and instead only set up the subscription.
That call can be immediately followed by pagination requests to
thread/turns/list to fetch pages of turns according to the UI's current
interactions.

codex-rs/app-server/README.md

@@ -138,7 +138,7 @@ Example with notification opt-out:
 
 - `thread/start` — create a new thread; emits `thread/started` (including the current `thread.status`) and auto-subscribes you to turn/item events for that thread. When the request includes a `cwd` and the resolved sandbox is `workspace-write` or full access, app-server also marks that project as trusted in the user `config.toml`. Pass `sessionStartSource: "clear"` when starting a replacement thread after clearing the current session so `SessionStart` hooks receive `source: "clear"` instead of the default `"startup"`. For permissions, prefer `permissionProfile`; the legacy `sandbox` shorthand is still accepted but cannot be combined with `permissionProfile`.
 - `thread/resume` — reopen an existing thread by id so subsequent `turn/start` calls append to it. Accepts the same permission override rules as `thread/start`.
-- `thread/fork` — fork an existing thread into a new thread id by copying the stored history; if the source thread is currently mid-turn, the fork records the same interruption marker as `turn/interrupt` instead of inheriting an unmarked partial turn suffix. The returned `thread.forkedFromId` points at the source thread when known. Accepts `ephemeral: true` for an in-memory temporary fork, emits `thread/started` (including the current `thread.status`), and auto-subscribes you to turn/item events for the new thread. Accepts the same permission override rules as `thread/start`.
+- `thread/fork` — fork an existing thread into a new thread id by copying the stored history; if the source thread is currently mid-turn, the fork records the same interruption marker as `turn/interrupt` instead of inheriting an unmarked partial turn suffix. The returned `thread.forkedFromId` points at the source thread when known. Accepts `ephemeral: true` for an in-memory temporary fork, emits `thread/started` (including the current `thread.status`), and auto-subscribes you to turn/item events for the new thread. Pass `excludeTurns: true` when the client plans to page fork history via `thread/turns/list` instead of receiving the full turn array immediately. Accepts the same permission override rules as `thread/start`.
 - `thread/list` — page through stored rollouts; supports cursor-based pagination and optional `modelProviders`, `sourceKinds`, `archived`, `cwd`, and `searchTerm` filters. Each returned `thread` includes `status` (`ThreadStatus`), defaulting to `notLoaded` when the thread is not currently loaded.
 - `thread/loaded/list` — list the thread ids currently loaded in memory.
 - `thread/read` — read a stored thread by id without resuming it; optionally include turns via `includeTurns`. The returned `thread` includes `status` (`ThreadStatus`), defaulting to `notLoaded` when the thread is not currently loaded.
@@ -259,6 +259,8 @@ Valid `personality` values are `"friendly"`, `"pragmatic"`, and `"none"`. When `
 
 To continue a stored session, call `thread/resume` with the `thread.id` you previously recorded. The response shape matches `thread/start`. When the stored session includes persisted token usage, the server emits `thread/tokenUsage/updated` immediately after the response so clients can render restored usage before the next turn starts. You can also pass the same configuration overrides supported by `thread/start`, including `approvalsReviewer`.
 
+By default, `thread/resume` includes the reconstructed turn history in `thread.turns`. Pass `excludeTurns: true` to return only thread metadata and live resume state, then call `thread/turns/list` separately if you want to page the turn history over the network. In that mode the server also skips replaying restored `thread/tokenUsage/updated`, which avoids rebuilding turns just to attribute historical usage.
+
 By default, resume uses the latest persisted `model` and `reasoningEffort` values associated with the thread. Supplying any of `model`, `modelProvider`, `config.model`, or `config.model_reasoning_effort` disables that persisted fallback and uses the explicit overrides plus normal config resolution instead.
 
 Example:
@@ -269,6 +271,12 @@ Example:
     "personality": "friendly"
 } }
 { "id": 11, "result": { "thread": { "id": "thr_123", … } } }
+
+{ "method": "thread/resume", "id": 12, "params": {
+    "threadId": "thr_123",
+    "excludeTurns": true
+} }
+{ "id": 12, "result": { "thread": { "id": "thr_123", "turns": [], … } } }
 ```
 
 To branch from a stored session, call `thread/fork` with the `thread.id`. This creates a new thread id and emits a `thread/started` notification for it. When the source history includes persisted token usage, the server also emits `thread/tokenUsage/updated` for the new thread immediately after the response. If the source thread is actively running, the fork snapshots it as if the current turn had been interrupted first. Pass `ephemeral: true` when the fork should stay in-memory only:
@@ -279,6 +287,8 @@ To branch from a stored session, call `thread/fork` with the `thread.id`. This c
 { "method": "thread/started", "params": { "thread": { … } } }
 ```
 
+Like `thread/resume`, `thread/fork` also accepts `excludeTurns: true` to return only thread metadata in `thread.turns` and let the client page history with `thread/turns/list`. In that mode the server skips replaying restored `thread/tokenUsage/updated`, which keeps the fork path from rebuilding turns just to attribute historical usage.
+
 Experimental API: `thread/start`, `thread/resume`, and `thread/fork` accept `persistExtendedHistory: true` to persist a richer subset of ThreadItems for non-lossy history when calling `thread/read`, `thread/resume`, and `thread/fork` later. This does not backfill events that were not persisted previously.
 
 ### Example: List threads (with pagination & filters)