feat(client): ISession.rename settles the title projection cell from the response

rename is a per-session verb on the outward session face (prompt/cancel
precedent), not a list-service verb: the Session calls session.rename and
applies the response {title, seq} to its projection store under
higher-seq-wins, so the list row updates before the push frame. The fixture
api and the test-runtime double follow the same face.

packages/client/runtime/src/client/contract/session.ts

@@ -41,6 +41,13 @@ export interface ISession {
    * @returns acceptance, or the business error.
    */
   cancel(): Promise<RpcResult<{ accepted: true }>>
+  /**
+   * Rename this session (explicit user title; pins it against automatic
+   * regeneration).
+   * @param title - raw title text (the host normalizes acceptance).
+   * @returns the normalized accepted title and its event seq, or the business error.
+   */
+  rename(title: string): Promise<RpcResult<{ title: string; seq: number }>>
   /**
    * Extend the history window backwards (older messages pagination).
    * @returns completion; failures land in snapshot.openState/loadingOlder.

packages/client/runtime/src/client/sessions/session.ts

@@ -252,6 +252,25 @@ export class Session implements SessionFace {
     return result
   }
 
+  /**
+   * Rename: contract session.rename 1:1. On success settle the 'title'
+   * projection cell from the response's `{title, seq}` under the store's
+   * higher-seq-wins rule (the push frame arriving later is a no-op replay),
+   * so the list row and any useProjection('title') reader update without
+   * waiting for the mux frame.
+   * @param title - raw title text (the host normalizes acceptance).
+   * @returns the rename result (normalized accepted title + title event seq).
+   */
+  async rename(title: string): Promise<RpcResult<{ title: string; seq: number }>> {
+    try {
+      const { result } = await this.api.sessions.rename({ sessionId: this.sessionId, title })
+      if (result.ok) this.projections.apply('title', result.value.title, result.value.seq)
+      return result
+    } catch (error) {
+      return transportError(error)
+    }
+  }
+
   /**
    * Execute one slash-command line against this session's agent — pure
    * admission semantics (the host executor durably logs the lifecycle;