feat(web): project plan mode through host API

packages/host/apiproxy/src/api/sessions.ts

@@ -44,6 +44,16 @@ export interface SessionSummary {
   cwd?: string
 }
 
+/**
+ * Plan collaboration state exposed to clients. `active` is the logged state
+ * shaping the current request; `pending`, when present, is the user's
+ * next-boundary selection.
+ */
+export interface PlanModeState {
+  active: boolean
+  pending?: boolean
+}
+
 /** Session-domain unary methods (the map keys session.* of RpcMethodMap). */
 export interface SessionsApi {
   /** Lists persisted sessions (updatedAt descending). v1 returns everything; cursor is a reserved seat, unimplemented. */
@@ -70,4 +80,18 @@ export interface SessionsApi {
 
   /** Stops: clears both FIFOs + aborts the current step (1:1 with agent.cancel). */
   cancel(request: RpcRequest<{ sessionId: SessionId }>): Promise<RpcResponse<{ accepted: true }>>
+
+  /**
+   * Reads plan collaboration state. `null` means the host did not compose the
+   * optional plan-mode service; it is distinct from inactive state.
+   */
+  planMode(request: RpcRequest<{ sessionId: SessionId }>): Promise<RpcResponse<PlanModeState | null>>
+
+  /**
+   * Selects plan collaboration state for the next model-request boundary.
+   * The returned state exposes the still-committed value and pending target;
+   * `null` means plan mode is unavailable on this host.
+   */
+  setPlanMode(request: RpcRequest<{ sessionId: SessionId; active: boolean }>):
+  Promise<RpcResponse<PlanModeState | null>>
 }