feat(gui): add ask-user question composer

packages/host/apiproxy/src/api/rpc.schema.ts

@@ -33,6 +33,7 @@ export const rpcIdSchema = z.string() as unknown as z.ZodType<RpcId>
 /** Error body: discriminated by code, per-branch details aligned to RpcErrorDetailsMap; details is required. */
 export const rpcErrorSchema: z.ZodType<RpcError> = z.discriminatedUnion('code', [
   z.object({ code: z.literal('bad-request'), message: z.string(), details: z.object({ issues: z.array(z.custom<ZodIssue>()) }) }),
+  z.object({ code: z.literal('cancelled'), message: z.string(), details: z.object({}) }),
   z.object({ code: z.literal('session-not-found'), message: z.string(), details: z.object({ sessionId: z.string() }) }),
   z.object({ code: z.literal('agent-busy'), message: z.string(), details: z.object({ reason: z.string() }) }),
   z.object({ code: z.literal('internal'), message: z.string(), details: z.object({}) }),

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

@@ -30,6 +30,7 @@ export function RpcId(id: string): RpcId {
 /** Error code → details type map (a second table isomorphic to RpcMethodMap). New code = one row here + one branch in the error schema. */
 export interface RpcErrorDetailsMap {
   'bad-request': { issues: ZodIssue[] }
+  'cancelled': {}
   'session-not-found': { sessionId: SessionId }
   'agent-busy': { reason: string }
   'internal': {}

packages/host/apiproxy/tests/rpc-schemas.spec.ts

@@ -29,6 +29,7 @@ describe('RpcId', () => {
 describe('rpcErrorSchema', () => {
   it('accepts every code branch with its required details', () => {
     expect(rpcErrorSchema.parse({ code: 'bad-request', message: 'm', details: { issues: [] } }).code).toBe('bad-request')
+    expect(rpcErrorSchema.parse({ code: 'cancelled', message: 'm', details: {} }).code).toBe('cancelled')
     expect(rpcErrorSchema.parse({ code: 'session-not-found', message: 'm', details: { sessionId: 's' } }).code).toBe('session-not-found')
     expect(rpcErrorSchema.parse({ code: 'agent-busy', message: 'm', details: { reason: 'r' } }).code).toBe('agent-busy')
     expect(rpcErrorSchema.parse({ code: 'internal', message: 'm', details: {} }).code).toBe('internal')