feat(core): expose session switching endpoints

packages/core/src/session.ts

@@ -129,7 +129,7 @@ export interface Interface {
   readonly switchAgent: (input: {
     sessionID: SessionSchema.ID
     agent: string
-  }) => Effect.Effect<void, OperationUnavailableError>
+  }) => Effect.Effect<void, NotFoundError>
   readonly switchModel: (input: {
     sessionID: SessionSchema.ID
     model: ModelV2.Ref
@@ -376,8 +376,14 @@ export const layer = Layer.effect(
       skill: Effect.fn("V2Session.skill")(function* () {
         return yield* new OperationUnavailableError({ operation: "skill" })
       }),
-      switchAgent: Effect.fn("V2Session.switchAgent")(function* () {
-        return yield* new OperationUnavailableError({ operation: "switchAgent" })
+      switchAgent: Effect.fn("V2Session.switchAgent")(function* (input) {
+        yield* result.get(input.sessionID)
+        yield* events.publish(SessionEvent.AgentSwitched, {
+          sessionID: input.sessionID,
+          messageID: SessionMessage.ID.create(),
+          timestamp: yield* DateTime.now,
+          agent: input.agent,
+        })
       }),
       switchModel: Effect.fn("V2Session.switchModel")(function* (input) {
         yield* result.get(input.sessionID)

packages/core/test/session-create.test.ts

@@ -336,7 +336,34 @@ describe("SessionV2.create", () => {
 
       expect(yield* unavailable(session.shell({ sessionID: created.id, command: "pwd" }))).toBe("shell")
       expect(yield* unavailable(session.skill({ sessionID: created.id, skill: "review" }))).toBe("skill")
-      expect(yield* unavailable(session.switchAgent({ sessionID: created.id, agent: "build" }))).toBe("switchAgent")
+    }),
+  )
+
+  it.effect("switches the selected agent through the durable Session event", () =>
+    Effect.gen(function* () {
+      const session = yield* SessionV2.Service
+      const created = yield* session.create({ location })
+
+      yield* session.switchAgent({ sessionID: created.id, agent: "plan" })
+
+      expect(yield* session.get(created.id)).toMatchObject({ agent: "plan" })
+      expect(
+        Array.from(yield* session.events({ sessionID: created.id }).pipe(Stream.take(1), Stream.runCollect)),
+      ).toMatchObject([{ type: "session.next.agent.switched", data: { agent: "plan" } }])
+    }),
+  )
+
+  it.effect("rejects an agent switch for a missing Session", () =>
+    Effect.gen(function* () {
+      const session = yield* SessionV2.Service
+      const missing = SessionV2.ID.make("ses_missing_agent_switch")
+
+      expect(
+        yield* session.switchAgent({ sessionID: missing, agent: "plan" }).pipe(
+          Effect.flip,
+          Effect.map((error) => error._tag),
+        ),
+      ).toBe("Session.NotFoundError")
     }),
   )