feat(core): expose session switching endpoints

packages/server/src/groups/session.ts

@@ -140,6 +140,38 @@ export const SessionGroup = HttpApiGroup.make("server.session")
         }),
       ),
   )
+  .add(
+    HttpApiEndpoint.post("session.switchAgent", "/api/session/:sessionID/agent", {
+      params: { sessionID: SessionV2.ID },
+      payload: Schema.Struct({ agent: AgentV2.ID }),
+      success: HttpApiSchema.NoContent,
+      error: SessionNotFoundError,
+    })
+      .middleware(SessionLocationMiddleware)
+      .annotateMerge(
+        OpenApi.annotations({
+          identifier: "v2.session.switchAgent",
+          summary: "Switch session agent",
+          description: "Switch the agent used by subsequent session activity.",
+        }),
+      ),
+  )
+  .add(
+    HttpApiEndpoint.post("session.switchModel", "/api/session/:sessionID/model", {
+      params: { sessionID: SessionV2.ID },
+      payload: Schema.Struct({ model: ModelV2.Ref }),
+      success: HttpApiSchema.NoContent,
+      error: SessionNotFoundError,
+    })
+      .middleware(SessionLocationMiddleware)
+      .annotateMerge(
+        OpenApi.annotations({
+          identifier: "v2.session.switchModel",
+          summary: "Switch session model",
+          description: "Switch the model used by subsequent session activity.",
+        }),
+      ),
+  )
   .add(
     HttpApiEndpoint.post("session.prompt", "/api/session/:sessionID/prompt", {
       params: { sessionID: SessionV2.ID },

packages/server/src/handlers/session.ts

@@ -92,6 +92,38 @@ export const SessionHandler = HttpApiBuilder.group(Api, "server.session", (handl
           }
         }),
       )
+      .handle(
+        "session.switchAgent",
+        Effect.fn(function* (ctx) {
+          yield* session.switchAgent({ sessionID: ctx.params.sessionID, agent: ctx.payload.agent }).pipe(
+            Effect.catchTag("Session.NotFoundError", (error) =>
+              Effect.fail(
+                new SessionNotFoundError({
+                  sessionID: error.sessionID,
+                  message: `Session not found: ${error.sessionID}`,
+                }),
+              ),
+            ),
+          )
+          return HttpApiSchema.NoContent.make()
+        }),
+      )
+      .handle(
+        "session.switchModel",
+        Effect.fn(function* (ctx) {
+          yield* session.switchModel({ sessionID: ctx.params.sessionID, model: ctx.payload.model }).pipe(
+            Effect.catchTag("Session.NotFoundError", (error) =>
+              Effect.fail(
+                new SessionNotFoundError({
+                  sessionID: error.sessionID,
+                  message: `Session not found: ${error.sessionID}`,
+                }),
+              ),
+            ),
+          )
+          return HttpApiSchema.NoContent.make()
+        }),
+      )
       .handle(
         "session.prompt",
         Effect.fn(function* (ctx) {