Handoff-style /model switch command and per-turn thinking level (#64)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/web/test/stream-model.test.ts

@@ -77,7 +77,6 @@ function meta(sessionId: string): OmniMessage<SessionMetaPayload> {
     model_context_window: 200000,
     system_prompt: "",
     tools: [],
-    thinking_level: "default",
     agent_state: "/a",
     workspace: "/w",
   });
@@ -279,34 +278,6 @@ describe("approvals and events", () => {
     expect(items(m)).toHaveLength(0);
   });
 
-  it("captures the session's thinking level from the main session_meta (read-only input-area tag)", () => {
-    const m = createStreamModel();
-    expect(m.thinkingLevel).toBeNull();
-    // The shared helper's meta carries thinking_level "default" (Agent config leaves it unset).
-    pushMessage(m, meta("session-x"));
-    expect(m.thinkingLevel).toBe("default");
-
-    const m2 = createStreamModel();
-    pushMessage(
-      m2,
-      sessionMeta({
-        session_id: "session-y",
-        model_id: "m",
-        provider: "custom",
-        model_context_window: 200000,
-        system_prompt: "",
-        tools: [],
-        thinking_level: "medium",
-        agent_state: "/a",
-        workspace: "/w",
-      }),
-    );
-    expect(m2.thinkingLevel).toBe("medium");
-    // An origin-tagged (sub-session) session_meta routes to the nested model and must not clobber the main session's level.
-    pushMessage(m2, withOrigin(meta("child"), "child"));
-    expect(m2.thinkingLevel).toBe("medium");
-  });
-
   it("request_end final state timeout/malformed produces a retry notice item (with attempt number); request_begin marks it as resent", () => {
     const m = createStreamModel();
     pushMessage(m, requestBegin());