fix: don't inject reasoning: { effort: "none" } for OpenRouter when thinking is off

"off" is a truthy string, so the existing guard `if (thinkingLevel && ...)`
was always entering the injection block and sending `reasoning: { effort: "none" }`
to every OpenRouter request — even when thinking wasn't enabled. Models that
require reasoning (e.g. deepseek/deepseek-r1) reject this with:
  400 Reasoning is mandatory for this endpoint and cannot be disabled.

Fix: skip the reasoning injection entirely when thinkingLevel is "off".
The reasoning_effort flat-field cleanup still runs. Omitting the reasoning
field lets each model use its own default behavior.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/agents/pi-embedded-runner-extraparams.test.ts

@@ -202,6 +202,58 @@ describe("applyExtraParamsToAgent", () => {
     return calls[0]?.headers;
   }
 
+  it("does not inject reasoning when thinkingLevel is off (default) for OpenRouter", () => {
+    // Regression: "off" is a truthy string, so the old code injected
+    // reasoning: { effort: "none" }, causing a 400 on models that require
+    // reasoning (e.g. deepseek/deepseek-r1).
+    const payloads: Record<string, unknown>[] = [];
+    const baseStreamFn: StreamFn = (_model, _context, options) => {
+      const payload: Record<string, unknown> = { model: "deepseek/deepseek-r1" };
+      options?.onPayload?.(payload);
+      payloads.push(payload);
+      return {} as ReturnType<StreamFn>;
+    };
+    const agent = { streamFn: baseStreamFn };
+
+    applyExtraParamsToAgent(agent, undefined, "openrouter", "deepseek/deepseek-r1", undefined, "off");
+
+    const model = {
+      api: "openai-completions",
+      provider: "openrouter",
+      id: "deepseek/deepseek-r1",
+    } as Model<"openai-completions">;
+    const context: Context = { messages: [] };
+    void agent.streamFn?.(model, context, {});
+
+    expect(payloads).toHaveLength(1);
+    expect(payloads[0]).not.toHaveProperty("reasoning");
+    expect(payloads[0]).not.toHaveProperty("reasoning_effort");
+  });
+
+  it("injects reasoning.effort when thinkingLevel is non-off for OpenRouter", () => {
+    const payloads: Record<string, unknown>[] = [];
+    const baseStreamFn: StreamFn = (_model, _context, options) => {
+      const payload: Record<string, unknown> = {};
+      options?.onPayload?.(payload);
+      payloads.push(payload);
+      return {} as ReturnType<StreamFn>;
+    };
+    const agent = { streamFn: baseStreamFn };
+
+    applyExtraParamsToAgent(agent, undefined, "openrouter", "openrouter/auto", undefined, "low");
+
+    const model = {
+      api: "openai-completions",
+      provider: "openrouter",
+      id: "openrouter/auto",
+    } as Model<"openai-completions">;
+    const context: Context = { messages: [] };
+    void agent.streamFn?.(model, context, {});
+
+    expect(payloads).toHaveLength(1);
+    expect(payloads[0]?.reasoning).toEqual({ effort: "low" });
+  });
+
   it("adds OpenRouter attribution headers to stream options", () => {
     const { calls, agent } = createOptionsCaptureAgent();