feat: per-model max output tokens and a conversation-time thinking level backed by agent settings (#28)

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

packages/core/test/state.test.ts

@@ -531,6 +531,7 @@ describe("project-config round trip", () => {
         provider: "custom",
         model_id: "gpt-test",
         context_window: 128000,
+        max_tokens: 8192,
         api_key: "sk-abc",
         base_url: "https://example.com/v1",
       },
@@ -549,6 +550,7 @@ describe("project-config round trip", () => {
       provider: "custom",
       model_id: "gpt-test",
       context_window: 128000,
+      max_tokens: 8192,
       api_key: "sk-abc",
       base_url: "https://example.com/v1",
     });
@@ -644,6 +646,32 @@ describe("project-config round trip", () => {
     expect(m?.vision).toBe(true);
   });
 
+  it("addModel persists max_tokens and upsert preserves it when not re-specified", async () => {
+    await addModel(tmpRoot, DEFAULT_PROJECT_ID, {
+      provider: "custom",
+      model_id: "small-window",
+      max_tokens: 4096,
+    });
+    // Only supplements context_window, without max_tokens: the original annotation is kept.
+    await addModel(tmpRoot, DEFAULT_PROJECT_ID, {
+      provider: "custom",
+      model_id: "small-window",
+      context_window: 32768,
+    });
+    const ref = { provider: "custom", model_id: "small-window" };
+    let m = getModel(await loadProjectConfig(tmpRoot, DEFAULT_PROJECT_ID), ref);
+    expect(m?.max_tokens).toBe(4096);
+    expect(m?.context_window).toBe(32768);
+    // Explicitly re-pins the cap.
+    await addModel(tmpRoot, DEFAULT_PROJECT_ID, {
+      provider: "custom",
+      model_id: "small-window",
+      max_tokens: 2048,
+    });
+    m = getModel(await loadProjectConfig(tmpRoot, DEFAULT_PROJECT_ID), ref);
+    expect(m?.max_tokens).toBe(2048);
+  });
+
   it("setVisionModel persists and validates the target", async () => {
     await addModel(tmpRoot, DEFAULT_PROJECT_ID, {
       provider: "custom",