Show thinking effort as segmented control for short lists

Present the runtime "Thinking effort" field as a single-click segmented
button group when the adapter's option set is small (Claude 4, Cursor 3),
matching the accepted runtime wireframe — all choices visible, one click
(Recognition-over-Recall, Fitts). Adapters with long effort lists
(Codex 6, OpenCode 7) keep the dropdown fallback to avoid overflow.

The segmented group is a keyboard-navigable radiogroup (arrow keys move
selection, roving tabindex). Behavior is covered by render tests for both
the segmented (short-list) and dropdown (long-list) branches.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/components/AgentConfigForm.render.test.tsx

@@ -650,4 +650,54 @@ describe("AgentConfigForm environment selector", () => {
     expect(mockAgentsApi.testEnvironment).toHaveBeenCalledTimes(1);
     expect(result.container.textContent).toContain("Network unavailable");
   });
+
+  it("renders thinking effort as a segmented group for adapters with a short effort list", async () => {
+    const result = await renderForm(
+      [makeEnvironment({ id: "local-1", name: "Local", driver: "local" })],
+      { adapterType: "claude_local" },
+    );
+    roots.push(result.root);
+
+    const group = result.container.querySelector<HTMLElement>(
+      '[role="radiogroup"][aria-label="Thinking effort"]',
+    );
+    expect(group).toBeTruthy();
+
+    const segments = Array.from(group!.querySelectorAll('[role="radio"]'));
+    expect(segments.map((segment) => segment.textContent?.trim())).toEqual([
+      "Auto",
+      "Low",
+      "Medium",
+      "High",
+    ]);
+    // "Auto" (the empty default) is selected when nothing is configured.
+    expect(segments[0]?.getAttribute("aria-checked")).toBe("true");
+
+    await act(async () => {
+      segments
+        .find((segment) => segment.textContent?.trim() === "High")
+        ?.dispatchEvent(new MouseEvent("click", { bubbles: true }));
+    });
+    await flushReact();
+
+    const updatedSegments = Array.from(
+      result.container.querySelectorAll('[role="radiogroup"][aria-label="Thinking effort"] [role="radio"]'),
+    );
+    const highSegment = updatedSegments.find((segment) => segment.textContent?.trim() === "High");
+    expect(highSegment?.getAttribute("aria-checked")).toBe("true");
+    expect(updatedSegments[0]?.getAttribute("aria-checked")).toBe("false");
+  });
+
+  it("keeps thinking effort as a dropdown for adapters with a long effort list", async () => {
+    const result = await renderForm(
+      [makeEnvironment({ id: "local-1", name: "Local", driver: "local" })],
+      { adapterType: "opencode_local" },
+    );
+    roots.push(result.root);
+
+    expect(
+      result.container.querySelector('[role="radiogroup"][aria-label="Thinking effort"]'),
+    ).toBeNull();
+    expect(result.container.textContent).toContain("Thinking effort");
+  });
 });