chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

third_party/pi/packages/ai/test/google-thinking-signature.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import { isThinkingPart, retainThoughtSignature } from "../src/api/google-shared.ts";
+
+describe("Google thinking detection (thoughtSignature)", () => {
+	it("treats part.thought === true as thinking", () => {
+		expect(isThinkingPart({ thought: true, thoughtSignature: undefined })).toBe(true);
+		expect(isThinkingPart({ thought: true, thoughtSignature: "opaque-signature" })).toBe(true);
+	});
+
+	it("does not treat thoughtSignature alone as thinking", () => {
+		// Per Google docs, thoughtSignature is for context replay and can appear on any part type.
+		// Only thought === true indicates thinking content.
+		// See: https://ai.google.dev/gemini-api/docs/thought-signatures
+		expect(isThinkingPart({ thought: undefined, thoughtSignature: "opaque-signature" })).toBe(false);
+		expect(isThinkingPart({ thought: false, thoughtSignature: "opaque-signature" })).toBe(false);
+	});
+
+	it("does not treat empty/missing signatures as thinking if thought is not set", () => {
+		expect(isThinkingPart({ thought: undefined, thoughtSignature: undefined })).toBe(false);
+		expect(isThinkingPart({ thought: false, thoughtSignature: "" })).toBe(false);
+	});
+
+	it("preserves the existing signature when subsequent deltas omit thoughtSignature", () => {
+		const first = retainThoughtSignature(undefined, "sig-1");
+		expect(first).toBe("sig-1");
+
+		const second = retainThoughtSignature(first, undefined);
+		expect(second).toBe("sig-1");
+
+		const third = retainThoughtSignature(second, "");
+		expect(third).toBe("sig-1");
+	});
+
+	it("updates the signature when a new non-empty signature arrives", () => {
+		const updated = retainThoughtSignature("sig-1", "sig-2");
+		expect(updated).toBe("sig-2");
+	});
+});