Story 27: Coverage tracking (full-stack)

Add end-to-end coverage tracking: backend collects vitest coverage,
records metrics with threshold/baseline tracking, and blocks acceptance
on regression. Frontend displays coverage in gate/review panels with
a "Collect Coverage" button. Includes 20 Rust tests, 17 Vitest tests,
and 14 Playwright E2E tests.

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

frontend/src/components/Chat.test.tsx

@@ -33,6 +33,8 @@ vi.mock("../api/workflow", () => {
 			getReviewQueue: vi.fn(),
 			getReviewQueueAll: vi.fn(),
 			ensureAcceptance: vi.fn(),
+			recordCoverage: vi.fn(),
+			collectCoverage: vi.fn(),
 		},
 	};
 });
@@ -390,4 +392,122 @@ describe("Chat review panel", () => {
 
 		expect(await screen.findByText("Ready to accept")).toBeInTheDocument();
 	});
+
+	it("shows coverage below threshold in gate panel (AC3)", async () => {
+		mockedWorkflow.getAcceptance.mockResolvedValueOnce({
+			can_accept: false,
+			reasons: ["Coverage below threshold (55.0% < 80.0%)."],
+			warning: null,
+			summary: { total: 3, passed: 3, failed: 0 },
+			missing_categories: [],
+			coverage_report: {
+				current_percent: 55.0,
+				threshold_percent: 80.0,
+				baseline_percent: null,
+			},
+		});
+
+		render(<Chat projectPath="/tmp/project" onCloseProject={vi.fn()} />);
+
+		expect(await screen.findByText("Blocked")).toBeInTheDocument();
+		expect(await screen.findByText(/Coverage: 55\.0%/)).toBeInTheDocument();
+		expect(await screen.findByText(/threshold: 80\.0%/)).toBeInTheDocument();
+		expect(
+			await screen.findByText("Coverage below threshold (55.0% < 80.0%)."),
+		).toBeInTheDocument();
+	});
+
+	it("shows coverage regression in review panel (AC4)", async () => {
+		const story: ReviewStory = {
+			story_id: "27_protect_tests_and_coverage",
+			can_accept: false,
+			reasons: ["Coverage regression: 90.0% → 82.0% (threshold: 80.0%)."],
+			warning: null,
+			summary: { total: 4, passed: 4, failed: 0 },
+			missing_categories: [],
+			coverage_report: {
+				current_percent: 82.0,
+				threshold_percent: 80.0,
+				baseline_percent: 90.0,
+			},
+		};
+
+		mockedWorkflow.getReviewQueueAll.mockResolvedValueOnce({
+			stories: [story],
+		});
+
+		render(<Chat projectPath="/tmp/project" onCloseProject={vi.fn()} />);
+
+		expect(
+			await screen.findByText(
+				"Coverage regression: 90.0% → 82.0% (threshold: 80.0%).",
+			),
+		).toBeInTheDocument();
+		expect(await screen.findByText(/Coverage: 82\.0%/)).toBeInTheDocument();
+	});
+
+	it("shows green coverage when above threshold (AC3)", async () => {
+		mockedWorkflow.getAcceptance.mockResolvedValueOnce({
+			can_accept: true,
+			reasons: [],
+			warning: null,
+			summary: { total: 5, passed: 5, failed: 0 },
+			missing_categories: [],
+			coverage_report: {
+				current_percent: 92.0,
+				threshold_percent: 80.0,
+				baseline_percent: 90.0,
+			},
+		});
+
+		render(<Chat projectPath="/tmp/project" onCloseProject={vi.fn()} />);
+
+		expect(await screen.findByText("Ready to accept")).toBeInTheDocument();
+		expect(await screen.findByText(/Coverage: 92\.0%/)).toBeInTheDocument();
+	});
+
+	it("collect coverage button triggers collection and refreshes gate", async () => {
+		const mockedCollectCoverage = vi.mocked(workflowApi.collectCoverage);
+		mockedCollectCoverage.mockResolvedValueOnce({
+			current_percent: 85.0,
+			threshold_percent: 80.0,
+			baseline_percent: null,
+		});
+
+		mockedWorkflow.getAcceptance
+			.mockResolvedValueOnce({
+				can_accept: false,
+				reasons: ["No test results recorded for the story."],
+				warning: null,
+				summary: { total: 0, passed: 0, failed: 0 },
+				missing_categories: ["unit", "integration"],
+			})
+			.mockResolvedValueOnce({
+				can_accept: true,
+				reasons: [],
+				warning: null,
+				summary: { total: 5, passed: 5, failed: 0 },
+				missing_categories: [],
+				coverage_report: {
+					current_percent: 85.0,
+					threshold_percent: 80.0,
+					baseline_percent: null,
+				},
+			});
+
+		render(<Chat projectPath="/tmp/project" onCloseProject={vi.fn()} />);
+
+		const collectButton = await screen.findByRole("button", {
+			name: "Collect Coverage",
+		});
+		await userEvent.click(collectButton);
+
+		await waitFor(() => {
+			expect(mockedCollectCoverage).toHaveBeenCalledWith({
+				story_id: "26_establish_tdd_workflow_and_gates",
+			});
+		});
+
+		expect(await screen.findByText(/Coverage: 85\.0%/)).toBeInTheDocument();
+	});
 });