feat: ripple-extend resize, timeline filmstrip, export hardening

Yesterday's verified web session (gates green: 316 tests, tsc, build):
- ripple-extend pushes right-hand chain on static-element resize
- per-position video filmstrip thumbnails with zoom-adaptive density
- fps-aware export bitrate, 2s keyframes, even-dim export canvas
- freeze frame uses fixed 3s duration, prompt removed

1 files changed, 60 insertions, 0 deletions

diff --git a/apps/web/src/services/renderer/__tests__/export-encoding.test.ts b/apps/web/src/services/renderer/__tests__/export-encoding.test.ts
new file mode 100644
index 00000000..fbf354eb
--- /dev/null
+++ b/apps/web/src/services/renderer/__tests__/export-encoding.test.ts
@@ -0,0 +1,60 @@
+import { describe, expect, test } from "bun:test";
+import { computeVideoBitrate } from "../export-encoding";
+
+describe("computeVideoBitrate", () => {
+	test("scales linearly with frame rate at the same resolution and quality", () => {
+		const at30 = computeVideoBitrate({
+			width: 1920,
+			height: 1080,
+			fps: 30,
+			quality: "high",
+		});
+		const at60 = computeVideoBitrate({
+			width: 1920,
+			height: 1080,
+			fps: 60,
+			quality: "high",
+		});
+
+		expect(at60).toBe(at30 * 2);
+	});
+
+	test("applies the bits-per-pixel ladder per quality tier", () => {
+		const params = { width: 1920, height: 1080, fps: 30 };
+
+		expect(computeVideoBitrate({ ...params, quality: "low" })).toBe(3_110_400);
+		expect(computeVideoBitrate({ ...params, quality: "medium" })).toBe(
+			6_220_800,
+		);
+		expect(computeVideoBitrate({ ...params, quality: "high" })).toBe(
+			12_441_600,
+		);
+		expect(computeVideoBitrate({ ...params, quality: "very_high" })).toBe(
+			24_883_200,
+		);
+	});
+
+	test("increases monotonically across quality tiers", () => {
+		const params = { width: 1280, height: 720, fps: 30 };
+		const bitrates = (["low", "medium", "high", "very_high"] as const).map(
+			(quality) => computeVideoBitrate({ ...params, quality }),
+		);
+
+		for (let i = 1; i < bitrates.length; i++) {
+			expect(bitrates[i]).toBeGreaterThan(bitrates[i - 1]);
+		}
+	});
+
+	test("returns a positive integer for fractional frame rates", () => {
+		const bitrate = computeVideoBitrate({
+			width: 1920,
+			height: 1080,
+			fps: 29.97,
+			quality: "high",
+		});
+
+		expect(bitrate).toBe(12_429_158);
+		expect(Number.isInteger(bitrate)).toBe(true);
+		expect(bitrate).toBeGreaterThan(0);
+	});
+});