diff --git a/packages/cli/src/capture/captureCompositionFrame.test.ts b/packages/cli/src/capture/captureCompositionFrame.test.ts
index 84bcb73be5..46840097a4 100644
--- a/packages/cli/src/capture/captureCompositionFrame.test.ts
+++ b/packages/cli/src/capture/captureCompositionFrame.test.ts
@@ -305,7 +305,11 @@ describe("captureRegionCrop", () => {
     const buffer = await captureRegionCrop(page, region, 3);
 
     expect(setViewport).toHaveBeenNthCalledWith(1, { ...original, deviceScaleFactor: 3 });
-    expect(screenshot).toHaveBeenCalledWith({ clip: region, type: "png" });
+    expect(screenshot).toHaveBeenCalledWith({
+      clip: region,
+      type: "png",
+      omitBackground: true,
+    });
     expect(setViewport).toHaveBeenNthCalledWith(2, original);
     expect(buffer).toBeInstanceOf(Buffer);
     expect(Array.from(buffer)).toEqual([1, 2, 3]);
diff --git a/packages/cli/src/capture/captureCompositionFrame.ts b/packages/cli/src/capture/captureCompositionFrame.ts
index 49c9af67b4..fff9bf4b2e 100644
--- a/packages/cli/src/capture/captureCompositionFrame.ts
+++ b/packages/cli/src/capture/captureCompositionFrame.ts
@@ -2,6 +2,7 @@ import { spawn } from "node:child_process";
 import type { Browser, Page } from "puppeteer-core";
 import { c } from "../ui/colors.js";
 import { resolveCompositionViewportFromHtml } from "../utils/compositionViewport.js";
+import { resolveDiagnosticNavigationTimeoutMs } from "../utils/renderArgs.js";
 
 const SHADER_TRANSITIONS_TIMEOUT_MS = 90_000;
 const CAPTURE_SETTLE_MS = 1500;
@@ -171,7 +172,10 @@ export async function openSettledCompositionPage(
     await installPageFunctionGuard(page);
     await page.setViewport(viewport);
     await options.beforeNavigate?.(page);
-    await page.goto(url, { waitUntil: "domcontentloaded", timeout: 10000 });
+    await page.goto(url, {
+      waitUntil: "domcontentloaded",
+      timeout: resolveDiagnosticNavigationTimeoutMs(),
+    });
     const renderReadyTimedOut = !(await waitForCompositionSettle(page, options));
     return { browser: chromeBrowser, page, renderReadyTimedOut };
   } catch (err) {
@@ -446,7 +450,7 @@ export interface CropCapturePage {
     height: number;
     deviceScaleFactor?: number;
   }): Promise<void>;
-  screenshot(options: { clip: CropRegion; type: "png" }): Promise<Uint8Array>;
+  screenshot(options: { clip: CropRegion; type: "png"; omitBackground: true }): Promise<Uint8Array>;
 }
 
 /**
@@ -465,7 +469,7 @@ export async function captureRegionCrop(
   const original = page.viewport();
   if (original) await page.setViewport({ ...original, deviceScaleFactor: scale });
   try {
-    const shot = await page.screenshot({ clip: region, type: "png" });
+    const shot = await page.screenshot({ clip: region, type: "png", omitBackground: true });
     return Buffer.isBuffer(shot) ? shot : Buffer.from(shot);
   } finally {
     if (original) await page.setViewport(original);
diff --git a/packages/cli/src/commands/keyframes.test.ts b/packages/cli/src/commands/keyframes.test.ts
index 62e10e595e..1408061646 100644
--- a/packages/cli/src/commands/keyframes.test.ts
+++ b/packages/cli/src/commands/keyframes.test.ts
@@ -1,9 +1,10 @@
-import { mkdtempSync, mkdirSync, writeFileSync } from "node:fs";
+import { existsSync, mkdtempSync, mkdirSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { beforeAll, describe, expect, it } from "vitest";
 import { ensureDOMParser } from "../utils/dom.js";
 import { collectShotSelectors, resolveScope, surfaceComposition } from "./keyframes.js";
+import { ensureShotOutputDir } from "./motionShot.js";
 
 beforeAll(() => ensureDOMParser());
 
@@ -26,6 +27,15 @@ describe("keyframes direct composition scope", () => {
   });
 });
 
+describe("keyframes shot output", () => {
+  it("creates a missing parent directory before writing --shot", () => {
+    const projectDir = mkdtempSync(join(tmpdir(), "hf-keyframes-shot-dir-"));
+    const outputDir = join(projectDir, "nested", "proofs");
+    ensureShotOutputDir(join(outputDir, "shot.png"));
+    expect(existsSync(outputDir)).toBe(true);
+  });
+});
+
 describe("keyframes multi-stroke traces", () => {
   it("composites ≥2 position strokes on one element into a single trace", () => {
     const html = wrap(`
diff --git a/packages/cli/src/commands/layout.ts b/packages/cli/src/commands/layout.ts
index a7025d787e..5879f21290 100644
--- a/packages/cli/src/commands/layout.ts
+++ b/packages/cli/src/commands/layout.ts
@@ -5,6 +5,7 @@ import { fileURLToPath } from "node:url";
 import type { Example } from "./_examples.js";
 import { c } from "../ui/colors.js";
 import { resolveProject } from "../utils/project.js";
+import { resolveDiagnosticNavigationTimeoutMs } from "../utils/renderArgs.js";
 import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { serveStaticProjectHtml } from "../utils/staticProjectServer.js";
 import { printDeprecationNotice, withMeta } from "../utils/updateCheck.js";
@@ -180,7 +181,10 @@ async function alignViewportToComposition(
   });
 
   await page.setViewport(size);
-  await page.goto(url, { waitUntil: "domcontentloaded", timeout: 10000 });
+  await page.goto(url, {
+    waitUntil: "domcontentloaded",
+    timeout: resolveDiagnosticNavigationTimeoutMs(),
+  });
 }
 
 async function runLayoutAudit(
@@ -217,7 +221,10 @@ async function runLayoutAudit(
     const page = await chromeBrowser.newPage();
     await installPageFunctionGuard(page);
     await page.setViewport({ width: 1920, height: 1080 });
-    await page.goto(server.url, { waitUntil: "domcontentloaded", timeout: 10000 });
+    await page.goto(server.url, {
+      waitUntil: "domcontentloaded",
+      timeout: resolveDiagnosticNavigationTimeoutMs(),
+    });
     await alignViewportToComposition(page, server.url);
     await page
       .waitForFunction(() => !!(window as unknown as { __timelines?: unknown }).__timelines, {
diff --git a/packages/cli/src/commands/motionShot.ts b/packages/cli/src/commands/motionShot.ts
index 0bf1061c6b..43ddf59929 100644
--- a/packages/cli/src/commands/motionShot.ts
+++ b/packages/cli/src/commands/motionShot.ts
@@ -10,7 +10,9 @@
 // exactly what it's editing. All geometry + SVG live in ./motionShotLayout.ts
 // (pure, tested); this file only drives the browser and SAMPLES.
 
-import { writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
+import { dirname } from "node:path";
+import { resolveDiagnosticNavigationTimeoutMs } from "../utils/renderArgs.js";
 import {
   buildOnionSvg,
   ghostAlphas,
@@ -25,6 +27,10 @@ export interface ShotRequest {
   selector: string;
 }
 
+export function ensureShotOutputDir(outPath: string): void {
+  mkdirSync(dirname(outPath), { recursive: true });
+}
+
 /** Returned by the in-browser selector resolver: which animated selectors a
  *  `--selector SCOPE` actually resolves to (scope itself, or its descendants),
  *  plus diagnostic context when nothing under the scope animates. */
@@ -258,7 +264,8 @@ async function openCompositionPage(
     ],
   });
   const page = await browser.newPage();
-  await page.goto(url, { waitUntil: "domcontentloaded", timeout: 10000 });
+  const navigationTimeout = resolveDiagnosticNavigationTimeoutMs();
+  await page.goto(url, { waitUntil: "domcontentloaded", timeout: navigationTimeout });
   const size = await page.evaluate(() => {
     const root = document.querySelector("[data-composition-id][data-width][data-height]");
     const w = root ? parseInt(root.getAttribute("data-width") ?? "", 10) : 0;
@@ -269,7 +276,7 @@ async function openCompositionPage(
     };
   });
   await page.setViewport(size);
-  await page.goto(url, { waitUntil: "domcontentloaded", timeout: 10000 });
+  await page.goto(url, { waitUntil: "domcontentloaded", timeout: navigationTimeout });
   await page
     .waitForFunction(() => !!(window as unknown as { __timelines?: unknown }).__timelines, {
       timeout: 10000,
@@ -611,6 +618,7 @@ export async function captureMotionPathShot(
   outPath: string,
   opts: ShotOptions = {},
 ): Promise<string> {
+  ensureShotOutputDir(outPath);
   let requests = requestsIn;
   const samples = Math.max(1, Math.min(60, opts.samples ?? 9));
   const layout = opts.layout ?? "path";
diff --git a/packages/cli/src/commands/snapshot.test.ts b/packages/cli/src/commands/snapshot.test.ts
index 4cb0d394c7..73397d845e 100644
--- a/packages/cli/src/commands/snapshot.test.ts
+++ b/packages/cli/src/commands/snapshot.test.ts
@@ -1,5 +1,11 @@
 import { describe, expect, it } from "vitest";
-import { computeSnapshotTimes, parseZoomScale, tailFrameTime } from "./snapshot.js";
+import { readFileSync } from "node:fs";
+import {
+  computeSnapshotTimes,
+  parseZoomScale,
+  requireSnapshotFfmpeg,
+  tailFrameTime,
+} from "./snapshot.js";
 
 // --zoom's crop-region math (selector bbox + padding + clamp, exact region
 // form, no-match error) is owned by and tested in
@@ -21,6 +27,15 @@ describe("tailFrameTime", () => {
   });
 });
 
+describe("transparent snapshot capture", () => {
+  it("asks Chrome to retain the alpha channel in review PNGs", () => {
+    const source = readFileSync(new URL("./snapshot.ts", import.meta.url), "utf8");
+    expect(source).toContain(
+      'page.screenshot({ path: framePath, type: "png", omitBackground: true })',
+    );
+  });
+});
+
 describe("computeSnapshotTimes (FINDING [7]: tail is always captured)", () => {
   it("default frames: last point is the readable tail, never exact duration", () => {
     const { times, appendedTail } = computeSnapshotTimes(8, { frames: 5 });
@@ -62,6 +77,16 @@ describe("computeSnapshotTimes (FINDING [7]: tail is always captured)", () => {
     expect(times).toEqual([1, 2]);
     expect(appendedTail).toBe(false);
   });
+
+  it("preserves exact explicit transition timestamps", () => {
+    const exactTransition = 3.3666666666666667;
+    const { times } = computeSnapshotTimes(8, {
+      frames: 5,
+      at: [exactTransition],
+      includeEnd: false,
+    });
+    expect(times).toEqual([exactTransition]);
+  });
 });
 
 describe("parseZoomScale (--zoom-scale)", () => {
@@ -79,3 +104,15 @@ describe("parseZoomScale (--zoom-scale)", () => {
     expect(parseZoomScale("-1")).toBe(3);
   });
 });
+
+describe("requireSnapshotFfmpeg", () => {
+  it("rejects video snapshot extraction when FFmpeg is unavailable", () => {
+    expect(() => requireSnapshotFfmpeg(undefined)).toThrow(
+      /FFmpeg is required to extract video frames for snapshots/,
+    );
+  });
+
+  it("preserves the resolved FFmpeg executable", () => {
+    expect(requireSnapshotFfmpeg("C:\\tools\\ffmpeg.exe")).toBe("C:\\tools\\ffmpeg.exe");
+  });
+});
diff --git a/packages/cli/src/commands/snapshot.ts b/packages/cli/src/commands/snapshot.ts
index ae8e8297b0..bbdbd6f914 100644
--- a/packages/cli/src/commands/snapshot.ts
+++ b/packages/cli/src/commands/snapshot.ts
@@ -17,7 +17,7 @@ import { resolveProject } from "../utils/project.js";
 import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { serveStaticProjectHtml } from "../utils/staticProjectServer.js";
 import { c } from "../ui/colors.js";
-import { findFFmpeg } from "../browser/ffmpeg.js";
+import { findFFmpeg, getFFmpegInstallHint } from "../browser/ffmpeg.js";
 import { parseAngle, type Camera } from "./motionShotLayout.js";
 import type { Example } from "./_examples.js";
 
@@ -60,6 +60,13 @@ function orbitStageSource(): string {
  * `hyperframes snapshot` indefinitely. */
 const FFMPEG_EXTRACT_TIMEOUT_MS = 30_000;
 
+export function requireSnapshotFfmpeg(ffmpegPath: string | undefined): string {
+  if (ffmpegPath) return ffmpegPath;
+  throw new Error(
+    `FFmpeg is required to extract video frames for snapshots. ${getFFmpegInstallHint()}`,
+  );
+}
+
 /**
  * Extract a single frame from a video file at `timeSeconds` via FFmpeg.
  * Used to work around Chrome-headless's inability to reliably seek
@@ -73,8 +80,7 @@ async function extractVideoFrameToBuffer(
   const tmp = mkdtempSync(join(tmpdir(), "hf-snapshot-frame-"));
   const outPath = join(tmp, "frame.png");
   try {
-    const ffmpegPath = findFFmpeg();
-    if (!ffmpegPath) return null;
+    const ffmpegPath = requireSnapshotFfmpeg(findFFmpeg());
     // `-ss` before `-i` performs a fast keyframe seek; adequate for snapshot accuracy
     // (±1 frame) and orders of magnitude faster than the decode-and-scan alternative.
     const args = ["-hide_banner", "-loglevel", "error"];
@@ -159,7 +165,11 @@ export function computeSnapshotTimes(
   const round = (t: number) => Math.round(t * 1000) / 1000;
 
   if (opts.at?.length) {
-    const times = opts.at.map(round);
+    // `--at` is an evidence contract: callers may pass exact fractional-frame
+    // boundaries (for example 101 / 30). Do not normalize their requested
+    // positions; rounding to milliseconds can move a transition sample to the
+    // other side of the boundary.
+    const times = [...opts.at];
     // Only append if the user didn't already sample at/near the readable tail.
     const hasTail = times.some((t) => Math.abs(t - tail) < 0.05 || t >= duration);
     if (includeEnd && duration > 0 && !hasTail) {
@@ -481,7 +491,7 @@ async function captureSnapshots(
           );
           writeFileSync(framePath, buffer);
         } else {
-          await page.screenshot({ path: framePath, type: "png" });
+          await page.screenshot({ path: framePath, type: "png", omitBackground: true });
         }
         const rel = relative(projectDir, framePath);
         savedPaths.push(rel.startsWith("..") || isAbsolute(rel) ? framePath : rel);
diff --git a/packages/cli/src/utils/renderArgs.test.ts b/packages/cli/src/utils/renderArgs.test.ts
index 3db8d6344c..864e5f3e4e 100644
--- a/packages/cli/src/utils/renderArgs.test.ts
+++ b/packages/cli/src/utils/renderArgs.test.ts
@@ -6,6 +6,7 @@ import {
   MAX_PAGE_NAVIGATION_TIMEOUT_SECONDS,
   hasExplicitCompositionArg,
   parseBrowserTimeoutMsArg,
+  resolveDiagnosticNavigationTimeoutMs,
   parseCompositionEntryArg,
   parseGifLoopArg,
   resolveDefaultFpsArg,
@@ -104,6 +105,21 @@ describe("parseBrowserTimeoutMsArg", () => {
   });
 });
 
+describe("resolveDiagnosticNavigationTimeoutMs", () => {
+  it("uses the render navigation timeout env override", () => {
+    expect(
+      resolveDiagnosticNavigationTimeoutMs({ PRODUCER_PAGE_NAVIGATION_TIMEOUT_MS: "90000" }),
+    ).toBe(90_000);
+  });
+
+  it("falls back to ten seconds for missing or invalid values", () => {
+    expect(resolveDiagnosticNavigationTimeoutMs({})).toBe(10_000);
+    expect(
+      resolveDiagnosticNavigationTimeoutMs({ PRODUCER_PAGE_NAVIGATION_TIMEOUT_MS: "invalid" }),
+    ).toBe(10_000);
+  });
+});
+
 describe("parseCompositionEntryArg", () => {
   it("uses one sentinel classifier for default and explicit composition values", () => {
     expect([undefined, "", "   ", ".", "./"].map(hasExplicitCompositionArg)).toEqual([
diff --git a/packages/cli/src/utils/renderArgs.ts b/packages/cli/src/utils/renderArgs.ts
index db23734ed6..c29d6e14fc 100644
--- a/packages/cli/src/utils/renderArgs.ts
+++ b/packages/cli/src/utils/renderArgs.ts
@@ -117,6 +117,14 @@ export function resolveBrowserTimeoutMsArg(raw: string | undefined): number | un
   return result.value;
 }
 
+/** Navigation budget shared by snapshot/check/inspect browser diagnostics. */
+export function resolveDiagnosticNavigationTimeoutMs(
+  env: Record<string, string | undefined> = process.env,
+): number {
+  const parsed = Number(env.PRODUCER_PAGE_NAVIGATION_TIMEOUT_MS);
+  return Number.isFinite(parsed) && parsed > 0 ? parsed : 10_000;
+}
+
 // ── --composition ──────────────────────────────────────────────────────
 
 export type CompositionEntryParseError =