From 7e8863fc7e65806f41e550fc42172685f31764ef Mon Sep 17 00:00:00 2001
From: Samraaj Bath <samraaj100@gmail.com>
Date: Sat, 4 Jul 2026 13:49:14 -0700
Subject: [PATCH] Capture hardening: deterministic env shim, extended lazy
 sweep, nav budget with bot-wall fast-fail

Salvaged and re-implemented from PR #15:
- Deterministic environment shim (seeded Math.random, pinned-but-advancing
  Date consistent across constructor/now/getTime/valueOf/toISOString) so
  time/random-dependent pages capture reproducibly; epoch and seed are
  recorded run metadata, performance.now stays real for motion sampling
- Post-snapshot lazy-asset discovery sweep for channels the walker misses:
  noscript contents (DOMParser), inline style url(), data-background(-image),
  img[loading=lazy] currentSrc
- Navigation gets a total 90s budget, an early bot-wall probe that aborts
  with a pollution-style error instead of capturing garbage (WALL_RE now
  shared with the validator gate), and one fresh-context retry scoped to
  the initial nav on retryable failure classes only

505 tests pass (29 new), typecheck clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 compiler/src/capture/capture.ts      | 291 ++++++++++++++++++++++-----
 compiler/src/util/captureFailure.ts  |  73 +++++++
 compiler/src/util/envShim.ts         | 103 ++++++++++
 compiler/src/validate/gates.ts       |   4 +-
 compiler/test/captureFailure.test.ts | 117 +++++++++++
 compiler/test/envShim.test.ts        | 162 +++++++++++++++
 compiler/test/lazySweep.test.ts      |  85 ++++++++
 7 files changed, 781 insertions(+), 54 deletions(-)
 create mode 100644 compiler/src/util/captureFailure.ts
 create mode 100644 compiler/src/util/envShim.ts
 create mode 100644 compiler/test/captureFailure.test.ts
 create mode 100644 compiler/test/envShim.test.ts
 create mode 100644 compiler/test/lazySweep.test.ts

diff --git a/compiler/src/capture/capture.ts b/compiler/src/capture/capture.ts
index 010a2aa..e6f45a8 100644
--- a/compiler/src/capture/capture.ts
+++ b/compiler/src/capture/capture.ts
@@ -15,6 +15,8 @@ import { discoverBreakpoints } from "./breakpoints.js";
 import { writeJSON, writeJSONCompact, writeBytes, ensureDir } from "../util/fsx.js";
 import { sha1_12, round } from "../util/canonical.js";
 import { isZipArchive, extractDotLottieJson } from "./dotlottie.js";
+import { buildDeterministicEnvShim, captureEpochMs, DEFAULT_PRNG_SEED } from "../util/envShim.js";
+import { isBotWall, classifyNavFailure } from "../util/captureFailure.js";
 
 export const REQUIRED_VIEWPORTS = [375, 768, 1280, 1920] as const;
 // The dense width set captured for SIZE INFERENCE: a node sampled at 9 widths reveals its sizing
@@ -65,6 +67,10 @@ export type SeoResource = {
 export type CaptureResult = {
   sourceUrl: string;
   capturedAt: string;
+  // Deterministic-env shim parameters actually used for this run (Item 1). Recorded
+  // so a recapture can reuse the exact {seed, epochMs} — the pinned wall clock is a
+  // run-metadata value, not a hardcoded constant. Absent when the shim was disabled.
+  deterministicEnv?: { seed: number; epochMs: number };
   viewports: number[];
   // Browser-as-oracle: the widths where the SOURCE layout actually restructures (display /
   // flex-direction / wrap / grid-track-count / position / visibility flips), found by sweeping the
@@ -797,6 +803,66 @@ async function captureCanvasStills(page: import("playwright").Page): Promise<Can
 // instead of returning a truncated image on pathologically tall pages.
 const CDP_MAX_SHOT_DIMENSION = 16_384;
 
+/**
+ * Item 2: extended lazy-asset DISCOVERY. Returns the deduped, sorted set of asset
+ * URLs referenced through channels the walker + promoteLazyMedia miss:
+ *   (1) <noscript> fallback markup (the walker skips <noscript> entirely) — parsed as
+ *       HTML so real img/source src + srcset are read, not regex-scraped;
+ *   (2) inline element style="…url(…)…" (the walker harvests url() from STYLESHEET
+ *       rules only, not from an element's own style attribute);
+ *   (3) data-background / data-background-image lazy-bg aliases (beyond promoteLazyMedia's
+ *       single data-bg);
+ *   (4) img[loading=lazy] currentSrc — the variant a below-fold image resolved to.
+ * data: URLs and unresolvable refs are dropped. Discovery-only: the caller RECORDS these
+ * for the fallback downloader; nothing here mutates the DOM (snapshots are already taken).
+ * Exported for the fixture tests (page.evaluate'd directly).
+ */
+export function discoverLazyAssetsInPage(): string[] {
+  const urls = new Set<string>();
+  const push = (v: string | null | undefined): void => {
+    if (!v) return;
+    const s = v.trim();
+    if (!s || s.startsWith("data:")) return;
+    try { urls.add(new URL(s, document.baseURI).href); } catch { /* not a URL */ }
+  };
+  const firstOfSrcset = (ss: string): void => {
+    for (const part of ss.split(",")) push(part.trim().split(/\s+/)[0]);
+  };
+  // (1) <noscript> fallback markup.
+  for (const ns of Array.from(document.querySelectorAll("noscript"))) {
+    const html = ns.textContent ?? "";
+    if (!html.includes("<")) continue;
+    let frag: Document;
+    try { frag = new DOMParser().parseFromString(html, "text/html"); } catch { continue; }
+    for (const el of Array.from(frag.querySelectorAll("img,source"))) {
+      push(el.getAttribute("src"));
+      const ss = el.getAttribute("srcset");
+      if (ss) firstOfSrcset(ss);
+    }
+  }
+  // (2) inline style url(...) on any element (background-image / mask / etc.).
+  for (const el of Array.from(document.querySelectorAll("[style]"))) {
+    const st = el.getAttribute("style") ?? "";
+    if (!st.includes("url(")) continue;
+    for (const m of st.matchAll(/url\(\s*(['"]?)([^'")]+)\1\s*\)/gi)) push(m[2]);
+  }
+  // (3) lazy-background data-* aliases the promoter doesn't cover.
+  const BG_ATTRS = ["data-background", "data-background-image"];
+  for (const el of Array.from(document.querySelectorAll(BG_ATTRS.map((a) => `[${a}]`).join(",")))) {
+    for (const a of BG_ATTRS) {
+      const raw = el.getAttribute(a);
+      if (!raw) continue;
+      const m = /url\(\s*(['"]?)([^'")]+)\1\s*\)/i.exec(raw);
+      push(m ? m[2] : raw);
+    }
+  }
+  // (4) the variant a lazy image actually resolved to.
+  for (const img of Array.from(document.querySelectorAll<HTMLImageElement>("img[loading=lazy]"))) {
+    push(img.currentSrc || img.src);
+  }
+  return [...urls].sort();
+}
+
 /**
  * Full-page screenshot via CDP `Page.captureScreenshot` with `captureBeyondViewport:true`.
  * Unlike Playwright's `fullPage:true` (which scroll-stitches — scrolling the page to render
@@ -1004,6 +1070,14 @@ export async function captureSite(opts: {
   interactions?: boolean; // Stage 4: opt-in interaction capture (hover/focus + patterns)
   motion?: boolean; // Stage 5: opt-in motion capture (WAAPI + rotating text)
   breakpoints?: boolean; // discover the source's real responsive band edges (default on; read-only sweep)
+  deterministicEnv?: boolean; // Item 1: seed Math.random + pin the Date epoch BEFORE page JS runs
+                              // (default on), so shuffled carousels / random ids / relative-time text
+                              // ("posted N minutes ago") render the same across captures. Relative time
+                              // still advances (timers behave) and performance.now() stays real.
+  captureEpochMs?: number | string; // pinned wall-clock origin for the shim (ms since epoch, or a
+                                     // date string). Recorded in the result; a recapture passes the
+                                     // previously-recorded value to reproduce time-dependent content.
+  prngSeed?: number; // mulberry32 seed for the pinned Math.random (recorded in the result).
   screenshots?: boolean; // write per-viewport full-page PNGs (default on). ONLY the validator reads these
                          // (generation never touches pixels), and full-page shots of tall pages are the
                          // dominant capture cost — so a production clone that won't be perceptually graded
@@ -1013,6 +1087,13 @@ export async function captureSite(opts: {
 }): Promise<CaptureResult> {
   const viewports = opts.viewports ?? [...REQUIRED_VIEWPORTS];
   const log = opts.log ?? (() => {});
+  // Item 1: resolve the deterministic-env parameters once, at run start, and record
+  // them in the result. The epoch is a run-metadata value (recorded, reproducible),
+  // not a hardcoded constant; performance.now() is left real so motion capture is
+  // unaffected. Defaults on; opts.deterministicEnv === false disables the shim.
+  const deterministicEnvOn = opts.deterministicEnv !== false;
+  const prngSeed = Number.isFinite(opts.prngSeed) ? Math.trunc(opts.prngSeed!) : DEFAULT_PRNG_SEED;
+  const epochMs = captureEpochMs(opts.captureEpochMs);
   const captureDir = join(opts.outDir, "capture");
   const screenshotsDir = join(opts.outDir, "screenshots");
   const cssDir = join(captureDir, "css");
@@ -1178,64 +1259,136 @@ export async function captureSite(opts: {
     // hero on each fresh load) and session-reuse degeneration (warbyparker returned
     // a 13-node shell when reloaded with a carried session). The IR's cross-viewport
     // alignment then operates on one logical DOM that CSS merely reflows.
-    const context: BrowserContext = await browser.newContext({
-      ignoreHTTPSErrors: true,
-      viewport: { width: canonical, height: viewportHeight(canonical) },
-      deviceScaleFactor: 1,
-      userAgent: DESKTOP_UA,
-      javaScriptEnabled: true,
-    });
-    const page = await context.newPage();
-    // tsx/esbuild wraps functions with a __name() helper for stack traces; that
-    // helper does not exist in the browser when we serialize page.evaluate
-    // callbacks. Shim it (as a raw string so it isn't itself transformed).
-    await page.addInitScript(ESBUILD_SHIM);
     const bodyPromises: Promise<void>[] = [];
 
-    page.on("response", (resp) => {
-      try {
-        const url = resp.url();
-        if (url.startsWith("data:") || url.startsWith("blob:")) return;
-        const ct = resp.headers()["content-type"] || null;
-        const type = classifyAsset(url, ct);
-        if (!type) return;
-        const status = resp.status();
-        recordAsset(url, type, ct, status, "network");
-        const existing = assetMap.get(url);
-        if (existing?.storedAs) return;
-        if (status >= 400) return;
-        // A 206 body is a RANGE FRAGMENT (media seek), not the asset — storing it would
-        // ship a corrupt file under first-stored-wins and the full-download fallback
-        // would then skip the asset. Record only; the fallback pass fetches the 200 body.
-        if (status === 206) return;
-        bodyPromises.push(
-          (async () => {
-            try {
-              const buf = await resp.body();
-              storeBytes(url, type, buf);
-              if (type === "css") cssTextsForParsing.push({ baseUrl: url, text: buf.toString("utf8") });
-              if (type === "manifest") parseManifestForAssets(buf.toString("utf8"), url);
-            } catch { /* body unavailable */ }
-          })(),
-        );
-      } catch { /* ignore */ }
-    });
+    // Response listener + init scripts are attached the same way to the initial page
+    // and to any fresh recovery page (Item 3c), so factor the wiring into one helper.
+    const attachResponseListener = (pg: import("playwright").Page): void => {
+      pg.on("response", (resp) => {
+        try {
+          const url = resp.url();
+          if (url.startsWith("data:") || url.startsWith("blob:")) return;
+          const ct = resp.headers()["content-type"] || null;
+          const type = classifyAsset(url, ct);
+          if (!type) return;
+          const status = resp.status();
+          recordAsset(url, type, ct, status, "network");
+          const existing = assetMap.get(url);
+          if (existing?.storedAs) return;
+          if (status >= 400) return;
+          // A 206 body is a RANGE FRAGMENT (media seek), not the asset — storing it would
+          // ship a corrupt file under first-stored-wins and the full-download fallback
+          // would then skip the asset. Record only; the fallback pass fetches the 200 body.
+          if (status === 206) return;
+          bodyPromises.push(
+            (async () => {
+              try {
+                const buf = await resp.body();
+                storeBytes(url, type, buf);
+                if (type === "css") cssTextsForParsing.push({ baseUrl: url, text: buf.toString("utf8") });
+                if (type === "manifest") parseManifestForAssets(buf.toString("utf8"), url);
+              } catch { /* body unavailable */ }
+            })(),
+          );
+        } catch { /* ignore */ }
+      });
+    };
 
-    // Single navigation at the canonical width; every viewport below is a resize.
-    log({ event: "goto", url: opts.url });
-    let navigated = false;
-    let navErr: unknown = null;
-    for (let attempt = 0; attempt < 3 && !navigated; attempt++) {
-      try {
-        await page.goto(opts.url, { waitUntil: attempt === 0 ? "load" : "domcontentloaded", timeout: 45000 });
-        navigated = true;
-      } catch (e) {
-        navErr = e;
-        await page.waitForTimeout(1000);
+    const newSession = async (): Promise<{ context: BrowserContext; page: import("playwright").Page }> => {
+      const ctx: BrowserContext = await browser.newContext({
+        ignoreHTTPSErrors: true,
+        viewport: { width: canonical, height: viewportHeight(canonical) },
+        deviceScaleFactor: 1,
+        userAgent: DESKTOP_UA,
+        javaScriptEnabled: true,
+      });
+      const pg = await ctx.newPage();
+      attachResponseListener(pg);
+      // tsx/esbuild wraps functions with a __name() helper for stack traces; that
+      // helper does not exist in the browser when we serialize page.evaluate
+      // callbacks. Shim it (as a raw string so it isn't itself transformed).
+      await pg.addInitScript(ESBUILD_SHIM);
+      // Item 1: deterministic-env shim — seed Math.random + pin the Date epoch BEFORE
+      // any page script runs. Raw string so tsx/esbuild leaves it byte-exact; the
+      // {seed, epochMs} are the recorded run-metadata values. performance.now() stays
+      // real, so motion.ts marquee/rotator velocity sampling is unaffected.
+      if (deterministicEnvOn) {
+        await pg.addInitScript(buildDeterministicEnvShim({ seed: prngSeed, epochMs }));
       }
+      return { context: ctx, page: pg };
+    };
+
+    // Single context + single navigation; every viewport is captured by RESIZING the
+    // same loaded page (see the block comment above). Item 3c: session recovery is
+    // deliberately scoped to the INITIAL navigation only — carrying one session across
+    // viewports is load-bearing (a reload can degenerate: warbyparker's 13-node shell),
+    // so we never recover mid-loop; we only retry the first nav with a fresh context
+    // when the page/browser died before any content was captured.
+    let { context, page } = await newSession();
+
+    // Total nav budget (Item 3a): a hung origin used to stall for up to ~3×45s + retries
+    // with no ceiling. Bound the WHOLE navigation phase so a dead host fails fast with a
+    // structured error instead of tying up the pipeline. Attempt 0 waits for `load`;
+    // later attempts fall back to `domcontentloaded` (a heavy page may never fire `load`).
+    const NAV_BUDGET_MS = 90_000;
+    const navigateLoaded = async (pg: import("playwright").Page): Promise<void> => {
+      log({ event: "goto", url: opts.url });
+      const navStart = Date.now();
+      let navigated = false;
+      let navErr: unknown = null;
+      for (let attempt = 0; attempt < 3 && !navigated; attempt++) {
+        const remaining = NAV_BUDGET_MS - (Date.now() - navStart);
+        if (remaining < 5_000) break; // not enough budget left for a meaningful attempt
+        try {
+          await pg.goto(opts.url, {
+            waitUntil: attempt === 0 ? "load" : "domcontentloaded",
+            timeout: Math.min(attempt === 0 ? 45_000 : 20_000, remaining),
+          });
+          navigated = true;
+        } catch (e) {
+          navErr = e;
+          await pg.waitForTimeout(1000);
+        }
+      }
+      if (!navigated) {
+        throw new Error(
+          `navigation failed for ${opts.url} within ${Math.round((Date.now() - navStart) / 1000)}s: ${String((navErr as { message?: string })?.message ?? navErr).slice(0, 300)}`,
+        );
+      }
+      await settle(pg);
+    };
+
+    try {
+      await navigateLoaded(page);
+    } catch (navErr) {
+      // Item 3c: one fresh-context retry, but ONLY for a session-death class of failure
+      // (browser/page/context closed, crash, transient reset/timeout). A wall or a hard
+      // terminal error (DNS/cert/refused) is not retried — a fresh context can't fix it.
+      const cls = classifyNavFailure(navErr);
+      if (cls !== "retryable") throw navErr;
+      log({ event: "capture_recover", reason: "session_death_on_initial_nav" });
+      try { if (!page.isClosed()) await page.close(); } catch { /* ignore */ }
+      try { await context.close(); } catch { /* ignore */ }
+      ({ context, page } = await newSession());
+      await navigateLoaded(page); // second failure propagates (no further retry)
+    }
+
+    // Item 3b: bot/auth-wall fast-fail. A wall page would otherwise burn the full
+    // multi-viewport capture and only get flagged by the pollution gate afterward.
+    // Uses the SAME signatures + node-count threshold as the gate (util/captureFailure.ts)
+    // so the abort and the grade agree; the pollution gate stays the shipped-capture
+    // authority, this only saves the wasted work of capturing an obvious wall.
+    const wallProbe = await page
+      .evaluate(() => ({
+        text: (document.body?.innerText ?? "").slice(0, 20_000),
+        nodes: document.querySelectorAll("*").length,
+      }))
+      .catch(() => null);
+    if (isBotWall(wallProbe)) {
+      throw new Error(
+        `auth/bot wall detected at ${opts.url} (${wallProbe!.nodes} nodes, wall text matched): capture aborted early`,
+      );
     }
-    if (!navigated) throw navErr;
-    await settle(page);
 
     // Stage 2: lazy-loader promotion. WP Rocket/lazysizes keep a 0-size placeholder in
     // `src` with the real URL in data attrs; autoScroll outruns their IntersectionObserver
@@ -1641,6 +1794,37 @@ export async function captureSite(opts: {
       log({ event: "captured", viewport: vw, nodes: snapshot.doc.nodeCount, scrollHeight: snapshot.doc.scrollHeight });
     }
 
+    // Item 2: extended lazy-asset discovery sweep. The walker + promoteLazyMedia
+    // already harvest img/source src/srcset and the common data-* lazy attrs
+    // (data-src / data-lazy-src / data-original / data-ll-src / data-(lazy-)srcset)
+    // and picture <source> variants — this sweep ONLY adds the references those miss:
+    //   • <noscript> contents — the walker skips <noscript> entirely, but the fallback
+    //     markup real browsers render with JS off often carries the true <img>/<source> URL;
+    //   • inline element style="…url(…)…" — the walker harvests url() from STYLESHEET
+    //     rules, not from an element's own style attribute (hero background-image inlined);
+    //   • data-background / data-background-image — lazy-bg aliases beyond promoteLazyMedia's
+    //     single data-bg;
+    //   • img[loading=lazy] currentSrc — the resolved variant a below-fold image settled on.
+    // Discovery-ONLY: URLs are recorded through recordAsset so the fallback downloader
+    // fetches them; nothing is promoted into the DOM (the snapshots are already taken, so
+    // this can never shift a captured layout). Bounded so a pathological page can't explode
+    // the fallback fetch phase.
+    try {
+      const sweptRefs: string[] = await page.evaluate(discoverLazyAssetsInPage);
+      let swept = 0;
+      for (const url of sweptRefs) {
+        if (swept >= 120) break; // bound pathological pages (fallback fetch is 30s/asset)
+        if (!/^https?:\/\//i.test(url) || assetMap.has(url)) continue;
+        const t = classifyAsset(url, null);
+        if (!t || !["image", "svg", "video", "font", "lottie"].includes(t)) continue;
+        recordAsset(url, t, null, null, "lazy-sweep");
+        swept++;
+      }
+      if (swept) log({ event: "lazy_sweep", recorded: swept, seen: sweptRefs.length });
+    } catch (e) {
+      log({ event: "lazy_sweep_error", error: String((e as { message?: string })?.message ?? e).slice(0, 160) });
+    }
+
     // Browser-as-oracle: discover the source's real responsive band edges by sweeping the viewport
     // and binary-searching each width where the discrete (media-query-toggled) layout signature
     // changes. Read-only and bounded; runs once here — overlays are dismissed and the DOM settled, so
@@ -1754,6 +1938,7 @@ export async function captureSite(opts: {
   const result: CaptureResult = {
     sourceUrl: opts.url,
     capturedAt: new Date().toISOString(),
+    ...(deterministicEnvOn ? { deterministicEnv: { seed: prngSeed, epochMs } } : {}),
     viewports,
     breakpoints: discoveredBreakpoints,
     perViewport,
diff --git a/compiler/src/util/captureFailure.ts b/compiler/src/util/captureFailure.ts
new file mode 100644
index 0000000..a964ce7
--- /dev/null
+++ b/compiler/src/util/captureFailure.ts
@@ -0,0 +1,73 @@
+/** Capture-side fast-fail helpers (Item 3).
+ *
+ *  Two concerns share this module because both are pure, testable predicates the
+ *  capture flow keys off:
+ *
+ *   1. Wall-text detection — the SAME signature set the validator's pollution gate
+ *      uses (validate/gates.ts imports WALL_RE from here). Extracted so the two
+ *      judgments — capture-side abort and validator-side grade — can never drift.
+ *      The pollution gate remains the AUTHORITY on whether a shipped capture is
+ *      polluted; this module only lets capture bail early on an obvious wall
+ *      instead of burning the full multi-viewport pass on garbage.
+ *
+ *   2. Nav-failure classification — decides whether a navigation/session error is
+ *      worth ONE fresh-context retry (transient: the browser/page died, a socket
+ *      reset, a nav timeout) versus terminal (a wall, a hard DNS/cert failure that
+ *      a retry cannot fix). Pure string classification so it unit-tests without a
+ *      browser.
+ */
+
+/** Bot/egress/auth-wall text signatures. One regex, shared with the pollution gate
+ *  (validate/gates.ts) so capture-abort and validator-grade use identical fingerprints. */
+export const WALL_RE =
+  /blocked by egress|access denied|access to this page has been denied|are you a (human|robot)|verify you are human|enable javascript to|please enable javascript|checking your browser|just a moment|attention required|request blocked|why have i been blocked|captcha|cf-browser-verification|ddos protection by/i;
+
+export function isWallText(text: string): boolean {
+  return WALL_RE.test(text);
+}
+
+/** Node-count ceiling under which wall text is treated as a genuine interstitial
+ *  rather than an incidental mention on a real page. Matches the pollution gate's
+ *  `wall && nodeCount < 220` threshold so the two agree on the same boundary. */
+export const WALL_MAX_NODES = 220;
+
+export type WallProbe = { text: string; nodes: number };
+
+/** Capture-side wall verdict: the page is a bot/auth wall worth aborting on iff it
+ *  is BOTH small (few nodes) AND carries wall text — identical to the gate's rule.
+ *  A large page that merely mentions "captcha" in body copy is NOT a wall. */
+export function isBotWall(probe: WallProbe | null | undefined): boolean {
+  if (!probe) return false;
+  return probe.nodes < WALL_MAX_NODES && isWallText(probe.text);
+}
+
+export type NavFailureClass = "retryable" | "wall" | "terminal";
+
+/** Classify a navigation/session failure by its error text.
+ *
+ *  - "wall"      → a bot/auth interstitial; a retry with a fresh context won't help
+ *                  and the caller should surface it as a pollution-style abort.
+ *  - "retryable" → the browser/page/context died, a transient socket/timeout/reset;
+ *                  ONE fresh-context retry is worthwhile.
+ *  - "terminal"  → a hard failure a retry cannot change (DNS, cert, refused, unknown).
+ *
+ *  Ordering matters: a wall signature wins over a transient one (a wall served over
+ *  a reset connection is still a wall). */
+export function classifyNavFailure(error: unknown): NavFailureClass {
+  const msg = String((error as { message?: string })?.message ?? error ?? "");
+  if (WALL_RE.test(msg)) return "wall";
+  // Session death / crash / transient network — a fresh context can recover these.
+  if (
+    /Target (page, context or browser|closed)|context or browser has been closed|page(?:,)? .*has been closed|browser has been closed|page closed|has crashed|Navigation .*interrupted|net::ERR_(?:CONNECTION_RESET|CONNECTION_CLOSED|TIMED_OUT|ABORTED|EMPTY_RESPONSE|NETWORK_CHANGED|SOCKET_NOT_CONNECTED)|Timeout .*exceeded|Navigation timeout/i.test(
+      msg,
+    )
+  ) {
+    return "retryable";
+  }
+  return "terminal";
+}
+
+/** Whether a classified failure earns the single fresh-context retry. */
+export function isRetryableNavFailure(error: unknown): boolean {
+  return classifyNavFailure(error) === "retryable";
+}
diff --git a/compiler/src/util/envShim.ts b/compiler/src/util/envShim.ts
new file mode 100644
index 0000000..49bc55b
--- /dev/null
+++ b/compiler/src/util/envShim.ts
@@ -0,0 +1,103 @@
+/** Deterministic capture-environment shim (Stage 0, runs before ANY page script).
+ *
+ *  Two entropy sources make a page render differently on each load — Math.random
+ *  (shuffled carousels, random ids, A/B jitter) and the wall clock ("posted N
+ *  minutes ago", schedule/countdown logic). Seeding the first and pinning the
+ *  second makes a capture reproducible: the same site captured under the same
+ *  {seed, epoch} paints the same DOM.
+ *
+ *  CAUTIONS (all honored below):
+ *   - performance.now() is left REAL. Motion capture (marquee/rotator sampling in
+ *     capture/motion.ts) measures real velocities and observation windows off it;
+ *     pinning it would corrupt those measurements. Only the Date wall clock moves.
+ *   - The Date epoch is a PARAMETER, recorded in capture metadata — a recapture
+ *     uses a fresh-but-recorded value. Generation determinism only requires a
+ *     frozen capture to produce byte-stable output, which is unaffected by which
+ *     epoch was chosen (the epoch is frozen into the capture, not re-derived).
+ *   - The clock still ADVANCES from the pinned epoch (via the real-clock delta),
+ *     so elapsed-time logic (setTimeout-driven reveals, animation timing that
+ *     reads Date, lazy-load debounces) behaves — only the absolute origin is
+ *     pinned, not the passage of time.
+ *   - Date is patched consistently across constructor / Date.now() / getTime() /
+ *     valueOf() / Symbol.toPrimitive by shifting the underlying instant for BOTH
+ *     the no-arg constructor and Date.now(); every instance method then reads the
+ *     shifted instant through the native prototype, so cookie-banner / schedule
+ *     gates that call getTime()/valueOf() see the same pinned clock as now().
+ */
+
+/** Default fixed epoch: 2026-01-01T00:00:00.000Z. Callers should pass an explicit,
+ *  recorded epoch (see captureEpochMs); this is only the fallback. */
+export const DEFAULT_CAPTURE_EPOCH_MS = 1767225600000;
+
+/** Default PRNG seed (mulberry32 initial state). A non-zero constant so the first
+ *  draw is well-mixed; recorded alongside the epoch for reproducibility. */
+export const DEFAULT_PRNG_SEED = 0x9e3779b9;
+
+/** Resolve the epoch a capture run should pin to. Env override lets a recapture
+ *  reuse a recorded value; otherwise a fresh timestamp is taken at run start and
+ *  recorded in metadata. Determinism of GENERATION does not depend on this value —
+ *  only on the capture being frozen once chosen. */
+export function captureEpochMs(override?: number | string): number {
+  if (typeof override === "number" && Number.isFinite(override)) return override;
+  if (typeof override === "string" && override.trim()) {
+    const parsed = Number(override);
+    if (Number.isFinite(parsed)) return parsed;
+    const asDate = Date.parse(override);
+    if (Number.isFinite(asDate)) return asDate;
+  }
+  return DEFAULT_CAPTURE_EPOCH_MS;
+}
+
+/**
+ * Build the init-script SOURCE STRING injected via page.addInitScript before any
+ * page script runs. Returned as a raw string (not a function) so tsx/esbuild never
+ * transforms it — the browser receives exactly these bytes.
+ *
+ * Interpolation is numeric-only (Number.isFinite-guarded), so no string escaping /
+ * injection surface exists.
+ */
+export function buildDeterministicEnvShim(opts?: { seed?: number; epochMs?: number }): string {
+  const seed = Number.isFinite(opts?.seed) ? Math.trunc(opts!.seed!) : DEFAULT_PRNG_SEED;
+  const epoch = Number.isFinite(opts?.epochMs) ? Math.trunc(opts!.epochMs!) : DEFAULT_CAPTURE_EPOCH_MS;
+  // NOTE: `delta` is computed once at shim-eval time (the earliest possible moment,
+  // before page scripts) so the pinned origin is stable; the real clock then adds
+  // elapsed time on top, keeping relative time truthful.
+  return `(() => {
+  "use strict";
+  // ---- Seeded PRNG (mulberry32): deterministic, well-distributed, cheap ----
+  let __s = ${seed} | 0;
+  const __rand = function random() {
+    __s = (__s + 0x6d2b79f5) | 0;
+    let t = Math.imul(__s ^ (__s >>> 15), 1 | __s);
+    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;
+    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
+  };
+  try { Object.defineProperty(Math, "random", { value: __rand, writable: true, configurable: true }); }
+  catch (e) { try { Math.random = __rand; } catch (e2) {} }
+
+  // ---- Pinned-but-advancing wall clock. performance.now() stays REAL. ----
+  const RealDate = Date;
+  const realNow = () => RealDate.now();
+  // Shift so the FIRST observed instant is the pinned epoch; real elapsed time is
+  // then added on top (delta is negative if the machine clock is ahead of epoch).
+  const delta = ${epoch} - realNow();
+  const shiftedNow = () => realNow() + delta;
+  function DittoDate(...args) {
+    // \`new Date()\` with no args => pinned clock; every other form is delegated to
+    // the native constructor unchanged (parsing a string, y/m/d, a millis value).
+    const inst = args.length === 0 ? new RealDate(shiftedNow()) : new RealDate(...args);
+    // Re-tag the prototype so instanceof + inherited getTime/valueOf/toISOString work.
+    Object.setPrototypeOf(inst, DittoDate.prototype);
+    return inst;
+  }
+  // Inherit the full native Date prototype (getTime, valueOf, getFullYear,
+  // toISOString, Symbol.toPrimitive, ...) so every read is consistent with now().
+  DittoDate.prototype = Object.create(RealDate.prototype);
+  DittoDate.prototype.constructor = DittoDate;
+  DittoDate.now = shiftedNow;
+  DittoDate.parse = RealDate.parse;
+  DittoDate.UTC = RealDate.UTC;
+  try { Object.defineProperty(globalThis, "Date", { value: DittoDate, writable: true, configurable: true }); }
+  catch (e) { try { globalThis.Date = DittoDate; } catch (e2) {} }
+})();`;
+}
diff --git a/compiler/src/validate/gates.ts b/compiler/src/validate/gates.ts
index 9f9ed4f..78a4d3f 100644
--- a/compiler/src/validate/gates.ts
+++ b/compiler/src/validate/gates.ts
@@ -7,6 +7,7 @@ import type { AssetGraph } from "../infer/assets.js";
 import type { FontGraph } from "../infer/fonts.js";
 import type { Section } from "../infer/sections.js";
 import type { CaptureResult } from "../capture/capture.js";
+import { WALL_RE } from "../util/captureFailure.js";
 
 export type GateResult = {
   gate: string;
@@ -117,7 +118,8 @@ export function countVisibleInCaptureHiddenInClone(
 // page: an egress/bot wall, a near-empty shell, or a cookie/consent modal that was
 // never dismissed (the clone then reproduces the modal, so the perceptual gate is
 // fooled too). This gate flags those captures so a "perfect" score can't hide them.
-const WALL_RE = /blocked by egress|access denied|access to this page has been denied|are you a (human|robot)|verify you are human|enable javascript to|please enable javascript|checking your browser|just a moment|attention required|request blocked|why have i been blocked|captcha|cf-browser-verification|ddos protection by/i;
+// WALL_RE lives in util/captureFailure.ts — shared with the capture-side fast-fail so
+// the abort and the grade can never drift on what counts as a wall.
 
 export function gatePollution(ir: IR, capture: CaptureResult, viewports: number[]): GateResult {
   const issues: string[] = [];
diff --git a/compiler/test/captureFailure.test.ts b/compiler/test/captureFailure.test.ts
new file mode 100644
index 0000000..4ed55ea
--- /dev/null
+++ b/compiler/test/captureFailure.test.ts
@@ -0,0 +1,117 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import {
+  WALL_RE,
+  isWallText,
+  isBotWall,
+  WALL_MAX_NODES,
+  classifyNavFailure,
+  isRetryableNavFailure,
+} from "../src/util/captureFailure.js";
+
+// ---------------------------------------------------------------------------
+// Item 3: capture-side fast-fail predicates (pure — no browser).
+// ---------------------------------------------------------------------------
+
+describe("captureFailure: wall-text detection", () => {
+  it("matches common bot/auth-wall fingerprints", () => {
+    for (const t of [
+      "Just a moment...",
+      "Checking your browser before accessing",
+      "Please enable JavaScript to continue",
+      "Access to this page has been denied",
+      "Are you a human?",
+      "Verify you are human",
+      "Attention Required! | Cloudflare",
+      "Please complete the CAPTCHA",
+      "DDoS protection by Cloudflare",
+    ]) {
+      assert.ok(isWallText(t), `expected wall text to match: ${t}`);
+    }
+  });
+
+  it("does not match ordinary marketing/body copy", () => {
+    for (const t of [
+      "Welcome to our store — shop the new collection",
+      "Our team of humans is here to help you 24/7",
+      "Enable notifications to get the latest deals",
+      "About us · Careers · Contact",
+    ]) {
+      assert.equal(isWallText(t), false, `expected NOT to match: ${t}`);
+    }
+  });
+
+  it("WALL_RE is the same instance shared with the pollution gate (single source of truth)", () => {
+    // gates.ts imports WALL_RE from this module; assert the export is a real RegExp
+    // so a refactor that turns it into a function would fail here.
+    assert.ok(WALL_RE instanceof RegExp);
+  });
+});
+
+describe("captureFailure: isBotWall (matches the pollution gate's small+wall rule)", () => {
+  it("flags a small page with wall text", () => {
+    assert.ok(isBotWall({ text: "Just a moment...", nodes: 8 }));
+    assert.ok(isBotWall({ text: "checking your browser", nodes: WALL_MAX_NODES - 1 }));
+  });
+
+  it("does NOT flag a large page that merely mentions a wall phrase", () => {
+    // A real page can say "captcha" in its help docs — node count is the discriminator.
+    assert.equal(isBotWall({ text: "how our captcha works", nodes: WALL_MAX_NODES }), false);
+    assert.equal(isBotWall({ text: "how our captcha works", nodes: 5000 }), false);
+  });
+
+  it("does NOT flag a small page with no wall text", () => {
+    assert.equal(isBotWall({ text: "Home · About · Contact", nodes: 10 }), false);
+  });
+
+  it("is null-safe", () => {
+    assert.equal(isBotWall(null), false);
+    assert.equal(isBotWall(undefined), false);
+  });
+});
+
+describe("captureFailure: classifyNavFailure", () => {
+  it("classifies session-death / crash / transient network as retryable", () => {
+    for (const msg of [
+      "Target page, context or browser has been closed",
+      "Target closed",
+      "browser has been closed",
+      "page has crashed",
+      "net::ERR_CONNECTION_RESET at https://example.com",
+      "net::ERR_TIMED_OUT",
+      "Timeout 45000ms exceeded",
+      "Navigation timeout of 30000 ms exceeded",
+    ]) {
+      assert.equal(classifyNavFailure(new Error(msg)), "retryable", msg);
+      assert.equal(isRetryableNavFailure(new Error(msg)), true, msg);
+    }
+  });
+
+  it("classifies wall fingerprints as wall (not retryable — a fresh context can't help)", () => {
+    const e = new Error("navigation failed: just a moment... checking your browser");
+    assert.equal(classifyNavFailure(e), "wall");
+    assert.equal(isRetryableNavFailure(e), false);
+  });
+
+  it("classifies hard failures as terminal (not retryable)", () => {
+    for (const msg of [
+      "net::ERR_NAME_NOT_RESOLVED",
+      "net::ERR_CERT_AUTHORITY_INVALID",
+      "net::ERR_CONNECTION_REFUSED",
+      "something totally unexpected",
+    ]) {
+      assert.equal(classifyNavFailure(new Error(msg)), "terminal", msg);
+      assert.equal(isRetryableNavFailure(new Error(msg)), false, msg);
+    }
+  });
+
+  it("wall wins over a transient signature (a wall served over a reset is still a wall)", () => {
+    const e = new Error("net::ERR_CONNECTION_RESET — access denied");
+    assert.equal(classifyNavFailure(e), "wall");
+  });
+
+  it("accepts a bare string or non-Error value", () => {
+    assert.equal(classifyNavFailure("Target closed"), "retryable");
+    assert.equal(classifyNavFailure(undefined), "terminal");
+  });
+});
diff --git a/compiler/test/envShim.test.ts b/compiler/test/envShim.test.ts
new file mode 100644
index 0000000..f0236b7
--- /dev/null
+++ b/compiler/test/envShim.test.ts
@@ -0,0 +1,162 @@
+import { describe, it, before, after } from "node:test";
+import assert from "node:assert/strict";
+import { chromium, type Browser, type Page } from "playwright";
+import {
+  buildDeterministicEnvShim,
+  captureEpochMs,
+  DEFAULT_CAPTURE_EPOCH_MS,
+  DEFAULT_PRNG_SEED,
+} from "../src/util/envShim.js";
+
+const ESBUILD_SHIM =
+  "globalThis.__name = globalThis.__name || ((fn) => fn);" +
+  "globalThis.__defProp = globalThis.__defProp || Object.defineProperty;";
+
+// ---------------------------------------------------------------------------
+// Item 1: deterministic-env shim — pure epoch resolution + in-browser behavior.
+// ---------------------------------------------------------------------------
+
+describe("envShim: captureEpochMs resolution", () => {
+  it("defaults to the fixed epoch when no override is given", () => {
+    assert.equal(captureEpochMs(), DEFAULT_CAPTURE_EPOCH_MS);
+    assert.equal(captureEpochMs(undefined), DEFAULT_CAPTURE_EPOCH_MS);
+  });
+
+  it("passes a finite numeric override through unchanged", () => {
+    assert.equal(captureEpochMs(1234567890), 1234567890);
+  });
+
+  it("parses a numeric string and an ISO date string", () => {
+    assert.equal(captureEpochMs("1234567890"), 1234567890);
+    assert.equal(captureEpochMs("2020-01-01T00:00:00Z"), Date.parse("2020-01-01T00:00:00Z"));
+  });
+
+  it("falls back to the default for garbage input", () => {
+    assert.equal(captureEpochMs("not-a-date"), DEFAULT_CAPTURE_EPOCH_MS);
+    assert.equal(captureEpochMs(NaN), DEFAULT_CAPTURE_EPOCH_MS);
+  });
+});
+
+describe("envShim: buildDeterministicEnvShim source safety", () => {
+  it("interpolates only numeric literals (no injection surface)", () => {
+    const src = buildDeterministicEnvShim({ seed: 42, epochMs: 1000 });
+    assert.match(src, /let __s = 42 \| 0;/);
+    assert.match(src, /const delta = 1000 - realNow\(\);/);
+    // performance.now must remain untouched — the shim only patches Math.random + Date,
+    // never assigns to performance.now (motion.ts velocity sampling depends on the real one).
+    assert.equal(/performance\s*\.\s*now\s*=/.test(src), false);
+    assert.equal(/defineProperty\s*\(\s*performance/.test(src), false);
+  });
+
+  it("truncates non-integer seed/epoch and uses defaults for non-finite", () => {
+    const src = buildDeterministicEnvShim({ seed: 3.9, epochMs: 5.9 });
+    assert.match(src, /let __s = 3 \| 0;/);
+    assert.match(src, /const delta = 5 - realNow\(\);/);
+    const dflt = buildDeterministicEnvShim({ seed: NaN, epochMs: Infinity });
+    assert.match(dflt, new RegExp(`let __s = ${DEFAULT_PRNG_SEED} \\| 0;`));
+    assert.match(dflt, new RegExp(`const delta = ${DEFAULT_CAPTURE_EPOCH_MS} - realNow\\(\\);`));
+  });
+});
+
+const VW = 1280, VH = 800;
+
+describe("envShim: in-browser behavior", () => {
+  let browser: Browser;
+  before(async () => { browser = await chromium.launch(); });
+  after(async () => { await browser.close(); });
+
+  // Fresh page with the shim installed BEFORE any page script (via addInitScript),
+  // exactly as capture.ts wires it. We navigate to a data: URL rather than setContent
+  // so the document is CREATED via navigation — addInitScript fires on document
+  // creation, which setContent (a content swap on the existing about:blank) skips.
+  // The inline <script> then runs after the init scripts and samples the pinned env.
+  const loadWithShim = async (opts: { seed?: number; epochMs?: number }, bodyScript: string): Promise<Page> => {
+    const page = await browser.newPage();
+    await page.setViewportSize({ width: VW, height: VH });
+    await page.addInitScript(ESBUILD_SHIM);
+    await page.addInitScript(buildDeterministicEnvShim(opts));
+    const html = `<!doctype html><html><body><script>${bodyScript}</script></body></html>`;
+    await page.goto("data:text/html," + encodeURIComponent(html));
+    return page;
+  };
+
+  it("seeds Math.random reproducibly across two independent loads (same seed → same sequence)", async () => {
+    const script = "window.__draws = Array.from({length: 10}, () => Math.random());";
+    const p1 = await loadWithShim({ seed: 12345, epochMs: DEFAULT_CAPTURE_EPOCH_MS }, script);
+    const p2 = await loadWithShim({ seed: 12345, epochMs: DEFAULT_CAPTURE_EPOCH_MS }, script);
+    const [a, b] = await Promise.all([
+      p1.evaluate(() => (window as unknown as { __draws: number[] }).__draws),
+      p2.evaluate(() => (window as unknown as { __draws: number[] }).__draws),
+    ]);
+    assert.deepEqual(a, b, "two loads with the same seed produce identical Math.random sequences");
+    assert.ok(a.every((n) => n >= 0 && n < 1), "draws are in [0,1)");
+    // Not a constant stream — a broken PRNG returning the same value would also be
+    // "stable"; assert genuine variation so the test can't pass trivially.
+    assert.ok(new Set(a).size > 1, "the sequence varies");
+    await p1.close(); await p2.close();
+  });
+
+  it("a different seed yields a different sequence", async () => {
+    const script = "window.__draws = Array.from({length: 10}, () => Math.random());";
+    const p1 = await loadWithShim({ seed: 1, epochMs: DEFAULT_CAPTURE_EPOCH_MS }, script);
+    const p2 = await loadWithShim({ seed: 2, epochMs: DEFAULT_CAPTURE_EPOCH_MS }, script);
+    const [a, b] = await Promise.all([
+      p1.evaluate(() => (window as unknown as { __draws: number[] }).__draws),
+      p2.evaluate(() => (window as unknown as { __draws: number[] }).__draws),
+    ]);
+    assert.notDeepEqual(a, b);
+    await p1.close(); await p2.close();
+  });
+
+  it("pins the Date epoch consistently across constructor / now() / getTime() / valueOf() / toISOString()", async () => {
+    const epoch = Date.parse("2021-06-15T12:00:00Z");
+    const page = await loadWithShim(
+      { seed: 1, epochMs: epoch },
+      `window.__t = {
+         now: Date.now(),
+         ctorGetTime: new Date().getTime(),
+         ctorValueOf: new Date().valueOf(),
+         iso: new Date().toISOString(),
+       };`,
+    );
+    const t = await page.evaluate(() => (window as unknown as { __t: { now: number; ctorGetTime: number; ctorValueOf: number; iso: string } }).__t);
+    // All reads land at the pinned epoch (within a few ms of real elapsed time between them).
+    assert.ok(Math.abs(t.now - epoch) < 5000, `Date.now near epoch: ${t.now} vs ${epoch}`);
+    assert.ok(Math.abs(t.ctorGetTime - epoch) < 5000, "new Date().getTime() near epoch");
+    assert.ok(Math.abs(t.ctorValueOf - epoch) < 5000, "new Date().valueOf() near epoch");
+    assert.match(t.iso, /^2021-06-15T12:00:0/, `toISOString pinned: ${t.iso}`);
+    // now() and getTime() must agree (both read the same shifted instant).
+    assert.ok(Math.abs(t.now - t.ctorGetTime) < 5000, "now() and getTime() agree");
+    await page.close();
+  });
+
+  it("keeps the clock ADVANCING from the pinned epoch (timers still behave)", async () => {
+    const epoch = DEFAULT_CAPTURE_EPOCH_MS;
+    const page = await loadWithShim(
+      { seed: 1, epochMs: epoch },
+      `window.__adv = new Promise((res) => {
+         const t0 = Date.now();
+         setTimeout(() => res({ t0, t1: Date.now() }), 60);
+       });`,
+    );
+    const { t0, t1 } = await page.evaluate(() => (window as unknown as { __adv: Promise<{ t0: number; t1: number }> }).__adv);
+    assert.ok(t0 >= epoch - 5000 && t0 <= epoch + 5000, "start is pinned near epoch");
+    assert.ok(t1 > t0, "time advances across a real setTimeout delay");
+    await page.close();
+  });
+
+  it("leaves performance.now() REAL (motion sampling depends on it) and advancing", async () => {
+    const page = await loadWithShim(
+      { seed: 1, epochMs: DEFAULT_CAPTURE_EPOCH_MS },
+      `window.__perf = new Promise((res) => {
+         const p0 = performance.now();
+         setTimeout(() => res({ p0, p1: performance.now() }), 40);
+       });`,
+    );
+    const { p0, p1 } = await page.evaluate(() => (window as unknown as { __perf: Promise<{ p0: number; p1: number }> }).__perf);
+    // performance.now() is a real monotonic clock from navigation start — small, not the epoch.
+    assert.ok(p0 >= 0 && p0 < 60_000, `performance.now() is real (not pinned to epoch): ${p0}`);
+    assert.ok(p1 > p0, "performance.now() advances");
+    await page.close();
+  });
+});
diff --git a/compiler/test/lazySweep.test.ts b/compiler/test/lazySweep.test.ts
new file mode 100644
index 0000000..3764e69
--- /dev/null
+++ b/compiler/test/lazySweep.test.ts
@@ -0,0 +1,85 @@
+import { describe, it, before, after } from "node:test";
+import assert from "node:assert/strict";
+import { chromium, type Browser, type Page } from "playwright";
+import { discoverLazyAssetsInPage } from "../src/capture/capture.js";
+
+const ESBUILD_SHIM =
+  "globalThis.__name = globalThis.__name || ((fn) => fn);" +
+  "globalThis.__defProp = globalThis.__defProp || Object.defineProperty;";
+
+const VW = 1280, VH = 800;
+const BASE = "https://example.com/page/";
+
+// ---------------------------------------------------------------------------
+// Item 2: extended lazy-asset discovery sweep (in-page discovery function).
+// ---------------------------------------------------------------------------
+describe("lazySweep: discoverLazyAssetsInPage", () => {
+  let browser: Browser;
+  before(async () => { browser = await chromium.launch(); });
+  after(async () => { await browser.close(); });
+
+  const discover = async (bodyHtml: string): Promise<string[]> => {
+    const page: Page = await browser.newPage();
+    await page.setViewportSize({ width: VW, height: VH });
+    await page.addInitScript(ESBUILD_SHIM);
+    // A <base> gives relative refs a stable absolute form to assert against.
+    await page.setContent(`<!doctype html><html><head><base href="${BASE}"></head><body>${bodyHtml}</body></html>`);
+    await page.evaluate(ESBUILD_SHIM);
+    const refs = await page.evaluate(discoverLazyAssetsInPage);
+    await page.close();
+    return refs;
+  };
+
+  it("discovers img/source src + srcset inside <noscript> fallback markup", async () => {
+    const refs = await discover(`
+      <noscript>
+        <img src="hero.jpg" srcset="hero-2x.jpg 2x, hero-3x.jpg 3x">
+        <picture><source srcset="alt.webp 1x, alt-2x.webp 2x"></picture>
+      </noscript>
+    `);
+    assert.ok(refs.includes(BASE + "hero.jpg"), "noscript img src");
+    assert.ok(refs.includes(BASE + "hero-2x.jpg"), "first srcset variant from noscript img");
+    assert.ok(refs.includes(BASE + "alt.webp"), "first srcset variant from noscript source");
+  });
+
+  it("discovers url(...) values from an element's inline style attribute", async () => {
+    const refs = await discover(`
+      <div style="background-image: url('bg.png'); color: red"></div>
+      <span style='background: url("sprite.svg") no-repeat'></span>
+    `);
+    assert.ok(refs.includes(BASE + "bg.png"), "inline background-image url()");
+    assert.ok(refs.includes(BASE + "sprite.svg"), "inline background shorthand url()");
+  });
+
+  it("discovers data-background / data-background-image (raw URL and url(...) forms)", async () => {
+    const refs = await discover(`
+      <div data-background="lazybg.jpg"></div>
+      <div data-background-image="url('lazybg2.png')"></div>
+    `);
+    assert.ok(refs.includes(BASE + "lazybg.jpg"), "raw data-background URL");
+    assert.ok(refs.includes(BASE + "lazybg2.png"), "url()-wrapped data-background-image");
+  });
+
+  it("discovers the resolved src of an img[loading=lazy]", async () => {
+    const refs = await discover(`<img loading="lazy" src="belowfold.jpg">`);
+    assert.ok(refs.includes(BASE + "belowfold.jpg"));
+  });
+
+  it("drops data: URIs and dedupes + sorts", async () => {
+    const refs = await discover(`
+      <div style="background: url('dup.png')"></div>
+      <div data-background="dup.png"></div>
+      <img loading="lazy" src="data:image/gif;base64,R0lGOD">
+    `);
+    assert.equal(refs.filter((u) => u.endsWith("dup.png")).length, 1, "deduped across channels");
+    assert.equal(refs.some((u) => u.startsWith("data:")), false, "data: URIs dropped");
+    assert.deepEqual(refs, [...refs].sort(), "sorted");
+  });
+
+  it("returns nothing for a page with no lazy references", async () => {
+    const refs = await discover(`<div><p>hello</p><img src="eager.jpg"></div>`);
+    // The eager <img src> is the walker's job, not this sweep — the sweep only harvests
+    // the channels the walker misses.
+    assert.deepEqual(refs, []);
+  });
+});