diff --git a/skills-manifest.json b/skills-manifest.json
index 27534f19e8..cff2dd75a7 100644
--- a/skills-manifest.json
+++ b/skills-manifest.json
@@ -6,8 +6,8 @@
       "files": 140
     },
     "faceless-explainer": {
-      "hash": "b772a9b6c8118c2c",
-      "files": 22
+      "hash": "5e64350379329147",
+      "files": 23
     },
     "figma": {
       "hash": "517e4dc53c13ea05",
@@ -30,7 +30,7 @@
       "files": 11
     },
     "hyperframes-core": {
-      "hash": "a270c70ced8cf952",
+      "hash": "5d3b652de1b652a4",
       "files": 19
     },
     "hyperframes-creative": {
diff --git a/skills/faceless-explainer/scripts/assemble-index.mjs b/skills/faceless-explainer/scripts/assemble-index.mjs
index 8a7554500a..90d6eef6ad 100644
--- a/skills/faceless-explainer/scripts/assemble-index.mjs
+++ b/skills/faceless-explainer/scripts/assemble-index.mjs
@@ -32,12 +32,14 @@
 //         [--audio-meta audio_meta.json]. On disk: each built frame's src html,
 //         capture/{assets,assets/videos,screenshots}/<basename> for staging, compositions/captions.html.
 // Writes: <project>/index.html  +  stages assets/<basename>  +  (guard ① below)
-//         repairs a frame file in place when its root is missing data-width/height.
+//         repairs a frame file in place when its root is missing
+//         data-width/data-height/data-duration.
 //
 // Pre-assembly frame guards (run in the same pass that reads each frame, so common
 // `lint` failures surface HERE instead of after assembly + a wasted render):
-//   ① AUTO-REPAIR — a sub-comp root missing data-width/data-height: inject the canvas
-//      dims (the renderer needs them on the cloned root; else lint root_missing_dimensions).
+//   ① AUTO-REPAIR — a sub-comp root missing data-width/data-height/data-duration:
+//      inject the canvas dims and storyboard duration. The transition injector
+//      extends that static duration when it pads the outgoing frame tail.
 //   ② HARD FAIL  — a timed element (data-start+duration+track-index) that is not the root
 //      and lacks class="clip" (shows the whole frame), or two same-track clips that overlap.
 //   (Media inside a sub-comp is NOT a violation: the runtime seeks + decodes nested
@@ -162,7 +164,7 @@ function findRootTag(html) {
 }
 
 // Returns { errors: string[], repairedHtml: string|null, repairNote: string|null }.
-function guardFrame(html, label) {
+function guardFrame(html, label, durationSeconds) {
   const errors = [];
   // Scan a copy with comments + <script>/<style> bodies blanked, so a tag-like string
   // in a comment (e.g. "<!-- match the host <video> coords -->") or in GSAP code can't
@@ -219,19 +221,25 @@ function guardFrame(html, label) {
     }
   }
 
-  // ① auto-repair: ensure the root carries data-width / data-height.
+  // ① auto-repair: ensure the root carries data-width / data-height / data-duration.
   let repairedHtml = null;
   let repairNote = null;
   const root = findRootTag(html);
   if (root) {
     const needW = !attrPresent(root.attrs, "data-width");
     const needH = !attrPresent(root.attrs, "data-height");
-    if (needW || needH) {
+    const needDuration = !attrPresent(root.attrs, "data-duration");
+    if (needW || needH || needDuration) {
       const inject =
-        (needW ? ` data-width="${WIDTH}"` : "") + (needH ? ` data-height="${HEIGHT}"` : "");
+        (needW ? ` data-width="${WIDTH}"` : "") +
+        (needH ? ` data-height="${HEIGHT}"` : "") +
+        (needDuration ? ` data-duration="${durationSeconds}"` : "");
       const newTag = root.full.replace(/(\/?>)$/, `${inject}$1`);
       repairedHtml = html.slice(0, root.start) + newTag + html.slice(root.end);
-      repairNote = `${label}: injected${needW ? " data-width" : ""}${needH ? " data-height" : ""} (${WIDTH}×${HEIGHT}) on the root — was missing (would lint root_missing_dimensions)`;
+      repairNote =
+        `${label}: injected${needW ? " data-width" : ""}${needH ? " data-height" : ""}` +
+        `${needDuration ? " data-duration" : ""} on the root` +
+        `${needW || needH ? ` (${WIDTH}×${HEIGHT})` : ""}`;
     }
   }
 
@@ -281,8 +289,8 @@ for (const f of manifest.frames) {
       `${label}: ${f.src} is empty or has no HTML — the worker wrote a blank/partial file. Re-dispatch that worker before assembling.`,
     );
   }
-  // pre-assembly guards: ① repair missing root dims in place, ② collects fatal violations.
-  const guard = guardFrame(html, label);
+  // pre-assembly guards: ① repair missing root metadata in place, ② collects violations.
+  const guard = guardFrame(html, label, r3(f.durationSeconds));
   if (guard.repairedHtml) {
     writeFileSync(compAbs, guard.repairedHtml);
     html = guard.repairedHtml;
diff --git a/skills/faceless-explainer/scripts/assemble-index.test.mjs b/skills/faceless-explainer/scripts/assemble-index.test.mjs
new file mode 100644
index 0000000000..ac0ba7fca6
--- /dev/null
+++ b/skills/faceless-explainer/scripts/assemble-index.test.mjs
@@ -0,0 +1,94 @@
+import assert from "node:assert/strict";
+import { execFileSync } from "node:child_process";
+import { mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { dirname, join } from "node:path";
+import test from "node:test";
+
+const scriptDir = dirname(new URL(import.meta.url).pathname);
+const assembleScript = join(scriptDir, "assemble-index.mjs");
+const transitionsScript = join(scriptDir, "transitions.mjs");
+
+function write(path, contents) {
+  mkdirSync(dirname(path), { recursive: true });
+  writeFileSync(path, contents);
+}
+
+function frameWithoutRootDuration(id, duration) {
+  return `<template>
+  <div data-composition-id="${id}" data-width="1920" data-height="1080">
+    <div class="clip" data-start="0" data-duration="${duration}" data-track-index="0"></div>
+    <script>
+      window.__timelines = window.__timelines || {};
+      window.__timelines["${id}"] = gsap.timeline({ paused: true }).to({}, { duration: ${duration} });
+    </script>
+  </div>
+</template>`;
+}
+
+test("assembly materializes frame root duration before transition injection", () => {
+  const project = mkdtempSync(join(tmpdir(), "frame-root-duration-"));
+  try {
+    write(
+      join(project, "STORYBOARD.md"),
+      `---
+format: 1920x1080
+---
+
+## Frame 1 — First
+
+- duration: 2s
+- transition_in: cut
+- status: animated
+- src: compositions/frames/01-first.html
+
+## Frame 2 — Second
+
+- duration: 2s
+- transition_in: crossfade 0.5s
+- status: animated
+- src: compositions/frames/02-second.html
+`,
+    );
+    const firstPath = join(project, "compositions", "frames", "01-first.html");
+    const secondPath = join(project, "compositions", "frames", "02-second.html");
+    write(firstPath, frameWithoutRootDuration("01-first", 2));
+    write(secondPath, frameWithoutRootDuration("02-second", 2));
+
+    execFileSync(
+      process.execPath,
+      [assembleScript, "--storyboard", join(project, "STORYBOARD.md"), "--hyperframes", project],
+      { encoding: "utf8" },
+    );
+
+    assert.match(
+      readFileSync(firstPath, "utf8"),
+      /data-composition-id="01-first"[^>]*data-duration="2"/,
+    );
+    assert.match(
+      readFileSync(secondPath, "utf8"),
+      /data-composition-id="02-second"[^>]*data-duration="2"/,
+    );
+
+    assert.doesNotThrow(() =>
+      execFileSync(
+        process.execPath,
+        [
+          transitionsScript,
+          "inject",
+          "--storyboard",
+          join(project, "STORYBOARD.md"),
+          "--hyperframes",
+          project,
+        ],
+        { encoding: "utf8", stdio: "pipe" },
+      ),
+    );
+    assert.match(
+      readFileSync(firstPath, "utf8"),
+      /data-composition-id="01-first"[^>]*data-duration="2.5"/,
+    );
+  } finally {
+    rmSync(project, { recursive: true, force: true });
+  }
+});
diff --git a/skills/hyperframes-core/references/frame-worker-core.md b/skills/hyperframes-core/references/frame-worker-core.md
index 6b1da927f2..3dbf5ade58 100644
--- a/skills/hyperframes-core/references/frame-worker-core.md
+++ b/skills/hyperframes-core/references/frame-worker-core.md
@@ -56,7 +56,7 @@ Shared law for every narrative frame, each load-bearing; your workflow's delta a
 
 1. **Read** — your packet top to bottom (your frame block, the inlined blueprint, the inlined rule recipes), then `frame.md` (the look). Internalize the self-check codes below before you write — most lethal is **template transport**: every `<style>` + `<script>` (including the gsap load) must live INSIDE `<template>`, because the runtime only clones template contents and the assembled-project `lint` / `check` gate can miss an unwired blank sub-composition.
 2. **Design** — turn the time-coded shot sequence into a timeline using `frame.md`'s components and type ramp: each Scene window becomes a phase revealed on its `voiceover` cue, each named motion built from the recipe in your packet, the blueprint's signature move kept recognizable. Find a visual idea that reinforces the beat, not a literal restyle of the words.
-3. **Author** — write the full sub-composition to `compositions/frames/<frame_id>.html` (rewrite to iterate; last write wins). `<template>`-wrapped root carrying `data-composition-id="<frame_id>"` and styled via `#root` (not a class on that element — see the self-check below), exactly one `gsap.timeline({ paused: true })` registered at `window.__timelines["<frame_id>"]`, built synchronously.
+3. **Author** — write the full sub-composition to `compositions/frames/<frame_id>.html` (rewrite to iterate; last write wins). `<template>`-wrapped root carrying `data-composition-id="<frame_id>"` and the packet's positive `data-duration`, styled via `#root` (not a class on that element — see the self-check below), exactly one `gsap.timeline({ paused: true })` registered at `window.__timelines["<frame_id>"]`, built synchronously.
    Prefix authored ids and globally reusable class names with `<frame_id>-` so sibling frames assembled from parallel workers cannot collide. Contract selectors such as `#root` and `.clip` are the only exceptions.
 4. **Self-check, then finish** — re-read your file against the checklist below and fix in place; then continue to your next assigned packet, if any. You do **not** run the CLI.
 
@@ -64,7 +64,7 @@ Shared law for every narrative frame, each load-bearing; your workflow's delta a
 
 You **can't** meaningfully run `hyperframes lint` / `check` here: they operate on the **assembled project** (the `index.html` graph / bundle), and your frame isn't wired in yet — so they report on _other_ files, not yours (a false green). The **orchestrator** runs them after assembly (the correct unit), and **re-dispatches you with the finding** if your frame fails (see **Retry** above). So get it right on write: re-read your file against this checklist before finishing — the codes in parens are `hyperframes lint`'s and what the orchestrator may cite back:
 
-- `missing_template_wrapper` / `missing_composition_id` — the entire file is exactly one bare `<template>…</template>` fragment (no DOCTYPE / full document); root carries `data-composition-id="<frame_id>"`.
+- `missing_template_wrapper` / `missing_composition_id` — the entire file is exactly one bare `<template>…</template>` fragment (no DOCTYPE / full document); root carries `data-composition-id="<frame_id>"` and a positive `data-duration` matching the packet.
 - **Template transport** — every `<style>` and `<script>` block, including the GSAP load, lives inside `<template>`.
 - `subcomposition_root_styled_by_class` — **style the frame root via `#root`, never a class on the `data-composition-id` element**: at render a class on the root gets scoped to a descendant selector that can't match it, so the **whole scene renders unstyled** (Studio preview still looks right — trust this rule, not the preview). Descendants use plain selectors.
 - **Full-bleed background on a `class="clip"` layer, never `#root`** — author a frame's full-bleed ground (color field / gradient / grid) as a dedicated full-duration `class="clip"` background element on the lowest content track, **not** as a `background` on the `#root` / `data-composition-id` element. At assembly the frame root is clip-gated to its scene window, so a background painted on the root is not a dependable full-frame ground — dark content can end up over the host `body` (black) and render invisible. The video's base ground is painted separately by the assembler from `frame.md`'s `canvas` color onto the index `#root`; your full-bleed clip rides on top of it.