تراكب التسميات التوضيحية

# مبدأ تراكب التسميات التوضيحية

> **مبدأ التراكب — يكمل مهارة `embedded-captions` الأصلية. يطبق فوقها؛ لا تتوقع دمجه في المهارة الأصلية.**

تتحد فكرتان هنا. أولا، **نموذج التسمية التوضيحية** — كل عبارة منطوقة هي `drop` أو `rail` أو `embed`، و`embed` هي الذروة النادرة المكتسبة، وليست الافتراضية. ثانيا، **قانون التراكب** — يتم تركيب سطر التسمية التوضيحية فوق الفيلم كتراكب؛ إنه ليس منطقة محجوزة، لذلك لا تقوم أبدا بتحريك المحتوى للأعلى أو ترك نطاق ميت "لإفساح المجال" له. الفكرتان تعززان بعضهما البعض: لأن التسميات التوضيحية تظهر كتراكب (ال `rail` الحرفي في الأمام، وال `embed` العرضي خلف الموضوع)، فإن التكوين يحافظ على إطاره الكامل ويتمركز حول المركز الرأسي الحقيقي.

## نموذج التسمية التوضيحية — drop / rail / embed

كل عبارة منطوقة هي واحدة من ثلاثة أشياء (حرفيا من `embedded-captions`):

| | ما هو | كيف يظهر RAIL — The rail is the default. It is a clean, readable lower-third subtitle, in front of the subject. It is the primary way to convey the verbatim spoken content. - **Embed** — An embed is a promoted peak, a headline beat. It is one big word composited behind the subject (matte occlusion), with a designed entrance and exit. It is scarce and earned, not the default.

**The rail carries most of the text; embed is the scarce, earned peak** — ≤1 per beat, never two adjacent/co-visible, spaced ≥ a beat apart. A short clip → usually one embed; a long explainer → ~one per section. Embedding every word is the common mistake.

This is the **Standard** mode shape (rail = the verbatim lower-third; embed = the climax composited behind the subject). **Cinematic** mode drops the rail and makes everything embed-style — use it only for pure-cinematic asks, never for explainer / voiceover where the words must read.

### Rail-first, embed-scarce (the load-bearing rules)

Quoted from the `embedded-captions` non-negotiables:

- **Rail-first for talking-head / explainer.** Don't embed the whole transcript — most text is the rail; embed only peaks. Embedding everything is the default mistake. - **Embed is scarce + spaced.** ≤1 embed per sentence/beat, never two adjacent or co-visible, ≥ a beat apart, at most one `apex`. climax = per-beat peak, **not** "the single payoff of the entire clip."

## The overlay law — captions are NOT a reserved band

In a generated launch composition, when captions are enabled, finalize composites a **small, minimal word-by-word caption line** as an overlay layer ON TOP of the whole film (a single text line, bottom-centered, roughly the bottom ~5-8% of canvas height). It is an overlay, not a reserved zone (verbatim from constraint #13 of the product-launch-video scene agent):

- **Center the composition on the TRUE vertical center — y = H / 2** (landscape 540, portrait 960). Do not shift content up to "make room" for captions; a composition centered at 0.42 × H with a dead lower band is the bug, not the fix. - Content may extend to the canvas bottom. Full-bleed subjects, rails, and backgrounds all welcome. - **One soft courtesy rule:** avoid parking _critical small readable text_ (a URL line, a legal line, a sub-caption) exactly in the bottom ~80px center span where the caption line sits — the overlay would fight it. Large imagery / cards / ambient content under the captions is fine; the caption skin is designed to read over content. - There is no machine keep-out gate (the old `captions.mjs keepout` check is retired). Finalize snapshot QA judges caption-over-content legibility visually.

**When captions are disabled:** identical positioning freedom — the overlay simply doesn't exist.

## Why these two rules are one doctrine

The model says the rail rides **in front** and an embed is a rare word composited **behind the subject** — both are layers added to footage that ships untouched. The overlay law says the caption line is a layer composited **on top** of the whole film, not a band carved out of the layout. So in both the captioning pipeline and the launch-video pipeline, captions are an overlay you add, not a zone you reserve:

- Keep the full frame; center on true center; let content run to the edges. - Make the rail (or the small overlay caption line) carry