feat(overlay): split secondary subtitles into dedicated top window

docs/subagents/agents/codex-overlay-three-window-layout-20260223T021606Z-9z2t.md

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+# Agent Session: codex-overlay-three-window-layout-20260223T021606Z-9z2t
+
+- alias: `codex-overlay-three-window-layout`
+- started_utc: `2026-02-23T02:16:06Z`
+- status: `handoff`
+- mission: `Implement top-anchored secondary subtitle overlay window (20%) plus swappable primary overlay region (80%).`
+- linked_backlog: `TASK-110`
+
+## Intent
+
+- Convert overlay runtime from 2 fullscreen windows to 3 windows:
+  - `secondary` window anchored top (max 20% height).
+  - `visible` / `invisible` windows constrained to remaining 80%.
+- Keep secondary subtitle bar independent from visible/invisible swapping.
+
+## Planned Files
+
+- `src/core/services/overlay-window.ts`
+- `src/core/services/overlay-runtime-init.ts`
+- `src/core/services/overlay-manager.ts`
+- `src/main.ts`
+- `src/preload.ts`
+- `src/types.ts`
+- `src/renderer/utils/platform.ts`
+- `src/renderer/renderer.ts`
+- `src/renderer/style.css`
+- `src/main/runtime/overlay-window-factory*.ts`
+- `src/main/runtime/overlay-window-runtime-handlers*.ts`
+- `src/main/runtime/overlay-runtime-options*.ts`
+- focused tests under `src/main/runtime/*` + `src/core/services/*`
+
+## Assumptions
+
+- Secondary bar window should remain independently present while visible/invisible overlays toggle.
+- Top bar height fixed at 20% of tracked mpv bounds (clamped to valid integer px).
+- Existing secondary mode semantics (`hidden`/`visible`/`hover`) remain; hover behavior stays functional.
+
+## Phase Log
+
+- `2026-02-23T02:16:06Z` plan: read overlay/runtime wiring, implement secondary window + geometry split, run focused tests.
+- `2026-02-23T02:24:10Z` implementation: added `secondary` overlay window kind/wiring, overlay-manager secondary window ownership, and geometry split helper (`top 20%` secondary + `bottom 80%` primary).
+- `2026-02-23T02:27:40Z` renderer updates: added `secondary` layer detection, disabled measurement reports for secondary layer, and CSS layer split (secondary hidden in primary layers; subtitle/modals hidden in secondary layer).
+- `2026-02-23T02:29:51Z` validation: `bun run tsc --noEmit`; `bun test src/main/runtime/overlay-window-factory.test.ts src/main/runtime/overlay-window-factory-main-deps.test.ts src/main/runtime/overlay-window-runtime-handlers.test.ts src/renderer/error-recovery.test.ts src/core/services/overlay-window.test.ts`; `bun run build`; `node --test dist/core/services/overlay-manager.test.js`.
+
+## Files Touched
+
+- `src/main.ts`
+- `src/core/services/overlay-window.ts`
+- `src/core/services/overlay-window-geometry.ts`
+- `src/core/services/overlay-window.test.ts`
+- `src/core/services/overlay-manager.ts`
+- `src/core/services/overlay-manager.test.ts`
+- `src/main/runtime/overlay-window-factory.ts`
+- `src/main/runtime/overlay-window-factory-main-deps.ts`
+- `src/main/runtime/overlay-window-runtime-handlers.ts`
+- `src/main/runtime/overlay-window-factory.test.ts`
+- `src/main/runtime/overlay-window-factory-main-deps.test.ts`
+- `src/main/runtime/overlay-window-runtime-handlers.test.ts`
+- `src/preload.ts`
+- `src/types.ts`
+- `src/renderer/utils/platform.ts`
+- `src/renderer/overlay-content-measurement.ts`
+- `src/renderer/error-recovery.ts`
+- `src/renderer/style.css`
+- `backlog/tasks/task-110 - Split-overlay-into-top-secondary-bar-and-bottom-primary-region.md`
+
+## Handoff
+
+- Implemented requested 3-window behavior:
+  - dedicated top secondary overlay window anchored by mpv geometry split,
+  - visible/invisible overlays constrained to lower region.
+- Secondary mode state now syncs window visibility (`hidden` hides window; non-hidden shows + interactive).
+- Remaining caution: source-level `overlay-manager.test.ts` still requires dist/node path (Bun ESM + electron named export limitation), but dist test lane passes.