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

backlog/tasks/task-110 - Split-overlay-into-top-secondary-bar-and-bottom-primary-region.md

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+---
+id: TASK-110
+title: Split overlay into top secondary bar and bottom primary region
+status: Done
+assignee:
+  - codex
+created_date: '2026-02-23 02:16'
+updated_date: '2026-02-23 02:29'
+labels:
+  - overlay
+  - subtitle
+  - ux
+dependencies: []
+priority: high
+ordinal: 110000
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+
+Implement a 3-window overlay layout:
+
+- Dedicated secondary subtitle window anchored to top of mpv bounds (max 20% of height).
+- Visible overlay window constrained to remaining lower region.
+- Invisible overlay window constrained to remaining lower region.
+
+Secondary subtitle bar must stay independently anchored while visible/invisible overlays swap.
+
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+
+<!-- AC:BEGIN -->
+
+- [x] #1 Runtime creates/manages a third overlay window dedicated to secondary subtitles.
+- [x] #2 Secondary window stays anchored to top region capped at 20% of tracked mpv bounds.
+- [x] #3 Visible and invisible overlay windows are constrained to remaining lower region.
+- [x] #4 Secondary subtitle rendering/mode updates reach dedicated top window without duplicate top bars in primary windows.
+- [x] #5 Focused runtime/core tests cover geometry split + window wiring regressions.
+
+<!-- AC:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+
+- Added new `secondary` overlay window kind and runtime factory wiring, plus manager ownership (`get/setSecondaryWindow`) and bounds setter.
+- Added geometry splitter `splitOverlayGeometryForSecondaryBar` (20% top secondary, 80% bottom primary), integrated into `updateVisibleOverlayBounds` / `updateInvisibleOverlayBounds` flow.
+- Main runtime now creates secondary window alongside primary overlays and syncs secondary window visibility with `secondarySubMode`.
+- Renderer now recognizes `layer=secondary`; secondary bar is hidden on primary layers, and primary subtitle/modals are hidden on secondary layer.
+- Secondary layer no longer reports overlay content measurements to avoid invalid payloads.
+- 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`
+
+<!-- SECTION:NOTES:END -->