feat(subtitles): add line-break display toggle and narrow-space normalization

backlog/tasks/task-90 - Normalize-narrow-Unicode-whitespace-in-tokenizer-input.md

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+---
+id: TASK-90
+title: Normalize narrow Unicode whitespace in tokenizer input
+status: Done
+assignee: []
+created_date: '2026-02-20 06:17'
+updated_date: '2026-02-20 06:20'
+labels: []
+dependencies: []
+priority: medium
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Fix tokenizer behavior where subtitle lines containing narrow/invisible Unicode spacing between Japanese segments can be split/grouped incorrectly compared with normal space handling.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [x] #1 A regression test reproduces the subtitle sample containing narrow/invisible Unicode spacing and fails before fix.
+- [x] #2 Tokenizer normalization treats narrow/invisible spacing variants consistently with regular spacing for grouping/highlight behavior.
+- [x] #3 Existing tokenizer tests still pass.
+<!-- AC:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+Linked from subagent session `codex-narrow-space-tokenizer-20260220T061716Z-p97s`.
+
+Added `src/subtitle/stages/normalize.test.ts` regression for `\u200B` separator in subtitle sample and updated `normalizeTokenizerInput` to map `U+200B/U+2060/U+FEFF` to regular spaces before whitespace collapsing.
+
+Validation:
+- `bun run build && node --test dist/subtitle/stages/normalize.test.js`
+- `node --test dist/core/services/tokenizer.test.js`
+<!-- SECTION:NOTES:END -->

backlog/tasks/task-91 - Add-config-toggle-to-preserve-visible-overlay-subtitle-line-breaks.md

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+---
+id: TASK-91
+title: Add config toggle to preserve visible overlay subtitle line breaks
+status: Done
+assignee: []
+created_date: '2026-02-20 06:35'
+updated_date: '2026-02-20 06:42'
+labels: []
+dependencies: []
+priority: medium
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Add a `subtitleStyle` config option that keeps visible-overlay subtitle line breaks (newline/carriage-return normalized to line breaks) instead of flattening them to spaces. Default should preserve current behavior for consistency with texthooker.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [x] #1 New config option exists with default disabled and validation/docs coverage.
+- [x] #2 When enabled, visible overlay preserves subtitle line breaks while rendering tokenized subtitles.
+- [x] #3 When disabled, current rendering behavior remains unchanged.
+- [x] #4 Relevant config + renderer tests pass.
+<!-- AC:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+Added `subtitleStyle.preserveLineBreaks` (default `false`) to types/default config/registry/config validation and docs/example configs.
+
+Renderer now supports line-break-preserving token output via `alignTokensToSourceText` in `src/renderer/subtitle-render.ts`, which inserts source-text separators (including `\n`) between token spans when enabled.
+
+Validation:
+- `bun run build && node --test dist/config/config.test.js dist/renderer/subtitle-render.test.js`
+<!-- SECTION:NOTES:END -->