Eliminate the smartSentenceSplitting configuration flag from application state, UI, and all TTS and audiobook adapter logic. Consolidate TTS segment planning to always include context units, streamlining code and reducing conditional branches. Update tests and type definitions to reflect the removal of this feature toggle.
Move daily quota exceeded problem response logic to a dedicated utility in `lib/server/rate-limit/problem-response`. Refactor API routes to use the new builder and remove duplicated formatting code. Update all relevant imports for consistency. This improves maintainability and ensures uniform error responses across TTS endpoints.
Implement strict validation for EPUB TTS segment locators, requiring stable spine coordinates (`spineHref`, `spineIndex`, `charOffset`) and rejecting legacy CFI-only locators. Introduce `segmentKey` as a normalized identity derived from segment text, used for robust merging and deduplication of synthesized and persisted segments. Update database schemas, API routes, and manifest logic to support the new locator format and segmentKey. Add helpers for locator resolution and segmentKey construction, with comprehensive unit tests for identity, normalization, and manifest grouping.
BREAKING CHANGE: Persisted EPUB TTS segment locators must now include stable spine coordinates; legacy CFI-only locators are no longer accepted. Consumers must handle the new `segmentKey` field for segment identity and merging.
