Suppress subtitle annotations for grammar fragments

- Hide annotation metadata for auxiliary inflection and ja-nai endings
- Preserve lexical `くれる` forms and add regression coverage

backlog/tasks/task-312 - Suppress-ja-nai-explanatory-ending-subtitle-annotations.md

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+---
+id: TASK-312
+title: Suppress ja-nai explanatory ending subtitle annotations
+status: Done
+assignee: []
+created_date: '2026-05-02 09:55'
+updated_date: '2026-05-02 10:03'
+labels:
+  - tokenizer
+  - annotations
+  - bug
+dependencies: []
+priority: medium
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Suppress subtitle annotation styling for grammar-only explanatory endings like `じゃない` and `じゃないですか` while preserving nearby lexical content annotations.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [x] #1 `じゃない` and `じゃないですか`-style endings render as plain hoverable subtitle tokens.
+- [x] #2 The reported phrase `みたいなのあるじゃないですか` does not annotate `じゃない`/`じゃないですか` as lexical/frequency content.
+- [x] #3 Regression tests cover unit filter behavior and tokenizer integration without suppressing lexical content tokens.
+- [x] #4 Standalone polite copula endings such as `です` / `ですよ` render as plain hoverable subtitle tokens even if POS metadata is missing or too lexical.
+<!-- AC:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+Added failing coverage first for `じゃない` / `じゃないですか` and `ですよ` leaking annotation metadata when POS metadata is missing or too lexical. Implemented term-family exclusions in the shared subtitle annotation filter for the `じゃない` explanatory family and polite copula suffix endings (`ですか`, `ですね`, `ですよ`, `ですな`). Kept bare `です` term-only behavior unchanged to preserve existing no-POS frequency tests; POS-tagged `です` is already stripped by the grammar POS exclusion path.
+<!-- SECTION:NOTES:END -->
+
+## Final Summary
+
+<!-- SECTION:FINAL_SUMMARY:BEGIN -->
+Suppressed subtitle annotation metadata for grammar-only endings like `じゃないですか` and `ですよ`, while preserving nearby lexical content annotations. Added unit and tokenizer regression coverage for the reported `みたいなのあるじゃないですか` and `感じですよ` shapes, plus changelog fragment `changes/312-grammar-ending-annotation-filter.md`.
+
+Validation: `bun test src/core/services/tokenizer/annotation-stage.test.ts`; `bun test src/core/services/tokenizer.test.ts`; `bun run typecheck`; `bun run changelog:lint`; `git diff --check`.
+<!-- SECTION:FINAL_SUMMARY:END -->