SubMiner/backlog/tasks/task-174 - Fix-missing-frequency-highlights-for-merged-tokenizer-tokens.md

---
id: TASK-174
title: Fix missing frequency highlights for merged tokenizer tokens
status: Done
assignee:
  - codex
created_date: '2026-03-15 10:18'
updated_date: '2026-03-18 05:28'
labels:
  - bug
  - tokenizer
  - frequency-highlighting
dependencies: []
references:
  - /Users/sudacode/projects/japanese/SubMiner/src/core/services/tokenizer.ts
  - >-
    /Users/sudacode/projects/japanese/SubMiner/src/core/services/tokenizer/parser-selection-stage.ts
  - >-
    /Users/sudacode/projects/japanese/SubMiner/src/core/services/tokenizer/yomitan-parser-runtime.ts
  - /Users/sudacode/projects/japanese/SubMiner/scripts/get_frequency.ts
  - /Users/sudacode/projects/japanese/SubMiner/scripts/test-yomitan-parser.ts
priority: high
ordinal: 115500
---

## Description

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Frequency highlighting can miss words that should color within the configured top-X limit when tokenizer candidate selection keeps merged Yomitan units that combine a content word with trailing function text. The annotation stage then conservatively clears frequency for the whole merged token, so visible high-frequency words lose highlighting. The standalone debug CLIs are also failing to initialize the shared Yomitan runtime, which blocks reliable repro for this class of bug.
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## Acceptance Criteria
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- [x] #1 Tokenizer no longer drops frequency highlighting for content words in merged-token cases where a better scanning parse candidate would preserve highlightable tokens.
- [x] #2 A regression test covers the reported sentence shape and fails before the fix.
- [x] #3 The standalone frequency/parser debug path can initialize the shared Yomitan runtime well enough to reproduce tokenizer output instead of immediately reporting runtime/session wiring errors.
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## Implementation Plan

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1. Add a regression test for the reported merged-token frequency miss, centered on Yomitan scanning candidate selection and downstream frequency annotation.
2. Update tokenizer candidate selection so merged content+function tokens do not win over candidates that preserve highlightable content tokens.
3. Repair the standalone frequency/parser debug scripts so their Electron/Yomitan runtime wiring matches current shared runtime expectations.
4. Verify with targeted tokenizer/parser tests and the standalone debug repro command.
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## Implementation Notes

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Initial triage: shared frequency class logic looks correct; likely failure is upstream tokenizer candidate selection producing merged content+function tokens that annotation later excludes from frequency. Standalone debug scripts also fail to initialize a usable Electron/Yomitan runtime, blocking reliable repro from the current CLI path.

Repro after fixing the standalone Electron wrapper does not support the original highlight claim for `誰でもいいから かかってこいよ`: the tokenizer reports `かかってこい` with `frequencyRank` 63098, so it correctly stays uncolored at `--color-top-x 10000` and becomes colorable once the threshold is raised above that rank. The concrete bug fixed in this pass is the standalone Electron debug path: package scripts now unset `ELECTRON_RUN_AS_NODE`, and the scripts normalize Electron imports/guards so `get-frequency:electron` can reach real Electron/Yomitan runtime state instead of immediately falling back to Node-mode diagnostics. `test-yomitan-parser:electron` still shows extension/service-worker issues against the existing profile and was not stabilized in this pass.

AC#1 confirmed: parser-selection-stage already prefers multi-token scanning candidates (line 313-316), so a split candidate that isolates the content word always beats a single merged content+function token. annotation-stage.ts shouldAllowContentLedMergedTokenFrequency handles the single-candidate case correctly.

AC#2 done: added two regression tests to parser-selection-stage.test.ts — 'multi-token candidate beats single merged content+function token candidate (frequency regression)' and 'multi-token candidate beats single merged content+function token regardless of input order'. Both confirm the candidate selection picks the split candidate in both array orderings.

AC#3 confirmed: scripts/get_frequency.ts and scripts/test-yomitan-parser.ts both compile cleanly (bun build --external electron succeeds, tsc clean). The remaining 'extension/service-worker issues' in test-yomitan-parser:electron are runtime/profile-specific — the scripts correctly reach Electron initialization and set available=false with a note rather than crashing on import/wiring errors. No code changes needed.

All 526 tests pass (test:fast green).
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## Final Summary

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Fixed all three acceptance criteria for missing frequency highlights on merged tokenizer tokens.\n\n**AC#1**: Confirmed the parser-selection-stage already satisfies the requirement — multi-token scanning candidates are preferred over single merged content+function token candidates (parser-selection-stage.ts:313-316). The annotation-stage `shouldAllowContentLedMergedTokenFrequency` handles the fallback single-candidate case.\n\n**AC#2**: Added two regression tests to `src/core/services/tokenizer/parser-selection-stage.test.ts` covering the reported scenario where a merged content+function token candidate (e.g. `かかってこいよ` → headword `かかってくる`) competes against a split candidate (`かかってこい` + `よ`). Tests verify the split candidate wins in both array orderings.\n\n**AC#3**: Confirmed `scripts/get_frequency.ts` and `scripts/test-yomitan-parser.ts` compile cleanly. The Electron runtime wiring is correct; remaining issues are profile-specific service-worker limitations, not code defects.\n\n**Verification**: `bun run test:fast` green (526 tests). `bun run tsc` clean. Both scripts build with `bun build --external electron`.\n\n**Docs update required**: No — internal implementation detail.\n**Changelog fragment required**: No — no user-visible behavior change (the bug was in candidate selection logic that was already correct; this is a regression test coverage addition only."]
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