perf(tokenizer): skip character-name lookups where no name can start

The greedy name pre-pass asked the Yomitan backend at every Japanese
position, because a character name can begin mid-token. With the character
dictionary enabled that roughly doubled the round trips per line (measured
10 -> 21 on a 23-char line).

SubMiner generates the character dictionary, so the cached snapshots already
list every form a character entry can be matched by (term and reading). Those
forms are installed into the scan runtime once per media and the pre-pass now
probes only positions where one of them starts, compared after kana
normalization so a katakana name still matches a hiragana reading form. The
overhead drops to zero (21 -> 10, the same as with the dictionary disabled).

Fail-safe: with no candidate list (no media id, no cached snapshot, failed
install) the pre-pass keeps its exhaustive behavior, so stale character data
costs speed rather than a missing name. Halfwidth katakana positions bypass
the filter since kana normalization does not fold them.

The candidate lookup is consulted per subtitle line, so it caches its snapshot
directory signature for 5s; dictionary writes still call invalidate().

src/core/services/tokenizer/yomitan-parser-runtime.ts

@@ -5,6 +5,7 @@ import * as path from 'path';
 import { selectYomitanParseTokens } from './parser-selection-stage';
 import {
   buildYomitanScanCallScript,
+  buildYomitanScanNameCandidatesScript,
   CHARACTER_DICTIONARY_TITLE_PREFIX,
   YOMITAN_SCAN_RUNTIME_INSTALL_SCRIPT,
   YOMITAN_SCAN_RUNTIME_MISSING_SENTINEL,
@@ -832,6 +833,40 @@ async function serveDictionaryZipOnce<T>(
 
 async function installYomitanScanRuntime(parserWindow: BrowserWindow): Promise<void> {
   await parserWindow.webContents.executeJavaScript(YOMITAN_SCAN_RUNTIME_INSTALL_SCRIPT, true);
+  // A fresh runtime has no candidate list; force the next scan to reinstall it.
+  yomitanScanNameCandidateKeyByWindow.delete(parserWindow);
+}
+
+// Key of the character-name candidate list currently installed in each parser
+// window, so an unchanged list costs nothing per line.
+const yomitanScanNameCandidateKeyByWindow = new WeakMap<BrowserWindow, string>();
+
+async function ensureYomitanScanNameCandidates(
+  parserWindow: BrowserWindow,
+  nameCandidates: { key: string; forms: string[] } | null,
+  logger: LoggerLike,
+): Promise<void> {
+  const installedKey = yomitanScanNameCandidateKeyByWindow.get(parserWindow);
+  const nextKey = nameCandidates?.key ?? '';
+  if (installedKey === nextKey) {
+    return;
+  }
+
+  try {
+    await parserWindow.webContents.executeJavaScript(
+      buildYomitanScanNameCandidatesScript(nameCandidates),
+      true,
+    );
+    yomitanScanNameCandidateKeyByWindow.set(parserWindow, nextKey);
+  } catch (err) {
+    // The scan falls back to checking every position when the list is absent,
+    // so a failed install costs speed, never a missed name.
+    logger.warn?.(
+      'Failed to install Yomitan character-name scan candidates:',
+      (err as Error).message,
+    );
+    yomitanScanNameCandidateKeyByWindow.delete(parserWindow);
+  }
 }
 
 export async function requestYomitanParseResults(
@@ -949,6 +984,7 @@ export async function requestYomitanScanTokens(
   options?: {
     includeNameMatchMetadata?: boolean;
     currentCharacterDictionaryMediaId?: number | null;
+    nameCandidates?: { key: string; forms: string[] } | null;
   },
 ): Promise<YomitanScanToken[] | null> {
   const yomitanExt = deps.getYomitanExt();
@@ -972,6 +1008,12 @@ export async function requestYomitanScanTokens(
       name.startsWith(CHARACTER_DICTIONARY_TITLE_PREFIX),
     );
 
+  // Candidate name forms let the in-page pre-pass skip positions where no
+  // character name can start. Installed only when it changes (per media), so
+  // the per-line call stays a single tiny script.
+  const nameCandidates = greedyNameScanEnabled ? (options?.nameCandidates ?? null) : null;
+  await ensureYomitanScanNameCandidates(parserWindow, nameCandidates, logger);
+
   const callScript = buildYomitanScanCallScript({
     text,
     profileIndex,
@@ -987,14 +1029,17 @@ export async function requestYomitanScanTokens(
     dictionaryPriorityByName: metadata?.dictionaryPriorityByName ?? {},
     dictionaryFrequencyModeByName: metadata?.dictionaryFrequencyModeByName ?? {},
     cacheEpoch: getYomitanScanCacheEpoch(parserWindow),
+    nameCandidateKey: nameCandidates?.key ?? null,
   });
 
   try {
     let rawResult = await parserWindow.webContents.executeJavaScript(callScript, true);
     if (rawResult === YOMITAN_SCAN_RUNTIME_MISSING_SENTINEL) {
       // First request for this window, or the page reloaded and dropped the
-      // installed runtime: install and retry once.
+      // installed runtime: install and retry once. The candidate list lives in
+      // the same page state, so it has to be reinstalled alongside it.
       await installYomitanScanRuntime(parserWindow);
+      await ensureYomitanScanNameCandidates(parserWindow, nameCandidates, logger);
       rawResult = await parserWindow.webContents.executeJavaScript(callScript, true);
     }
     if (isScanTokenArray(rawResult)) {