fix(immersion): use localtime rollup keys and guard sentence search limi

- Remove UTC-based UNION branch from getRollupGroupsForSessions; keep only localtime rollup
- Add resolveSentenceSearchLimit to clamp/sanitize infinity and negative limit values
- Switch onMiningImageEvent from queued to latest-value IPC listener (drop stale frames)
- Add regression tests for rollup key locality and sentence search limit edge cases

src/core/services/immersion-tracker/__tests__/maintenance-source.test.ts

@@ -0,0 +1,18 @@
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import path from 'node:path';
+import test from 'node:test';
+
+test('getRollupGroupsForSessions uses only localtime rollup keys', () => {
+  const source = fs.readFileSync(
+    path.join(process.cwd(), 'src/core/services/immersion-tracker/maintenance.ts'),
+    'utf8',
+  );
+  const start = source.indexOf('export function getRollupGroupsForSessions');
+  const end = source.indexOf('export function refreshRollupsForGroupsInTransaction');
+  const functionSource = source.slice(start, end);
+
+  assert.match(functionSource, /'unixepoch', 'localtime'/);
+  assert.doesNotMatch(functionSource, /UNION/);
+  assert.doesNotMatch(functionSource, /86400000/);
+});

src/core/services/immersion-tracker/__tests__/query.test.ts

@@ -39,6 +39,7 @@ import {
   upsertCoverArt,
 } from '../query.js';
 import {
+  getLocalEpochDay,
   getShiftedLocalDaySec,
   getStartOfLocalDayTimestamp,
   toDbTimestamp,
@@ -3776,6 +3777,8 @@ test('searchSubtitleSentences searches known subtitle lines and returns media co
     ]);
 
     assert.deepEqual(searchSubtitleSentences(db, 'monsters', 10), []);
+    assert.doesNotThrow(() => searchSubtitleSentences(db, '魔物', Number.POSITIVE_INFINITY));
+    assert.equal(searchSubtitleSentences(db, '魔物', -1).length, 1);
   } finally {
     db.close();
     cleanupDbPath(dbPath);
@@ -4196,8 +4199,14 @@ test('deleteSession removes zero-session media from library and trends', () => {
 
     const startedAtMs = 9_000_000;
     const endedAtMs = startedAtMs + 120_000;
-    const rollupDay = Math.floor(startedAtMs / 86_400_000);
-    const rollupMonth = 197001;
+    const rollupDay = getLocalEpochDay(db, startedAtMs);
+    const rollupMonth = (
+      db
+        .prepare(
+          "SELECT CAST(strftime('%Y%m', CAST(? AS REAL) / 1000, 'unixepoch', 'localtime') AS INTEGER) AS rollupMonth",
+        )
+        .get(startedAtMs) as { rollupMonth: number }
+    ).rollupMonth;
     const { sessionId } = startSessionRecord(db, videoId, startedAtMs);
 
     db.prepare(

src/core/services/immersion-tracker/maintenance.ts

@@ -319,16 +319,9 @@ export function getRollupGroupsForSessions(db: DatabaseSync, sessionIds: number[
           video_id
         FROM imm_sessions
         WHERE session_id IN (${placeholders})
-        UNION
-        SELECT DISTINCT
-          CAST(CAST(started_at_ms AS REAL) / 86400000 AS INTEGER) AS rollup_day,
-          CAST(strftime('%Y%m', CAST(started_at_ms AS REAL) / 1000, 'unixepoch') AS INTEGER) AS rollup_month,
-          video_id
-        FROM imm_sessions
-        WHERE session_id IN (${placeholders})
       `,
     )
-    .all(...sessionIds, ...sessionIds) as RollupGroupRow[];
+    .all(...sessionIds) as RollupGroupRow[];
 
   return rows.map((row) => ({
     rollupDay: row.rollup_day,

src/core/services/immersion-tracker/query-lexical.ts

@@ -21,6 +21,15 @@ import { nowMs } from './time';
 
 const VOCABULARY_STATS_FILTER_OVERSAMPLE_FACTOR = 4;
 const VOCABULARY_STATS_FILTER_OVERSAMPLE_MIN = 100;
+const SENTENCE_SEARCH_DEFAULT_LIMIT = 50;
+const SENTENCE_SEARCH_MAX_LIMIT = 100;
+
+function resolveSentenceSearchLimit(limit: number): number {
+  if (!Number.isFinite(limit)) return SENTENCE_SEARCH_DEFAULT_LIMIT;
+  const normalized = Math.floor(limit);
+  if (normalized <= 0) return SENTENCE_SEARCH_DEFAULT_LIMIT;
+  return Math.min(normalized, SENTENCE_SEARCH_MAX_LIMIT);
+}
 
 function splitSearchTerms(query: string): string[] {
   return query
@@ -228,10 +237,11 @@ export function getKanjiOccurrences(
 export function searchSubtitleSentences(
   db: DatabaseSync,
   query: string,
-  limit = 50,
+  limit = SENTENCE_SEARCH_DEFAULT_LIMIT,
 ): SentenceSearchResultRow[] {
   const terms = splitSearchTerms(query);
   if (terms.length === 0) return [];
+  const resolvedLimit = resolveSentenceSearchLimit(limit);
 
   const clauses: string[] = [];
   const params: string[] = [];
@@ -270,7 +280,7 @@ export function searchSubtitleSentences(
         LIMIT ?
       `,
     )
-    .all(...params, limit) as unknown as SentenceSearchResultRow[];
+    .all(...params, resolvedLimit) as unknown as SentenceSearchResultRow[];
 }
 
 export function getSessionEvents(