fix: resolve media detail from sessions when lifetime summary is absent

- Change `getMediaDetail` JOIN to LEFT JOIN on `imm_lifetime_media` and fall back to aggregated session metrics when no lifetime row exists
- Add filter `AND (lm.video_id IS NOT NULL OR s.session_id IS NOT NULL)` to keep results valid
- Add regression test covering the session-visible / media-detail-missing mismatch

backlog/tasks/task-346 - Fix-stats-session-detail-when-recent-media-is-missing.md

@@ -0,0 +1,57 @@
+---
+id: TASK-346
+title: Fix stats session detail when recent media is missing
+status: Done
+assignee:
+  - Codex
+created_date: '2026-05-12 06:41'
+updated_date: '2026-05-12 06:44'
+labels:
+  - bug
+  - stats
+dependencies: []
+priority: high
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Stats overview can show a completed session, but clicking it opens a detail view that says "Media not found". The details view should resolve the session/media consistently for recently completed local playback so users can inspect session cards, words, timeline, and media stats after a video finishes.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [x] #1 A completed session listed on the stats overview opens a usable details view instead of "Media not found" when its media is still present in stats data.
+- [x] #2 Regression coverage reproduces the overview-to-detail lookup mismatch and verifies the corrected behavior.
+- [x] #3 Relevant stats/detail documentation is updated if behavior or APIs change.
+<!-- AC:END -->
+
+## Implementation Plan
+
+<!-- SECTION:PLAN:BEGIN -->
+1. Add a focused regression test in `src/core/services/immersion-tracker/__tests__/query.test.ts` covering a video/session visible from session summaries before `imm_lifetime_media` exists.
+2. Update `getMediaDetail` in `src/core/services/immersion-tracker/query-library.ts` so detail rows can resolve from `imm_videos` plus session metrics when lifetime summary is absent.
+3. Run the focused query test lane and update task notes/acceptance criteria.
+<!-- SECTION:PLAN:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+Implemented root-cause fix in `getMediaDetail`: media detail now resolves from `imm_videos` plus session metrics when `imm_lifetime_media` is not populated yet, while still preferring lifetime summary totals when available. Added regression test for session-visible/media-detail-missing mismatch. No docs update required because the API shape is unchanged; added changelog fragment `changes/346-stats-session-detail.md`. Verification: `bun test src/core/services/immersion-tracker/__tests__/query.test.ts`, `bun run typecheck`, `bun run format:check:src`, `bun run test:fast`, `bun run changelog:lint`.
+<!-- SECTION:NOTES:END -->
+
+## Final Summary
+
+<!-- SECTION:FINAL_SUMMARY:BEGIN -->
+Summary:
+- Fixed stats media detail lookup so sessions visible in overview can open detail even before lifetime media summaries exist.
+- Preserved lifetime-summary totals when available and added a regression test for the missing-lifetime case.
+- Added `changes/346-stats-session-detail.md` for the user-visible fix.
+
+Tests:
+- `bun test src/core/services/immersion-tracker/__tests__/query.test.ts`
+- `bun run typecheck`
+- `bun run format:check:src`
+- `bun run test:fast`
+- `bun run changelog:lint`
+<!-- SECTION:FINAL_SUMMARY:END -->

changes/346-stats-session-detail.md

@@ -0,0 +1,4 @@
+type: fixed
+area: stats
+
+- Fixed recent session detail pages showing "Media not found" before lifetime media summaries are available.

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

@@ -3050,6 +3050,53 @@ test('anime and media detail prefer lifetime totals over partial retained sessio
   }
 });
 
+test('media detail resolves retained sessions before lifetime summary exists', () => {
+  const dbPath = makeDbPath();
+  const db = new Database(dbPath);
+
+  try {
+    ensureSchema(db);
+
+    const videoId = getOrCreateVideoRecord(db, 'local:/tmp/recent-session.mkv', {
+      canonicalTitle: 'Recent Session Episode',
+      sourcePath: '/tmp/recent-session.mkv',
+      sourceUrl: null,
+      sourceType: SOURCE_TYPE_LOCAL,
+    });
+    const startedAtMs = 1_700_000_000_000;
+    const { sessionId } = startSessionRecord(db, videoId, startedAtMs);
+    db.prepare(
+      `
+      UPDATE imm_sessions
+      SET ended_at_ms = ?, status = 2, active_watched_ms = ?, lines_seen = ?, tokens_seen = ?, cards_mined = ?
+      WHERE session_id = ?
+      `,
+    ).run(startedAtMs + 600_000, 600_000, 100, 990, 1, sessionId);
+
+    assert.equal(getSessionSummaries(db, 1)[0]?.videoId, videoId);
+    assert.equal(
+      (
+        db
+          .prepare('SELECT COUNT(*) AS total FROM imm_lifetime_media WHERE video_id = ?')
+          .get(videoId) as { total: number }
+      ).total,
+      0,
+    );
+
+    const detail = getMediaDetail(db, videoId);
+    assert.ok(detail);
+    assert.equal(detail.canonicalTitle, 'Recent Session Episode');
+    assert.equal(detail.totalSessions, 1);
+    assert.equal(detail.totalActiveMs, 600_000);
+    assert.equal(detail.totalLinesSeen, 100);
+    assert.equal(detail.totalTokensSeen, 990);
+    assert.equal(detail.totalCards, 1);
+  } finally {
+    db.close();
+    cleanupDbPath(dbPath);
+  }
+});
+
 test('media library and detail queries read lifetime totals', () => {
   const dbPath = makeDbPath();
   const db = new Database(dbPath);

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

@@ -251,11 +251,26 @@ export function getMediaDetail(db: DatabaseSync, videoId: number): MediaDetailRo
       v.video_id AS videoId,
       v.canonical_title AS canonicalTitle,
       v.anime_id AS animeId,
-      COALESCE(lm.total_sessions, 0) AS totalSessions,
-      COALESCE(lm.total_active_ms, 0) AS totalActiveMs,
-      COALESCE(lm.total_cards, 0) AS totalCards,
-      COALESCE(lm.total_tokens_seen, 0) AS totalTokensSeen,
-      COALESCE(lm.total_lines_seen, 0) AS totalLinesSeen,
+      CASE
+        WHEN lm.video_id IS NOT NULL THEN COALESCE(lm.total_sessions, 0)
+        ELSE COUNT(DISTINCT s.session_id)
+      END AS totalSessions,
+      CASE
+        WHEN lm.video_id IS NOT NULL THEN COALESCE(lm.total_active_ms, 0)
+        ELSE COALESCE(SUM(COALESCE(asm.activeWatchedMs, s.active_watched_ms, 0)), 0)
+      END AS totalActiveMs,
+      CASE
+        WHEN lm.video_id IS NOT NULL THEN COALESCE(lm.total_cards, 0)
+        ELSE COALESCE(SUM(COALESCE(asm.cardsMined, s.cards_mined, 0)), 0)
+      END AS totalCards,
+      CASE
+        WHEN lm.video_id IS NOT NULL THEN COALESCE(lm.total_tokens_seen, 0)
+        ELSE COALESCE(SUM(COALESCE(asm.tokensSeen, s.tokens_seen, 0)), 0)
+      END AS totalTokensSeen,
+      CASE
+        WHEN lm.video_id IS NOT NULL THEN COALESCE(lm.total_lines_seen, 0)
+        ELSE COALESCE(SUM(COALESCE(asm.linesSeen, s.lines_seen, 0)), 0)
+      END AS totalLinesSeen,
       COALESCE(SUM(COALESCE(asm.lookupCount, s.lookup_count, 0)), 0) AS totalLookupCount,
       COALESCE(SUM(COALESCE(asm.lookupHits, s.lookup_hits, 0)), 0) AS totalLookupHits,
       COALESCE(SUM(COALESCE(asm.yomitanLookupCount, s.yomitan_lookup_count, 0)), 0) AS totalYomitanLookupCount,
@@ -271,11 +286,12 @@ export function getMediaDetail(db: DatabaseSync, videoId: number): MediaDetailRo
       yv.uploader_url AS uploaderUrl,
       yv.description AS description
     FROM imm_videos v
-    JOIN imm_lifetime_media lm ON lm.video_id = v.video_id
+    LEFT JOIN imm_lifetime_media lm ON lm.video_id = v.video_id
     LEFT JOIN imm_youtube_videos yv ON yv.video_id = v.video_id
     LEFT JOIN imm_sessions s ON s.video_id = v.video_id
     LEFT JOIN active_session_metrics asm ON asm.sessionId = s.session_id
     WHERE v.video_id = ?
+      AND (lm.video_id IS NOT NULL OR s.session_id IS NOT NULL)
     GROUP BY v.video_id
   `,
     )