fix(db): atomic saveMnemonic, const normalizedLetter, updateProfileSeen guard, ?? 0 for avgScore

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/db.js

@@ -73,7 +73,8 @@ function initDb(dbPath) {
   }
 
   function updateProfileSeen(id) {
-    instance.prepare('UPDATE profiles SET last_seen = ? WHERE id = ?').run(Date.now(), id)
+    const result = instance.prepare('UPDATE profiles SET last_seen = ? WHERE id = ?').run(Date.now(), id)
+    if (result.changes === 0) console.warn(`[db] updateProfileSeen: no profile id=${id}`)
   }
 
   function createMagicToken(token, profileId, expiresAt) {
@@ -128,7 +129,7 @@ function initDb(dbPath) {
   }
 
   function recordAnswer(profileId, letter, correct) {
-    letter = letter.toUpperCase()
+    const normalizedLetter = letter.toUpperCase()
     const progress = getOrCreateProgress(profileId)
     const now = Date.now()
     const isFirstToday = !progress.last_session_at ||
@@ -156,15 +157,15 @@ function initDb(dbPath) {
     // Update letter stats
     const existing = instance
       .prepare('SELECT * FROM letter_stats WHERE profile_id = ? AND letter = ?')
-      .get(profileId, letter)
+      .get(profileId, normalizedLetter)
     if (existing) {
       instance.prepare(
         'UPDATE letter_stats SET correct = correct + ?, attempts = attempts + 1, updated_at = ? WHERE profile_id = ? AND letter = ?'
-      ).run(correct ? 1 : 0, now, profileId, letter)
+      ).run(correct ? 1 : 0, now, profileId, normalizedLetter)
     } else {
       instance.prepare(
         'INSERT INTO letter_stats (profile_id, letter, correct, attempts, updated_at) VALUES (?,?,?,1,?)'
-      ).run(profileId, letter, correct ? 1 : 0, now)
+      ).run(profileId, normalizedLetter, correct ? 1 : 0, now)
     }
 
     return instance.prepare('SELECT * FROM user_progress WHERE profile_id = ?').get(profileId)
@@ -181,17 +182,17 @@ function initDb(dbPath) {
     const now = Date.now()
     const upperLetter = letter.toUpperCase()
 
-    instance.prepare(
-      `INSERT INTO user_mnemonics (profile_id, letter, phrase, created_at) VALUES (?,?,?,?)
-       ON CONFLICT(profile_id, letter) DO UPDATE SET phrase = excluded.phrase`
+    // Try insert first — changes=1 means new row (first save), changes=0 means update path
+    const insertResult = instance.prepare(
+      'INSERT OR IGNORE INTO user_mnemonics (profile_id, letter, phrase, created_at) VALUES (?,?,?,?)'
     ).run(profileId, upperLetter, phrase, now)
 
-    // Only award 50 pts on first save — if created_at = now, it was just inserted
-    const row = instance.prepare(
-      'SELECT created_at FROM user_mnemonics WHERE profile_id = ? AND letter = ?'
-    ).get(profileId, upperLetter)
-
-    if (row.created_at === now) {
+    if (insertResult.changes === 0) {
+      // Existing mnemonic — update phrase only, no point award
+      instance.prepare('UPDATE user_mnemonics SET phrase = ? WHERE profile_id = ? AND letter = ?')
+        .run(phrase, profileId, upperLetter)
+    } else {
+      // First save — award 50 points
       getOrCreateProgress(profileId)
       instance.prepare('UPDATE user_progress SET score = score + 50, updated_at = ? WHERE profile_id = ?')
         .run(now, profileId)
@@ -218,7 +219,7 @@ function initDb(dbPath) {
 
   function getAdminStats() {
     const totalUsers = instance.prepare('SELECT COUNT(*) as c FROM profiles').get().c
-    const avgScore = instance.prepare('SELECT AVG(score) as a FROM user_progress').get().a || 0
+    const avgScore = instance.prepare('SELECT AVG(score) as a FROM user_progress').get().a ?? 0
     const mostMissed = instance.prepare(`
       SELECT letter, SUM(attempts - correct) as misses
       FROM letter_stats GROUP BY letter ORDER BY misses DESC LIMIT 5

server/tests/db.test.js

@@ -159,6 +159,17 @@ describe('mnemonics', () => {
     assert.equal(m.A, 'go WALKING')
     assert.equal(m.E, 'go')
   })
+
+  test('saveMnemonic awards 50 pts on first save, not on update', () => {
+    const p1 = db.getOrCreateProgress(profileId)
+    db.saveMnemonic(profileId, 'T', 'dash')           // first save → +50 pts
+    const p2 = db.getOrCreateProgress(profileId)
+    assert.equal(p2.score, p1.score + 50)
+
+    db.saveMnemonic(profileId, 'T', 'updated dash')   // update → no extra pts
+    const p3 = db.getOrCreateProgress(profileId)
+    assert.equal(p3.score, p2.score)
+  })
 })
 
 describe('letter stats', () => {