fix: unique index words.titel_en als partial index + robuster Upsert ohne ON CONFLICT

- Migration: partiell WHERE IS NOT NULL, dedup vorher, kein silent-catch
- Route: INSERT mit .catch(23505) → UPDATE statt ON CONFLICT (partial index inkompatibel)

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

src/db-migrate.js

@@ -861,8 +861,20 @@ async function migrate() {
   await query(`ALTER TABLE words ADD CONSTRAINT words_level_check CHECK (level IN ('A1', 'A2', 'B1'))`).catch(() => {});
 
   // Unique-Index auf titel_en — Voraussetzung für ON CONFLICT im CSV-Import.
-  // Falls bestehende Duplikate den Index verhindern, muss erst bereinigt werden.
-  await query(`CREATE UNIQUE INDEX IF NOT EXISTS words_titel_en_key ON words (titel_en)`).catch(() => {});
+  // Partiell (WHERE IS NOT NULL) damit bestehende NULL-Zeilen den Index nicht blockieren.
+  // Doppelte non-null titel_en erst bereinigen, dann Index anlegen.
+  await query(`
+    DELETE FROM words w
+    USING (
+      SELECT titel_en, MAX(created_at) AS keep_at
+        FROM words WHERE titel_en IS NOT NULL
+        GROUP BY titel_en HAVING COUNT(*) > 1
+    ) dup
+    WHERE w.titel_en = dup.titel_en AND w.created_at < dup.keep_at
+  `).catch(() => {});
+  await query(
+    `CREATE UNIQUE INDEX IF NOT EXISTS words_titel_en_key ON words (titel_en) WHERE titel_en IS NOT NULL`
+  );
 
   // enrich_batches — Status-Tracking für Wort-Anreicherungs-Batches (analog category_batches)
   await query(`

src/routes/words.js

@@ -77,17 +77,26 @@ router.post('/', async (req, res, next) => {
     // Auto: alle 3 Sprachen direkt mitgeliefert + kein expliziter Status → 'translated'
     const allLangs = titel_de && titel_en && titel_sv;
     const effectiveStatus = status || (allLangs ? 'translated' : 'requested');
-    const result = await query(
+    // Upsert: neu anlegen oder bei doppeltem titel_en nur conc_m aktualisieren
+    let result = await query(
       `INSERT INTO words (titel_de, titel_en, titel_sv, difficulty_level, status, conc_m, requested_at)
-       VALUES ($1, $2, $3, $4, $5, $6, NOW())
-       ON CONFLICT (titel_en) DO UPDATE SET conc_m = EXCLUDED.conc_m
-       RETURNING *, (xmax = 0) AS is_insert`,
+       VALUES ($1, $2, $3, $4, $5, $6, NOW()) RETURNING *, true AS is_insert`,
       [titel_de || null, titel_en || null, titel_sv || null,
        difficulty_level || null, effectiveStatus, conc_m ?? null]
-    );
+    ).catch(async err => {
+      if (err.code === '23505' && titel_en) {
+        // Duplikat auf titel_en → conc_m aktualisieren und bestehende Zeile zurückgeben
+        const upd = await query(
+          `UPDATE words SET conc_m = $1 WHERE titel_en = $2 RETURNING *, false AS is_insert`,
+          [conc_m ?? null, titel_en]
+        );
+        return upd;
+      }
+      throw err;
+    });
     const row = result.rows[0];
-    const { is_insert: _, ...word } = row;
-    res.status(row.is_insert ? 201 : 200).json({ ...word, picture_ids: [], category_ids: [] });
+    const { is_insert, ...word } = row;
+    res.status(is_insert ? 201 : 200).json({ ...word, picture_ids: [], category_ids: [] });
   } catch (err) { next(err); }
 });