Phase 3: Express backend, SQLite persistence, auto-save

- server/db.ts: sql.js with migration system (hex_maps, hexes, hex_features)
- server/routes/maps.ts: CRUD for hex maps
- server/routes/hexes.ts: Bulk hex upsert, region load, sparse storage
- server/index.ts: Express 5, CORS, tile serving, SPA fallback
- src/data/api-client.ts: Frontend HTTP client for all API endpoints
- src/main.ts: Auto-save with 1s debounce, load map state on startup
- Port 3002 (Kiepenkerl uses 3001)
- Graceful fallback when API unavailable (works without server too)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/routes/hexes.ts

@@ -0,0 +1,141 @@
+import { Router } from 'express';
+import { getDb, saveDb } from '../db.js';
+
+const router = Router();
+
+// Get all hexes for a map (bulk load)
+router.get('/:mapId/hexes', (req, res) => {
+  const db = getDb();
+  const mapId = req.params.mapId;
+
+  const hexRows = db.exec(
+    'SELECT id, q, r, base_terrain FROM hexes WHERE map_id = ?',
+    [mapId],
+  );
+
+  if (hexRows.length === 0) {
+    res.json([]);
+    return;
+  }
+
+  const hexIds = hexRows[0].values.map(row => row[0] as number);
+  const hexes: any[] = [];
+
+  // Fetch features for all hexes
+  const featureMap = new Map<number, any[]>();
+  if (hexIds.length > 0) {
+    // Batch query — SQLite doesn't have great IN with params for large sets,
+    // so we query all features for this map's hexes
+    const featureRows = db.exec(
+      `SELECT hf.hex_id, hf.terrain_id, hf.edge_mask
+       FROM hex_features hf
+       JOIN hexes h ON hf.hex_id = h.id
+       WHERE h.map_id = ?`,
+      [mapId],
+    );
+
+    if (featureRows.length > 0) {
+      for (const row of featureRows[0].values) {
+        const hexId = row[0] as number;
+        if (!featureMap.has(hexId)) featureMap.set(hexId, []);
+        featureMap.get(hexId)!.push({
+          terrainId: row[1],
+          edgeMask: row[2],
+        });
+      }
+    }
+  }
+
+  for (const row of hexRows[0].values) {
+    const hexId = row[0] as number;
+    hexes.push({
+      q: row[1],
+      r: row[2],
+      base: row[3],
+      features: featureMap.get(hexId) ?? [],
+    });
+  }
+
+  res.json(hexes);
+});
+
+// Bulk upsert hexes
+router.put('/:mapId/hexes', (req, res) => {
+  const db = getDb();
+  const mapId = req.params.mapId;
+  const hexes: Array<{
+    q: number;
+    r: number;
+    base: string;
+    features: Array<{ terrainId: string; edgeMask: number }>;
+  }> = req.body;
+
+  if (!Array.isArray(hexes)) {
+    res.status(400).json({ error: 'Expected array of hex updates' });
+    return;
+  }
+
+  db.run('BEGIN TRANSACTION');
+
+  try {
+    for (const hex of hexes) {
+      // Upsert the hex
+      db.run(
+        `INSERT INTO hexes (map_id, q, r, base_terrain, updated_at)
+         VALUES (?, ?, ?, ?, datetime('now'))
+         ON CONFLICT(map_id, q, r)
+         DO UPDATE SET base_terrain = excluded.base_terrain, updated_at = datetime('now')`,
+        [mapId, hex.q, hex.r, hex.base],
+      );
+
+      // Get the hex id
+      const idRows = db.exec(
+        'SELECT id FROM hexes WHERE map_id = ? AND q = ? AND r = ?',
+        [mapId, hex.q, hex.r],
+      );
+      const hexId = idRows[0].values[0][0] as number;
+
+      // Replace features
+      db.run('DELETE FROM hex_features WHERE hex_id = ?', [hexId]);
+      for (const feature of hex.features) {
+        if (feature.edgeMask === 0) continue;
+        db.run(
+          'INSERT INTO hex_features (hex_id, terrain_id, edge_mask) VALUES (?, ?, ?)',
+          [hexId, feature.terrainId, feature.edgeMask],
+        );
+      }
+    }
+
+    // Update map timestamp
+    db.run("UPDATE hex_maps SET updated_at = datetime('now') WHERE id = ?", [mapId]);
+
+    db.run('COMMIT');
+    saveDb();
+    res.json({ ok: true, count: hexes.length });
+  } catch (err) {
+    db.run('ROLLBACK');
+    res.status(500).json({ error: String(err) });
+  }
+});
+
+// Delete a hex (reset to default)
+router.delete('/:mapId/hexes/:q/:r', (req, res) => {
+  const db = getDb();
+  const { mapId, q, r } = req.params;
+
+  const idRows = db.exec(
+    'SELECT id FROM hexes WHERE map_id = ? AND q = ? AND r = ?',
+    [mapId, q, r],
+  );
+
+  if (idRows.length > 0 && idRows[0].values.length > 0) {
+    const hexId = idRows[0].values[0][0];
+    db.run('DELETE FROM hex_features WHERE hex_id = ?', [hexId]);
+    db.run('DELETE FROM hexes WHERE id = ?', [hexId]);
+    saveDb();
+  }
+
+  res.json({ ok: true });
+});
+
+export default router;