Add a bisect hook (?limit=) to the internal snapshot trigger

The cap raise 25 -> 500 made an induced snapshot 502 at 13.4s and the run
did not complete in background either, while a 25-prop run had completed
in 16.3s. That rules out a simple duration timeout and means the cause has
to be measured, not guessed. ?limit= bounds one run so the regression can
be bisected without a prod env change; omitted, the real DEFAULT_LIMIT
applies.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QJs13VsyiSKYQP6rj3NNmc

src/routes/internal.js

@@ -177,8 +177,12 @@ router.get('/snapshot/status', async (req, res) => {
 router.post('/snapshot/:sport', async (req, res) => {
   const snapshot = require('../services/snapshotService');
   try {
-    const summary = await snapshot.runSnapshot(req.params.sport);
-    return res.json({ ok: true, summary });
+    // ?limit= is a BISECT HOOK, not a production knob: it bounds the graded
+    // slate for one run so a cap regression can be isolated by measurement
+    // rather than guessed at. Omitted => gradeSlateService's real DEFAULT_LIMIT.
+    const limit = Number(req.query.limit) > 0 ? Number(req.query.limit) : undefined;
+    const summary = await snapshot.runSnapshot(req.params.sport, limit ? { limit } : {});
+    return res.json({ ok: true, ...(limit ? { limit_override: limit } : {}), summary });
   } catch (err) {
     const message = err && err.message ? err.message : String(err);
     console.error('[internal/snapshot] failed:', message);