diff --git a/src/routes/internal.js b/src/routes/internal.js
index e968e90..e2ca9f5 100644
--- a/src/routes/internal.js
+++ b/src/routes/internal.js
@@ -652,4 +652,73 @@ router.get('/feature-coverage', async (req, res) => {
   }
 });
 
+/**
+ * GET /api/internal/env-context-audit (matchup/park audit, Step 0)
+ *
+ * READ-ONLY. The arch-v1 environment and matchup axes fired on ZERO prod rows
+ * while archetype axes fired normally, so the question is WHERE the resolution
+ * chain drops off. This replays buildContext + contextFor against the CURRENT
+ * cached snapshot grades and counts the drop-off at each hop, instead of
+ * inferring it from an absence.
+ */
+router.get('/env-context-audit', async (req, res) => {
+  try {
+    const sport = String(req.query.sport || 'mlb').toLowerCase();
+    const { cacheGet } = require('../utils/redis');
+    const envCtx = require('../services/environmentContext');
+
+    const snap = await cacheGet(`snapshot:${sport}:latest`);
+    const grades = (snap && Array.isArray(snap.grades) ? snap.grades : []).slice(0, 120);
+
+    const ctx = await envCtx.buildContext(sport, {
+      origin: process.env.BACKEND_SELF_ORIGIN || 'http://localhost:3000',
+    });
+    const i = ctx._internals || {};
+
+    const counts = {
+      grades_examined: grades.length,
+      with_team_field: 0,
+      team_resolves_to_abbr: 0,
+      abbr_matches_a_game: 0,
+      got_environment: 0,
+      with_bats: 0,
+      with_playerId: 0,
+      opp_pitcher_known: 0,
+      got_matchup: 0,
+    };
+    const sampleTeams = [];
+    for (const g of grades) {
+      const team = g.team;
+      if (team) counts.with_team_field += 1;
+      const abbr = envCtx.abbrOf(team);
+      if (abbr) counts.team_resolves_to_abbr += 1;
+      if (sampleTeams.length < 8 && team) sampleTeams.push({ team, abbr: abbr || null });
+      if (abbr && i.gameByTeam && i.gameByTeam.has(abbr)) counts.abbr_matches_a_game += 1;
+      if (g.bats) counts.with_bats += 1;
+      if (g.playerId != null) counts.with_playerId += 1;
+      if (abbr && i.oppPitcherByTeam && i.oppPitcherByTeam.get(abbr) != null) counts.opp_pitcher_known += 1;
+      const r = await ctx.contextFor(g);
+      if (r && r.environment) counts.got_environment += 1;
+      if (r && r.matchup) counts.got_matchup += 1;
+    }
+
+    res.set('Cache-Control', 'no-store');
+    return res.json({
+      ok: true,
+      read_only: true,
+      build_context_stats: ctx.stats,
+      internals_sizes: {
+        gameByTeam: i.gameByTeam ? i.gameByTeam.size : null,
+        forecastByHome: i.forecastByHome ? i.forecastByHome.size : null,
+        oppPitcherByTeam: i.oppPitcherByTeam ? i.oppPitcherByTeam.size : null,
+        handById: i.handById ? i.handById.size : null,
+      },
+      drop_off: counts,
+      sample_team_values: sampleTeams,
+    });
+  } catch (err) {
+    return res.status(500).json({ ok: false, error: err && err.message, stack_head: String(err && err.stack || '').split('\n')[1] || null });
+  }
+});
+
 module.exports = router;