Wave 5B: Pitcher Arsenal via Baseball Savant (Statcast)

D4 — build the FREE Baseball Savant adapter for pitch-level identity
(mix / velo / usage% / whiff%), the missing layer statsapi doesn't carry.

- savantAdapter.getPitcherArsenal(id|name) — normalizes two public Savant
  CSV leaderboards (csv=true, NO parsing dependency): pitch-arsenal-stats
  (usage% + whiff% + K%) + pitch-arsenals avg_speed (velo). League-wide,
  cached 24h + in-memory mirror, indexed by MLBAM id. Defensive: null on any
  unrecognized shape; a missing velo/whiff is ABSENT (null), never 0.
  Injectable (fetchImpl/statsCsv/veloCsv/resolveId) → tests hit no network.
  Live endpoints VERIFIED (200, exact columns) from the sandbox.
- GET /api/stats/pitcher/:name/arsenal (stats.js) + Next proxy. MLB-only;
  an error/miss returns { found:false } so the card self-hides honestly.
- PitcherArsenal.tsx (+ barrel) — the mockup's PITCHER IDENTITY strip:
  pitch mix % + velo + whiff%, mono/tabular, ranked by usage, sharpest-whiff
  pitch highlighted green. Self-hides (heading included) when arsenal absent.
  Mounted on the MLB player profile (a pitcher surface). Context, not a
  graded market value.
- Tests: savantAdapter (fake CSV → ranked arsenal; unknown shape/blank cells
  → absent not 0; name→id resolve) + PitcherArsenal source locks (self-hide,
  mono/tabular, em-dash-not-zero). +2 suites / +17 tests (3012 → 3029).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/api/stats/pitcher/[name]/arsenal/route.ts

@@ -0,0 +1,27 @@
+import { NextRequest, NextResponse } from 'next/server';
+
+export const dynamic = 'force-dynamic';
+
+const BACKEND_URL = process.env.BACKEND_URL || 'http://localhost:3000';
+
+/**
+ * Pitcher arsenal proxy (Wave 5B). Forwards GET
+ * /api/stats/pitcher/:name/arsenal to the Express stats route (Baseball Savant
+ * pitch mix / velo / whiff). Thin pass-through; preserves ?sport=. On any
+ * upstream failure it returns { found:false } so the PitcherArsenal card
+ * self-hides honestly rather than showing an error.
+ */
+export async function GET(req: NextRequest, ctx: { params: Promise<{ name: string }> }) {
+  const { name } = await ctx.params;
+  const qs = req.nextUrl.search;
+  try {
+    const upstream = await fetch(
+      `${BACKEND_URL}/api/stats/pitcher/${encodeURIComponent(name)}/arsenal${qs}`,
+      { method: 'GET', headers: { Accept: 'application/json' } },
+    );
+    const data = await upstream.json().catch(() => ({ found: false }));
+    return NextResponse.json(data, { status: upstream.ok ? 200 : upstream.status });
+  } catch {
+    return NextResponse.json({ found: false }, { status: 200 });
+  }
+}