evals: preflight ping once in the sharded parent, not per shard

The Anthropic fail-fast ping ran at module load in every paid test file
importing e2e-helpers — ~30 paid claude -p calls (30s timeout each) per
full sharded run for one bit of information. The parent now pings once
before spawning shards and sets EVALS_PREFLIGHT_OK=1; the module-load
path honors the flag. Extracted to test/helpers/anthropic-preflight.ts
(injectable spawn seam) with regression pins in both directions: the
flag must skip, its absence must ping exactly once, dead API must throw.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/helpers/anthropic-preflight.ts

@@ -0,0 +1,35 @@
+/**
+ * Anthropic-API preflight ping, shared by e2e-helpers (module load in every
+ * paid test file) and the sharded paid runner (once, in the parent).
+ *
+ * The ping is a real `claude -p` call with a 30s timeout. Before the parent
+ * dedup, every one of the ~30 paid test files that import e2e-helpers fired
+ * it at module load — 30 paid pings per full sharded run for one bit of
+ * information. The sharded runner now pings ONCE and sets
+ * EVALS_PREFLIGHT_OK=1 in each shard's env; the module-load path honors the
+ * flag and skips.
+ *
+ * Lives in its own module (not e2e-helpers) so the runner can import it
+ * without dragging in bun:test.
+ */
+
+import { spawnSync } from 'child_process';
+
+export type PreflightResult = 'skipped' | 'ok';
+
+export function preflightAnthropicApi(
+  env: NodeJS.ProcessEnv = process.env,
+  spawn: typeof spawnSync = spawnSync,
+): PreflightResult {
+  if (env.EVALS_PREFLIGHT_OK === '1') return 'skipped';
+  const check = spawn(
+    'sh',
+    ['-c', 'echo "ping" | claude -p --max-turns 1 --output-format stream-json --verbose --dangerously-skip-permissions'],
+    { stdio: 'pipe', timeout: 30_000 },
+  );
+  const output = check.stdout?.toString() || '';
+  if (output.includes('ConnectionRefused') || output.includes('Unable to connect')) {
+    throw new Error('Anthropic API unreachable — aborting E2E suite. Fix connectivity and retry.');
+  }
+  return 'ok';
+}