fix(webhooks): make health route service-binding-only (#104)

## Summary

Closes the last finding from the public-surface sweep that followed
#103: `webhooks.trycheatcode.com/health` answered publicly (200,
unauthenticated, unrate-limited) with `releaseSha`/`versionId`, while
its only real consumer — the gateway's release aggregation — reaches it
through the WEBHOOKS service binding as
`https://webhooks.internal/health`.

The route now gates on the internal hostname and returns Hono's plain
`notFound()` on any other host, indistinguishable from a route that does
not exist. Same rule as #103: every public route must have a named
external consumer. The four provider webhook POST endpoints
(signature-verified) are untouched.

## Deploy safety

Gateway is unchanged; its binding fetch already carries the
`webhooks.internal` hostname, so the gate passes for old and new gateway
alike — no deploy-order coupling, no skew window. Roll-forward as usual.

## Verification

- Gates: lint, typecheck, full `turbo build --force` (19 packages incl.
web), knip, dependency-cruiser (844 modules, 0 violations), skills
bundle — all green
- Post-deploy: public `GET webhooks.trycheatcode.com/health` → 404;
gateway `/health/release` still 200 with the webhooks leg (proves the
internal path intact)

Author: iamjr15

apps/webhooks-worker/README.md

@@ -137,7 +137,9 @@ The handler therefore resolves that Composio-project-global ID through the datab
 primary key; ownership and toolkit assignment are immutable after insertion,
 and terminal status changes atomically reconcile the user's active default.
 
-Production binds one immutable `CHEATCODE_RELEASE_SHA`, exposed by `/health`.
+Production binds one immutable `CHEATCODE_RELEASE_SHA`, exposed by `/health`
+only to the gateway's service-binding probe (`https://webhooks.internal/health`);
+on the public webhook host the route answers as not found.
 HTTP, cron, idempotency, deletion, and workflow continuation paths use their
 normal durable ownership and idempotency contracts; database migrations retain
 their separate target, role, lock, and schema validation.

apps/webhooks-worker/src/index.ts

@@ -165,14 +165,20 @@ webhooksApp.use(
   }),
 );
 
-webhooksApp.get("/health", (c) =>
-  c.json({
+webhooksApp.get("/health", (c) => {
+  // Service-binding-only surface: the gateway probes https://webhooks.internal/health
+  // for release aggregation. The public webhook host must answer like the route does
+  // not exist so release metadata never leaks on an unauthenticated endpoint.
+  if (new URL(c.req.url).hostname !== "webhooks.internal") {
+    return c.notFound();
+  }
+  return c.json({
     ok: true,
     releaseSha: c.env.CHEATCODE_RELEASE_SHA ?? "development",
     versionId: c.env.CF_VERSION_METADATA?.id ?? null,
     worker: "webhooks",
-  }),
-);
+  });
+});
 
 webhooksApp.post("/clerk", async (c) => {
   const signingSecret = await clerkWebhookSigningSecret(c.env);