feat(06-04): /api/route engine-A arm + http-source backend #2 — Bearer-gated, honest-null, RP re-pinned (GREEN)

- bot/src/routing/worker-router.ts: module-scope per-env graph memo (1 R2 GET per
  cold isolate, shared with the 06-07 cron arm via loadGraph), snap+A*+deriveSteps,
  claim-gated 401 / 4096-cap 413 / V5 bbox 400, 200-null on every miss class,
  ONE best route (no alternatives), category-only logs
- webhook.ts: /api/route arm delegating to handleRoute (405 non-POST)
- config.ts: ROAD_GRAPH: R2Bucket — first R2 binding (never a KV namespace, GE5)
- wrangler.jsonc: r2_buckets ROAD_GRAPH -> araharah-graphs with the fork law comment
- routing/src/http-source.ts: createHttpRoutingSource — slug-guard-first, fail-honest
  (throw/non-200/malformed/null-body -> null), defensive RouteResult validation;
  exported from index.ts; ladder note: backend #2 LIVE
- A7 re-pinned (06-01 named 06-04 as the owner of createHttpRoutingSource)
- test-side fix during GREEN: the R2 fake hands decodeGraph an exact ArrayBuffer
  (Node Buffers are views; encodeGraph output is already an ArrayBuffer)
- bot 103 passed / routing 65 passed; both typechecks clean

bot/src/config.ts

@@ -9,6 +9,13 @@ export interface Env {
   // accept-everything.
   WEBHOOK_SECRET: string; // wrangler secret (D-15) — value Telegram echoes in X-Telegram-Bot-Api-Secret-Token
   chat_sessions: KVNamespace; // TTL-only namespace — first durable KV namespace (PRIV-02)
+  // D-01 graph binary — the repo's FIRST R2 binding. A bucket, NEVER a KV
+  // namespace (GE5: exactly one kv_namespaces). worker-router's loadGraph
+  // memoizes the decoded graph per isolate; an absent/corrupt object
+  // degrades honest (null → router-pending, D-03), never a crash. The
+  // bucket itself (araharah-graphs) is fork provisioning, not a secret —
+  // docs/ROAD-GRAPH.md owns the fork contract.
+  ROAD_GRAPH: R2Bucket;
   // The deployed Mini App ORIGIN (public, not a secret) — used to build the
   // OPEN button's deep link. NOT derived from user input: the deep-link
   // origin is a configured value (RESEARCH §Security V4 — an unvalidated