Revert "Warm the Start server graph on isolate first fetch (#1681)" (#1682)

This reverts commit 29a0aea.

Author: RhysSullivan

apps/cloud/src/env-augment.d.ts

@@ -95,9 +95,6 @@ declare global {
       MCP_REQUEST_STATE_KEY?: string;
       /** Emergency rollback for inbound MCP 2026-07-28 traffic only. */
       MCP_2026_07_28_ENABLED?: string;
-      // Kill switch for the Start server-graph warmup (server.ts). Set to
-      // "false" to disable without a deploy if memory pressure returns.
-      START_GRAPH_WARM?: string;
       NODE_ENV?: string;
 
       // Shared with frontend

apps/cloud/src/server.ts

@@ -178,59 +178,8 @@ const mcpAgentHandler = makeCloudMcpAgentHandler({
   traceRequest: traceCloudMcpRequest,
 });
 
-// ---------------------------------------------------------------------------
-// Start server-graph warmup
-// ---------------------------------------------------------------------------
-//
-// Page latency was p50 19-49ms every day up to 2026-08-16 and 2728ms the day
-// after the 21:20 UTC deploy. It is not load: 2026-08-11 served MORE total
-// traffic (5.43M requests vs 4.38M) with pages at p50 41ms, so the
-// reconnect-storm/volume explanation does not hold.
-//
-// What changed is where MCP work runs. The old hibernatable Agent bridge
-// handed `/mcp` to the Durable Object almost immediately; the v2 stack
-// authenticates and dispatches in the WORKER (`mcp.auth.jwt_verify` alone runs
-// ~35k times per 6h there). That spins up far more worker isolates, and `/mcp`
-// returns above without ever touching `fetchHandler` — so those isolates never
-// load the Start graph. Page requests then land on them cold and pay
-// `loadEntries`: measured p50 **3.1s**, against p50 33ms for the request's own
-// work and 9-104ms for a warm isolate. The same bundle in local workerd serves
-// the same path in ~3ms, so this is a cold-isolate cost, not slow code.
-//
-// So warm on the isolate's FIRST fetch, in the background: MCP traffic then
-// pre-warms an isolate before a page request reaches it. This is #1628, which
-// worked; it was reverted (#1634) when memory-limit kills jumped, but that
-// landed during the 2026-08-17 storm — 11.67M requests in a day against a
-// 2.6-4.3M baseline. Volume is back to baseline and `exceededMemory` is
-// currently zero, so the condition that made it expensive is gone.
-// `START_GRAPH_WARM=false` disables it without a deploy.
-//
-// Deliberately NOT at module scope: a full warmup there trips workerd's
-// global-scope I/O restriction, and DO-only isolates should not carry the SSR
-// graph.
-// ---------------------------------------------------------------------------
-
-let startGraphWarmupStarted = false;
-
-const warmStartGraph = (env: Env): void => {
-  if (startGraphWarmupStarted) return;
-  if (env.START_GRAPH_WARM === "false") return;
-  startGraphWarmupStarted = true;
-  // oxlint-disable-next-line executor/no-promise-catch -- adapter boundary; fire-and-forget warmup outside any Effect runtime
-  void Promise.all([import("#tanstack-router-entry"), import("#tanstack-start-entry")]).catch(
-    () => {
-      // Advisory only — the request path still loads the graph lazily.
-      startGraphWarmupStarted = false;
-    },
-  );
-};
-
 const cloudflareHandler: ExportedHandler<Env> = {
   fetch: async (request, env, ctx) => {
-    // First fetch in this isolate kicks the graph load off in the background,
-    // including for /mcp — MCP traffic is what reaches these isolates first.
-    warmStartGraph(env);
-
     // Public pages must not enter TanStack Start: its first-request dynamic
     // import loads the entire React + Effect server graph and can take seconds
     // on a cold isolate. Classify and service-bind marketing at the Worker