From a92f13b3fd8324c09ff7fe747912cc86db4e861c Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Wed, 19 Aug 2026 07:17:25 -0700
Subject: [PATCH 1/7] Revert "Fix lint: do not stringify the unknown warmup
 error (#1688)"

This reverts commit 1c57887ba90d23d778eab2713f2d5f56fd7cfb03.
---
 apps/cloud/src/server.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/apps/cloud/src/server.ts b/apps/cloud/src/server.ts
index 7566ad45e9..9821de48f8 100644
--- a/apps/cloud/src/server.ts
+++ b/apps/cloud/src/server.ts
@@ -253,7 +253,7 @@ const warmStartGraph = (env: Env, ctx: ExecutionContext): void => {
           ctx,
         );
         console.log(JSON.stringify({ probe: "warm", ok: true, ms: Date.now() - startedAt }));
-      } catch {
+      } catch (err) {
         // Advisory only — the request path still loads the graph lazily.
         startGraphWarmupStarted = false;
         console.log(
@@ -261,6 +261,7 @@ const warmStartGraph = (env: Env, ctx: ExecutionContext): void => {
             probe: "warm",
             ok: false,
             ms: Date.now() - startedAt,
+            err: String(err),
           }),
         );
       }

From 892dbca4e396977bb2874c0680ca0ac50570c19c Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Wed, 19 Aug 2026 07:17:25 -0700
Subject: [PATCH 2/7] Revert "Log whether the warmup runs and whether warm
 isolates still pay for Start (#1687)"

This reverts commit 1b2509c9f688df6d4a53ecf23f03428fe4e3db48.
---
 apps/cloud/src/server.ts | 38 ++------------------------------------
 1 file changed, 2 insertions(+), 36 deletions(-)

diff --git a/apps/cloud/src/server.ts b/apps/cloud/src/server.ts
index 9821de48f8..828e408878 100644
--- a/apps/cloud/src/server.ts
+++ b/apps/cloud/src/server.ts
@@ -103,36 +103,12 @@ export { McpExecutionOwnerDirectoryDO } from "@executor-js/cloudflare/mcp/execut
 // until the in-flight export resolves.
 // ---------------------------------------------------------------------------
 
-const rawFetchHandler = handler.fetch as (
+const fetchHandler = handler.fetch as (
   request: Request,
   env: Env,
   ctx: ExecutionContext,
 ) => Response | Promise<Response>;
 
-// TEMPORARY: does an isolate that already warmed still pay for Start?
-let startEverHandled = false;
-const fetchHandler = async (
-  request: Request,
-  env: Env,
-  ctx: ExecutionContext,
-): Promise<Response> => {
-  const wasWarm = startEverHandled;
-  startEverHandled = true;
-  await scheduler.wait(0);
-  const startedAt = Date.now();
-  const response = await rawFetchHandler(request, env, ctx);
-  await scheduler.wait(0);
-  console.log(
-    JSON.stringify({
-      probe: "start",
-      path: new URL(request.url).pathname,
-      wasWarm,
-      ms: Date.now() - startedAt,
-    }),
-  );
-  return response;
-};
-
 const tracer = trace.getTracer("executor-cloud-worker");
 
 const traceparentValueFor = (spanContext: SpanContext): string =>
@@ -244,7 +220,6 @@ const warmStartGraph = (env: Env, ctx: ExecutionContext): void => {
 
   ctx.waitUntil(
     (async () => {
-      const startedAt = Date.now();
       // oxlint-disable-next-line executor/no-try-catch-or-throw -- adapter boundary; a warmup failure must never affect the request that triggered it
       try {
         await fetchHandler(
@@ -252,18 +227,9 @@ const warmStartGraph = (env: Env, ctx: ExecutionContext): void => {
           env,
           ctx,
         );
-        console.log(JSON.stringify({ probe: "warm", ok: true, ms: Date.now() - startedAt }));
-      } catch (err) {
+      } catch {
         // Advisory only — the request path still loads the graph lazily.
         startGraphWarmupStarted = false;
-        console.log(
-          JSON.stringify({
-            probe: "warm",
-            ok: false,
-            ms: Date.now() - startedAt,
-            err: String(err),
-          }),
-        );
       }
     })(),
   );

From 6c58d57761e6c7a16ac1e0da18119b5a009222a0 Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Wed, 19 Aug 2026 07:17:25 -0700
Subject: [PATCH 3/7] Revert "Warm the Start graph by replaying a real request
 per isolate (#1686)"

This reverts commit 46625d2090f58fe5cfd236872dc4a37a8ea1cc06.
---
 apps/cloud/src/env-augment.d.ts |  2 --
 apps/cloud/src/server.ts        | 62 ---------------------------------
 2 files changed, 64 deletions(-)

diff --git a/apps/cloud/src/env-augment.d.ts b/apps/cloud/src/env-augment.d.ts
index 952d5c9978..cb8070ae63 100644
--- a/apps/cloud/src/env-augment.d.ts
+++ b/apps/cloud/src/env-augment.d.ts
@@ -95,8 +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).
-      START_GRAPH_WARM?: string;
       NODE_ENV?: string;
 
       // Shared with frontend
diff --git a/apps/cloud/src/server.ts b/apps/cloud/src/server.ts
index 828e408878..0304ab0246 100644
--- a/apps/cloud/src/server.ts
+++ b/apps/cloud/src/server.ts
@@ -178,70 +178,8 @@ const mcpAgentHandler = makeCloudMcpAgentHandler({
   traceRequest: traceCloudMcpRequest,
 });
 
-// ---------------------------------------------------------------------------
-// Start server-graph warmup
-// ---------------------------------------------------------------------------
-//
-// Page latency was p50 19-49ms daily through 2026-08-16 and 2728ms the day
-// after the 21:20 deploy. Not load: 2026-08-11 served MORE traffic (5.43M vs
-// 4.38M requests) with pages at p50 41ms.
-//
-// 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` returns above without touching
-// `fetchHandler`, so an isolate can serve a lot of MCP traffic and still have
-// never loaded the Start graph. Measured: isolates that served a page request
-// had already served a median of 19 spans across 3 paths — they are reused,
-// they are just cold for Start. The page request then pays `loadEntries`: p50
-// **3.1s**, against p50 33ms for the request's own work and 9-104ms warm. The
-// same bundle in local workerd serves the same path in ~3ms.
-//
-// Warm by REPLAYING A REAL REQUEST through the handler, not by importing the
-// virtual entry ids. Two attempts at the import approach (#1679, #1681) moved
-// nothing in production: `loadEntries` awaits THREE specifiers
-// (`#tanstack-router-entry`, `#tanstack-start-entry`,
-// `#tanstack-start-plugin-adapters`) plus a separately-cached manifest, so
-// warming a subset leaves the request paying for the rest. Driving the real
-// handler populates whatever those caches are, by construction, and cannot
-// drift when Start changes its internals.
-//
-// `/robots.txt` is the cheapest Start-served route. It runs once per isolate,
-// under `waitUntil` so it outlives the request that triggered it, and costs one
-// extra synthetic request per isolate in telemetry.
-// `START_GRAPH_WARM=false` disables it without a deploy.
-// ---------------------------------------------------------------------------
-
-let startGraphWarmupStarted = false;
-
-const warmStartGraph = (env: Env, ctx: ExecutionContext): void => {
-  if (startGraphWarmupStarted) return;
-  if (env.START_GRAPH_WARM === "false") return;
-  startGraphWarmupStarted = true;
-
-  ctx.waitUntil(
-    (async () => {
-      // oxlint-disable-next-line executor/no-try-catch-or-throw -- adapter boundary; a warmup failure must never affect the request that triggered it
-      try {
-        await fetchHandler(
-          new Request("https://executor.sh/robots.txt", { method: "GET" }),
-          env,
-          ctx,
-        );
-      } 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 drives one real request through Start in the
-    // background, including for /mcp — MCP traffic is what reaches these
-    // isolates first, and is why they are otherwise never warmed.
-    warmStartGraph(env, ctx);
-
     // 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

From a7e5869da682780b91927e81bcb82af79bdff13c Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Wed, 19 Aug 2026 07:17:25 -0700
Subject: [PATCH 4/7] Reapply "Warm the Start server graph on isolate first
 fetch (#1681)" (#1682)

This reverts commit aff1f3946bb57acfd05336329589f6f6ca3d9e24.
---
 apps/cloud/src/env-augment.d.ts           |  3 ++
 apps/cloud/src/server.ts                  | 51 +++++++++++++++++++++++
 apps/cloud/src/start-virtual-entries.d.ts |  8 ++++
 3 files changed, 62 insertions(+)
 create mode 100644 apps/cloud/src/start-virtual-entries.d.ts

diff --git a/apps/cloud/src/env-augment.d.ts b/apps/cloud/src/env-augment.d.ts
index cb8070ae63..88b300ccb5 100644
--- a/apps/cloud/src/env-augment.d.ts
+++ b/apps/cloud/src/env-augment.d.ts
@@ -95,6 +95,9 @@ 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
diff --git a/apps/cloud/src/server.ts b/apps/cloud/src/server.ts
index 0304ab0246..11e88cb5c8 100644
--- a/apps/cloud/src/server.ts
+++ b/apps/cloud/src/server.ts
@@ -178,8 +178,59 @@ 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
diff --git a/apps/cloud/src/start-virtual-entries.d.ts b/apps/cloud/src/start-virtual-entries.d.ts
new file mode 100644
index 0000000000..9fb43d8206
--- /dev/null
+++ b/apps/cloud/src/start-virtual-entries.d.ts
@@ -0,0 +1,8 @@
+// TanStack Start's internal virtual server-entry modules (registered by the
+// Start vite plugin; the same ids `start-server-core`'s `loadEntries`
+// imports). server.ts imports them for the isolate warmup — only the
+// module-evaluation side effect matters there, so the value shape is left
+// untyped. Kept in a standalone declaration file: shorthand ambient modules
+// only register from a non-module file (env-augment.d.ts is a module).
+declare module "#tanstack-router-entry";
+declare module "#tanstack-start-entry";

From ab283b60baf295ac7b5a45e2af72e837a3e6e7ae Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Wed, 19 Aug 2026 07:17:25 -0700
Subject: [PATCH 5/7] Revert "Warm the Start server graph on isolate first
 fetch (#1681)"

This reverts commit 29a0aea7e11f8ae54577c5bb3f62fc94302d2a0d.
---
 apps/cloud/src/env-augment.d.ts           |  3 --
 apps/cloud/src/server.ts                  | 51 -----------------------
 apps/cloud/src/start-virtual-entries.d.ts |  8 ----
 3 files changed, 62 deletions(-)
 delete mode 100644 apps/cloud/src/start-virtual-entries.d.ts

diff --git a/apps/cloud/src/env-augment.d.ts b/apps/cloud/src/env-augment.d.ts
index 88b300ccb5..cb8070ae63 100644
--- a/apps/cloud/src/env-augment.d.ts
+++ b/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
diff --git a/apps/cloud/src/server.ts b/apps/cloud/src/server.ts
index 11e88cb5c8..0304ab0246 100644
--- a/apps/cloud/src/server.ts
+++ b/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
diff --git a/apps/cloud/src/start-virtual-entries.d.ts b/apps/cloud/src/start-virtual-entries.d.ts
deleted file mode 100644
index 9fb43d8206..0000000000
--- a/apps/cloud/src/start-virtual-entries.d.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-// TanStack Start's internal virtual server-entry modules (registered by the
-// Start vite plugin; the same ids `start-server-core`'s `loadEntries`
-// imports). server.ts imports them for the isolate warmup — only the
-// module-evaluation side effect matters there, so the value shape is left
-// untyped. Kept in a standalone declaration file: shorthand ambient modules
-// only register from a non-module file (env-augment.d.ts is a module).
-declare module "#tanstack-router-entry";
-declare module "#tanstack-start-entry";

From 6b37e009f01ec367f4deaf635d2ac02181700338 Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Wed, 19 Aug 2026 07:17:25 -0700
Subject: [PATCH 6/7] Reapply "Warm the Start server graph on isolates that
 persist (#1679)" (#1680)

This reverts commit 332955f80a83d432779135ab684e7259b6a0c864.
---
 apps/cloud/src/env-augment.d.ts           |  6 +++
 apps/cloud/src/server.ts                  | 60 +++++++++++++++++++++++
 apps/cloud/src/start-virtual-entries.d.ts |  8 +++
 3 files changed, 74 insertions(+)
 create mode 100644 apps/cloud/src/start-virtual-entries.d.ts

diff --git a/apps/cloud/src/env-augment.d.ts b/apps/cloud/src/env-augment.d.ts
index cb8070ae63..c163d61b9d 100644
--- a/apps/cloud/src/env-augment.d.ts
+++ b/apps/cloud/src/env-augment.d.ts
@@ -95,6 +95,12 @@ 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 it ever costs memory again.
+      START_GRAPH_WARM?: string;
+      // How many fetches an isolate must serve before it is considered
+      // persistent enough to warm. Defaults to 2.
+      START_GRAPH_WARM_AFTER?: string;
       NODE_ENV?: string;
 
       // Shared with frontend
diff --git a/apps/cloud/src/server.ts b/apps/cloud/src/server.ts
index 0304ab0246..52da6cd201 100644
--- a/apps/cloud/src/server.ts
+++ b/apps/cloud/src/server.ts
@@ -178,8 +178,68 @@ const mcpAgentHandler = makeCloudMcpAgentHandler({
   traceRequest: traceCloudMcpRequest,
 });
 
+// ---------------------------------------------------------------------------
+// Start server-graph warmup
+// ---------------------------------------------------------------------------
+//
+// TanStack Start loads the router + start instance behind a dynamic import on
+// the first Start-handled request per isolate (`start-server-core`'s
+// `loadEntries`). Measured in production by timing that import apart from the
+// request's own work: the import is **p50 3.1s**, the work is **p50 33ms**,
+// and a warm isolate answers in **9-104ms**. The same bundle in local workerd
+// serves the same path in ~3ms, so this is a cold-isolate cost on production
+// metal, not slow code.
+//
+// Nearly every page request pays it. `/mcp` is dispatched above, before
+// `fetchHandler`, so MCP traffic — the large majority — creates and occupies
+// isolates without ever loading the graph. Page requests then land on those:
+// `worker.dispatch` ran 1,666 requests across 1,608 isolates (1.04 each).
+//
+// #1628 warmed on every isolate's FIRST fetch and was reverted: it pulled the
+// SSR graph into every isolate including MCP-only ones, and memory-limit kills
+// went from ~500-900 to 3.7k-9.4k per 5min. The fix for that is to stop
+// warming isolates that will not live long enough to use it. An isolate that
+// has already served several requests is one that persists — exactly the kind
+// a later page request can land on — so warming waits for that evidence.
+// Single-shot isolates, which is what the memory blowup was made of, are never
+// warmed.
+//
+// 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. `START_GRAPH_WARM=false` disables it without a deploy.
+// ---------------------------------------------------------------------------
+
+const DEFAULT_WARM_AFTER_FETCHES = 2;
+
+let isolateFetchCount = 0;
+let startGraphWarmupStarted = false;
+
+const maybeWarmStartGraph = (env: Env): void => {
+  if (startGraphWarmupStarted) return;
+  if (env.START_GRAPH_WARM === "false") return;
+
+  isolateFetchCount += 1;
+  const parsed = Number.parseInt(env.START_GRAPH_WARM_AFTER ?? "", 10);
+  const warmAfter = Number.isFinite(parsed) && parsed > 0 ? parsed : DEFAULT_WARM_AFTER_FETCHES;
+  if (isolateFetchCount < warmAfter) 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) => {
+    // Every request counts toward this isolate's persistence, including /mcp
+    // (which returns below without ever loading the graph) — MCP traffic is
+    // precisely what keeps these isolates alive for a later page request.
+    maybeWarmStartGraph(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
diff --git a/apps/cloud/src/start-virtual-entries.d.ts b/apps/cloud/src/start-virtual-entries.d.ts
new file mode 100644
index 0000000000..9fb43d8206
--- /dev/null
+++ b/apps/cloud/src/start-virtual-entries.d.ts
@@ -0,0 +1,8 @@
+// TanStack Start's internal virtual server-entry modules (registered by the
+// Start vite plugin; the same ids `start-server-core`'s `loadEntries`
+// imports). server.ts imports them for the isolate warmup — only the
+// module-evaluation side effect matters there, so the value shape is left
+// untyped. Kept in a standalone declaration file: shorthand ambient modules
+// only register from a non-module file (env-augment.d.ts is a module).
+declare module "#tanstack-router-entry";
+declare module "#tanstack-start-entry";

From c8c9e91653d104896c4a668cbe25e46e6cd0da97 Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Wed, 19 Aug 2026 07:17:25 -0700
Subject: [PATCH 7/7] Revert "Warm the Start server graph on isolates that
 persist (#1679)"

This reverts commit ca9617e89b7d9e38a87918864e1911bee4019dd9.
---
 apps/cloud/src/env-augment.d.ts           |  6 ---
 apps/cloud/src/server.ts                  | 60 -----------------------
 apps/cloud/src/start-virtual-entries.d.ts |  8 ---
 3 files changed, 74 deletions(-)
 delete mode 100644 apps/cloud/src/start-virtual-entries.d.ts

diff --git a/apps/cloud/src/env-augment.d.ts b/apps/cloud/src/env-augment.d.ts
index c163d61b9d..cb8070ae63 100644
--- a/apps/cloud/src/env-augment.d.ts
+++ b/apps/cloud/src/env-augment.d.ts
@@ -95,12 +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 it ever costs memory again.
-      START_GRAPH_WARM?: string;
-      // How many fetches an isolate must serve before it is considered
-      // persistent enough to warm. Defaults to 2.
-      START_GRAPH_WARM_AFTER?: string;
       NODE_ENV?: string;
 
       // Shared with frontend
diff --git a/apps/cloud/src/server.ts b/apps/cloud/src/server.ts
index 52da6cd201..0304ab0246 100644
--- a/apps/cloud/src/server.ts
+++ b/apps/cloud/src/server.ts
@@ -178,68 +178,8 @@ const mcpAgentHandler = makeCloudMcpAgentHandler({
   traceRequest: traceCloudMcpRequest,
 });
 
-// ---------------------------------------------------------------------------
-// Start server-graph warmup
-// ---------------------------------------------------------------------------
-//
-// TanStack Start loads the router + start instance behind a dynamic import on
-// the first Start-handled request per isolate (`start-server-core`'s
-// `loadEntries`). Measured in production by timing that import apart from the
-// request's own work: the import is **p50 3.1s**, the work is **p50 33ms**,
-// and a warm isolate answers in **9-104ms**. The same bundle in local workerd
-// serves the same path in ~3ms, so this is a cold-isolate cost on production
-// metal, not slow code.
-//
-// Nearly every page request pays it. `/mcp` is dispatched above, before
-// `fetchHandler`, so MCP traffic — the large majority — creates and occupies
-// isolates without ever loading the graph. Page requests then land on those:
-// `worker.dispatch` ran 1,666 requests across 1,608 isolates (1.04 each).
-//
-// #1628 warmed on every isolate's FIRST fetch and was reverted: it pulled the
-// SSR graph into every isolate including MCP-only ones, and memory-limit kills
-// went from ~500-900 to 3.7k-9.4k per 5min. The fix for that is to stop
-// warming isolates that will not live long enough to use it. An isolate that
-// has already served several requests is one that persists — exactly the kind
-// a later page request can land on — so warming waits for that evidence.
-// Single-shot isolates, which is what the memory blowup was made of, are never
-// warmed.
-//
-// 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. `START_GRAPH_WARM=false` disables it without a deploy.
-// ---------------------------------------------------------------------------
-
-const DEFAULT_WARM_AFTER_FETCHES = 2;
-
-let isolateFetchCount = 0;
-let startGraphWarmupStarted = false;
-
-const maybeWarmStartGraph = (env: Env): void => {
-  if (startGraphWarmupStarted) return;
-  if (env.START_GRAPH_WARM === "false") return;
-
-  isolateFetchCount += 1;
-  const parsed = Number.parseInt(env.START_GRAPH_WARM_AFTER ?? "", 10);
-  const warmAfter = Number.isFinite(parsed) && parsed > 0 ? parsed : DEFAULT_WARM_AFTER_FETCHES;
-  if (isolateFetchCount < warmAfter) 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) => {
-    // Every request counts toward this isolate's persistence, including /mcp
-    // (which returns below without ever loading the graph) — MCP traffic is
-    // precisely what keeps these isolates alive for a later page request.
-    maybeWarmStartGraph(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
diff --git a/apps/cloud/src/start-virtual-entries.d.ts b/apps/cloud/src/start-virtual-entries.d.ts
deleted file mode 100644
index 9fb43d8206..0000000000
--- a/apps/cloud/src/start-virtual-entries.d.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-// TanStack Start's internal virtual server-entry modules (registered by the
-// Start vite plugin; the same ids `start-server-core`'s `loadEntries`
-// imports). server.ts imports them for the isolate warmup — only the
-// module-evaluation side effect matters there, so the value shape is left
-// untyped. Kept in a standalone declaration file: shorthand ambient modules
-// only register from a non-module file (env-augment.d.ts is a module).
-declare module "#tanstack-router-entry";
-declare module "#tanstack-start-entry";