chore(cloud): delete orphaned KV McpSessionDO + stop PR builds failing on DO migrations

- v3 deletes the orphaned KV McpSessionDO (the MCP_SESSION binding moved to the
  SQLite class in v2, so nothing references it now); drop the stub export.
- build.mjs strips DO migrations from the generated deploy config on non-main CI
  branches. Preview deploys use 'wrangler versions upload', which rejects
  unapplied migrations (error 10211); previews share prod's applied DO state so
  they neither need nor can apply them. main keeps migrations and applies them on
  the real deploy. Fail-safe: only strips on a confirmed non-main CI branch.

Author: RhysSullivan

apps/cloud/scripts/build.mjs

@@ -9,7 +9,7 @@
 
 import { spawnSync } from "node:child_process";
 import { randomBytes } from "node:crypto";
-import { rmSync } from "node:fs";
+import { readFileSync, rmSync, writeFileSync } from "node:fs";
 
 if (!process.env.VITE_PUBLIC_ANALYTICS_PATH) {
   process.env.VITE_PUBLIC_ANALYTICS_PATH = randomBytes(4).toString("hex");
@@ -32,3 +32,26 @@ for (const step of steps) {
     process.exit(result.status ?? 1);
   }
 }
+
+// Preview (non-production) Cloudflare Workers Builds deploy via `wrangler versions
+// upload`, which REJECTS any config containing an unapplied Durable Object
+// migration (error 10211 — "migrations must be applied via a non-versioned
+// deployment"). Preview versions share production's already-applied DO state, so
+// they neither need nor can apply migrations. Strip `migrations` from the
+// generated deploy config on non-`main` CI branches so PR preview builds stop
+// failing. Production (`main`) keeps migrations and applies them on the real,
+// non-versioned deploy. Fail-safe: only triggers on a confirmed non-`main` CI
+// branch, so it can never drop migrations from a production deploy.
+const ciBranch = process.env.WORKERS_CI_BRANCH;
+if (process.env.WORKERS_CI === "1" && ciBranch && ciBranch !== "main") {
+  const cfgUrl = new URL("../dist/server/wrangler.json", import.meta.url);
+  const cfg = JSON.parse(readFileSync(cfgUrl, "utf8"));
+  if (Array.isArray(cfg.migrations) && cfg.migrations.length > 0) {
+    delete cfg.migrations;
+    writeFileSync(cfgUrl, JSON.stringify(cfg));
+    console.log(
+      `[build] preview branch '${ciBranch}': stripped Durable Object migrations from ` +
+        `dist/server/wrangler.json (versions upload cannot apply migrations)`,
+    );
+  }
+}

apps/cloud/src/server.ts

@@ -1,4 +1,3 @@
-import { DurableObject } from "cloudflare:workers";
 import { SpanKind, SpanStatusCode, context, trace } from "@opentelemetry/api";
 import {
   ATTR_HTTP_REQUEST_METHOD,
@@ -47,14 +46,6 @@ export const McpSessionDOSqlite = Sentry.instrumentDurableObjectWithSentry(
   McpSessionDOBase,
 );
 
-// Orphaned placeholder for the original key-value `McpSessionDO` class (migration
-// v1). The live MCP session DO is now `McpSessionDOSqlite` (SQLite); the
-// `MCP_SESSION` binding moved to it. Cloudflare won't delete `McpSessionDO` in the
-// same deploy that moves its binding, so the class is left unbound and is kept
-// exported here only to satisfy the migration. It can be removed in a later deploy
-// (with a `deleted_classes: ["McpSessionDO"]` migration) now that nothing binds it.
-export class McpSessionDO extends DurableObject {}
-
 // ---------------------------------------------------------------------------
 // Worker fetch handler
 //

apps/cloud/wrangler.jsonc

@@ -27,12 +27,11 @@
   // The MCP session DO moved to the Cloudflare Agents (`McpAgent`) base, which
   // stores state in SQLite. The original `McpSessionDO` was created on the
   // key-value backend (`new_classes`) and cannot be converted in place. Cloudflare
-  // also refuses to delete a class in the same deploy that moves its binding (it
-  // validates the delete against the live binding), so v2 only CREATES the new
-  // SQLite class `McpSessionDOSqlite` and the `MCP_SESSION` binding moves to it.
-  // The old KV `McpSessionDO` is left orphaned (unbound, kept as a stub export in
-  // server.ts so the migration stays valid); it can be deleted in a later deploy
-  // now that nothing binds it. Session state is ephemeral, so nothing is lost.
+  // also refuses to delete a class in the same deploy that moves its binding, so
+  // the move happened over two deploys: v2 created the new SQLite class
+  // `McpSessionDOSqlite` and moved the `MCP_SESSION` binding to it; now that
+  // nothing binds the old KV `McpSessionDO`, v3 deletes it. Session state is
+  // ephemeral, so nothing is lost.
   "migrations": [
     {
       "tag": "v1",
@@ -42,6 +41,10 @@
       "tag": "v2",
       "new_sqlite_classes": ["McpSessionDOSqlite"],
     },
+    {
+      "tag": "v3",
+      "deleted_classes": ["McpSessionDO"],
+    },
   ],
   "services": [
     {