fix(cloud): back the MCP session Durable Object with SQLite

The MCP session DO now extends the Cloudflare Agents `McpAgent` base, which
stores its state in SQLite. apps/cloud still had the original `McpSessionDO`
class on the key-value backend (`new_classes`), and Cloudflare cannot convert a
live class to SQLite in place, so every session 500'd with
"This Durable Object is not backed by SQLite storage".

Session state is ephemeral, so delete the old KV class and create a new
SQLite-backed class (`McpSessionDOSqlite`) in migration v2, repointing the
`MCP_SESSION` binding. The DO is addressed by binding + idFromName, so the
rename is transparent at runtime. host-cloudflare was already on
`new_sqlite_classes`, so only cloud was affected.

Author: RhysSullivan

apps/cloud/src/server.ts

@@ -41,7 +41,11 @@ const sentryOptions = (env: Env) => ({
 // not a global fetch wrapper.
 // ---------------------------------------------------------------------------
 
-export const McpSessionDO = Sentry.instrumentDurableObjectWithSentry(
+// Exported under `McpSessionDOSqlite` (not `McpSessionDO`) to match the SQLite
+// class migration in wrangler.jsonc: the Agents (`McpAgent`) base needs a
+// SQLite-backed DO, and the original KV-backed `McpSessionDO` class cannot be
+// converted in place, so it is deleted and replaced by this new class.
+export const McpSessionDOSqlite = Sentry.instrumentDurableObjectWithSentry(
   sentryOptions,
   McpSessionDOBase,
 );

apps/cloud/wrangler.jsonc

@@ -20,15 +20,27 @@
     "bindings": [
       {
         "name": "MCP_SESSION",
-        "class_name": "McpSessionDO",
+        "class_name": "McpSessionDOSqlite",
       },
     ],
   },
+  // The MCP session DO moved to the Cloudflare Agents (`McpAgent`) base, which
+  // stores its state in SQLite. The original `McpSessionDO` class was deployed
+  // with the key-value backend (`new_classes`), and Cloudflare cannot convert a
+  // live class to SQLite in place. Session state is ephemeral, so v2 deletes the
+  // old KV class and creates a new SQLite-backed class under a new name; the
+  // `MCP_SESSION` binding repoints to it. The DO is addressed by binding +
+  // `idFromName`, so the class rename is transparent at runtime.
   "migrations": [
     {
       "tag": "v1",
       "new_classes": ["McpSessionDO"],
     },
+    {
+      "tag": "v2",
+      "deleted_classes": ["McpSessionDO"],
+      "new_sqlite_classes": ["McpSessionDOSqlite"],
+    },
   ],
   "services": [
     {