fix(cloud): strip DO migrations from preview deploy config so PR builds stop failing

Preview (non-main) Workers Builds deploy via 'wrangler versions upload', which
rejects any config containing Durable Object migrations (error 10211). Previews
share production's already-applied DO state, so they neither need nor can apply
migrations. build.mjs strips 'migrations' from the generated dist/server/wrangler.json
on non-main CI branches; main keeps them and applies on the real deploy. Fail-safe:
only strips on a confirmed non-main CI branch, never on a production deploy.

Leaves the orphaned KV McpSessionDO + its stub export in place (harmless, unbound);
not worth a delete migration whose own preview build can't pass.

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)`,
+    );
+  }
+}