fix(build): invalidate freshness marker when watch writes dist (#5416)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: adrians5j

packages/build-tools/packages/watchPackage.js

@@ -1,6 +1,16 @@
+import fs from "node:fs";
+import { join } from "node:path";
+
 export default async options => {
     const { cwd } = options;
 
+    // Invalidate the build-cache freshness marker (see scripts/buildPackages
+    // distBuildHash.ts, ".webiny-build-hash"). Watch writes into dist without
+    // updating that marker, so its contents no longer match the last full
+    // build — a later `yarn build` must restore/rebuild instead of trusting the
+    // marker and skipping the cache→dist copy.
+    fs.rmSync(join(cwd, "dist", ".webiny-build-hash"), { force: true });
+
     // Must be a dynamic import — see rslibCompile.js for the reason.
     const [{ createRslib }, { pluginSvgr }] = await Promise.all([
         import("@rslib/core"),