Fix embedded-postgres PID file written before initialization

The PID file was written to the database directory before
`pg.initialise()`, which prevented initialization from succeeding.
Moved the PID file write to just after initialization but before
starting the database.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

.changeset/fix-embedded-db-pid-file-timing.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli-module-build': patch
+---
+
+Fixed the embedded-postgres PID file being written before database initialization, which prevented the database from initializing successfully.

packages/cli-module-build/src/lib/runner/startEmbeddedDb.ts

@@ -78,8 +78,6 @@ export async function startEmbeddedDb() {
   const port = await getPortPromise();
   const tmpDir = await fs.mkdtemp(resolvePath(os.tmpdir(), TEMP_DIR_PREFIX));
 
-  await fs.writeFile(resolvePath(tmpDir, PID_FILE), String(process.pid));
-
   const pg = new EmbeddedPostgres({
     databaseDir: tmpDir,
     user,
@@ -94,6 +92,7 @@ export async function startEmbeddedDb() {
 
   try {
     await pg.initialise();
+    await fs.writeFile(resolvePath(tmpDir, PID_FILE), String(process.pid));
     await pg.start();
   } catch (error) {
     await pg.stop().catch(() => {});