cli: make next backend start the default

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

.changeset/itchy-rabbits-exist.md

@@ -0,0 +1,7 @@
+---
+'@backstage/cli': minor
+---
+
+The new backend start command that used to be enabled by setting `EXPERIMENTAL_BACKEND_START` is now the default. To revert to the old behavior, set `LEGACY_BACKEND_START` instead.
+
+This new command is no longer based on Webpack, but instead uses Node.js loaders to transpile on the fly. Rather than hot reloading modules the entire backend is now restarted on change, but the SQLite database state is still maintained across restarts via a parent process.

.github/vale/Vocab/Backstage/accept.txt

@@ -401,6 +401,7 @@ tooltip
 tooltips
 touchpoint
 transpilation
+transpile
 transpiled
 transpiler
 transpilers

packages/backend-next/package.json

@@ -18,7 +18,7 @@
     "backstage"
   ],
   "scripts": {
-    "start": "EXPERIMENTAL_BACKEND_START=1 backstage-cli package start",
+    "start": "backstage-cli package start",
     "build": "backstage-cli package build",
     "lint": "backstage-cli package lint",
     "test": "backstage-cli package test",

packages/cli/src/commands/start/startBackend.ts

@@ -36,7 +36,7 @@ export async function startBackend(options: StartBackendOptions) {
     });
 
     await waitForExit();
-  } else if (process.env.EXPERIMENTAL_BACKEND_START) {
+  } else if (!process.env.LEGACY_BACKEND_START) {
     const waitForExit = await startBackendExperimental({
       entry: 'src/index',
       checksEnabled: false, // not supported