Make the dist directory configurable

Set it with `dist_dir` in bunext.config.ts or `--dist-dir` on any CLI
command (precedence: --dist-dir > BUNEXT_DIST_DIR > dist_dir > .bunext).
setupDistDir() resolves it in the CLI's preAction hook and at the start
of bunextInit(), so custom servers get the config value too.

- Read dist-derived paths from grabDirNames() inside functions instead of
  at import time; a guard test enforces this.
- Derive the client asset URL prefix from the dist dir instead of
  hard-coding /.bunext.
- Make the dev watcher ignore rules and probe follow the dist dir.
- Validate the dir: inside the project root, outside src/, public/ and
  node_modules/, URL-safe characters only.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/commands/index.ts

@@ -6,6 +6,7 @@ import dev from "./dev";
 import build from "./build";
 import sitemap from "./sitemap";
 import { log } from "../utils/log";
+import setupDistDir from "../functions/setup-dist-dir";
 
 /**
  * # Describe Program
@@ -23,6 +24,20 @@ program.addCommand(start());
 program.addCommand(build());
 program.addCommand(sitemap());
 
+/**
+ * # Resolve the Dist Directory
+ * Before any command runs, from `--dist-dir` or the config. Child server
+ * processes inherit it through `BUNEXT_DIST_DIR`.
+ */
+program.hook("preAction", async (_program, action_command) => {
+    try {
+        await setupDistDir({ dist_dir: action_command.opts().distDir });
+    } catch (error: any) {
+        log.error(error?.message || String(error));
+        process.exit(1);
+    }
+});
+
 /**
  * # Handle Unavailable Commands
  */
@@ -39,4 +54,4 @@ program.on("command:*", () => {
 /**
  * # Parse Arguments
  */
-program.parse(Bun.argv);
+await program.parseAsync(Bun.argv);