build(shared): nest internal build chunks under _chunks/

Rolldown's content-hashed shared chunks were emitted flat in dist/runtime alongside the entry points. Since the package exposes "./*" mapping to dist/runtime/*, those chunks were enumerated as public subpaths and surfaced as phantom breaking changes in API-diff tooling whenever a chunk hash changed. Route them into dist/runtime/_chunks/ so the single-segment wildcard glob only matches real entry points. Runtime and type resolution are unchanged.

Author: jacekradko

.changeset/shared-nest-internal-chunks.md

@@ -0,0 +1,5 @@
+---
+'@clerk/shared': patch
+---
+
+Nest rolldown's shared build chunks under `dist/runtime/_chunks/` instead of emitting them flat next to the entry points. The package exposes `"./*"`, which resolves to `dist/runtime/*`, so the content-hashed internal chunks were being surfaced as public subpaths and showed up as phantom breaking changes in API-diff tooling whenever a chunk hash shifted. Entry and type resolution are unchanged; the chunks are still referenced by relative path.

packages/shared/tsdown.config.mts

@@ -55,6 +55,23 @@ export default defineConfig(({ watch, env }) => {
       ],
       outDir: './dist/runtime',
       unbundle: false,
+      // Route rolldown's shared chunks into a nested `_chunks/` directory. The
+      // package's `"./*"` wildcard export resolves to `dist/runtime/*`, and
+      // tooling that globs that surface (e.g. break-check's API snapshot) uses
+      // a single-segment `*`, so content-hashed internal chunks sitting flat in
+      // `dist/runtime` get enumerated as phantom public subpaths. Nesting them
+      // one level down keeps them out of the wildcard's reach while runtime
+      // resolution (relative imports between entries and chunks) is unchanged.
+      outputOptions: options => {
+        const { chunkFileNames } = options;
+        return {
+          ...options,
+          chunkFileNames:
+            typeof chunkFileNames === 'function'
+              ? info => `_chunks/${chunkFileNames(info)}`
+              : `_chunks/${chunkFileNames ?? '[name]-[hash].js'}`,
+        };
+      },
     },
   ];
 });