refactor(core): split types.ts into co-located types/ domain modules (#2024 PR 1)

packages/core/rollup.config.ts

@@ -1,8 +1,46 @@
+import { readFileSync } from "node:fs";
 import { readFile, rm } from "node:fs/promises";
 import { builtinModules } from "node:module";
+import { fileURLToPath } from "node:url";
 import type { Plugin, RollupOptions } from "rollup";
 import typescript from "@rollup/plugin-typescript";
 
+/**
+ * Build one rollup entry point per published subpath export.
+ *
+ * `package.json` `exports` is the source of truth for the public API: each
+ * `"./x": { import: "./dist/x.js" }` must have a real `dist/x.js` on disk.
+ * With `preserveModules`, rollup tree-shakes any module that is a *pure
+ * re-export barrel* (no runtime side effects) — index's `export *` gets
+ * flattened straight to the underlying modules, so the barrel's own chunk is
+ * never emitted. `tsc` still emits the `.d.ts`, so typecheck passes while the
+ * runtime/bundler resolution of the subpath fails. Making every exported
+ * entrypoint an explicit input prevents that: entry points are never
+ * tree-shaken away. This keeps barrel entrypoints (e.g. `types.ts`) emitted.
+ */
+function exportEntryPoints(): Record<string, string> {
+  // Resolve package.json relative to this config file (not the CWD) so the
+  // build works regardless of where rollup is invoked from. fileURLToPath
+  // (not URL.pathname) keeps this correct on Windows.
+  const pkgPath = fileURLToPath(new URL("./package.json", import.meta.url));
+  const pkg = JSON.parse(readFileSync(pkgPath, "utf8")) as {
+    exports: Record<string, { import?: string }>;
+  };
+  const input: Record<string, string> = {};
+  // Only entries with an `import` condition map to an emitted dist chunk.
+  // Warn (don't silently skip) on any other shape — e.g. a future string-form
+  // or require-only export — so a missing emit is visible at build time.
+  for (const [name, entry] of Object.entries(pkg.exports)) {
+    if (!entry?.import) {
+      console.warn(`[rollup] export "${name}" has no { import } field — not emitting a dist entry for it`);
+      continue;
+    }
+    const key = entry.import.replace(/^\.\/dist\//, "").replace(/\.js$/, "");
+    input[key] = `src/${key}.ts`;
+  }
+  return input;
+}
+
 const externalPackages = new Set(["yaml", "zod"]);
 const nodeBuiltins = new Set([
   ...builtinModules,
@@ -41,10 +79,7 @@ function cleanDist(): Plugin {
 }
 
 const config: RollupOptions = {
-  input: {
-    index: "src/index.ts",
-    "migration/storage-v2": "src/migration/storage-v2.ts",
-  },
+  input: exportEntryPoints(),
   output: {
     dir: "dist",
     format: "es",