FN-6409: inline core types in plugin SDK declarations

Make the published plugin SDK declaration bundle self-contained for external plugins.

- Resolve private @fusion/core specifiers while emitting plugin-sdk declarations.
- Add a regression test covering built plugin-sdk .d.ts artifacts when present.
- Record a patch changeset for the published @runfusion/fusion package.

Files changed:
 .changeset/FN-6409-plugin-sdk-dts-inline.md          |  5 +++++
 packages/cli/src/__tests__/plugin-sdk-export.test.ts |  9 +++++++++
 packages/cli/tsup.config.ts                          | 11 ++++++++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

Fusion-Task-Id: FN-6409

Fusion-Task-Lineage: b7590e39-763d-48ca-9301-5131d0a94b89

.changeset/FN-6409-plugin-sdk-dts-inline.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Inline the private `@fusion/core` types into the published `@runfusion/fusion/plugin-sdk` declaration entry so standalone external plugins created with `fn plugin new` can typecheck and `pnpm build` cleanly against released Fusion. Human spot-check: `npx @runfusion/fusion@0.42.0 plugin new proof-point-plugin && cd proof-point-plugin && pnpm install && pnpm build`.

packages/cli/src/__tests__/plugin-sdk-export.test.ts

@@ -51,4 +51,13 @@ describe("plugin-sdk export surface", () => {
     const built = readFileSync(distPath, "utf-8");
     expect(built.includes("@fusion/")).toBe(false);
   });
+
+  it("has no @fusion specifiers in built plugin-sdk declaration artifact when present", () => {
+    const distPath = join(workspaceRoot, "packages", "cli", "dist", "plugin-sdk", "index.d.ts");
+    if (!existsSync(distPath)) {
+      return;
+    }
+    const built = readFileSync(distPath, "utf-8");
+    expect(built.includes("@fusion/")).toBe(false);
+  });
 });

packages/cli/tsup.config.ts

@@ -316,9 +316,18 @@ const pluginSdkBuildConfig = {
   target: "node22",
   tsconfig: join(__dirname, "..", "plugin-sdk", "tsconfig.json"),
   dts: {
-    resolve: true,
+    /*
+     * FNXC:PluginSDK 2026-06-13-12:00:
+     * FN-6409 requires the published @runfusion/fusion/plugin-sdk declaration entry to be self-contained. External plugin authors cannot resolve private @fusion/core types from scaffolded projects, so leaving @fusion/* imports in dist/plugin-sdk/index.d.ts makes tsc fail with TS2307 before ctx parameters can typecheck.
+     */
+    resolve: [/^@fusion\//],
     compilerOptions: {
       rootDir: join(__dirname, ".."),
+      baseUrl: ".",
+      paths: {
+        "@fusion/core": ["../core/src/index.ts"],
+      },
+      removeComments: true,
     },
   },
   noExternal: [/^@fusion\//],