Make action a thin wrapper around game-ci/unity-engine-core

Delegates build logic to the extracted implementation in
game-ci/unity-engine-core instead of maintaining a local copy, per
game-ci/roadmap#11 workstream 2 (Option A) — third and final engine
repo to make this move, after unity-activate and unity-test-runner.
src/model/* removed; build/test coverage (including the index.ts
orchestration integration tests) now lives in the destination repo.

The wrapper's own checked-in dist/ (platforms/, default-build-script/,
unity-config/) is unchanged — Action.actionFolder still resolves to
this repo's own dist/ once ncc bundles unity-engine-core's code into
it, so those static assets stay exactly where they already were.

src/index.ts

@@ -1,85 +1,9 @@
-import * as core from '@actions/core';
-import { Action, BuildParameters, Cache, Docker, ImageTag, Output } from './model';
-import MacBuilder from './model/mac-builder';
-import PlatformSetup from './model/platform-setup';
-import { Plugin, loadPlugin } from './model/plugin';
+// Thin wrapper: the actual build logic lives in game-ci/unity-engine-core.
+// See game-ci/roadmap#11 (workstream 2) for the "thin wrapper" migration this is part of.
+import { runMain } from '@game-ci/unity-engine-core/dist/unity-builder';
 
-// Exported so tests can drive the lifecycle directly without depending on
-// vitest's module re-loading (which changed in vitest 4).
-export async function runMain() {
-  try {
-    Action.checkCompatibility();
-    Cache.verify();
+export { runMain };
 
-    const { workspace, actionFolder } = Action;
-    const buildParameters = await BuildParameters.create();
-    const baseImage = new ImageTag(buildParameters);
-
-    // Load optional plugin. The default implementation is @game-ci/orchestrator.
-    const plugin = await loadPlugin();
-    await plugin?.initialize(buildParameters, workspace);
-
-    let exitCode = -1;
-
-    if (plugin?.canHandleBuild()) {
-      // Plugin handles the build entirely (remote providers, hot runner, test workflows)
-      const result = await plugin.handleBuild(baseImage.toString());
-
-      exitCode = result.fallbackToLocal
-        ? await runLocalBuild(buildParameters, baseImage, workspace, actionFolder, plugin)
-        : result.exitCode;
-    } else if (buildParameters.providerStrategy === 'local') {
-      exitCode = await runLocalBuild(buildParameters, baseImage, workspace, actionFolder, plugin);
-    } else {
-      throw new Error(
-        `Provider strategy "${buildParameters.providerStrategy}" requires @game-ci/orchestrator. ` +
-          'Install it via the game-ci/orchestrator action, or use providerStrategy=local.',
-      );
-    }
-
-    // Set core outputs
-    await Output.setBuildVersion(buildParameters.buildVersion);
-    await Output.setAndroidVersionCode(buildParameters.androidVersionCode);
-    await Output.setEngineExitCode(exitCode);
-
-    // Plugin handles post-build (artifacts, archiving, retention)
-    await plugin?.handlePostBuild(exitCode);
-
-    if (exitCode !== 0) {
-      core.setFailed(`Build failed with exit code ${exitCode}`);
-    }
-  } catch (error) {
-    core.setFailed((error as Error).message);
-  }
-}
-
-async function runLocalBuild(
-  buildParameters: BuildParameters,
-  baseImage: ImageTag,
-  workspace: string,
-  actionFolder: string,
-  plugin?: Plugin,
-): Promise<number> {
-  await plugin?.beforeLocalBuild(workspace);
-
-  await PlatformSetup.setup(buildParameters, actionFolder);
-  const exitCode =
-    process.platform === 'darwin'
-      ? await MacBuilder.run(actionFolder)
-      : await Docker.run(baseImage.toString(), {
-          workspace,
-          actionFolder,
-          ...buildParameters,
-        });
-
-  await plugin?.afterLocalBuild(workspace, exitCode);
-
-  return exitCode;
-}
-
-// Auto-run when this module is the entry point. Tests import the file via
-// `await import('./index')` purely to register the mock factories and then
-// call `runMain()` directly.
 if (process.env.NODE_ENV !== 'test') {
   runMain();
 }