feat(hot-runner): implement hot runner protocol with registry, health monitoring, and job dispatch (#791)

Adds persistent Unity editor instance support to reduce build iteration time
by eliminating cold-start overhead. Includes:

- HotRunnerTypes: interfaces for config, status, job request/result, transport
- HotRunnerRegistry: in-memory runner management with file-based persistence
- HotRunnerHealthMonitor: periodic health checks, idle recycling, job-count recycling
- HotRunnerDispatcher: job routing with wait-for-runner, timeout, and output streaming
- HotRunnerService: high-level API integrating registry, health, and dispatch
- 34 unit tests covering registration, filtering, health, dispatch, timeout, fallback
- action.yml inputs for hot runner configuration (7 new inputs)
- Input/BuildParameters integration for hot runner settings
- index.ts wiring with cold-build fallback when hot runner unavailable

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/index.ts

@@ -3,6 +3,8 @@ import { Action, BuildParameters, Cache, Orchestrator, Docker, ImageTag, Output
 import { Cli } from './model/cli/cli';
 import MacBuilder from './model/mac-builder';
 import PlatformSetup from './model/platform-setup';
+import { HotRunnerService } from './model/orchestrator/services/hot-runner';
+import { HotRunnerConfig } from './model/orchestrator/services/hot-runner/hot-runner-types';
 
 async function runMain() {
   try {
@@ -21,17 +23,46 @@ async function runMain() {
 
     let exitCode = -1;
 
-    if (buildParameters.providerStrategy === 'local') {
+    // Hot runner path: attempt to use a persistent Unity editor instance
+    if (buildParameters.hotRunnerEnabled) {
+      core.info('[HotRunner] Hot runner mode enabled, attempting hot build...');
+
+      const hotRunnerConfig: HotRunnerConfig = {
+        enabled: true,
+        transport: buildParameters.hotRunnerTransport,
+        host: buildParameters.hotRunnerHost,
+        port: buildParameters.hotRunnerPort,
+        healthCheckInterval: buildParameters.hotRunnerHealthInterval,
+        maxIdleTime: buildParameters.hotRunnerMaxIdle,
+        maxJobsBeforeRecycle: 0, // no automatic recycle by job count
+      };
+
+      const hotRunnerService = new HotRunnerService();
+
+      try {
+        await hotRunnerService.initialize(hotRunnerConfig);
+        const result = await hotRunnerService.submitBuild(buildParameters, (output) => {
+          core.info(output);
+        });
+
+        exitCode = result.exitCode;
+        core.info(`[HotRunner] Build completed with exit code ${exitCode}`);
+        await hotRunnerService.shutdown();
+      } catch (hotRunnerError) {
+        await hotRunnerService.shutdown();
+
+        if (buildParameters.hotRunnerFallbackToCold) {
+          core.warning(
+            `[HotRunner] Hot runner failed: ${(hotRunnerError as Error).message}. Falling back to cold build.`,
+          );
+          exitCode = await runColdBuild(buildParameters, baseImage, workspace, actionFolder);
+        } else {
+          throw hotRunnerError;
+        }
+      }
+    } else if (buildParameters.providerStrategy === 'local') {
       core.info('Building locally');
-      await PlatformSetup.setup(buildParameters, actionFolder);
-      exitCode =
-        process.platform === 'darwin'
-          ? await MacBuilder.run(actionFolder)
-          : await Docker.run(baseImage.toString(), {
-              workspace,
-              actionFolder,
-              ...buildParameters,
-            });
+      exitCode = await runColdBuild(buildParameters, baseImage, workspace, actionFolder);
     } else {
       await Orchestrator.run(buildParameters, baseImage.toString());
       exitCode = 0;
@@ -50,4 +81,28 @@ async function runMain() {
   }
 }
 
+async function runColdBuild(
+  buildParameters: BuildParameters,
+  baseImage: ImageTag,
+  workspace: string,
+  actionFolder: string,
+): Promise<number> {
+  if (buildParameters.providerStrategy === 'local') {
+    core.info('Building locally');
+    await PlatformSetup.setup(buildParameters, actionFolder);
+
+    return process.platform === 'darwin'
+      ? await MacBuilder.run(actionFolder)
+      : await Docker.run(baseImage.toString(), {
+          workspace,
+          actionFolder,
+          ...buildParameters,
+        });
+  } else {
+    await Orchestrator.run(buildParameters, baseImage.toString());
+
+    return 0;
+  }
+}
+
 runMain();