feat: add packaging and validation coverage

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/sidecar/sidecarProcess.ts

@@ -1,6 +1,5 @@
 import { app } from 'electron';
 import { spawn, type ChildProcessWithoutNullStreams } from 'node:child_process';
-import { join } from 'node:path';
 
 import type {
   SidecarCapabilities,
@@ -11,6 +10,7 @@ import type {
   RunTurnCommand,
 } from '@shared/contracts/sidecar';
 import type { ChatMessageRecord } from '@shared/domain/session';
+import { resolveSidecarProcess } from '@main/sidecar/sidecarRuntime';
 
 type PendingCommand =
   | {
@@ -30,30 +30,6 @@ type PendingCommand =
       onDelta: (event: TurnDeltaEvent) => void;
     };
 
-function getProjectRoot(): string {
-  return app.getAppPath();
-}
-
-function resolveSidecarProcess(): { command: string; args: string[] } {
-  if (app.isPackaged) {
-    return {
-      command: join(process.resourcesPath, 'sidecar', 'Kopaya.AgentHost.exe'),
-      args: ['--stdio'],
-    };
-  }
-
-  return {
-    command: 'dotnet',
-    args: [
-      'run',
-      '--project',
-      join(getProjectRoot(), 'sidecar', 'src', 'Kopaya.AgentHost', 'Kopaya.AgentHost.csproj'),
-      '--',
-      '--stdio',
-    ],
-  };
-}
-
 export class SidecarClient {
   private process?: ChildProcessWithoutNullStreams;
   private stdoutBuffer = '';
@@ -94,9 +70,14 @@ export class SidecarClient {
       return this.process;
     }
 
-    const sidecar = resolveSidecarProcess();
+    const sidecar = resolveSidecarProcess({
+      isPackaged: app.isPackaged,
+      appPath: app.getAppPath(),
+      resourcesPath: process.resourcesPath,
+      platform: process.platform,
+    });
     this.process = spawn(sidecar.command, sidecar.args, {
-      cwd: getProjectRoot(),
+      cwd: sidecar.cwd,
       stdio: 'pipe',
       windowsHide: true,
     });

src/main/sidecar/sidecarRuntime.ts

@@ -0,0 +1,48 @@
+import { posix, win32 } from 'node:path';
+
+export interface SidecarRuntimeContext {
+  readonly isPackaged: boolean;
+  readonly appPath: string;
+  readonly resourcesPath: string;
+  readonly platform: NodeJS.Platform;
+}
+
+export interface ResolvedSidecarProcess {
+  readonly command: string;
+  readonly args: string[];
+  readonly cwd: string;
+}
+
+function getPathModule(platform: NodeJS.Platform) {
+  return platform === 'win32' ? win32 : posix;
+}
+
+function getBundledSidecarExecutableName(platform: NodeJS.Platform): string {
+  return platform === 'win32' ? 'Kopaya.AgentHost.exe' : 'Kopaya.AgentHost';
+}
+
+export function resolveSidecarProcess(context: SidecarRuntimeContext): ResolvedSidecarProcess {
+  const pathModule = getPathModule(context.platform);
+
+  if (context.isPackaged) {
+    const sidecarDirectory = pathModule.join(context.resourcesPath, 'sidecar');
+
+    return {
+      command: pathModule.join(sidecarDirectory, getBundledSidecarExecutableName(context.platform)),
+      args: ['--stdio'],
+      cwd: sidecarDirectory,
+    };
+  }
+
+  return {
+    command: 'dotnet',
+    args: [
+      'run',
+      '--project',
+      pathModule.join(context.appPath, 'sidecar', 'src', 'Kopaya.AgentHost', 'Kopaya.AgentHost.csproj'),
+      '--',
+      '--stdio',
+    ],
+    cwd: context.appPath,
+  };
+}