Add Windows PowerShell fallback support when pwsh is unavailable (#7)

The extension previously hardcoded the use of `pwsh` (PowerShell 7+) as
the PowerShell executable, which would fail in environments where only
Windows PowerShell 5.1 (`powershell.exe`) is available. This is common
in enterprise Windows environments where PowerShell 7+ hasn't been
deployed yet.

## Changes Made

- **Replaced hardcoded executable**: Removed the static
`POWERSHELL_EXECUTABLE = 'pwsh'` constant
- **Added dynamic detection**: Implemented
`detectPowerShellExecutable()` method that:
  1. First attempts to use `pwsh` (PowerShell 7+)
2. Falls back to `powershell` (Windows PowerShell 5.1) if `pwsh` is
unavailable
  3. Caches the detected executable to avoid repeated detection calls
- **Enhanced error handling**: Added `testExecutable()` method with
improved error messages
- **Updated all execution paths**: Modified `executeScript()` and
`isPowerShellAvailable()` methods to use the fallback logic

## Example Behavior

**Before (fails on Windows without PowerShell 7+):**
```
Error: spawn pwsh ENOENT
```

**After (automatically falls back):**
```
Using PowerShell executable: powershell
Detected PowerShell version using powershell: 5.1.19041.4648
```

## Testing

- ✅ Verified compatibility with PowerShell 7+ environments (existing
functionality preserved)
- ✅ Validated fallback logic for Windows PowerShell scenarios
- ✅ Confirmed localization parsing continues to work correctly
- ✅ Extension builds and packages successfully

The extension now works seamlessly across different Windows PowerShell
configurations without requiring users to install PowerShell 7+.

Fixes #6.

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: HeyItsGilbert <615265+HeyItsGilbert@users.noreply.github.com>

Author: Copilot

CHANGELOG.md

@@ -9,6 +9,12 @@ to structure this file.
 ## [Unreleased]
 
 ### Added
+- Windows PowerShell fallback support for better compatibility
+  - Extension now automatically detects and uses available PowerShell executable
+  - Tries PowerShell 7+ (`pwsh`) first, then falls back to Windows PowerShell 5.1 (`powershell`)
+  - Enables extension to work in enterprise environments where only Windows PowerShell is available
+  - Caches detected executable to avoid repeated detection calls
+  - Enhanced error handling with clearer error messages when no PowerShell is found
 - Changelog update instructions to Copilot instructions
   - Clear process for updating CHANGELOG.md for every PR
   - Guidelines for using Keep a Changelog format categories

src/powershellExecutor.ts

@@ -8,7 +8,7 @@ import { Logger } from './logger';
  */
 export class PowerShellExecutor {
   private logger: Logger;
-  private static readonly POWERSHELL_EXECUTABLE = 'pwsh';
+  private powershellExecutable: string | null = null;
 
   constructor() {
     this.logger = Logger.getInstance();
@@ -43,13 +43,71 @@ export class PowerShellExecutor {
     }
   }
 
+  /**
+   * Detects which PowerShell executable is available on the system
+   * Checks for pwsh first (PowerShell 7+), then falls back to powershell (Windows PowerShell 5.1)
+   */
+  private async detectPowerShellExecutable(): Promise<string> {
+    if (this.powershellExecutable) {
+      return this.powershellExecutable;
+    }
+
+    const executablesToTry = ['pwsh', 'powershell'];
+    
+    for (const executable of executablesToTry) {
+      try {
+        await this.testExecutable(executable);
+        this.powershellExecutable = executable;
+        this.logger.info(`Using PowerShell executable: ${executable}`);
+        return executable;
+      } catch (error) {
+        this.logger.debug(`${executable} not available: ${error}`);
+      }
+    }
+
+    throw new Error('No PowerShell executable found. Please install PowerShell 7+ (pwsh) or ensure Windows PowerShell (powershell) is available.');
+  }
+
+  /**
+   * Tests if a PowerShell executable is available and working
+   */
+  private testExecutable(executable: string): Promise<void> {
+    return new Promise<void>((resolve, reject) => {
+      const ps = childProcess.spawn(
+        executable,
+        ['-NoLogo', '-NoProfile', '-NonInteractive', '-Command', 'Write-Host "OK"'],
+        { shell: true }
+      );
+
+      let hasOutput = false;
+
+      ps.stdout.on('data', () => {
+        hasOutput = true;
+      });
+
+      ps.on('close', (code: number) => {
+        if (code === 0 && hasOutput) {
+          resolve();
+        } else {
+          reject(new Error(`Executable ${executable} exited with code ${code} or produced no output`));
+        }
+      });
+
+      ps.on('error', (error: Error) => {
+        // This typically happens when the executable is not found
+        reject(new Error(`Executable ${executable} not found or failed to start: ${error.message}`));
+      });
+    });
+  }
+
   /**
    * Checks if PowerShell is available on the system
    */
   public async isPowerShellAvailable(): Promise<boolean> {
     try {
+      const executable = await this.detectPowerShellExecutable();
       const output = await this.executeScript('', ['-Command', 'Write-Host "$($PSVersionTable.PSVersion)"']);
-      this.logger.info(`Detected PowerShell version: ${output.trim()}`);
+      this.logger.info(`Detected PowerShell version using ${executable}: ${output.trim()}`);
       return true;
     } catch (error) {
       this.logger.warn(`PowerShell not available or failed to execute: ${error}`);
@@ -69,9 +127,11 @@ export class PowerShellExecutor {
   * - Supports both script file execution and direct command execution
   * - Filters out potentially dangerous arguments for security
   */
-  public executeScript(scriptPath: string, args: string[] = []): Promise<string> {
+  public async executeScript(scriptPath: string, args: string[] = []): Promise<string> {
     this.logger.debug(`Executing PowerShell script: ${scriptPath} with args: ${args.join(' ')}`);
 
+    const executable = await this.detectPowerShellExecutable();
+
     // Filter arguments to prevent potentially dangerous operations
     // Allow only safe PowerShell parameters and user arguments
     const allowedArgPrefixes = [
@@ -120,7 +180,7 @@ export class PowerShellExecutor {
       }
 
       const ps = childProcess.spawn(
-        PowerShellExecutor.POWERSHELL_EXECUTABLE,
+        executable,
         pwshArguments,
         { shell: true }
       );