diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3bb778cf..972a7e13 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,23 @@ Format based on [Keep a Changelog](https://keepachangelog.com/).
 ## [2.4.1] - 2025-11-04
 
 ### Fixed
+- **CRITICAL: Windows npm Installation PATH Detection**: Fixed Node.js spawn() unable to resolve claude on Windows
+  - **Root Cause**: Node.js spawn() doesn't use Windows PATHEXT, can't resolve bare command names in SSH/npm context
+  - **Solution**:
+    1. Pre-resolve absolute path using `where.exe`/`which` before spawning
+    2. Prefer executables with extensions (.exe, .cmd, .bat) - `where.exe` returns no-extension file first
+    3. Use `shell: true` for .cmd/.bat/.ps1 files (required to execute batch scripts on Windows)
+  - **Windows-specific Issues Solved**:
+    - `where.exe claude` returns both `claude` (no ext) and `claude.cmd`, but spawn() needs the .cmd wrapper
+    - `.cmd` files can't be spawned directly (EINVAL error), need shell: true to execute via cmd.exe
+  - **Impact**: Windows users can now use npm-installed CCS in SSH sessions with npm-installed Claude CLI
+  - **Files**:
+    - `bin/claude-detector.js`: Added execSync PATH resolution + extension preference logic
+    - `bin/ccs.js`: Added null checks + getSpawnOptions() helper for shell: true on .cmd files
+  - **Security**: Added 5-second timeout, documented command injection safety (hardcoded literals, controlled shell usage)
+  - **Diagnostics**: Enhanced error messages with platform, PATH directory count, executable name
+  - **Tested**: Verified with `where.exe claude` returning both entries, spawn EINVAL fixed with shell: true
+  - Native installation always worked; only affected npm global installs on Windows
 - **CRITICAL: PowerShell Terminal Termination**: Fixed PowerShell 7 terminal closing when using `irm | iex` installation
   - Changed `exit 1` to `return` in install.ps1 line 229 for piped script contexts
   - Terminal now stays open on installation errors, showing error messages properly
diff --git a/bin/ccs.js b/bin/ccs.js
index 01e34113..5b31660e 100755
--- a/bin/ccs.js
+++ b/bin/ccs.js
@@ -11,6 +11,18 @@ const { getSettingsPath } = require('./config-manager');
 // Version (sync with package.json)
 const CCS_VERSION = require('../package.json').version;
 
+// Helper: Get spawn options for claude execution
+// On Windows, .cmd/.bat/.ps1 files need shell: true
+function getSpawnOptions(claudePath) {
+  const isWindows = process.platform === 'win32';
+  const needsShell = isWindows && /\.(cmd|bat|ps1)$/i.test(claudePath);
+
+  return {
+    stdio: 'inherit',
+    shell: needsShell  // Required for .cmd files on Windows
+  };
+}
+
 // Special command handlers
 function handleVersionCommand() {
   console.log(`CCS (Claude Code Switch) version ${CCS_VERSION}`);
@@ -28,8 +40,15 @@ function handleVersionCommand() {
 function handleHelpCommand(remainingArgs) {
   const claudeCli = detectClaudeCli();
 
+  // Check if claude was found
+  if (!claudeCli) {
+    showClaudeNotFoundError();
+    process.exit(1);
+  }
+
   // Execute claude --help
-  const child = spawn(claudeCli, ['--help', ...remainingArgs], { stdio: 'inherit' });
+  const spawnOpts = getSpawnOptions(claudeCli);
+  const child = spawn(claudeCli, ['--help', ...remainingArgs], spawnOpts);
 
   child.on('exit', (code, signal) => {
     if (signal) {
@@ -111,8 +130,15 @@ function main() {
   if (profile === 'default') {
     const claudeCli = detectClaudeCli();
 
+    // Check if claude was found
+    if (!claudeCli) {
+      showClaudeNotFoundError();
+      process.exit(1);
+    }
+
     // Execute claude with args
-    const child = spawn(claudeCli, remainingArgs, { stdio: 'inherit' });
+    const spawnOpts = getSpawnOptions(claudeCli);
+    const child = spawn(claudeCli, remainingArgs, spawnOpts);
 
     child.on('exit', (code, signal) => {
       if (signal) {
@@ -136,9 +162,16 @@ function main() {
   // Detect Claude CLI
   const claudeCli = detectClaudeCli();
 
+  // Check if claude was found
+  if (!claudeCli) {
+    showClaudeNotFoundError();
+    process.exit(1);
+  }
+
   // Execute claude with --settings
   const claudeArgs = ['--settings', settingsPath, ...remainingArgs];
-  const child = spawn(claudeCli, claudeArgs, { stdio: 'inherit' });
+  const spawnOpts = getSpawnOptions(claudeCli);
+  const child = spawn(claudeCli, claudeArgs, spawnOpts);
 
   child.on('exit', (code, signal) => {
     if (signal) {
diff --git a/bin/claude-detector.js b/bin/claude-detector.js
index 78006848..2315fb4f 100644
--- a/bin/claude-detector.js
+++ b/bin/claude-detector.js
@@ -1,6 +1,7 @@
 'use strict';
 
 const fs = require('fs');
+const { execSync } = require('child_process');
 const { showError, expandPath } = require('./helpers');
 
 // Detect Claude CLI executable
@@ -17,19 +18,62 @@ function detectClaudeCli() {
     console.warn('    Falling back to system PATH lookup...');
   }
 
-  // Priority 2: Use 'claude' from PATH (trust the system)
-  // This is the standard case - if user installed Claude CLI, it's in their PATH
-  return 'claude';
+  // Priority 2: Resolve 'claude' from PATH using which/where.exe
+  // This fixes Windows npm installation where spawn() can't resolve bare command names
+  // SECURITY: Commands are hardcoded literals with no user input - safe from injection
+  const isWindows = process.platform === 'win32';
+
+  try {
+    const cmd = isWindows ? 'where.exe claude' : 'which claude';
+    const result = execSync(cmd, {
+      encoding: 'utf8',
+      stdio: ['ignore', 'pipe', 'ignore'],
+      timeout: 5000  // 5 second timeout to prevent hangs
+    }).trim();
+
+    // where.exe may return multiple lines (all matches in PATH order)
+    const matches = result.split('\n').map(p => p.trim()).filter(p => p);
+
+    if (isWindows) {
+      // On Windows, prefer executables with extensions (.exe, .cmd, .bat)
+      // where.exe often returns file without extension first, then the actual .cmd wrapper
+      const withExtension = matches.find(p => /\.(exe|cmd|bat|ps1)$/i.test(p));
+      const claudePath = withExtension || matches[0];
+
+      if (claudePath && fs.existsSync(claudePath)) {
+        return claudePath;
+      }
+    } else {
+      // On Unix, first match is fine
+      const claudePath = matches[0];
+
+      if (claudePath && fs.existsSync(claudePath)) {
+        return claudePath;
+      }
+    }
+  } catch (err) {
+    // Command failed - claude not in PATH
+    // Fall through to return null
+  }
+
+  // Priority 3: Claude not found
+  return null;
 }
 
-// Show Claude not found error
+// Show Claude not found error with diagnostics
 function showClaudeNotFoundError() {
   const isWindows = process.platform === 'win32';
+  const pathDirs = (process.env.PATH || '').split(isWindows ? ';' : ':');
 
   const errorMsg = `Claude CLI not found in PATH
 
 CCS requires Claude CLI to be installed and available in your PATH.
 
+[i] Diagnostic Info:
+    Platform: ${process.platform}
+    PATH directories: ${pathDirs.length}
+    Looking for: claude${isWindows ? '.exe' : ''}
+
 Solutions:
   1. Install Claude CLI:
      https://docs.claude.com/en/docs/claude-code/installation