fix: preserve user-added PATH entries by detecting PATH changes in cache

Fixes #606

When users manually export PATH (e.g., `export PATH="xxx/bin:$PATH"`),
the new paths were lost after vfox activation due to caching mechanism
only checking config file changes.

Root Cause:
- `vfox env` caches output based on config file modification times
- Cache didn't account for user-made changes to PATH environment variable
- Hook would return stale cached output without user's manual PATH exports

Solution:
- Add `CachedPath` field to ConfigState to track PATH value used for cache
- Update `HasChanged()` to detect when current PATH differs from cached PATH
- Update `Update()` to store current PATH when updating cache
- Use cross-platform `PathVarName` constant (Unix: "PATH", Windows: "Path")

Changes:
- internal/env/state.go: Add PATH tracking to detect user-made changes
- internal/env/state_test.go: Add TestConfigState_HasChanged_PathChanged

Testing:
- Added comprehensive test for PATH change detection
- All existing tests pass
- Cross-platform compatible (Unix/Linux/macOS/Windows)

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: aooohan

internal/env/state.go

@@ -39,6 +39,9 @@ type ConfigState struct {
 	SessionMtime int64 `json:"session_mtime,omitempty"`
 	ProjectMtime int64 `json:"project_mtime,omitempty"`
 
+	// Cached PATH value (to detect user-made PATH changes)
+	CachedPath string `json:"cached_path,omitempty"`
+
 	// Cached env output (shell script)
 	CachedOutput string `json:"cached_output,omitempty"`
 
@@ -95,7 +98,7 @@ func (s *ConfigState) saveLocked() error {
 }
 
 // HasChanged checks if any config file has changed based on modification time
-// Returns true if any config file has been modified since last check, or if project directory changed
+// Returns true if any config file has been modified since last check, or if project directory changed, or if PATH changed
 func (s *ConfigState) HasChanged(configPaths map[UseScope]string) (bool, error) {
 	s.mu.RLock()
 	defer s.mu.RUnlock()
@@ -107,6 +110,13 @@ func (s *ConfigState) HasChanged(configPaths map[UseScope]string) (bool, error)
 		return true, nil
 	}
 
+	// Check if PATH has changed since last cache
+	currentPath := os.Getenv(PathVarName)
+	if currentPath != s.CachedPath {
+		// User has modified PATH since last cache
+		return true, nil
+	}
+
 	// Check each config file
 	for scope, path := range configPaths {
 		if path == "" {
@@ -143,7 +153,7 @@ func (s *ConfigState) HasChanged(configPaths map[UseScope]string) (bool, error)
 	return false, nil
 }
 
-// Update updates the state with new config mtimes and cached output
+// Update updates the state with new config mtimes, current PATH, and cached output
 func (s *ConfigState) Update(configPaths map[UseScope]string, output string) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -175,6 +185,8 @@ func (s *ConfigState) Update(configPaths map[UseScope]string, output string) err
 		}
 	}
 
+	// Store current PATH to detect user-made changes later
+	s.CachedPath = os.Getenv(PathVarName)
 	s.CachedOutput = output
 
 	return s.saveLocked()

internal/env/state_test.go

@@ -272,3 +272,64 @@ func TestConfigState_GetCachedOutput(t *testing.T) {
 		t.Errorf("GetCachedOutput() = %q, want %q", output, "export TEST=value")
 	}
 }
+
+func TestConfigState_HasChanged_PathChanged(t *testing.T) {
+	// Save original PATH
+	origPath := os.Getenv("PATH")
+	defer func() {
+		os.Setenv("PATH", origPath)
+	}()
+
+	tmpDir := t.TempDir()
+	stateFile := filepath.Join(tmpDir, "state.json")
+	configFile := filepath.Join(tmpDir, ".vfox.toml")
+
+	// Create config file
+	err := os.WriteFile(configFile, []byte("test"), 0644)
+	if err != nil {
+		t.Fatalf("Failed to create config file: %v", err)
+	}
+
+	// Set initial PATH
+	initialPath := "/usr/bin:/bin"
+	os.Setenv("PATH", initialPath)
+
+	// Create state and update with current mtime and PATH
+	state := NewConfigState(stateFile)
+	configPaths := map[UseScope]string{
+		Global: configFile,
+	}
+
+	err = state.Update(configPaths, "export PATH=/test")
+	if err != nil {
+		t.Fatalf("Update() failed: %v", err)
+	}
+
+	// Verify cached PATH
+	if state.CachedPath != initialPath {
+		t.Errorf("CachedPath = %q, want %q", state.CachedPath, initialPath)
+	}
+
+	// Check if changed (should be false, PATH and configs are the same)
+	changed, err := state.HasChanged(configPaths)
+	if err != nil {
+		t.Fatalf("HasChanged() failed: %v", err)
+	}
+	if changed {
+		t.Error("HasChanged() should return false when nothing has changed")
+	}
+
+	// User manually adds a path
+	modifiedPath := "/home/user/bin:/usr/bin:/bin"
+	os.Setenv("PATH", modifiedPath)
+
+	// Check if changed (should be true, PATH changed)
+	changed, err = state.HasChanged(configPaths)
+	if err != nil {
+		t.Fatalf("HasChanged() failed: %v", err)
+	}
+	if !changed {
+		t.Error("HasChanged() should return true when PATH has changed")
+	}
+}
+