fix: keep vim interceptor active in both modes so Esc returns to normal

The interceptor now stays installed for the entire vim session, handling
both normal and insert modes. Esc switches from insert back to normal,
and /vim toggles the entire interceptor on/off.

examples/extensions/custom-editor-demo.go

@@ -9,35 +9,34 @@ import (
 	"kit/ext"
 )
 
-// normalMode tracks whether the vim-like normal mode is active.
-// When false, all keys pass through to the default editor (insert mode).
+// vimActive tracks whether the vim interceptor is installed at all.
+// normalMode tracks whether we are in normal mode (true) or insert mode (false).
+var vimActive bool
 var normalMode bool
 
-// savedCtx holds the extension context for use in the HandleKey callback.
-var savedCtx ext.Context
-
 // Init demonstrates the editor interceptor system. Extensions can intercept
 // key events before they reach the built-in editor and wrap the editor's
 // rendered output. This example implements a simple vim-like modal editor
 // with normal/insert mode switching.
 //
 // Slash commands:
-//   - /vim       — toggle vim mode (normal ↔ insert)
+//   - /vim       — toggle vim mode on/off
 //   - /vim-info  — show current editor mode
 func Init(api ext.API) {
-	// /vim — toggle vim-like normal/insert mode.
+	// /vim — toggle the vim interceptor on/off.
 	api.RegisterCommand(ext.CommandDef{
 		Name:        "vim",
-		Description: "Toggle vim-like normal/insert mode",
+		Description: "Toggle vim-like modal editing",
 		Execute: func(args string, ctx ext.Context) (string, error) {
-			savedCtx = ctx
-			if normalMode {
-				// Switch to insert mode (remove interceptor).
+			if vimActive {
+				// Turn off vim mode entirely.
+				vimActive = false
 				normalMode = false
 				ctx.ResetEditor()
-				return "Switched to INSERT mode (default editor).", nil
+				return "Vim mode OFF. Default editor restored.", nil
 			}
-			// Switch to normal mode (install interceptor).
+			// Turn on vim mode, start in normal mode.
+			vimActive = true
 			normalMode = true
 			ctx.SetEditor(ext.EditorConfig{
 				HandleKey: func(key string, currentText string) ext.EditorKeyAction {
@@ -47,7 +46,7 @@ func Init(api ext.API) {
 					return renderVimMode(width, defaultContent)
 				},
 			})
-			return "Switched to NORMAL mode. Press 'i' to insert, 'h/j/k/l' to navigate.", nil
+			return "Vim mode ON (NORMAL). Press 'i' to insert, Esc to return to normal, h/j/k/l to navigate.", nil
 		},
 	})
 
@@ -56,16 +55,30 @@ func Init(api ext.API) {
 		Name:        "vim-info",
 		Description: "Show current vim mode",
 		Execute: func(args string, ctx ext.Context) (string, error) {
-			if normalMode {
-				return "Current mode: NORMAL (vim interceptor active)", nil
+			if !vimActive {
+				return "Vim mode is OFF (default editor).", nil
 			}
-			return "Current mode: INSERT (default editor)", nil
+			if normalMode {
+				return "Vim mode ON — NORMAL mode", nil
+			}
+			return "Vim mode ON — INSERT mode (Esc to return to normal)", nil
 		},
 	})
 }
 
-// handleVimKey processes keys in vim normal mode.
+// handleVimKey processes keys for both normal and insert modes.
+// The interceptor stays active in both modes so Esc can switch back.
 func handleVimKey(key string, currentText string) ext.EditorKeyAction {
+	if !normalMode {
+		// ── Insert mode: pass everything through except Esc ──
+		if key == "esc" {
+			normalMode = true
+			return ext.EditorKeyAction{Type: ext.EditorKeyConsumed}
+		}
+		return ext.EditorKeyAction{Type: ext.EditorKeyPassthrough}
+	}
+
+	// ── Normal mode ──
 	switch key {
 	// Navigation: remap hjkl to arrow keys.
 	case "h":
@@ -79,27 +92,19 @@ func handleVimKey(key string, currentText string) ext.EditorKeyAction {
 
 	// Mode switching.
 	case "i":
-		// Enter insert mode.
 		normalMode = false
-		if savedCtx.ResetEditor != nil {
-			savedCtx.ResetEditor()
-		}
 		return ext.EditorKeyAction{Type: ext.EditorKeyConsumed}
 
 	// Editing shortcuts.
 	case "x":
-		// Delete character under cursor (remap to delete key).
 		return ext.EditorKeyAction{Type: ext.EditorKeyRemap, RemappedKey: "delete"}
 	case "0":
-		// Jump to beginning of line.
 		return ext.EditorKeyAction{Type: ext.EditorKeyRemap, RemappedKey: "home"}
 	case "$":
-		// Jump to end of line.
 		return ext.EditorKeyAction{Type: ext.EditorKeyRemap, RemappedKey: "end"}
 
 	// Submission.
 	case "enter":
-		// In normal mode, Enter submits the current text.
 		if strings.TrimSpace(currentText) != "" {
 			return ext.EditorKeyAction{Type: ext.EditorKeySubmit}
 		}
@@ -107,11 +112,10 @@ func handleVimKey(key string, currentText string) ext.EditorKeyAction {
 
 	// Block most printable keys in normal mode.
 	default:
-		// Let control sequences and special keys through (e.g., ctrl+c, esc).
+		// Let control sequences and special keys through (e.g., ctrl+c).
 		if len(key) > 1 && key != "space" {
 			return ext.EditorKeyAction{Type: ext.EditorKeyPassthrough}
 		}
-		// Consume single printable characters — don't insert in normal mode.
 		return ext.EditorKeyAction{Type: ext.EditorKeyConsumed}
 	}
 }
@@ -123,10 +127,7 @@ func renderVimMode(width int, defaultContent string) string {
 		mode = "-- INSERT --"
 	}
 
-	// Build a mode indicator line.
 	indicator := fmt.Sprintf("  %s", mode)
-
-	// Pad to fill width.
 	padding := width - len(indicator)
 	if padding > 0 {
 		indicator += strings.Repeat(" ", padding)