fix: address 7 issues found in xterm-zerolag-input audit

1. Regex global flag safety — strip `g` flag before matching to prevent
   lastIndex mutation and missing .index on match results
2. state.visible false before activate — null overlay no longer reports
   visible: true
3. removeChar() returns 'pending' | 'flushed' | false instead of boolean
   so consumers can distinguish whether to send backspace to PTY
4. removeChar() implements buffer detection cascade (step 3) — detects
   existing prompt text when both pending and flushed are empty
5. RenderKey includes text content, not just length — prevents stale
   renders when setFlushed() called with same count but different text
6. Remove dead `import type { Terminal }` from test file
7. Remove internal `FontStyle` from public exports

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/xterm-zerolag-input/src/index.ts

@@ -7,5 +7,4 @@ export type {
     PromptFinder,
     PromptPosition,
     CellDimensions,
-    FontStyle,
 } from './types.js';

packages/xterm-zerolag-input/src/prompt-finder.ts

@@ -27,11 +27,17 @@ export function findPrompt(
             }
 
             case 'regex': {
+                // Create a fresh non-global regex to avoid lastIndex mutation
+                // and ensure .match() returns a single result with .index
+                const pattern = finder.pattern;
+                const safePattern = pattern.global
+                    ? new RegExp(pattern.source, pattern.flags.replace('g', ''))
+                    : pattern;
                 for (let row = terminal.rows - 1; row >= 0; row--) {
                     const line = buffer.getLine(viewportTop + row);
                     if (!line) continue;
                     const text = line.translateToString(true);
-                    const match = text.match(finder.pattern);
+                    const match = text.match(safePattern);
                     if (match) {
                         const col = match.index ?? 0;
                         return { row, col };

packages/xterm-zerolag-input/src/zerolag-input-addon.ts

@@ -48,7 +48,8 @@ const DEFAULT_CURSOR = '#e0e0e0';
  *     zerolag.clear();
  *     ws.send(text + '\r');
  *   } else if (data === '\x7f') {
- *     if (zerolag.removeChar()) ws.send(data);
+ *     const source = zerolag.removeChar();
+ *     if (source === 'flushed') ws.send(data); // only send if text was already in PTY
  *   } else if (data.length === 1 && data.charCodeAt(0) >= 32) {
  *     zerolag.addChar(data);
  *   }
@@ -194,14 +195,19 @@ export class ZerolagInputAddon implements XtermAddon {
      * Remove the last character from the overlay.
      *
      * Cascade order:
-     * 1. Remove from `pendingText` if non-empty
-     * 2. Decrement `flushedOffset` if pending is empty but flushed exists
-     * 3. Try `detectBufferText()` if both are empty
+     * 1. Remove from `pendingText` if non-empty → returns `'pending'`
+     * 2. Decrement `flushedOffset` if pending is empty but flushed exists → returns `'flushed'`
+     * 3. Try `detectBufferText()` if both are empty, then decrement → returns `'flushed'`
      *
-     * @returns `true` if a character was removed, `false` if nothing to remove.
-     *          When `false`, the consumer should NOT send backspace to the PTY.
+     * @returns The source of the removed character, or `false` if nothing to remove.
+     *
+     * - `'pending'`: A character was removed from unsent text. The consumer
+     *   should NOT send backspace to the PTY (the text was never transmitted).
+     * - `'flushed'`: A character was removed from text already sent to the PTY.
+     *   The consumer SHOULD send backspace to the PTY.
+     * - `false`: Nothing to remove. The consumer should NOT send backspace.
      */
-    removeChar(): boolean {
+    removeChar(): 'pending' | 'flushed' | false {
         if (this._pendingText.length > 0) {
             this._pendingText = this._pendingText.slice(0, -1);
             if (this._pendingText.length > 0 || this._flushedOffset > 0) {
@@ -209,7 +215,7 @@ export class ZerolagInputAddon implements XtermAddon {
             } else {
                 this._hide();
             }
-            return true;
+            return 'pending';
         }
 
         if (this._flushedOffset > 0) {
@@ -220,7 +226,21 @@ export class ZerolagInputAddon implements XtermAddon {
             } else {
                 this._hide();
             }
-            return true;
+            return 'flushed';
+        }
+
+        // Both empty — try detecting text already on the prompt line
+        // (handles tab completion, arrow-key edits, etc.)
+        this._detectBufferText();
+        if (this._flushedOffset > 0) {
+            this._flushedOffset--;
+            this._flushedText = this._flushedText.slice(0, -1);
+            if (this._flushedOffset > 0) {
+                this._render();
+            } else {
+                this._hide();
+            }
+            return 'flushed';
         }
 
         return false;
@@ -369,7 +389,7 @@ export class ZerolagInputAddon implements XtermAddon {
             pendingText: this._pendingText,
             flushedLength: this._flushedOffset,
             flushedText: this._flushedText,
-            visible: this._overlay?.style.display !== 'none',
+            visible: this._overlay !== null && this._overlay.style.display !== 'none',
             promptPosition: this._lastPromptPos ? { ...this._lastPromptPos } : null,
         };
     }
@@ -500,8 +520,9 @@ export class ZerolagInputAddon implements XtermAddon {
                 }
             }
 
-            // Skip redundant re-renders
-            const renderKey = `${displayText.length}:${startCol}:${activePrompt.row}:${activePrompt.col}:${totalCols}:${this._flushedOffset}`;
+            // Skip redundant re-renders — include text content to detect
+            // same-length changes (e.g., setFlushed with different text)
+            const renderKey = `${displayText}:${startCol}:${activePrompt.row}:${activePrompt.col}:${totalCols}:${this._flushedOffset}`;
             if (renderKey === this._lastRenderKey && this._overlay.style.display !== 'none') return;
             this._lastRenderKey = renderKey;