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/test/prompt-finder.test.ts

@@ -88,6 +88,18 @@ describe('findPrompt', () => {
             expect(pos).toBeNull();
             cleanup();
         });
+
+        it('handles global flag safely (strips g to avoid lastIndex)', () => {
+            const { terminal, cleanup } = term(['user@host:~$ cmd']);
+            const finder: PromptFinder = { type: 'regex', pattern: /\$/g };
+            const pos = findPrompt(terminal as unknown as XtermTerminal, finder);
+            expect(pos).not.toBeNull();
+            expect(pos!.col).toBe(11);
+            // Call again — should return same result (no lastIndex drift)
+            const pos2 = findPrompt(terminal as unknown as XtermTerminal, finder);
+            expect(pos2).toEqual(pos);
+            cleanup();
+        });
     });
 
     describe('custom strategy', () => {

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

@@ -1,7 +1,6 @@
 import { describe, it, expect, afterEach } from 'vitest';
 import { createMockTerminal } from './helpers.js';
 import { ZerolagInputAddon } from '../src/zerolag-input-addon.js';
-import type { Terminal } from '../src/types.js';
 
 function setup(lines: string[] = ['$ '], promptChar = '$') {
     const mock = createMockTerminal({ buffer: { lines } });
@@ -83,12 +82,12 @@ describe('ZerolagInputAddon', () => {
     });
 
     describe('removeChar', () => {
-        it('removes last character from pendingText', () => {
+        it('returns "pending" when removing from pendingText', () => {
             const { addon } = tracked();
             addon.addChar('a');
             addon.addChar('b');
-            const removed = addon.removeChar();
-            expect(removed).toBe(true);
+            const source = addon.removeChar();
+            expect(source).toBe('pending');
             expect(addon.pendingText).toBe('a');
         });
 
@@ -97,10 +96,11 @@ describe('ZerolagInputAddon', () => {
             expect(addon.removeChar()).toBe(false);
         });
 
-        it('decrements flushed when pending is empty', () => {
+        it('returns "flushed" when removing from flushed text', () => {
             const { addon } = tracked();
             addon.setFlushed(3, 'abc');
-            expect(addon.removeChar()).toBe(true);
+            const source = addon.removeChar();
+            expect(source).toBe('flushed');
             expect(addon.getFlushed().count).toBe(2);
             expect(addon.getFlushed().text).toBe('ab');
         });
@@ -109,7 +109,8 @@ describe('ZerolagInputAddon', () => {
             const { addon } = tracked();
             addon.setFlushed(2, 'ab');
             addon.addChar('c');
-            expect(addon.removeChar()).toBe(true);
+            const source = addon.removeChar();
+            expect(source).toBe('pending');
             expect(addon.pendingText).toBe('');
             expect(addon.getFlushed().count).toBe(2); // flushed unchanged
         });
@@ -120,6 +121,21 @@ describe('ZerolagInputAddon', () => {
             addon.removeChar();
             expect(addon.hasPending).toBe(false);
         });
+
+        it('detects buffer text and removes from it when both empty', () => {
+            const { addon } = tracked(['$ hello']);
+            // Both pending and flushed are empty, but buffer has text
+            const source = addon.removeChar();
+            expect(source).toBe('flushed');
+            // "hello" (5 chars) detected, then one removed = 4
+            expect(addon.getFlushed().count).toBe(4);
+            expect(addon.getFlushed().text).toBe('hell');
+        });
+
+        it('returns false on empty prompt with no buffer text', () => {
+            const { addon } = tracked(['$ ']);
+            expect(addon.removeChar()).toBe(false);
+        });
     });
 
     describe('clear', () => {
@@ -276,6 +292,22 @@ describe('ZerolagInputAddon', () => {
         });
     });
 
+    describe('state.visible', () => {
+        it('is false before activate', () => {
+            const addon = new ZerolagInputAddon();
+            expect(addon.state.visible).toBe(false);
+            // No cleanup needed — never activated
+        });
+
+        it('is false after dispose', () => {
+            const { addon, mock } = tracked();
+            addon.addChar('x');
+            addon.dispose();
+            expect(addon.state.visible).toBe(false);
+            mock.cleanup();
+        });
+    });
+
     describe('rerender / refreshFont', () => {
         it('rerender does not crash when no text', () => {
             const { addon } = tracked();