fix(terminal): also restore charset designation after a dropped-byte gap

A gap can strand more than the pen: a dropped `ESC(B` leaves line-drawing
selected and ordinary text renders as box characters. Route both recovery
paths through one RESET_AFTER_BYTE_GAP profile covering SGR + charset.

Deliberately not a soft reset (DECSTR): xterm's DECSTR wipes kitty flags and
stacks (terminal-kitty-keyboard-mode-tracker applySoftReset), which would
silence Option chords for a live agent that negotiates them only at startup.
Reset what a gap strands and no running TUI re-asserts on its own; leave the
rest to its next repaint.

src/renderer/src/components/terminal-pane/pty-connection.test.ts

@@ -10210,7 +10210,7 @@ describe('connectPanePty', () => {
       claim: true
     })
     expect(written).toContain(viewportClear)
-    expect(written).not.toContain('\x1b[0m\x1b[2J\x1b[3J\x1b[H')
+    expect(written).not.toContain('\x1b[0m\x1b(B\x0f\x1b[2J\x1b[3J\x1b[H')
     expect(written).toEqual(
       expect.arrayContaining([coldScrollback, POST_REPLAY_MODE_RESET, blankViewport])
     )
@@ -15466,7 +15466,7 @@ describe('connectPanePty', () => {
     expect(getMainBufferSnapshot).toHaveBeenCalledWith('pty-id', { scrollbackRows: 5000 })
     expect(pane.terminal.resize).toHaveBeenCalledWith(100, 30)
     expect(pane.terminal.write).toHaveBeenCalledWith(
-      '\x1b[0m\x1b[2J\x1b[3J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[2J\x1b[3J\x1b[H',
       expect.any(Function)
     )
     expect(pane.terminal.write).toHaveBeenCalledWith('snapshot-state\r\n', expect.any(Function))
@@ -15519,7 +15519,7 @@ describe('connectPanePty', () => {
 
     expect(getMainBufferSnapshot).toHaveBeenCalledWith('pty-id', { scrollbackRows: 5000 })
     expect(pane.terminal.write).toHaveBeenCalledWith(
-      '\x1b[0m\x1b[?1049l\x1b[2J\x1b[3J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[?1049l\x1b[2J\x1b[3J\x1b[H',
       expect.any(Function)
     )
     expect(pane.terminal.write).toHaveBeenCalledWith(
@@ -15527,16 +15527,16 @@ describe('connectPanePty', () => {
       expect.any(Function)
     )
     expect(pane.terminal.write).toHaveBeenCalledWith(
-      '\x1b[0m\x1b[?1049h\x1b[2J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[?1049h\x1b[2J\x1b[H',
       expect.any(Function)
     )
     const writes = (pane.terminal.write as ReturnType<typeof vi.fn>).mock.calls.map(
       (call) => call[0]
     )
     expect(writes.indexOf('preserved-shell-history\r\n')).toBeLessThan(
-      writes.indexOf('\x1b[0m\x1b[?1049h\x1b[2J\x1b[H')
+      writes.indexOf('\x1b[0m\x1b(B\x0f\x1b[?1049h\x1b[2J\x1b[H')
     )
-    expect(writes.indexOf('\x1b[0m\x1b[?1049h\x1b[2J\x1b[H')).toBeLessThan(
+    expect(writes.indexOf('\x1b[0m\x1b(B\x0f\x1b[?1049h\x1b[2J\x1b[H')).toBeLessThan(
       writes.indexOf('altscreen-snapshot\r\n')
     )
     expect(pane.terminal.write).toHaveBeenCalledWith('altscreen-snapshot\r\n', expect.any(Function))
@@ -15866,7 +15866,7 @@ describe('connectPanePty', () => {
     await flushAsyncTicks(10)
 
     const written = pane.terminal.write.mock.calls.map(([data]) => data as string)
-    const resetIndex = written.indexOf('\x1b[0m')
+    const resetIndex = written.findIndex((data) => data.startsWith('\x1b[0m'))
     const liveIndex = written.findIndex((data) => data.includes('live-after-reveal'))
     expect(resetIndex).toBeGreaterThanOrEqual(0)
     expect(liveIndex).toBeGreaterThanOrEqual(0)
@@ -16390,7 +16390,7 @@ describe('connectPanePty', () => {
     expect(pane.terminal.clear).toHaveBeenCalled()
     expect(pane.terminal.write).not.toHaveBeenCalledWith(live, expect.any(Function))
     expect(pane.terminal.write).not.toHaveBeenCalledWith(
-      '\x1b[0m\x1b[2J\x1b[3J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[2J\x1b[3J\x1b[H',
       expect.any(Function)
     )
     disposable.dispose()
@@ -17288,7 +17288,7 @@ describe('connectPanePty', () => {
     await flushAsyncTicks(6)
 
     expect(pane.terminal.write).not.toHaveBeenCalledWith(
-      '\x1b[0m\x1b[2J\x1b[3J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[2J\x1b[3J\x1b[H',
       expect.any(Function)
     )
     expect(pane.terminal.write).toHaveBeenCalledWith(

src/renderer/src/components/terminal-pane/pty-connection.ts

@@ -124,7 +124,7 @@ import {
   POST_REPLAY_MODE_RESET,
   POST_REPLAY_REATTACH_RESET,
   POST_REPLAY_REATTACH_RESET_KEEP_MOUSE,
-  RESET_GRAPHIC_RENDITION,
+  RESET_AFTER_BYTE_GAP,
   RESET_KITTY_KEYBOARD_PROTOCOL,
   RESET_TERMINAL_CURSOR_STYLE
 } from '../../../../shared/terminal-mode-reset-profiles'
@@ -7064,9 +7064,10 @@ export function connectPanePty(
       // held the `ESC[22m`/`ESC[0m` closing a run, xterm still has bold (or any
       // other attribute) latched. Abandoning means no snapshot will rebuild the
       // buffer, so nothing else ever clears it and every later cell inherits it
-      // (STA-4042). Cheap and idempotent; a live TUI re-arms its own attributes
-      // on the next write.
-      writePtyOutputToXterm(RESET_GRAPHIC_RENDITION, true)
+      // (STA-4042). Same for the charset designation, whose loss renders text as
+      // box characters. Cheap and idempotent; a live TUI re-asserts both on its
+      // next write.
+      writePtyOutputToXterm(RESET_AFTER_BYTE_GAP, true)
       if (hadPendingOverflow) {
         return
       }

src/renderer/src/components/terminal-pane/terminal-snapshot-replay-paint.test.ts

@@ -42,7 +42,7 @@ describe('resolvePositiveTerminalDimensions', () => {
 describe('buildMainModelSnapshotReplayWrites', () => {
   it('clears normal buffer + scrollback before a normal-buffer snapshot', () => {
     expect(buildMainModelSnapshotReplayWrites({ data: 'shell-output' })).toEqual([
-      '\x1b[0m\x1b[2J\x1b[3J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[2J\x1b[3J\x1b[H',
       'shell-output'
     ])
   })
@@ -59,9 +59,9 @@ describe('buildMainModelSnapshotReplayWrites', () => {
         scrollbackAnsi: 'normal-history'
       })
     ).toEqual([
-      '\x1b[0m\x1b[?1049l\x1b[2J\x1b[3J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[?1049l\x1b[2J\x1b[3J\x1b[H',
       'normal-history',
-      '\x1b[0m\x1b[?1049h\x1b[2J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[?1049h\x1b[2J\x1b[H',
       'alt-frame'
     ])
   })
@@ -69,7 +69,7 @@ describe('buildMainModelSnapshotReplayWrites', () => {
   it('enters a cleared alt screen when no split scrollback is available', () => {
     expect(
       buildMainModelSnapshotReplayWrites({ data: 'alt-frame', alternateScreen: true })
-    ).toEqual(['\x1b[0m\x1b[?1049h\x1b[2J\x1b[H', 'alt-frame'])
+    ).toEqual(['\x1b[0m\x1b(B\x0f\x1b[?1049h\x1b[2J\x1b[H', 'alt-frame'])
   })
 })
 
@@ -153,9 +153,9 @@ describe('buildMainModelSnapshotReplayWrites alt-frame skip', () => {
         { skipAltFrame: true }
       )
     ).toEqual([
-      '\x1b[0m\x1b[?1049l\x1b[2J\x1b[3J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[?1049l\x1b[2J\x1b[3J\x1b[H',
       'normal-history',
-      '\x1b[0m\x1b[?1049h\x1b[2J\x1b[H',
+      '\x1b[0m\x1b(B\x0f\x1b[?1049h\x1b[2J\x1b[H',
       'complete-live-state'
     ])
   })
@@ -172,7 +172,7 @@ describe('buildMainModelSnapshotReplayWrites alt-frame skip', () => {
         },
         { skipAltFrame: true }
       )
-    ).toEqual(['\x1b[0m\x1b[?1049h\x1b[2J\x1b[H', 'complete-live-state'])
+    ).toEqual(['\x1b[0m\x1b(B\x0f\x1b[?1049h\x1b[2J\x1b[H', 'complete-live-state'])
   })
 
   it('keeps composed data when an older producer omits the mode boundary', () => {
@@ -181,13 +181,13 @@ describe('buildMainModelSnapshotReplayWrites alt-frame skip', () => {
         { data: 'legacy-modes-and-frame', alternateScreen: true },
         { skipAltFrame: true }
       )
-    ).toEqual(['\x1b[0m\x1b[?1049h\x1b[2J\x1b[H', 'legacy-modes-and-frame'])
+    ).toEqual(['\x1b[0m\x1b(B\x0f\x1b[?1049h\x1b[2J\x1b[H', 'legacy-modes-and-frame'])
   })
 
   it('never drops a normal-buffer snapshot, whose rows reflow correctly', () => {
     expect(
       buildMainModelSnapshotReplayWrites({ data: 'shell-output' }, { skipAltFrame: true })
-    ).toEqual(['\x1b[0m\x1b[2J\x1b[3J\x1b[H', 'shell-output'])
+    ).toEqual(['\x1b[0m\x1b(B\x0f\x1b[2J\x1b[3J\x1b[H', 'shell-output'])
   })
 
   // STA-4042: a replay only runs because renderer-bound bytes were dropped, so
@@ -206,6 +206,8 @@ describe('buildMainModelSnapshotReplayWrites alt-frame skip', () => {
     ]
     for (const writes of branches) {
       expect(writes[0].startsWith('\x1b[0m')).toBe(true)
+      // charset too: a dropped ESC(B renders text as box characters
+      expect(writes[0].includes('\x1b(B')).toBe(true)
       // Nothing may be replayed ahead of the first reset.
       expect(writes.indexOf('scrollback')).not.toBe(0)
     }

src/renderer/src/components/terminal-pane/terminal-snapshot-replay-paint.ts

@@ -1,6 +1,6 @@
 import type { ManagedPane } from '@/lib/pane-manager/pane-manager-types'
 import { readProposedPaneFitDimensions } from '@/lib/pane-manager/pane-fit'
-import { RESET_GRAPHIC_RENDITION } from '../../../../shared/terminal-mode-reset-profiles'
+import { RESET_AFTER_BYTE_GAP } from '../../../../shared/terminal-mode-reset-profiles'
 
 /**
  * Shared guards and write choreography for painting a main-model snapshot into
@@ -86,7 +86,7 @@ export function buildMainModelSnapshotReplayWrites(
     // bytes were dropped, so the pen the drop interrupted is unknown — without
     // clearing it the whole replayed buffer inherits it (STA-4042). The
     // alt-screen branches below already reset; this one did not.
-    return [`${RESET_GRAPHIC_RENDITION}\x1b[2J\x1b[3J\x1b[H`, snapshot.data]
+    return [`${RESET_AFTER_BYTE_GAP}\x1b[2J\x1b[3J\x1b[H`, snapshot.data]
   }
   // Older snapshot producers do not expose the mode/frame boundary. Keep their
   // composed data rather than dropping terminal modes together with the frame.
@@ -101,14 +101,14 @@ export function buildMainModelSnapshotReplayWrites(
     // the existing \x1b[0m, so the normal-buffer history inherited the stale pen
     // even though the alt frame after it did not (STA-4042).
     return [
-      `${RESET_GRAPHIC_RENDITION}\x1b[?1049l\x1b[2J\x1b[3J\x1b[H`,
+      `${RESET_AFTER_BYTE_GAP}\x1b[?1049l\x1b[2J\x1b[3J\x1b[H`,
       snapshot.scrollbackAnsi,
-      `${RESET_GRAPHIC_RENDITION}\x1b[?1049h\x1b[2J\x1b[H`,
+      `${RESET_AFTER_BYTE_GAP}\x1b[?1049h\x1b[2J\x1b[H`,
       ...altFrame
     ]
   }
   // Why: the snapshot's ?1049h no-ops when already on alt screen and skips
   // blank cells; clear the alt buffer so the pre-hide frame can't bleed
   // through blank cells (spares normal-buffer scrollback).
-  return ['\x1b[0m\x1b[?1049h\x1b[2J\x1b[H', ...altFrame]
+  return [`${RESET_AFTER_BYTE_GAP}\x1b[?1049h\x1b[2J\x1b[H`, ...altFrame]
 }

src/shared/terminal-mode-reset-profiles.ts

@@ -40,6 +40,21 @@ export const COLD_RESTORE_SEED_MODE_RESET = RESET_MOUSE_REPORTING
 // drains queued foreground chunks under the stale pen).
 export const RESET_GRAPHIC_RENDITION = '\x1b[0m'
 
+// Designate ASCII into G0 and shift back to it. Same failure as the pen but a
+// louder symptom: a dropped `ESC(B` leaves line-drawing selected and ordinary
+// text renders as box characters.
+const RESET_CHARSET_TO_ASCII = '\x1b(B\x0f'
+
+/**
+ * State to re-establish when renderer-bound bytes were dropped and the gap
+ * cannot be replayed away. Deliberately NOT a soft reset (DECSTR): xterm's
+ * DECSTR wipes kitty flags and stacks (see terminal-kitty-keyboard-mode-tracker
+ * applySoftReset), which would silence Option chords for a live agent that only
+ * negotiates them at startup. So reset the state a gap can strand and that no
+ * running TUI re-asserts on its own, and leave the rest to its next repaint.
+ */
+export const RESET_AFTER_BYTE_GAP = `${RESET_GRAPHIC_RENDITION}${RESET_CHARSET_TO_ASCII}`
+
 // Why: DECTCEM applies in emission order, so the payload's last ?25l/?25h is the cursor state the TUI left.
 export function replayPayloadEndsWithCursorHidden(payload: string): boolean {
   const hideIndex = payload.lastIndexOf('\x1b[?25l')