A reattach stops disarming the modes a live program still holds

web/src/components/terminal.test.tsx

@@ -186,41 +186,24 @@ describe('Terminal', () => {
     expect(em.live().text()).toBe('\x1bcfresh')
   })
 
-  it('stops reporting the pointer once the replayed backlog has drained', () => {
-    // The bug: a daemon restart replays a snapshot's scrollback, and that
-    // scrollback carries the mouse-tracking sequence of a program that was
-    // killed with the daemon and so never wrote its own reset. The emulator
-    // ends the replay armed, with a brand new shell behind it, and every
-    // pointer move over the terminal is an SGR report typed at the prompt.
+  it('leaves a live program its modes once the replayed backlog has drained', () => {
+    // A replay ends at the live program's present state: mouse tracking in
+    // the backlog of a running session is not the orphan of a dead shell, it
+    // is what the program on the other end believes is armed right now.
+    // Clearing it here desynced this emulator from that program — with
+    // claude's fullscreen renderer (alternate screen plus tracking) the
+    // cleared emulator turned every wheel tick into arrow keys at the
+    // program's stdin until its next full redraw. A revived session needs no
+    // clearing from this side either: the daemon ends every revive preload
+    // with settleModes, so a dead shell's reset is already in these bytes.
     const { sock, em } = mountTerminal((e) => <Terminal sessionId="s1" createEmulator={e.create} />)
 
     act(() => sock.emitControl(attached({ ref: 1, id: 's1', seq: 0, head: 8 })))
-    act(() => sock.emitOutput(1, 'backlog!'))
-
-    // After the backlog, never before it: clearing the modes first would be
-    // undone by the very bytes that set them.
-    expect(em.live().reportingStops).toEqual([1])
-  })
-
-  it('leaves the modes alone until the whole backlog is in', () => {
-    const { sock, em } = mountTerminal((e) => <Terminal sessionId="s1" createEmulator={e.create} />)
-
-    act(() => sock.emitControl(attached({ ref: 1, id: 's1', seq: 0, head: 12 })))
-    act(() => sock.emitOutput(1, 'part'))
-
-    expect(em.live().reportingStops).toEqual([])
-  })
-
-  it('says nothing about the modes when there is no backlog to replay', () => {
-    // A freshly spawned session has head === seq. Nothing was replayed, so
-    // there is no stale state to answer for, and a program that armed
-    // tracking on its first line must keep it.
-    const { sock, em } = mountTerminal((e) => <Terminal sessionId="s1" createEmulator={e.create} />)
-
-    act(() => sock.emitControl(attached({ ref: 1, id: 's1', seq: 0 })))
     act(() => sock.emitOutput(1, '\x1b[?1003h'))
 
-    expect(em.live().reportingStops).toEqual([])
+    // The backlog and nothing after it: any settle sequence appended here
+    // would be this client overruling a program that is still running.
+    expect(em.live().text()).toBe('\x1b[?1003h')
   })
 
   it('does not reset when the attach is an ordinary continuation', () => {

web/src/components/terminal.tsx

@@ -389,19 +389,12 @@ export function Terminal({
     // the shell's stdin. head === seq on a fresh spawn opens it immediately.
     let consumed = 0
     let muteUntil = 0
-    // Whether a replayed backlog is still arriving under this attachment.
-    //
-    // The gate above keeps the emulator's *answers* off the wire while the
-    // scrollback replays. This is the other half of the same problem: a
-    // replay also re-runs every mode change in that scrollback, and the
-    // modes outlive it. A shell killed with the daemon inside a
-    // mouse-tracking program wrote the sequence that turned tracking on and
-    // never the one that turns it off, so replaying its snapshot leaves this
-    // emulator reporting the pointer at a fresh prompt — see stopReporting.
-    // Turned off the moment the backlog has been consumed, which is where
-    // the reset goes; false already on a fresh spawn, whose head === seq
-    // means there is nothing replayed to answer for.
-    let replaying = false
+    // The modes a replay re-runs — mouse tracking, focus reporting — are
+    // deliberately left exactly where the backlog puts them. A live
+    // session's replay ends at the program's present state, so clearing
+    // anything here desyncs this emulator from a program that still holds
+    // those modes armed; and a revived session's preload already ends with
+    // the daemon's settleModes, so a dead shell's reset is in the bytes.
     // The attachment's epoch, stepped with every reseed. Each done callback
     // below closes over the value it was written under: one enqueued under a
     // previous attachment can fire after the reseed, and its bytes are
@@ -878,7 +871,6 @@ export function Terminal({
         epoch++
         consumed = a.seq
         muteUntil = a.head
-        replaying = a.head > a.seq
         if (a.truncated) emulator.write(RESET)
         emulator.resize(a.cols, a.rows)
         tabOsc = a.title
@@ -897,13 +889,6 @@ export function Terminal({
         emulator.write(bytes, () => {
           if (e !== epoch) return
           consumed += bytes.length
-          // In the done callback and not at frame arrival, for the same
-          // reason the gate is: this has to land after the parser has read
-          // the backlog, or the modes it clears are set again behind it.
-          if (replaying && consumed >= muteUntil) {
-            replaying = false
-            emulator.stopReporting()
-          }
         })
       }),
     )

web/src/emulator/emulator.test.ts

@@ -241,49 +241,6 @@ describe('Emulator interface', () => {
     })
   })
 
-  it('stops reporting the pointer a replayed program had asked for', async () => {
-    // The bug this is the floor for: a snapshot's scrollback carries the
-    // mouse-tracking sequence of a program that died with the daemon, so
-    // replaying it arms an emulator sitting in front of a fresh shell. From
-    // there every mouse move is an SGR report typed at the prompt.
-    const el = document.createElement('div')
-    document.body.appendChild(el)
-    const em = createXtermEmulator({ cols: 10, rows: 4 })
-    em.attachTo(el)
-    const seen: string[] = []
-    em.onData((b) => seen.push(new TextDecoder().decode(b)))
-    await settled(em, '\x1b[?1003h\x1b[?1006h\x1b[?1004h')
-
-    expect(em.reportsPointer()).toBe(true)
-    // Everything the arming itself put on the wire is the bug, not the fix —
-    // an unfocused terminal answers ESC[?1004h with a focus-out report right
-    // away, which is exactly the kind of typing-with-nobody-there this
-    // clears. What matters below is that the clearing adds none of its own.
-    seen.length = 0
-    em.stopReporting()
-    await settled(em, '')
-
-    expect(em.reportsPointer()).toBe(false)
-    expect(seen.join('')).toBe('')
-    em.dispose()
-    el.remove()
-  })
-
-  it('leaves a live program its pointer reporting', async () => {
-    // stopReporting is aimed at a replay, never at output. A program that
-    // turns tracking on after the backlog has drained keeps it.
-    const el = document.createElement('div')
-    document.body.appendChild(el)
-    const em = createXtermEmulator({ cols: 10, rows: 4 })
-    em.attachTo(el)
-    em.stopReporting()
-    await settled(em, '\x1b[?1002h')
-
-    expect(em.reportsPointer()).toBe(true)
-    em.dispose()
-    el.remove()
-  })
-
   describe('alt-screen scrolling', () => {
     // Fullscreen TUIs — claude's fullscreen mode, vim, less — live on the
     // alternate buffer, which keeps no scrollback, so the viewport scroll
@@ -442,12 +399,10 @@ describe('Emulator interface', () => {
     em.dispose()
 
     expect(() => em.focus()).not.toThrow()
-    expect(() => em.stopReporting()).not.toThrow()
     expect(() => em.setTheme({ background: '#000000' })).not.toThrow()
     expect(em.contentSize()).toBeNull()
     expect(() => em.answerQueries(true)).not.toThrow()
     expect(em.applicationCursorKeys()).toBe(false)
-    expect(em.reportsPointer()).toBe(false)
   })
 
   it('attaches to an element with no WebGL context available', () => {

web/src/emulator/types.ts

@@ -211,34 +211,6 @@ export interface Emulator {
    * run rather than land in the line editor.
    */
   paste(text: string): void
-  /**
-   * Forget the reporting modes a replayed backlog turned on.
-   *
-   * A session's scrollback is bytes, not state, so replaying it re-runs
-   * every mode change the shell ever wrote — including the ones belonging to
-   * a program that has since exited or been killed with the daemon. Mouse
-   * tracking and focus reporting are the two that matter, because they are
-   * the only modes that put bytes on the wire with nobody typing: an armed
-   * emulator sends an SGR report for every pointer move, and the shell
-   * behind it receives that as somebody typing "35;61;22M" at the prompt.
-   *
-   * Only those two, and deliberately. Application cursor keys and bracketed
-   * paste are also replayable and also stale, but they change what a
-   * keystroke means rather than inventing keystrokes, so clearing them
-   * against a live program would break arrows and pastes in a client that
-   * had nothing wrong with it. See settleModes in internal/session for the
-   * wider reset, which runs where there is no live program to break.
-   *
-   * Local to this emulator. Nothing reaches the shell.
-   */
-  stopReporting(): void
-  /**
-   * Whether this emulator would report pointer movement to the program.
-   *
-   * Exists so the reset above can be tested for what it does rather than for
-   * the bytes it writes.
-   */
-  reportsPointer(): boolean
   /**
    * Mount into the DOM.
    *

web/src/emulator/xterm.ts

@@ -52,19 +52,6 @@ export const TERMINAL_FONT_FAMILY =
  */
 export const NEWLINE_CHORD_BYTES = '\x1b\r'
 
-/**
- * Every mouse protocol off, every mouse encoding off, focus reporting off.
- *
- * The set is exhaustive on purpose. The protocols (1000 press-only, 1002
- * drag, 1003 any motion) and the encodings (1005 UTF-8, 1006 SGR, 1015
- * urxvt, 1016 SGR-pixels) are separate switches in the terminal, and a
- * program may have set any combination of them; clearing the protocol a
- * particular program happened to use is how this fix would work on one
- * machine and not the next.
- */
-const STOP_REPORTING =
-  '\x1b[?1000l\x1b[?1002l\x1b[?1003l\x1b[?1005l\x1b[?1006l\x1b[?1015l\x1b[?1016l\x1b[?1004l'
-
 /**
  * xterm.js behind the Emulator seam.
  *
@@ -364,21 +351,6 @@ export function createXtermEmulator(opts: XtermOptions = {}): Emulator {
       term.paste(text)
     },
 
-    stopReporting() {
-      if (disposed) return
-      // Written as output rather than set on xterm's services, because the
-      // parser is the only supported way in and because it keeps the ordering
-      // honest: this lands in the stream where the caller put it, so live
-      // output arriving after it is applied after it. A program that turns
-      // tracking back on a moment later still gets tracking.
-      term.write(STOP_REPORTING)
-    },
-
-    reportsPointer() {
-      if (disposed) return false
-      return term.modes.mouseTrackingMode !== 'none'
-    },
-
     attachTo(el: HTMLElement) {
       term.open(el)
       // Best-effort GPU rendering; the DOM renderer is a fine fallback, and

web/src/testing/emulator.ts

@@ -29,16 +29,6 @@ export interface FakeEmulator extends Emulator {
   appCursor: boolean
   /** Simulate the user typing. */
   send(text: string): void
-  /**
-   * Where each stopReporting() call landed, as a count of written chunks.
-   *
-   * A count rather than a flag because the ordering against the output
-   * stream is the property worth testing: clearing the modes before a
-   * replayed backlog has been written would be undone by the backlog.
-   */
-  readonly reportingStops: number[]
-  /** What reportsPointer() answers; set by hand like measured. */
-  pointerReports: boolean
   /** Every selectWordAt() cell, in order. */
   readonly wordPresses: Cell[]
   /** Every extendSelectionTo() cell, in order. */
@@ -74,7 +64,6 @@ export function createFakeEmulator(opts: FakeEmulatorOptions = {}): FakeEmulator
   const written: string[] = []
   const themes: TerminalTheme[] = []
   const queryAnswers: boolean[] = []
-  const reportingStops: number[] = []
   const wordPresses: Cell[] = []
   const extensions: Cell[] = []
   const pasted: string[] = []
@@ -83,7 +72,6 @@ export function createFakeEmulator(opts: FakeEmulatorOptions = {}): FakeEmulator
     written,
     themes,
     queryAnswers,
-    reportingStops,
     wordPresses,
     extensions,
     pasted,
@@ -99,7 +87,6 @@ export function createFakeEmulator(opts: FakeEmulatorOptions = {}): FakeEmulator
     measured: null,
     onGlass: null,
     appCursor: false,
-    pointerReports: false,
     detector: null,
 
     text: () => written.join(''),
@@ -156,13 +143,6 @@ export function createFakeEmulator(opts: FakeEmulatorOptions = {}): FakeEmulator
       self.send(text)
     },
 
-    stopReporting() {
-      reportingStops.push(written.length)
-      mutable(self).pointerReports = false
-    },
-
-    reportsPointer: () => self.pointerReports,
-
     attachTo(el: HTMLElement) {
       mutable(self).mountedOn = el
     },