fix(desktop-terminal): stop idle prompt accumulation across relaunches

An idle terminal tab (no command ever typed) grew one extra copy of the
shell's boot prompt on every close/reopen: persistSnapshot re-serialized a
buffer that was just the replayed old prompt plus the fresh shell's new
prompt, and cleanReviveSnapshot's blank-line trim can't strip prompts on
shells like default PowerShell that print no separator line.

Track real user input (keystrokes/paste, drag-and-drop paths, injected
commands) and, when a session had none, skip re-serializing. If the buffer
we loaded carried no real scrollback (empty or only a repeated prompt),
clear it so the next launch shows a single fresh prompt and any existing
accumulation heals; otherwise leave the prior snapshot untouched so real
history from an earlier active session survives an idle reopen.

Salvages #61584 (activity tracking) and #61577 (clearing content-free idle
buffers) into one path: it also heals already-polluted buffers, counts
drag-and-drop and injected input as activity, and never discards genuine
short command history (only empty/all-identical buffers are cleared).

Co-authored-by: alelpoan <alelpoan@proton.me>
Co-authored-by: liuhao1024 <sunsky.lau@gmail.com>

apps/desktop/src/app/right-sidebar/terminal/revive-buffer.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, it } from 'vitest'
+
+import { cleanReviveSnapshot, isIdlePromptOnly } from './use-terminal-session'
+
+// A default-PowerShell idle prompt: no blank-line separator before it.
+const PS_PROMPT = 'PS C:\\Users\\Aleksandr>'
+
+describe('isIdlePromptOnly', () => {
+  it('is true for an empty or whitespace-only buffer', () => {
+    expect(isIdlePromptOnly('')).toBe(true)
+    expect(isIdlePromptOnly('\r\n  \r\n')).toBe(true)
+  })
+
+  it('is true for a lone prompt line', () => {
+    expect(isIdlePromptOnly(PS_PROMPT)).toBe(true)
+  })
+
+  it('is true for a buffer that is only repeated identical prompts (accumulation)', () => {
+    expect(isIdlePromptOnly([PS_PROMPT, PS_PROMPT, PS_PROMPT].join('\r\n'))).toBe(true)
+  })
+
+  it('ignores blank gaps between repeated prompts (the "gapped" variant)', () => {
+    expect(isIdlePromptOnly([PS_PROMPT, '', '', PS_PROMPT].join('\r\n'))).toBe(true)
+  })
+
+  it('is false when the buffer holds a real command and output', () => {
+    expect(isIdlePromptOnly([PS_PROMPT, 'cd project', 'PS C:\\Users\\Aleksandr\\project>'].join('\r\n'))).toBe(false)
+  })
+
+  it('is false when two different prompts are present (cwd actually changed)', () => {
+    expect(isIdlePromptOnly([PS_PROMPT, 'PS C:\\Users\\Aleksandr\\project>'].join('\r\n'))).toBe(false)
+  })
+})
+
+describe('cleanReviveSnapshot', () => {
+  it('drops a short trailing prompt block after a blank separator', () => {
+    const snapshot = ['echo hi', 'hi', '', PS_PROMPT].join('\r\n')
+
+    expect(cleanReviveSnapshot(snapshot)).toBe('echo hi\r\nhi')
+  })
+
+  it('keeps real output when the tail after the blank line is long', () => {
+    const tail = ['line1', 'line2', 'line3', 'line4', 'line5']
+    const snapshot = ['start', '', ...tail].join('\r\n')
+
+    expect(cleanReviveSnapshot(snapshot)).toBe(['start', '', ...tail].join('\r\n'))
+  })
+
+  it('leaves a prompt with no preceding blank line untouched (heuristic limitation)', () => {
+    // Default PowerShell prints no blank line before its prompt, so the trailing
+    // prompt survives here — the idle-accumulation path (isIdlePromptOnly) is what
+    // actually covers that shell, not this trimmer.
+    const snapshot = ['echo hi', 'hi', PS_PROMPT].join('\r\n')
+
+    expect(cleanReviveSnapshot(snapshot)).toBe(snapshot)
+  })
+})

apps/desktop/src/app/right-sidebar/terminal/use-terminal-session.ts

@@ -168,13 +168,17 @@ function stripInitialPromptGap(data: string) {
   return prefix
 }
 
+// A row's content with ANSI escapes and all whitespace stripped — '' for a
+// spacer / prompt-gap / zsh `%` marker row.
+const visibleText = (line: string) => stripEscapeSequences(line).replace(/[\s%]/g, '')
+
 // Trim the shell's trailing idle prompt from a serialized snapshot before it's
 // persisted. Without it, the saved buffer ends in the old prompt, so the next
 // launch replays it directly above the fresh shell's prompt ("double bar"). The
 // prompt is the short block after the last blank line (starship's add_newline
 // gap); only a short tail is dropped, so real command output is never trimmed and
 // configs without that blank line simply keep the historical prompt (no loss).
-function cleanReviveSnapshot(serialized: string): string {
+export function cleanReviveSnapshot(serialized: string): string {
   const visible = (line: string) => stripEscapeSequences(line).replace(/[\s%]/g, '')
   const lines = serialized.split(/\r?\n/)
 
@@ -200,6 +204,17 @@ function cleanReviveSnapshot(serialized: string): string {
   return lines.join('\r\n')
 }
 
+// True when a revive buffer holds no real scrollback: empty, or only repeats of
+// one line (the idle prompt). This is the idle-accumulation signature (#61572) —
+// each relaunch replayed the saved prompt(s) and the fresh shell printed one more
+// below, growing the tab by a line per cycle. Real sessions vary (prompt +
+// command + output), so genuine short histories are never mistaken for idle.
+export function isIdlePromptOnly(serialized: string): boolean {
+  const lines = serialized.split(/\r?\n/).map(visibleText).filter(Boolean)
+
+  return lines.length === 0 || lines.every(line => line === lines[0])
+}
+
 interface UseTerminalSessionOptions {
   /** Renderer-side terminal id (the tab handle), used to key the agent reader. */
   id: string
@@ -336,6 +351,10 @@ export function useTerminalSession({
   // Snapshot the revive buffer once: live snapshots feed updateTerminalReviveBuffer
   // and would otherwise re-arm replay on every store-driven re-render.
   const initialReviveBufferRef = useRef(reviveBuffer)
+  // Whether the user ever fed input into this session (keystrokes, paste,
+  // drag-and-drop paths, or an injected command). Gates idle-buffer handling in
+  // persistSnapshot so an untouched tab never re-saves an accumulating snapshot.
+  const hasSessionActivityRef = useRef(false)
   const shellNameRef = useRef('shell')
   const selectionLabelRef = useRef('')
   const selectionRef = useRef('')
@@ -486,6 +505,22 @@ export function useTerminalSession({
 
       lastSnapshotAt = Date.now()
 
+      // No user input this session: never re-serialize. The live buffer now holds
+      // the replayed history plus a fresh boot prompt, and re-saving that is
+      // exactly what grew idle tabs by one prompt line per relaunch (#61572).
+      // If the buffer we loaded carried no real scrollback (empty, or only a
+      // repeated prompt), clear it so the next launch shows a single fresh prompt
+      // and any pre-existing accumulation heals. Otherwise leave the prior
+      // snapshot untouched so real history from an earlier active session
+      // survives an idle reopen instead of being overwritten.
+      if (!hasSessionActivityRef.current) {
+        if (isIdlePromptOnly(initialReviveBufferRef.current ?? '')) {
+          updateTerminalReviveBuffer(id, '')
+        }
+
+        return
+      }
+
       try {
         const snapshot = serialize.serialize({ scrollback: PERSISTENT_SESSION_SCROLLBACK })
         updateTerminalReviveBuffer(id, cleanReviveSnapshot(snapshot))
@@ -544,6 +579,7 @@ export function useTerminalSession({
         return
       }
 
+      hasSessionActivityRef.current = true
       void terminalApi.write(id, `${paths.map(p => quotePathForShell(p, shellNameRef.current)).join(' ')} `)
       term.focus()
       triggerHaptic('selection')
@@ -640,6 +676,7 @@ export function useTerminalSession({
     })
 
     const dataDisposable = term.onData(data => {
+      hasSessionActivityRef.current = true
       const id = sessionIdRef.current
 
       if (id) {
@@ -846,6 +883,7 @@ export function useTerminalSession({
         return
       }
 
+      hasSessionActivityRef.current = true
       void window.hermesDesktop?.terminal?.write(sessionId, `${command}\r`)
       $terminalInjection.set(null)
       termRef.current?.focus()