fix(desktop-terminal): trim trailing idle prompt on no-separator shells

cleanReviveSnapshot only dropped the trailing prompt when a blank separator
sat above it (starship add_newline), so shells that print the prompt with no
preceding blank line — default PowerShell (PS C:\..>), bash user@host:~$ —
kept the idle prompt in the saved buffer and showed a duplicate under the
fresh boot prompt on every relaunch of an *active* session.

An interactive shell always reprints its prompt after a command, so the tail
of an idle buffer is the prompt, never history. Drop the short block after a
blank separator when present, otherwise drop the trailing single-line prompt.
Command output is preserved; the fresh shell reprints the live prompt on boot.

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

@@ -33,25 +33,40 @@ describe('isIdlePromptOnly', () => {
 })
 
 describe('cleanReviveSnapshot', () => {
-  it('drops a short trailing prompt block after a blank separator', () => {
+  it('drops a spaced trailing prompt block after a blank separator (starship)', () => {
     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')
+  it('drops a multi-line prompt block after a blank separator (powerline)', () => {
+    const snapshot = ['work', '', '┌─ user@host ~/project', '└─$'].join('\r\n')
 
-    expect(cleanReviveSnapshot(snapshot)).toBe(['start', '', ...tail].join('\r\n'))
+    expect(cleanReviveSnapshot(snapshot)).toBe('work')
   })
 
-  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.
+  it('drops a single-line trailing prompt with no preceding blank line (PowerShell)', () => {
+    // Default PowerShell prints no blank line before its prompt; the fresh shell
+    // reprints it on boot, so the redundant idle prompt must be trimmed here.
     const snapshot = ['echo hi', 'hi', PS_PROMPT].join('\r\n')
 
-    expect(cleanReviveSnapshot(snapshot)).toBe(snapshot)
+    expect(cleanReviveSnapshot(snapshot)).toBe('echo hi\r\nhi')
+  })
+
+  it('keeps command output and drops only the trailing prompt on a long history', () => {
+    const history = ['cmd1', 'out1', 'cmd2', 'out2']
+    const snapshot = [...history, PS_PROMPT].join('\r\n')
+
+    expect(cleanReviveSnapshot(snapshot)).toBe(history.join('\r\n'))
+  })
+
+  it('reduces a lone prompt to an empty buffer', () => {
+    expect(cleanReviveSnapshot(PS_PROMPT)).toBe('')
+    expect(cleanReviveSnapshot([PS_PROMPT, '', ''].join('\r\n'))).toBe('')
+  })
+
+  it('returns empty for a blank-only buffer without throwing', () => {
+    expect(cleanReviveSnapshot('')).toBe('')
+    expect(cleanReviveSnapshot('\r\n  \r\n')).toBe('')
   })
 })

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

@@ -174,32 +174,34 @@ const visibleText = (line: string) => stripEscapeSequences(line).replace(/[\s%]/
 
 // 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).
+// launch replays it directly above the fresh shell's prompt ("double bar").
+//
+// An interactive shell always reprints its prompt after a command finishes, so
+// the tail of an idle buffer is the prompt, never real history. Two prompt
+// shapes exist:
+//   - Spaced/multi-line (starship add_newline, powerline): a blank line sits
+//     just above the prompt, so the short block after the last blank is dropped.
+//   - Single-line (default PowerShell `PS C:\..>`, bash `user@host:~$`): no blank
+//     separator, so the final line itself is the prompt and is dropped.
+// The fresh shell reprints the current prompt on boot either way, so only the
+// redundant idle prompt is removed — command output is preserved.
 export function cleanReviveSnapshot(serialized: string): string {
-  const visible = (line: string) => stripEscapeSequences(line).replace(/[\s%]/g, '')
   const lines = serialized.split(/\r?\n/)
 
-  while (lines.length && visible(lines[lines.length - 1]) === '') {
+  while (lines.length && !visibleText(lines[lines.length - 1])) {
     lines.pop()
   }
 
-  let lastBlank = -1
-
-  for (let i = lines.length - 1; i >= 0; i -= 1) {
-    if (visible(lines[i]) === '') {
-      lastBlank = i
-
-      break
-    }
+  if (lines.length === 0) {
+    return ''
   }
 
-  // A prompt is a short block; a long tail after the blank is real output, leave it.
-  if (lastBlank >= 0 && lines.length - 1 - lastBlank <= 3) {
-    lines.length = lastBlank
-  }
+  const lastBlank = lines.findLastIndex(line => !visibleText(line))
+  const spacedPrompt = lastBlank >= 0 && lines.length - 1 - lastBlank <= 3
+
+  // Spaced prompt (starship/powerline): drop the block after the blank
+  // separator. Otherwise the last line is the single-line prompt itself.
+  lines.length = spacedPrompt ? lastBlank : lines.length - 1
 
   return lines.join('\r\n')
 }