Fix duplicated helper command echo in Argos snapshots

docs/specs/terminal-context.md

@@ -53,11 +53,13 @@ Source of truth: `context` in `standalone/sidecar/pty-core.js`; `terminalContext
 
 **Must make diagnostic text drag-selectable**, including detail-dialog errors, without focusing the helper. Copy routing follows `docs/specs/mouse-and-clipboard.md` → "Terminal context input".
 
+**Must drain the helper's queued xterm writes and verify a single autorun command echo before placement snapshots.**
+
 **Must suppress xterm's auto-revealed scrollbar in visual snapshots**, while retaining terminal scrolling and layout.
 
 **Must fit every control inside the panel at its minimum width, label included.** Port action overflow follows `docs/specs/layout.md` → "Header context menu". The gallery's play check measures each button against the panel and against its own box.
 
-Source of truth: `TerminalContextView` in `lib/src/components/wall/TerminalContextView.tsx`; `lib/src/stories/TerminalContext.stories.tsx` supplies sample output; `lib/src/stories/Wall.stories.tsx` exercises the live helper. `lib/src/stories/HelperPlacement.stories.tsx` checks rendered placement and real xterm input/focus retention; the gallery checks narrow controls and always-visible details. `visualSnapshot` in `lib/.storybook/preview.ts` suppresses scrollbar paint.
+Source of truth: `TerminalContextView` in `lib/src/components/wall/TerminalContextView.tsx`; `lib/src/stories/TerminalContext.stories.tsx` supplies sample output; `lib/src/stories/Wall.stories.tsx` exercises the live helper. `lib/src/stories/HelperPlacement.stories.tsx` checks rendered placement and real xterm input/focus retention; the gallery checks narrow controls and always-visible details. `visualSnapshot` in `lib/.storybook/preview.ts` suppresses scrollbar paint. Tests: `lib/src/lib/platform/fake-adapter-helper.test.ts`.
 
 The Window-host workspace picker follows `docs/specs/layout.md` → Moving Surfaces between Workspaces.
 

lib/src/lib/platform/fake-adapter-helper.test.ts

@@ -0,0 +1,40 @@
+// @vitest-environment jsdom
+import { afterEach, expect, it, vi } from 'vitest';
+import { Terminal } from '@xterm/xterm';
+import { UnicodeGraphemesAddon } from '@xterm/addon-unicode-graphemes';
+import { FakePtyAdapter } from './fake-adapter';
+import { removeTerminalPaneState } from '../terminal-state-store';
+
+const ID = 'helper-reflow';
+afterEach(() => { vi.restoreAllMocks(); removeTerminalPaneState(ID); });
+
+it('preserves one command echo when the helper resizes between PTY chunks', async () => {
+  const adapter = new FakePtyAdapter();
+  const terminal = new Terminal({ cols: 33, rows: 7, allowProposedApi: true });
+  terminal.loadAddon(new UnicodeGraphemesAddon());
+  adapter.onPtyData(({ data }) => terminal.write(data));
+  const drain = () => new Promise<void>(resolve => terminal.write('', resolve));
+  try {
+    adapter.spawnPty(ID, { helper: { parentId: 'source', command: 'git status' } });
+    await Promise.resolve();
+    await drain();
+    // Make xterm yield after ten small writes: the echo, before its CRLF.
+    let clockReads = 0;
+    const clock = vi.spyOn(performance, 'now').mockImplementation(() => Math.floor(++clockReads / 11) * 20);
+    const resized = new Promise<void>(resolve => {
+      const listener = terminal.onWriteParsed(() => {
+        listener.dispose();
+        terminal.resize(26, 7);
+        resolve();
+      });
+    });
+    adapter.writePty(ID, 'git status\r');
+    await resized;
+    clock.mockRestore();
+    await drain();
+    const text = Array.from({ length: terminal.buffer.active.length }, (_, i) =>
+      terminal.buffer.active.getLine(i)?.translateToString(true) ?? '').join('');
+    expect(text.match(/git status/g)).toHaveLength(1);
+    expect(text.match(/On branch main/g)).toHaveLength(1);
+  } finally { terminal.dispose(); adapter.shutdown(); }
+});

lib/src/lib/platform/fake-adapter.ts

@@ -223,23 +223,29 @@ export class FakePtyAdapter implements PlatformAdapter {
   private startHelperShell(id: string): void {
     const helper = this.helpers.get(id)!;
     let input = '';
-    const prompt = () => this.sendOutput(id, `\x1b]633;A\x07${helper.cwd} ❯ \x1b]633;B\x07`);
+    const prompt = () => `\x1b]633;A\x07${helper.cwd} ❯ \x1b]633;B\x07`;
     this.inputHandlers.set(id, data => {
-      if (data === '\x03') { helper.busy = false; input = ''; this.sendOutput(id, '^C\r\n\x1b]633;D;130\x07'); prompt(); return; }
+      if (data === '\x03') { helper.busy = false; input = ''; this.sendOutput(id, '^C\r\n\x1b]633;D;130\x07' + prompt()); return; }
       if (helper.busy) return;
+      // Submit the echo, command output, and returned prompt as one PTY chunk.
+      // xterm 6.1.0-beta.304 can yield after parsing the echo, then replay that
+      // parsed prefix when a resize flushes the remaining queue. Keep the CRLF
+      // in the same write as the echo (fake-adapter-helper.test.ts).
+      let output = '';
       for (const char of data) {
         if (char === '\r' || char === '\n') {
           const command = input; input = '';
-          this.sendOutput(id, `\r\n\x1b]633;E;${command}\x07\x1b]633;C\x07`);
-          if (/^(sleep|nano|vim)\b/.test(command)) { helper.busy = true; this.sendOutput(id, 'Demo process running. Ctrl+C stops it.\r\n'); continue; }
-          const output = command === 'git status' ? 'On branch main\r\nnothing to commit, working tree clean' : command.startsWith('echo ') ? command.slice(5) : command === 'pwd' ? helper.cwd : command ? `Demo shell: ${command}` : '';
-          if (output) this.sendOutput(id, output + '\r\n');
-          this.sendOutput(id, '\x1b]633;D;0\x07'); prompt();
-        } else if (char === '\x7f') { if (input) { input = input.slice(0, -1); this.sendOutput(id, '\b \b'); } }
-        else { input += char; this.sendOutput(id, char); }
+          output += `\r\n\x1b]633;E;${command}\x07\x1b]633;C\x07`;
+          if (/^(sleep|nano|vim)\b/.test(command)) { helper.busy = true; output += 'Demo process running. Ctrl+C stops it.\r\n'; continue; }
+          const result = command === 'git status' ? 'On branch main\r\nnothing to commit, working tree clean' : command.startsWith('echo ') ? command.slice(5) : command === 'pwd' ? helper.cwd : command ? `Demo shell: ${command}` : '';
+          if (result) output += result + '\r\n';
+          output += '\x1b]633;D;0\x07' + prompt();
+        } else if (char === '\x7f') { if (input) { input = input.slice(0, -1); output += '\b \b'; } }
+        else { input += char; output += char; }
       }
+      if (output) this.sendOutput(id, output);
     });
-    queueMicrotask(prompt);
+    queueMicrotask(() => this.sendOutput(id, prompt()));
   }
 
   private resolveScenario(id: string): FakeScenario | null {

lib/src/stories/HelperPlacement.stories.tsx

@@ -65,6 +65,10 @@ async function openContext() {
   void flushTerminal(helper.id).then(() => { written = true; });
   await waitFor(() => expect(written).toBe(true), { timeout: 4000 });
   await settleTerminals();
+  const input = terminal(helper.id);
+  const text = Array.from({ length: input.buffer.active.length }, (_, i) =>
+    input.buffer.active.getLine(i)?.translateToString(true) ?? '').join('');
+  expect(text.match(/git status/g)).toHaveLength(1);
 }
 function expectedSide({ layout, zoomed, cursor, sourceAtEnd }: Props) {
   // Alone in the Wall, the helper avoids the cursor; beside a neighbor, it takes the neighbor's side.