cli(sync): quiet stderr/stdout capture for structured output

Author: tony

src/vcspull/cli/sync.py

@@ -2,12 +2,14 @@
 
 from __future__ import annotations
 
+import contextlib
 import logging
 import sys
 import typing as t
 from collections.abc import Callable
 from copy import deepcopy
 from datetime import datetime
+from io import StringIO
 
 from libvcs._internal.shortcuts import create_project
 from libvcs.url import registry as url_tools
@@ -173,7 +175,7 @@ def sync(
         progress_callback = progress_cb
     else:
 
-        def silent_progress(_output: str, _timestamp: datetime) -> None:
+        def silent_progress(output: str, timestamp: datetime) -> None:
             """Suppress progress for machine-readable output."""
             return None
 
@@ -205,12 +207,29 @@ def silent_progress(_output: str, _timestamp: datetime) -> None:
             )
             continue
 
+        buffer: StringIO | None = None
+        captured_output: str | None = None
         try:
-            update_repo(repo, progress_callback=progress_callback)
+            if is_human:
+                update_repo(repo, progress_callback=progress_callback)
+            else:
+                buffer = StringIO()
+                with (
+                    contextlib.redirect_stdout(buffer),
+                    contextlib.redirect_stderr(
+                        buffer,
+                    ),
+                ):
+                    update_repo(repo, progress_callback=progress_callback)
+                captured_output = buffer.getvalue()
         except Exception as e:
             summary["failed"] += 1
             event["status"] = "error"
             event["error"] = str(e)
+            if not is_human and buffer is not None and not captured_output:
+                captured_output = buffer.getvalue()
+            if captured_output:
+                event["details"] = captured_output.strip()
             formatter.emit(event)
             if is_human:
                 log.info(

tests/test_cli.py

@@ -663,3 +663,39 @@ def test_sync_ndjson_machine_output(
         event.get("status") for event in events if event["reason"] == "sync"
     }
     assert preview_statuses == {"preview"}
+
+
+def test_sync_json_machine_output(
+    tmp_path: pathlib.Path,
+    capsys: pytest.CaptureFixture[str],
+    monkeypatch: pytest.MonkeyPatch,
+    user_path: pathlib.Path,
+    config_path: pathlib.Path,
+    git_repo: GitSync,
+) -> None:
+    """JSON mode should emit a single array without progress chatter."""
+    config = {
+        "~/github_projects/": {
+            "my_git_repo": {
+                "url": f"git+file://{git_repo.path}",
+                "remotes": {"origin": f"git+file://{git_repo.path}"},
+            },
+        },
+    }
+    yaml_config = config_path / ".vcspull.yaml"
+    yaml_config.write_text(
+        yaml.dump(config, default_flow_style=False), encoding="utf-8"
+    )
+
+    monkeypatch.chdir(tmp_path)
+
+    with contextlib.suppress(SystemExit):
+        cli(["sync", "--json", "--dry-run", "my_git_repo"])
+
+    captured = capsys.readouterr()
+    payload = captured.out.strip()
+    assert payload.startswith("[") and payload.endswith("]"), payload
+    events = json.loads(payload)
+    assert isinstance(events, list)
+    reasons = {event["reason"] for event in events}
+    assert reasons >= {"sync", "summary"}