fix(tests): harden env isolation and replace remaining sleep-sync races

The full 42k-test run and complete npm check surfaced three more classes:

- Environment isolation: local ~/.honcho defaultHost and SSH_* variables
  leaked into Python/TUI tests. Pin the default Honcho host in the
  hermetic fixture, isolate the one fallback test from ~/.honcho, and
  blank SSH_* around terminalSetup tests. This flipped 20 false failures
  back to deterministic behavior on developer machines.
- Background-thread sleep-sync: Honcho async writer tests patched
  time.sleep globally, then busy-polled with that same mocked sleep. Under
  full-suite load the poller could starve the writer. Each test now waits
  on an Event emitted by the exact flush/retry transition; 30/30 passed
  under 15-way contention.
- Desktop streaming: the test slept 80ms and assumed a 500ms timer could
  not fire before its assertion. A loaded runner descheduled the test for
  >500ms and both chunks arrived. Producer controls now gate second-chunk
  and completion transitions explicitly.

Also make file-retry observability complete: a self-healed flaky file now
prints BOTH attempts' full output in the FLAKY summary. Two behavioral
runner tests prove pass-on-retry is green+loud+traceback-preserving, while
a deterministic failure remains red.

tests/test_run_tests_parallel.py

@@ -277,3 +277,85 @@ def test_positional_path_not_treated_as_flag(tmp_path: Path) -> None:
     # Discovery found the probe file (2 tests), proving the positional path
     # was consumed as a root, not forwarded to pytest as a bad flag.
     assert "test_flagprobe.py" in proc.stdout, proc.stdout
+
+
+def test_file_retry_self_heals_and_prints_both_attempts(tmp_path: Path) -> None:
+    """A pass-on-retry is green, loud, and retains the failing traceback."""
+    repo_root = Path(__file__).resolve().parent.parent
+    runner = repo_root / "scripts" / "run_tests_parallel.py"
+    marker = tmp_path / "ran-once"
+    probe = tmp_path / "test_flaky_probe.py"
+    probe.write_text(
+        textwrap.dedent(
+            f"""
+            from pathlib import Path
+
+            def test_flaky_once():
+                marker = Path({str(marker)!r})
+                if not marker.exists():
+                    marker.write_text("failed once")
+                    assert False, "simulated first-attempt flake"
+                assert True
+            """
+        ),
+        encoding="utf-8",
+    )
+
+    proc = subprocess.run(
+        [
+            sys.executable,
+            str(runner),
+            "--files",
+            str(probe),
+            "--file-retries",
+            "1",
+            "-j",
+            "1",
+            "-q",
+        ],
+        cwd=repo_root,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        text=True,
+        timeout=60,
+    )
+
+    assert proc.returncode == 0, proc.stdout
+    assert "FLAKY file" in proc.stdout
+    assert "simulated first-attempt flake" in proc.stdout
+    assert "first-attempt output" in proc.stdout
+    assert "retry output" in proc.stdout
+
+
+def test_file_retry_does_not_launder_deterministic_failure(tmp_path: Path) -> None:
+    """A real regression fails both attempts and the runner remains red."""
+    repo_root = Path(__file__).resolve().parent.parent
+    runner = repo_root / "scripts" / "run_tests_parallel.py"
+    probe = tmp_path / "test_red_probe.py"
+    probe.write_text(
+        "def test_always_red():\n    assert False, 'deterministic regression'\n",
+        encoding="utf-8",
+    )
+
+    proc = subprocess.run(
+        [
+            sys.executable,
+            str(runner),
+            "--files",
+            str(probe),
+            "--file-retries",
+            "1",
+            "-j",
+            "1",
+            "-q",
+        ],
+        cwd=repo_root,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        text=True,
+        timeout=60,
+    )
+
+    assert proc.returncode == 1, proc.stdout
+    assert "deterministic regression" in proc.stdout
+    assert "FLAKY file" not in proc.stdout