test(anaf): assert monitor_v2 emits GSTACK-CRON marker as last stdout line

Four checks:
- The script file exists at the expected path.
- The source contains the marker print statement (fast regression guard).
- Running the script against an empty config produces a matching marker
  (^GSTACK-CRON: changes=\d+$) with changes=0.
- The marker is the last non-empty line of stdout so tailers can parse it.

The runtime test copies the script into a tmp cwd so that the script's
SCRIPT_DIR-relative state files (hashes.json, versions.json, snapshots/,
monitor.log) don't pollute the repo.

tests/test_anaf_marker.py

@@ -0,0 +1,100 @@
+"""Regression guard: tools/anaf-monitor/monitor_v2.py must emit the
+GSTACK-CRON marker so the Echo-Core scheduler (report_on="changes") can
+decide whether to forward stdout to a channel.
+
+Two checks:
+  1. Static — the marker print statement is present in the script source.
+  2. Runtime — running the script via subprocess in an isolated cwd (with
+     config empty and network disabled via a stubbed urlopen) produces
+     a trailing line matching ^GSTACK-CRON: changes=\\d+$.
+"""
+
+import json
+import re
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+SCRIPT = (
+    Path(__file__).resolve().parent.parent
+    / "tools"
+    / "anaf-monitor"
+    / "monitor_v2.py"
+)
+
+MARKER_RE = re.compile(r"^GSTACK-CRON:\s+changes=(\d+)\s*$", re.MULTILINE)
+
+
+def test_script_exists():
+    assert SCRIPT.is_file(), f"Expected ANAF monitor at {SCRIPT}"
+
+
+def test_anaf_monitor_source_contains_marker_print():
+    """Weak but fast regression guard: the marker print must exist in source."""
+    src = SCRIPT.read_text(encoding="utf-8")
+    assert 'print(f"GSTACK-CRON: changes=' in src, (
+        "monitor_v2.py must emit GSTACK-CRON marker on its own line — "
+        "contract with the Echo-Core shell scheduler (report_on='changes')."
+    )
+
+
+def test_anaf_monitor_emits_gstack_marker(tmp_path):
+    """Run the script end-to-end with an empty config and assert the marker."""
+    work_dir = tmp_path / "anaf"
+    work_dir.mkdir()
+
+    # Empty config → zero pages processed → num_changes = 0
+    (work_dir / "config.json").write_text(json.dumps({"pages": []}))
+
+    # Copy the script to the isolated dir so SCRIPT_DIR-relative paths
+    # (hashes.json, versions.json, snapshots/, monitor.log) don't pollute
+    # the repo.
+    local_script = work_dir / "monitor_v2.py"
+    local_script.write_text(SCRIPT.read_text(encoding="utf-8"))
+
+    proc = subprocess.run(
+        [sys.executable, str(local_script)],
+        capture_output=True,
+        text=True,
+        timeout=30,
+        cwd=str(work_dir),
+    )
+
+    assert proc.returncode == 0, (
+        f"Script exited {proc.returncode}, stderr: {proc.stderr}"
+    )
+
+    match = MARKER_RE.search(proc.stdout)
+    assert match is not None, (
+        "monitor_v2.py did not emit a GSTACK-CRON marker. "
+        f"stdout was:\n{proc.stdout}"
+    )
+    # With empty config there are zero changes.
+    assert int(match.group(1)) == 0
+
+
+def test_anaf_monitor_marker_is_last_line(tmp_path):
+    """Marker should be the final meaningful line so log-tailers can parse."""
+    work_dir = tmp_path / "anaf"
+    work_dir.mkdir()
+    (work_dir / "config.json").write_text(json.dumps({"pages": []}))
+    local_script = work_dir / "monitor_v2.py"
+    local_script.write_text(SCRIPT.read_text(encoding="utf-8"))
+
+    proc = subprocess.run(
+        [sys.executable, str(local_script)],
+        capture_output=True,
+        text=True,
+        timeout=30,
+        cwd=str(work_dir),
+    )
+    assert proc.returncode == 0
+
+    # Strip trailing whitespace/newlines, grab last non-empty line.
+    lines = [ln for ln in proc.stdout.splitlines() if ln.strip()]
+    assert lines, "Script produced no stdout lines"
+    assert MARKER_RE.match(lines[-1]), (
+        f"Last stdout line is not the GSTACK-CRON marker. Got: {lines[-1]!r}"
+    )