Sanitise the diff and explain markdown content like we do with README

tests/test_explain_sanitize.py

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+"""Security regression (audit finding): the human-readable ``enroll explain``
+text output embeds harvested, attacker-influenceable values (host name, captured
+file paths shown as examples, include/exclude patterns, snapshot notes). A value
+containing a raw newline could forge an additional output line, and a control
+byte could smuggle a terminal escape sequence when the explanation is printed to
+a terminal or written with ``--out``. These must be neutralised. The JSON output
+is unaffected (json.dumps escapes control characters and cannot be restructured
+by a string value).
+"""
+
+from __future__ import annotations
+
+import json
+
+from enroll.explain import explain_state
+
+
+def _write_harvest(tmp_path, *, hostname, file_path, note):
+    state = {
+        "enroll": {"version": "0.1", "harvest_time": 1},
+        "host": {
+            "hostname": hostname,
+            "os": "debian",
+            "pkg_backend": "dpkg",
+            "os_release": {},
+        },
+        "inventory": {"packages": {}},
+        "roles": {
+            "etc_custom": {
+                "role_name": "etc_custom",
+                "managed_files": [
+                    {
+                        "path": file_path,
+                        "src_rel": "etc/x",
+                        "owner": "root",
+                        "group": "root",
+                        "mode": "0644",
+                        "reason": "custom_unowned",
+                    }
+                ],
+                "managed_dirs": [],
+                "excluded": [],
+                "notes": [note],
+            }
+        },
+    }
+    d = tmp_path / "harvest"
+    (d / "artifacts" / "etc_custom" / "etc").mkdir(parents=True)
+    (d / "state.json").write_text(json.dumps(state))
+    (d / "artifacts" / "etc_custom" / "etc" / "x").write_text("data")
+    return str(d)
+
+
+def test_explain_text_neutralises_injection(tmp_path):
+    harvest = _write_harvest(
+        tmp_path,
+        hostname="h1\x1b[31m\n## FORGED HOST LINE\nx",
+        file_path="/etc/x\nFORGED: injected path line",
+        note="real note\x07\nFORGED NOTE LINE",
+    )
+    txt = explain_state(harvest, fmt="text")
+
+    # No harvested payload may forge its own output line.
+    for line in txt.splitlines():
+        stripped = line.lstrip()
+        assert not stripped.startswith("## FORGED HOST LINE")
+        assert not stripped.startswith("FORGED:")
+        assert not stripped.startswith("FORGED NOTE LINE")
+    # No terminal escape / control bytes survive into the printed text.
+    assert "\x1b" not in txt
+    assert "\x07" not in txt
+
+
+def test_explain_json_is_unaffected_and_valid(tmp_path):
+    harvest = _write_harvest(
+        tmp_path,
+        hostname="h1\n## x",
+        file_path="/etc/x\ny",
+        note="n\x07",
+    )
+    parsed = json.loads(explain_state(harvest, fmt="json"))
+    # JSON faithfully preserves the raw values (escaped) and stays structurally
+    # valid; the control bytes are encoded, not executable.
+    assert parsed["host"]["hostname"].startswith("h1")