diff --git a/tests/unit/test_supervise_edge.py b/tests/unit/test_supervise_edge.py
new file mode 100644
index 0000000..7f05450
--- /dev/null
+++ b/tests/unit/test_supervise_edge.py
@@ -0,0 +1,132 @@
+"""Unit: supervise queue/audit error + edge branches (coverage ratchet,
+ADR 0004). Complements test_supervise.py with the malformed-input and
+fallback paths."""
+
+from __future__ import annotations
+
+import os
+import tempfile
+import time
+import unittest
+from pathlib import Path
+from unittest.mock import patch
+
+from bot_bottle import supervise
+from bot_bottle.supervise import (
+    Proposal,
+    TOOL_EGRESS_ALLOW,
+    list_pending_proposals,
+    read_audit_entries,
+    read_proposal,
+    read_response,
+    wait_for_response,
+)
+
+
+def _proposal() -> Proposal:
+    return Proposal.new(
+        bottle_slug="slug",
+        tool=TOOL_EGRESS_ALLOW,
+        proposed_file="x",
+        justification="j",
+        current_file_hash="h",
+    )
+
+
+class TestPathHelpers(unittest.TestCase):
+    def test_bot_bottle_root(self) -> None:
+        self.assertTrue(str(supervise.bot_bottle_root()).endswith(".bot-bottle"))
+
+    def test_queue_dir_for_slug(self) -> None:
+        self.assertIn("slug", str(supervise.queue_dir_for_slug("slug")))
+
+    def test_id_from_non_proposal_filename(self) -> None:
+        self.assertIsNone(supervise._id_from_proposal_filename(Path("x.response.json")))
+
+
+class TestReadMalformed(unittest.TestCase):
+    def test_read_proposal_non_dict(self) -> None:
+        with tempfile.TemporaryDirectory() as d:
+            (Path(d) / "p.proposal.json").write_text("[]")
+            with self.assertRaises(ValueError):
+                read_proposal(Path(d), "p")
+
+    def test_read_response_non_dict(self) -> None:
+        with tempfile.TemporaryDirectory() as d:
+            (Path(d) / "p.response.json").write_text("[]")
+            with self.assertRaises(ValueError):
+                read_response(Path(d), "p")
+
+    def test_list_pending_skips_malformed(self) -> None:
+        with tempfile.TemporaryDirectory() as d:
+            qd = Path(d)
+            (qd / "bad.proposal.json").write_text("{ not json")
+            (qd / "arr.proposal.json").write_text("[]")
+            (qd / "incomplete.proposal.json").write_text("{}")  # from_dict raises
+            supervise.write_proposal(qd, _proposal())  # one valid
+            pending = list_pending_proposals(qd)
+            self.assertEqual(1, len(pending))
+            self.assertEqual("slug", pending[0].bottle_slug)
+
+    def test_list_pending_skips_when_response_present(self) -> None:
+        with tempfile.TemporaryDirectory() as d:
+            qd = Path(d)
+            p = _proposal()
+            supervise.write_proposal(qd, p)
+            (qd / f"{p.id}.response.json").write_text("{}")  # response exists -> skipped
+            self.assertEqual([], list_pending_proposals(qd))
+
+
+class TestWaitForResponse(unittest.TestCase):
+    def test_malformed_response_then_timeout(self) -> None:
+        with tempfile.TemporaryDirectory() as d:
+            (Path(d) / "p.response.json").write_text("{ not json")
+            with self.assertRaises(TimeoutError):
+                wait_for_response(Path(d), "p", deadline=time.monotonic())
+
+    def test_incomplete_response_then_timeout(self) -> None:
+        with tempfile.TemporaryDirectory() as d:
+            (Path(d) / "p.response.json").write_text("{}")  # dict but from_dict raises
+            with self.assertRaises(TimeoutError):
+                wait_for_response(Path(d), "p", deadline=time.monotonic())
+
+
+class TestReadAuditEntries(unittest.TestCase):
+    def test_missing_log_returns_empty(self) -> None:
+        with tempfile.TemporaryDirectory() as home, \
+                patch.dict("os.environ", {"HOME": home}):
+            self.assertEqual([], read_audit_entries("egress", "nope"))
+
+    def test_skips_malformed_lines(self) -> None:
+        with tempfile.TemporaryDirectory() as home, \
+                patch.dict("os.environ", {"HOME": home}):
+            path = supervise.audit_log_path("egress", "slug")
+            path.parent.mkdir(parents=True, exist_ok=True)
+            valid = (
+                '{"timestamp": "t", "bottle_slug": "slug", "component": "egress",'
+                ' "operator_action": "approve", "operator_notes": "",'
+                ' "justification": "", "diff": ""}'
+            )
+            path.write_text(
+                "\n"               # blank line skipped
+                "{ not json\n"     # JSONDecodeError skipped
+                "[]\n"             # not a dict skipped
+                "{}\n"             # missing fields -> ValueError skipped
+                + valid + "\n"
+            )
+            entries = read_audit_entries("egress", "slug")
+            self.assertEqual(1, len(entries))
+            self.assertEqual("approve", entries[0].operator_action)
+
+
+class TestFlockFallback(unittest.TestCase):
+    def test_flock_on_closed_fd_is_swallowed(self) -> None:
+        # flock on a closed fd raises OSError(EBADF), which the helpers swallow.
+        fd = os.open(os.devnull, os.O_RDONLY)
+        os.close(fd)
+        supervise._try_flock(fd)
+        supervise._try_funlock(fd)
+
+
+if __name__ == "__main__":
+    unittest.main()