fix(reset,stop): warn before a reset purges, skip and prune stale registries, refuse a guessed purge

reset.sh without --yes says the conversations are deleted for good before it
asks; without a terminal the refusal says so too. A registry that cannot be
created is skipped, since nothing can be registered there, and the directories
the fence created are removed on exit when still empty. stop --purge-conversation
refuses a conversation the row does not record instead of deleting the folder's
newest one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

tests/test_issue63_same_cwd_ids.py

@@ -622,6 +622,35 @@ def test_rev2_claude_unpinned_sibling_row_skips_creator_claimed_id(mam_sandbox,
 
 # --------------------------------------------------------------------------- Done Criterion 6 (id_order & create/resume wait)
 
+@pytest.mark.parametrize("recorded", [None, UB])
+def test_purge_refuses_a_conversation_the_row_does_not_record(mam_sandbox, mock_herdr, mock_agents, recorded):
+    """A pre-assigned row with no usable id: the folder's newest conversation may be
+    anyone's, so a purge refuses and changes nothing. A plain stop records it, and
+    the purge after that (a deliberate second step) deletes it."""
+    ws = mam_sandbox / "claude-guess-ws"
+    ws.mkdir(parents=True, exist_ok=True)
+    epoch = int(time.time()) - 100
+    transcript = _claude_transcript(mam_sandbox / ".claude" / "projects", ws, UA)
+    name = "claude-guess-ws-creator-claude"
+    _mock_herdr_agent(mock_herdr, name, ws, 5001, epoch, agent="claude")
+    _write_rows(mam_sandbox, [_row(name, "claude", ws, epoch, pid=5001, claude_session_id_own=recorded)])
+
+    res = _run_stop(mam_sandbox, name, "claude", purge=True)
+    assert res.returncode == 1, res.stdout + res.stderr
+    assert "refusing to purge" in res.stderr and UA in res.stderr
+    assert transcript.exists()
+    row = _read_rows(mam_sandbox)[name]
+    assert row["status"] == "running" and row["claude_session_id_own"] == recorded
+    assert name in json.loads(Path(mock_herdr).read_text())["agents"]
+
+    if recorded is None:
+        assert _run_stop(mam_sandbox, name, "claude").returncode == 0
+        assert _read_rows(mam_sandbox)[name]["claude_session_id_own"] == UA
+        purge = _run_stop(mam_sandbox, name, "claude", purge=True)
+        assert purge.returncode == 0, purge.stdout + purge.stderr
+        assert not transcript.exists()
+
+
 def test_c6_create_waits_or_refuses_while_same_cwd_post_discovered_row_has_no_id(
     mam_sandbox, mock_herdr, mock_agents
 ):