fix(config): classify malformed TOML as user error, not internal crash

interlocks/behavior_coverage.py

@@ -373,6 +373,12 @@ def duplicates(self) -> tuple[DuplicateBehavior, ...]:
         "a subprocess gate failure exits via SystemExit without entering capture",
         "interlocks.crash.boundary:CrashBoundary",
     ),
+    Behavior(
+        "crash-malformed-config-no-capture",
+        "crash",
+        "malformed pyproject.toml raises InterlockConfigError (user error) — no crash capture",
+        "interlocks.config:InterlockConfigError",
+    ),
 )
 
 

interlocks/config.py

@@ -469,8 +469,11 @@ def _load_pyproject(project_root: Path) -> dict[str, Any]:
     path = project_root / "pyproject.toml"
     if not path.is_file():
         return {}
-    with path.open("rb") as f:
-        return tomllib.load(f)
+    try:
+        with path.open("rb") as f:
+            return tomllib.load(f)
+    except tomllib.TOMLDecodeError as exc:
+        raise InterlockConfigError(f"pyproject.toml is not valid TOML: {exc}") from exc
 
 
 def _interlock_table(pyproject: dict[str, Any]) -> dict[str, Any]:
@@ -686,7 +689,7 @@ def load_optional_config(start: Path | None = None) -> InterlockConfig | None:
     """
     try:
         return load_config(start)
-    except (OSError, tomllib.TOMLDecodeError):
+    except (OSError, InterlockConfigError):
         return None
 
 

interlocks/tasks/doctor.py

@@ -10,13 +10,12 @@
 import shutil
 import sys
 import time
-import tomllib
 from dataclasses import dataclass
 from datetime import UTC, datetime
 from typing import TYPE_CHECKING
 
 from interlocks import ui
-from interlocks.config import find_project_root, kv_with_source, load_config
+from interlocks.config import InterlockConfigError, find_project_root, kv_with_source, load_config
 from interlocks.crash.storage import cache_dir as _crash_cache_dir
 from interlocks.detect import expected_target_interpreter
 from interlocks.setup_state import (
@@ -125,7 +124,7 @@ def _safe_load_config(pyproject_path: Path, failures: list[str]) -> InterlockCon
     """Load config, recording a failure when ``pyproject.toml`` is unreadable."""
     try:
         return load_config()
-    except (OSError, tomllib.TOMLDecodeError) as exc:
+    except (OSError, InterlockConfigError) as exc:
         failures.append(f"cannot read {pyproject_path}: {exc}")
         return None
 

tests/features/interlock_crash.feature

@@ -55,3 +55,13 @@ Feature: interlocks CLI crash boundary
     Then the exit code is not 0
     And stderr does not contain "github.com/0xjgv/interlocks/issues/new"
     And no crash file exists in the cache directory
+
+  # req: crash-malformed-config-no-capture
+  Scenario: Malformed pyproject.toml fails as clean user error without crash report
+    Given a project with a malformed pyproject.toml
+    When I run "interlocks lint"
+    Then the exit code is 2
+    And stderr contains "interlocks:"
+    And stderr does not contain "Traceback"
+    And stderr does not contain "github.com/0xjgv/interlocks/issues/new"
+    And no crash file exists in the cache directory

tests/step_defs/test_interlock_crash.py

@@ -211,6 +211,13 @@ def _lint_failure_project(crash_session: CrashSession) -> None:
     _scaffold_crash_project(crash_session.project_root, broken_module=True)
 
 
+@given("a project with a malformed pyproject.toml")
+def _malformed_pyproject(crash_session: CrashSession) -> None:
+    (crash_session.project_root / "pyproject.toml").write_text(
+        "[invalid\nnot valid toml\n", encoding="utf-8"
+    )
+
+
 @given("the first run printed a GitHub issue URL")
 def _first_run_printed_url(crash_run: CrashRun, crash_session: CrashSession) -> None:
     assert "github.com/0xjgv/interlocks/issues/new" in crash_run.stderr, (

tests/test_crash_boundary.py

@@ -2,6 +2,10 @@
 
 Focus: classification semantics and invariant I6 — a bug inside the crash
 reporter MUST NOT mask the original exception.
+
+Also probes preflight / user-config error cases:
+- Missing pyproject.toml exits 2 without crash capture (via existing BDD scenario).
+- Malformed pyproject.toml raises InterlockConfigError, handled as user error.
 """
 
 from __future__ import annotations
@@ -10,7 +14,12 @@
 
 import pytest
 
-from interlocks.config import InterlockConfigError, InterlockUserError
+from interlocks.config import (
+    InterlockConfigError,
+    InterlockUserError,
+    clear_cache,
+    load_config,
+)
 from interlocks.crash import boundary as boundary_mod
 from interlocks.crash.boundary import CrashBoundary
 
@@ -155,3 +164,54 @@ def test_safe_load_config_returns_cfg_and_project_root_on_success(
     loaded, root = boundary_mod._safe_load_config()
     assert loaded is cfg
     assert root == tmp_path
+
+
+# ---------------------------------------------------------------------------
+# Preflight / user-config error classification probes
+# ---------------------------------------------------------------------------
+
+
+def test_malformed_toml_is_user_error_not_crash(tmp_path: Path) -> None:
+    """_load_pyproject converts TOMLDecodeError to InterlockConfigError.
+
+    If raw TOMLDecodeError escaped, the boundary would misclassify it as an
+    internal crash (call stack has interlocks frames) and trigger crash capture.
+    InterlockConfigError is an InterlockUserError, so the boundary exits 2 cleanly.
+    pytest.raises(InterlockConfigError) proves no raw TOMLDecodeError escaped.
+    """
+    from interlocks.config import _load_pyproject
+
+    (tmp_path / "pyproject.toml").write_text("[invalid\nnot toml\n", encoding="utf-8")
+    with pytest.raises(InterlockConfigError, match=r"pyproject\.toml is not valid TOML"):
+        _load_pyproject(tmp_path)
+
+
+def test_config_error_from_malformed_toml_exits_2_via_boundary(
+    tmp_path: Path,
+    capsys: pytest.CaptureFixture[str],
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """InterlockConfigError raised inside the boundary exits 2, no crash capture.
+
+    Simulates a PREFLIGHT_EXEMPT task calling load_config() for a malformed TOML
+    while inside the CrashBoundary — boundary handles it as a user error, not a crash.
+    """
+    captured: list[str] = []
+    monkeypatch.setattr(
+        boundary_mod,
+        "_capture_and_transport",
+        lambda exc, sub: captured.append(sub),
+    )
+
+    (tmp_path / "pyproject.toml").write_text("[bad\n", encoding="utf-8")
+    clear_cache()
+
+    boundary = CrashBoundary(subcommand="lint")
+    with pytest.raises(SystemExit) as excinfo, boundary:
+        load_config(tmp_path)
+
+    assert excinfo.value.code == 2
+    err = capsys.readouterr().err
+    assert "interlocks:" in err
+    assert "not valid TOML" in err
+    assert captured == []