fix(learning-harness): the three defects the group 2 review found

Task 2.3: two of the five unscorable reasons had no code path, so an unparsable
row was reported as a corpus labelling defect when the true cause was a tooling
gap. They have different owners and different fixes, and conflating them is the
dishonesty this spec exists to remove. The design's unscorable_reason is
reinstated with the parse result as an input, and a handler that arrived without
its registration is now named as missing context for the families whose bug
shape is a missing check.

Task 2.6: a verification stamped its own word for proof onto the shared evidence
level, which is not a value the project's ladder defines, and three existing
helpers raised on it. Nothing in production called it yet, so the suite stayed
green while the wiring in the next group would have broken a scan. A
verification now writes only its tag, and a caller that wants to move a claim up
the ladder goes through an explicit mapping that can only produce a level the
ladder has.

Task 2.7: the injection canary planted its row in a private in-memory database
the target could never reach, so it could not fire; the fake sandbox handed the
token back regardless of the snippet, which is why nothing noticed. It is now an
execution canary whose marker only an interpreter could write, and each template
is tested by running it for real against a vulnerable fixture and its fixed
twin. That test immediately caught a second flaw: a handler that merely echoes
its input printed the oracle token and satisfied the oracle without any
vulnerability, so an injected payload now carries a value unrelated to the token
the oracle looks for.

Also from the review: a configuration with no tools is refused instead of
producing a detector that silently reports nothing, the classifier abstains when
its fallback call fails too, and the archive docstring says which version wins.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG

tests/test_learning_detectors.py

@@ -156,3 +156,12 @@ def test_round_zero_can_write_a_configuration_for_every_family(tmp_path: Path) -
     assert all(config.version == "0" for config in configs.values())
     assert all(config.prompt.startswith("You are a security hunter.") for config in configs.values())
     assert configs["access_control"].prompt != configs["injection"].prompt  # each carries its own family's definition
+
+
+def test_a_configuration_with_no_tools_is_refused_rather_than_reporting_nothing(tmp_path: Path) -> None:
+    """A detector offered no tools never calls one, and the hunter loop then returns nothing at all."""
+    from openultrasast.learning.detectors import DetectorConfigError, load_family_configs
+
+    _write_config(tmp_path, "injection", tools=[])
+    with pytest.raises(DetectorConfigError, match="tools"):
+        load_family_configs(tmp_path, load_families())