fix(detectors): preserve TriggerListDetector result alignment

[SarveshaKumarKS]

Summary

• return one None score per applicable output when attempt.notes["triggers"] is absent
• add direct regression coverage for multiple outputs
• update PIILeakExact's inherited-behaviour test to expect aligned unscored results

Root cause and impact

TriggerListDetector.detect initialised an empty result list, but its entire scoring loop was guarded by if "triggers" in attempt.notes. When a probe did not populate that note, the detector returned [] regardless of the number of outputs.

The evaluator enumerates detector scores, so an empty result list increments neither pass, fail, nor None counters. Returning [None] * len(all_outputs) preserves the detector/output alignment and records each output as unscorable. This change only handles an absent note; it does not alter the existing semantics of an explicitly empty trigger list.

Verification

• Red proof on main: a two-output attempt with no triggers note returned []
• Green proof after the fix: the same attempt returns [None, None]
• python -m pytest tests/detectors/test_detectors_base.py tests/detectors/test_detectors_propile.py tests/detectors/test_detectors_trigger_list.py -q — 42 passed
• python -m pytest tests/probes/test_probes_propile.py -q — 18 passed
• python -m black --check -W 1 garak/detectors/base.py tests/detectors/test_detectors_propile.py tests/detectors/test_detectors_trigger_list.py — passed with Black 26.1.0
• git diff --check — passed
• Full tests/detectors run was environment-limited: 707 passed, 34 skipped, and 46 tests requiring external Hugging Face models or package-registry data failed because those resources were unavailable in the restricted test environment

Not a duplicate

• No open or closed issue or PR specifically fixes the missing-notes["triggers"] path in TriggerListDetector.
• Add MCP Security Probes (Tool Poisoning & Injection) #1687 describes an adjacent explicitly-empty-trigger-list change, but its current patch does not modify garak/detectors/base.py.
• fix(eval): surface ASR denominator-drop from None detector scores (unscoreable-as-pass) #1954 addresses the downstream treatment of None scores in evaluator metrics, not the detector's missing result entries.
• update: unify on attempt.notes["triggers"] #1147 standardised consumers on notes["triggers"] but did not add this guard to TriggerListDetector.
• fix(detectors): guard MarkdownExfilContent against missing terms note #1935 is related precedent for safely handling missing detector note metadata, but targets MarkdownExfilContent and notes["terms"].

AI assistance

OpenAI Codex assisted with investigation, implementation, testing, and drafting this description. The human submitter reviewed every changed line, understands and approves the change, and the commit includes both AI attribution and the required DCO sign-off.