add-investigationlisted

# Investigation Skill <!-- uses: - agent: architecture-agent - agent: feature-history-agent - agent: git-history-agent - command: /add.diagnose - command: /add.hotfix - skill: add-investigation/references/5-whys.md - skill: add-investigation/references/agans-9-rules.md - skill: add-investigation/references/backward-tracing.md - skill: add-investigation/references/differential-diagnosis.md - skill: add-investigation/references/flow-tracing.md - skill: add-investigation/references/symptom-disambiguation.md --> ## Overview Vague symptoms, hard-to-find bugs, and information-flow inconsistencies are NOT solved by jumping into code — they require rigorous disambiguation, backward tracing, and differential diagnosis BEFORE any fix or route decision. This skill encodes a 5-phase methodology with a hard Iron Law (see Credits for attribution). ## ⛔ Iron Law ``` NO ROUTE RECOMMENDATION WITHOUT DIFFERENTIAL DIAGNOSIS FIRST ``` Corollaries: - No "I think it is X" without at least 3 candidate hypotheses ranked. - No code change proposal without backward tracing the data flow. - No "this is a bug" classification without reproducing the observable predicate. - After 3 failed hypothesis tests → STOP and question the framing (not the code). ## When to Use - Vague symptom reports: "something seems off in X", "I don't know if this is a bug or missing feature", "this behavior looks weird". - Pre-decision triage: before opening feature, hotfix, or dismissing as no-action. - Pre-hotfix inve