feat: introduce reasoning pattern selection

docs/v0.7-question-simplicity-experiment.md

@@ -94,6 +94,95 @@ The engine now decomposes whenever either of these is true:
 
 This prevents a broad container node from becoming the selected question target even when its wording looks grammatically singular.
 
+## Reasoning Pattern
+
+The next failure exposed a deeper issue: even after atomicity and answerability were added, the engine could still choose a question template from the wrong reasoning family.
+
+The live failure was an explanation-style prompt appearing in a commercial validation scenario:
+
+> What changed during the period that could help explain why ...
+
+That was wrong not because of wording, but because the engine had selected an **explanation family** when the actual task was a **decision investigation**.
+
+To correct that, the deterministic pipeline now explicitly inserts a reasoning-pattern stage:
+
+```text
+selected unknown
+→ atomicity
+→ answerability
+→ reasoning pattern
+→ investigation strategy
+→ question family
+→ question
+```
+
+This matters because each stage must constrain the next.
+
+- **Reasoning Pattern** decides what kind of reasoning is happening
+- **Investigation Strategy** decides how to reduce uncertainty within that pattern
+- **Question Family** decides what template space is allowed
+- **Question** is the final concrete wording
+
+Without this stage separation, strategy and template selection can leak across domains and reuse relationship/explanation prompts too broadly.
+
+## Deterministic reasoning-pattern vocabulary
+
+The current deterministic pattern vocabulary is intentionally small:
+
+- decision
+- explanation
+- contradiction
+- definition
+- diagnosis
+- comparison
+- prioritisation
+
+Pattern selection uses graph structure rather than wording alone, including:
+
+- node kind
+- relationship / observation topology
+- parent context
+- reasoning state
+- selected unknown role in the graph
+
+## Question-family mapping
+
+Patterns now constrain which question families are allowed.
+
+- **decision**
+  - decision_foundation
+  - decision_evidence
+  - decision_threshold
+  - definition
+- **explanation**
+  - explanation
+  - comparison
+- **contradiction**
+  - contradiction
+  - comparison
+  - explanation
+- **definition**
+  - definition
+- **diagnosis**
+  - diagnosis
+  - comparison
+- **comparison**
+  - comparison
+- **prioritisation**
+  - prioritisation
+  - decision_threshold
+
+Most importantly:
+
+- explanation templates are only allowed for `explanation` or `contradiction`
+- decision investigations cannot emit explanation-family questions
+
+## Live correction
+
+For the commercial-method scenario, the engine now classifies the reasoning as a **decision** pattern rather than an explanation pattern.
+
+That means explanation-family templates are explicitly rejected, and the selected child unknown must be questioned using a decision-compatible family instead.
+
 ## UI result
 
 The long compound question no longer survives as the first follow-up in the tested path.