diff --git a/docs/v0.6-reasoning-architecture.md b/docs/v0.6-reasoning-architecture.md
new file mode 100644
index 0000000..0c456d6
--- /dev/null
+++ b/docs/v0.6-reasoning-architecture.md
@@ -0,0 +1,375 @@
+# v0.6 Reasoning Architecture
+
+## Purpose
+
+This document describes the implemented deterministic reasoning architecture on branch `feature/question-strategy-alignment-v0.6`.
+
+It is written for future developers who need to understand how v0.6 actually executes, what invariants it relies on, where the recursive loops are, and what the system deliberately does **not** attempt to do.
+
+## End-to-end pipeline
+
+The implemented runtime pipeline is:
+
+```text
+Scenario input
+↓
+LLM analysis / reconstruction
+↓
+Initial graph build
+↓
+Deterministic unknown selection
+↓
+Selected question
+↓
+User answer
+↓
+LLM graph-update proposal
+↓
+Proposal parsing / normalisation
+↓
+Proposal compatibility validation
+↓
+Deterministic graph update application
+↓
+Reasoning-state rebuild
+↓
+Comparability assessment
+↓
+Relationship classification
+↓
+Explicit emergent unknown creation / reuse (if required)
+↓
+Deterministic reselection
+↓
+Atomicity assessment
+↓
+Optional decomposition into child unknowns
+↓
+Deterministic reselection
+↓
+Resolved-child propagation upward
+↓
+Confidence / completeness / corroboration update
+↓
+Next active unknown
+↓
+Question formulation
+```
+
+## Deterministic stages
+
+### 1. Scenario analysis / reconstruction
+
+- **Purpose**: obtain structured reconstruction material from scenario text
+- **Input**: scenario, prompt version
+- **Output**: analysis payload containing reconstruction, evidence, diagnostics, and optional next question
+- **Why it exists**: provides the initial structured substrate from which the graph is built
+- **What breaks if removed**: the graph builder has no structured reconstruction to convert into nodes and edges
+
+### 2. Initial graph build
+
+- **Purpose**: convert reconstruction output into an initial `SituationGraph`
+- **Input**: reconstruction + evidence
+- **Output**: graph nodes and edges, then `makeGraph(...)` wraps them with active/resolved/summary state
+- **Why it exists**: all later reasoning is graph-based, not free text
+- **What breaks if removed**: no explicit unknown nodes, no deterministic selection, no validated update loop
+
+### 3. Deterministic unknown selection
+
+- **Purpose**: choose the next active unknown from unresolved graph nodes
+- **Input**: graph, resolved node IDs
+- **Output**: selected candidate or explicit ambiguity result
+- **Why it exists**: the system needs a deterministic next investigation target
+- **What breaks if removed**: question ordering becomes arbitrary or hidden in prompts
+
+### 4. Selected question exposure
+
+- **Purpose**: expose the chosen unknown as the next question to the user
+- **Input**: selected unknown + question formulation or tie-resolution logic
+- **Output**: selected question object
+- **Why it exists**: the user-facing loop must ask a concrete next question
+- **What breaks if removed**: the system can build a graph but cannot continue interaction coherently
+
+### 5. LLM graph-update proposal
+
+- **Purpose**: transform a user answer into a proposed graph change set
+- **Input**: current graph, previous question, answer, prompt version
+- **Output**: raw JSON-like proposal
+- **Why it exists**: the LLM is limited to proposing changes; it does not mutate the graph directly
+- **What breaks if removed**: answers cannot affect the graph except through manual hard-coded logic
+
+### 6. Proposal parsing / normalisation
+
+- **Purpose**: parse JSON, remove null array items, apply known aliases, fill omitted optional fields
+- **Input**: raw model response
+- **Output**: validated `graphUpdateSchema` payload or structured parser failure
+- **Why it exists**: model outputs are not trusted as-is
+- **What breaks if removed**: malformed or partially missing model output would reach graph logic directly
+
+### 7. Proposal compatibility validation
+
+- **Purpose**: ensure the proposal is graph-safe and semantically valid before application
+- **Input**: current graph + proposed update
+- **Output**: accepted proposal or compatibility errors
+- **Why it exists**: protects graph integrity and reasoning invariants
+- **What breaks if removed**: duplicate IDs, missing references, fake selected questions, and no-op updates could corrupt the graph
+
+### 8. Deterministic graph update application
+
+- **Purpose**: apply only validated graph changes to a copied graph
+- **Input**: graph + validated proposal
+- **Output**: updated nodes, edges, resolved node IDs
+- **Why it exists**: separates safe application from generation
+- **What breaks if removed**: no explicit, replayable state transition exists
+
+### 9. Reasoning-state rebuild
+
+- **Purpose**: derive fresh comparability/relationship state from the updated graph
+- **Input**: updated graph + optional override state
+- **Output**: `reasoningState`
+- **Why it exists**: reasoning stages are derived from graph state, not stored blindly
+- **What breaks if removed**: comparability and relationship decisions drift from actual graph contents
+
+### 10. Comparability assessment
+
+- **Purpose**: decide whether supported observations are comparable enough for relationship reasoning
+- **Input**: graph observations + central statement + optional stored override
+- **Output**: comparability status/reason + contradiction permission
+- **Why it exists**: relationship reasoning is gated by comparability
+- **What breaks if removed**: contradiction or relationship reasoning would run over incomparable observations
+
+### 11. Relationship classification
+
+- **Purpose**: classify observation relationships once comparability permits it
+- **Input**: graph + comparability result
+- **Output**: relationship status, reason, whether a follow-up question is justified
+- **Why it exists**: determines whether explanation-style follow-up is needed
+- **What breaks if removed**: the system cannot distinguish compatible, duplicate, insufficient, and contradiction-adjacent observation sets
+
+### 12. Explicit emergent unknown creation / reuse
+
+- **Purpose**: ensure any justified relationship follow-up is represented by an explicit unresolved graph node
+- **Input**: provisional graph + relationship assessment
+- **Output**: reused or newly added explanation unknown and edges
+- **Why it exists**: preserves the invariant that a question must originate from an explicit unknown
+- **What breaks if removed**: relationship follow-up would revert to fallback-only question text not backed by the graph
+
+### 13. Atomicity assessment
+
+- **Purpose**: determine whether the selected unknown is directly investigable or too composite
+- **Input**: selected unknown + graph context
+- **Output**: `atomic` or `composite` decision with decomposition kind/reason
+- **Why it exists**: prevents asking broad explanation unknowns directly
+- **What breaks if removed**: the system asks high-level composite unknowns instead of decomposing them first
+
+### 14. Optional decomposition
+
+- **Purpose**: split a composite unknown into deterministic child unknowns
+- **Input**: composite selected unknown + graph context
+- **Output**: 2–5 child unknowns, edges, quality summary, rejection diagnostics
+- **Why it exists**: narrows broad unknowns into explicit candidate dimensions
+- **What breaks if removed**: recursive reasoning stops at broad parents and loses graph-backed substructure
+
+### 15. Resolved-child propagation upward
+
+- **Purpose**: move resolved child effects to parent and ancestor chain without prematurely resolving them
+- **Input**: updated graph + proposal snapshot
+- **Output**: parent/ancestor status and confidence updates, additional diagnostics
+- **Why it exists**: decomposition requires deterministic reconstruction as well as decomposition
+- **What breaks if removed**: child answers stay local and parents never become progressively better-supported
+
+### 16. Confidence / completeness / corroboration update
+
+- **Purpose**: derive parent-level `confidenceAssessment` from resolved children and branch interactions
+- **Input**: parent child set + branch evidence/status interactions
+- **Output**: `evidenceConfidence`, `completenessStatus`, `conclusionConfidence`, plus derived display `confidence`
+- **Why it exists**: reasoning support must be separated from completion and contradiction state
+- **What breaks if removed**: parent confidence collapses back into vague status-driven heuristics
+
+### 17. Next active unknown + question formulation
+
+- **Purpose**: reselect the next unresolved unknown and formulate a concrete next question
+- **Input**: updated graph + selection state + graph context
+- **Output**: next active unknown and question object
+- **Why it exists**: closes the recursive interaction loop
+- **What breaks if removed**: the system updates the graph but cannot continue investigation deterministically
+
+## Architectural invariants
+
+The current implementation enforces these invariants:
+
+1. **A question must originate from an explicit unresolved unknown node.**
+2. **Unknown selection is deterministic.**
+3. **Alphabetical ordering is not treated as reasoning.**
+4. **Relationship reasoning does not precede comparability.**
+5. **The LLM never mutates the graph directly; it only proposes updates.**
+6. **All graph updates are schema-validated before application.**
+7. **All node/edge references must resolve to existing nodes.**
+8. **Duplicate node IDs are rejected.**
+9. **Duplicate added edge IDs are rejected.**
+10. **A selected question cannot target a resolved unknown.**
+11. **A resolved unknown updated to `resolved` must also appear in `resolvedUnknownNodeIds`.**
+12. **A proposal must contain a meaningful change.**
+13. **Every newly added unknown must include why-it-matters language.**
+14. **Every newly added unknown must be explicitly connected to answer-derived graph structure.**
+15. **Composite selected unknowns are decomposed before direct questioning when atomicity rules require it.**
+16. **Parent unknowns remain unresolved until completion rules are satisfied.**
+17. **Confidence must not outrun completeness.**
+18. **Duplicate evidence cannot increase confidence.**
+19. **Conflicting evidence caps conclusion confidence.**
+20. **Cross-branch corroboration only counts for distinct branches with distinct evidence keys.**
+21. **Ambiguous leading unknowns remain explicit ambiguity, not silent forced choice.**
+
+## Recursive loops and stopping rules
+
+### Main investigation loop
+
+```text
+Unknown
+↓
+Question
+↓
+Answer
+↓
+Proposal
+↓
+Graph update
+↓
+Propagation
+↓
+Next unknown
+```
+
+- **Exit condition**: no unresolved candidates remain, or no next question is justified, or proposal/application fails
+- **Stopping rule**: deterministic selection returns `null` or explicit ambiguity, or update validation blocks progress
+- **Completion behaviour**: continues only while the graph contains justified unresolved unknowns
+
+### Decomposition loop
+
+```text
+Selected unknown
+↓
+Atomicity assessment
+↓
+If composite: decompose
+↓
+Reselect child
+↓
+Atomicity assessment again
+```
+
+- **Exit condition**: selected child is atomic; parent already has children; max decomposition depth reached; or decomposition quality fails
+- **Stopping rule**: `MAX_DECOMPOSITION_DEPTH`, reuse instead of regeneration, or inability to produce enough valid child unknowns
+- **Completion behaviour**: deterministic and bounded; no infinite recursive decomposition path is intentionally allowed
+
+### Propagation loop
+
+```text
+Resolved child
+↓
+Ancestor chain walk
+↓
+Recompute parent state
+↓
+Stop when no ancestor state changes
+```
+
+- **Exit condition**: no more parents in the ancestor chain or no state change
+- **Stopping rule**: ancestor chain is explicit and finite; propagation does not invent new ancestors
+- **Completion behaviour**: deterministic upward traversal with explicit stop on unchanged state
+
+### Potential infinite loops reviewed
+
+- **Unknown/question recursion**: bounded by unresolved unknown set, proposal validation, and explicit no-candidate states
+- **Decomposition recursion**: bounded by max depth and child reuse rules
+- **Propagation recursion**: bounded by finite ancestor chain and no-change stop condition
+
+No intentional infinite reasoning loop is present in the implemented architecture.
+
+## Graph lifecycle summary
+
+### Node lifecycle
+
+1. node created by `buildInitialGraph` or later proposal/decomposition/emergent-unknown logic
+2. node validated by schema
+3. node may become active unknown
+4. node may be updated by proposal application
+5. unknown node may become `resolved`, `provisional`, `contradicted`, or remain `unknown`
+6. resolved unknown ID is tracked in `resolvedNodeIds`
+
+### Edge lifecycle
+
+1. edge created in initial graph or by deterministic proposal augmentation
+2. edge validated against existing node IDs
+3. edge may be removed only through explicit `removedEdgeIds`
+4. edge relationships also update `dependsOn` / `childIds` projections during application
+
+### Unknown lifecycle
+
+1. initial unknown discovered from reconstruction
+2. selected deterministically or left ambiguous
+3. may be decomposed if composite
+4. may be resolved directly by answer
+5. may cause emergent reasoning unknown creation when relationship reasoning demands a new explicit question target
+
+### Resolved lifecycle
+
+1. proposal marks unresolved unknown resolved
+2. reconciliation ensures resolution semantics are explicit
+3. `resolvedUnknownNodeIds` feed graph application
+4. propagation may resolve parent only when completion rule is met
+
+### Confidence lifecycle
+
+1. nodes begin with base `confidence`
+2. parent/ancestor propagation derives `confidenceAssessment`
+3. display `confidence` is derived from `conclusionConfidence`
+4. completeness, duplicate evidence, contradiction, and corroboration constrain the result
+
+### Question lifecycle
+
+1. selected unknown becomes question target
+2. `formulateQuestion` or tie-resolution logic produces question text
+3. answer returns through update route
+4. proposal may select a new question target or leave reselection to deterministic logic
+
+Every major transition above is explicit in the current codebase rather than implicit in model text alone.
+
+## Duplicated or overlapping concepts
+
+The following concepts are intentionally close and may look duplicated:
+
+- **status vs confidence**: status captures lifecycle/progression; confidence captures support strength
+- **confidence vs confidenceAssessment**: `confidence` is now a derived display field, while `confidenceAssessment` carries separated reasoning dimensions
+- **resolvedNodeIds vs node.status === resolved**: both are maintained; the first is a graph-level index, the second is node-local state
+- **selectedQuestion in proposal vs selectedQuestion in final result**: proposal may omit or propose one, final result recomputes deterministic selection/questioning after graph logic
+- **comparability state in reasoningState vs derived comparability from graph**: overrides may carry forward prior confirmed reasoning, but `buildReasoningState` still rebuilds from graph + override context
+
+These are not necessarily defects, but they are the main places where future simplification pressure is likely.
+
+## Known boundaries and deliberate exclusions
+
+v0.6 deliberately does **not** attempt the following:
+
+- probabilistic reasoning
+- Bayesian inference
+- persistence
+- semantic embeddings
+- fuzzy semantic similarity
+- autonomous exploration outside explicit user answers
+- multi-hop corroboration across unrelated subtrees without a shared direct parent
+- expert-only jargon-specific reasoning modes
+- UI-heavy reasoning visualisation beyond existing graph/update displays
+- arbitrary non-deterministic tie breaking
+
+## Defects found during this review
+
+No new production defect was intentionally introduced or fixed as part of this architecture review.
+
+## Developer notes
+
+- `startCase` owns reconstruction → graph build → first deterministic selection.
+- `updateCaseWithDependencies` owns proposal generation / parsing and delegates deterministic graph semantics to `applyValidatedProposal`.
+- `applyValidatedProposal` is the main reasoning pipeline coordinator for update-time graph evolution.
+- `question-formulator.js` owns comparability, relationship classification, atomicity assessment, investigation strategy selection, and question formulation.
+- `utils.js` owns selection scoring, ordering, graph validation, and safe graph update application.