Calculation Coach Domain Model

Object	Purpose	Required fields
CalculationProblem	Frozen assessable task	id, version, prompt, archetypeId, givens, equation, answer requirements, sourceEvidence, reviewStatus
CalculationArchetype	Reusable path contract	id, version, nodeKinds, allowed_variations, scope
GivenQuantity	Typed supplied value	symbol, value, unit, significantFigures, species/context
Unit	Dimensional representation	symbol, dimension, scale, power
ChemicalEquation	Balanced species relationship	species, coefficients, phases, reversible
Expression	Canonical or accepted symbolic form	AST, variables, equivalence rules, dimensional expectation
SolutionGraph	Authoritative dependency graph	id, version, nodes, edges, problemId
SolutionNode	One reasoning/calculation obligation	id, kind, validator, expected, accepted_alternatives
DependencyEdge	Required upstream relationship	fromNodeId, toNodeId, role
StudentStep	Learner-provided structured work	id, sequence, kind, value/expression, unit, note
StepAlignment	Mapping from student work to graph	studentStepId, solutionNodeId, score, basis, alternatives
MarkingPolicy	Frozen question-specific assessment contract	id, version, problemId, markNodes, ecfRules, sourceEvidence, reviewStatus
MarkNode	One allocatable mark	id, solutionNodeId, criterion, dependencies, marks
ECFRule	Bounded error-carried-forward rule	id, triggerNode, downstreamNodes, exclusions, award
Diagnosis	First invalid step and evidence	firstInvalidNodeId, reasonCode, dimensions, evidence, reviewRequired
MisconceptionSignal	Bounded inference from observed work	code, sourceNodeId, evidence, confidence
HintDecision	Least-revealing intervention	level, targetNodeId, rationale, blockedContent
LearnerWeakness	Aggregated reviewed signal	learnerKey, archetypeId, nodeKind, weight, evidenceIds, updatedAt
FollowUpProblem	Reviewed next-practice candidate	problemId, targetWeaknesses, variationAxes, reviewStatus

Separation Of Concerns

• Mathematical correctness: numeric and symbolic validity.
• Chemistry-model correctness: correct species, equation, quantities, and Kp model.
• Dependency consistency: whether downstream work validly uses upstream work.
• Marking policy: allocation of marks for this frozen question.
• ECF: policy-bounded preservation of downstream credit after a named error.
• Hinting: pedagogical disclosure decision.
• Learner modelling: longitudinal aggregation, never a substitute for current-step validation.

Versioning And Tenancy

Content and policies are immutable by version; traces reference exact versions. V0 local demo attempts have no production-tenancy claim. Any future user-data table requires an owner/tenant field, membership rules, RLS notes, and tests before production claims.