initiative/specs/018-combatant-concentration/data-model.md

Data Model: Combatant Concentration

Feature: 018-combatant-concentration | Date: 2026-03-06

Entity Changes

Combatant (modified)

Field	Type	Required	Default	Notes
id	CombatantId	yes	-	Existing, unchanged
name	string	yes	-	Existing, unchanged
initiative	number	no	undefined	Existing, unchanged
maxHp	number	no	undefined	Existing, unchanged
currentHp	number	no	undefined	Existing, unchanged
ac	number	no	undefined	Existing, unchanged
conditions	ConditionId[]	no	undefined	Existing, unchanged
isConcentrating	boolean	no	undefined (falsy)	New field. Independent of conditions.

Domain Events (new)

Event	Fields	Emitted When
ConcentrationStarted	type, combatantId	Concentration toggled from off to on
ConcentrationEnded	type, combatantId	Concentration toggled from on to off

State Transitions

toggleConcentration(encounter, combatantId)
  ├── combatant not found → DomainError("combatant-not-found")
  ├── isConcentrating is falsy → set to true, emit ConcentrationStarted
  └── isConcentrating is true → set to undefined, emit ConcentrationEnded

Validation Rules

• combatantId must reference an existing combatant in the encounter.
• No other validation needed (boolean toggle has no invalid input beyond missing combatant).

Storage Impact

• Format: JSON via localStorage (existing adapter).
• Migration: None. Field is optional; absent field is treated as false.
• Backward compatibility: Old data loads without isConcentrating; new data with the field serializes/deserializes transparently.