diagnose-slice

name	diagnose-slice
description	Use this skill to diagnose why a Cratis slice misbehaves — read model not updating, TypeScript proxy missing, command rejected unexpectedly, projection/observer quarantined, AutoMap mismatch, reactor side effects not appended, or specs flaking. Symptom → likely cause → the rule/skill that owns the fix. Use when something "isn't working" and the cause isn't obvious.

Symptom → likely cause → fix for the common ways a Cratis application slice misbehaves. Each row routes to the rule/skill that owns the detail — start there. Reproduce a real defect with a spec before and after the fix.

Backend / Chronicle

Symptom	Likely cause	Fix →
Read model query returns empty / stale	projection not wired: event→read-model property names differ (AutoMap only maps matching names), or a default value masks missing wiring	add-projection, cratis-readmodel; [SetFrom<T>] for name diffs; no default values on [ReadModel] props
App crashes on startup with a projection error	duplicate [FromEvent<T>] for the same event on one read model	add-projection (one [FromEvent<T>] per event)
Command always "not successful" with no validation errors	[Roles]/authorization: an unauthorized result isn't successful and carries no validation errors	auth-and-identity, cratis-command; assert ShouldNotBeAuthorized()
Command rejected unexpectedly	a CommandValidator/ConceptValidator rule, or Provide() short-circuited with ValidationResult.Error	add-business-rule, cratis-command
Handler returns HTTP 500 instead of rejecting	threw from Provide()/Handle() for a business rule (that's an exception, not a rejection)	return Result<TEvent, ValidationResult> — add-business-rule
Reactor's returned events never appended	returned EventForEventSourceId on a Chronicle version before reactor support	return event objects, or ReactorSideEffect for another target — reactors.md
Projection/reactor stops processing ("quarantined")	a handler threw; the partition paused and the observer quarantined (does not auto-resume)	fix the handler (make it idempotent); an operator calls ClearObserverQuarantine() — reactors.md
Duplicate side effect on replay	non-idempotent reactor without [OnceOnly]	mark the handler [OnceOnly] — reactors.md
Chronicle analyzer warns on an event property	a nullable event property	model the optional fact as a separate event — vertical-slices.md, event-modeling
A read model needs a field from another slice	wrong stream boundary / missing event	re-model (information completeness) — event-modeling; never cross-read another read model at runtime

Frontend / proxies

Symptom	Likely cause	Fix →
TS can't find the command/query proxy (Cannot find module)	proxies regenerate only on a Release build; you built Debug	build Release — new-vertical-slice (backend phase)
Edited a generated file and it reverted	generated proxies (// @generated by Cratis) are never hand-edited	fix the C# source and rebuild — general.md
DataPage won't show live data	passed a snapshot query, or expected a non-existent observableQuery prop	pass the observable query to the single query prop (auto-detected) — cratis-react-page, components.md
Dialog/dropdown renders behind an overlay	used raw primereact/dialog or primereact/dropdown	use the Cratis wrappers from @cratis/components/* — dialogs.md, components.md

Specs

Symptom	Likely cause	Fix →
Spec code leaks into the Release/proxy build	spec not wrapped in #if DEBUG … #endif	wrap the file — specs.scenarios.csharp.md
Off-by-one in event-tail assertions	sequence numbers are zero-based (tail of one event is 0)	specs.scenarios.csharp.md
Order-dependent flake on a uniqueness rule	a hardcoded value collides across tests	use a per-test value (Guid.NewGuid()); don't reach for [Collection] for collisions — specs.scenarios.csharp.md

When nothing here fits

Re-read the owning rule (vertical-slices.md, reactors.md, cratis-readmodel), confirm the build is clean in both Debug and Release, and reproduce the symptom with a spec. Don't infer framework behavior from package internals — if the rules/skills don't answer it, ask.