createMatStepHandle

Description#

Translates a Material MatStep into a cngx CngxStepRegistration.

• id - always a fresh idSeed() value. Mirrors the tabs instrumentation handle: a label-keyed id would collide when two steps share a label.
• kind - fixed at 'step'. The instrumentation path does not project nested <mat-step> groups (Material's stepper has no group-of-steps concept; group-aware semantics belong to the <cngx-stepper> thin-wrapper organism).
• label - snapshot signal resolved through a four-tier fallback at registration time so cngx-side phrases (announcements, aria-label composition, telemetry) never read empty when Material consumers project a <ng-template matStepLabel>:
  1. MatStep.label when it is a plain string - the canonical shape and the only one that emits a runtime change Material itself observes.
  2. MatStep.ariaLabel when the consumer set the input - designed exactly as the substitute for template labels.
  3. Static-text read from MatStep.stepLabel.template via a throwaway detached EmbeddedViewRef (readMatStepLabelTemplateText). Captures literal matStepLabel markup; dynamic interpolation bails through to (4).
  4. Step <id> - deterministic, derived from the cngx handle id. Always non-empty. Documented limitation: runtime label changes do not propagate. CDK's CdkStep does not expose a _stateChanges Subject analogous to MatTab._stateChanges, so cngx cannot re-trigger the snapshot when Material flips the input later. Surface the same Material-internal coupling family typed in MaterialPrivateSurfaces.CompletedOverrideSource.
• disabled - fixed false. Material owns step gating via linear + editable + completed; surfacing a cngx-side disabled would duplicate Material's own click-time enforcement and is ignored by <mat-stepper> itself.
• state - computed() over MatStep.hasError / MatStep.completed. CdkStep.completed's getter reads _completedOverride() - a WritableSignal<boolean | null> typed in MaterialPrivateSurfaces.CompletedOverrideSource. The cngx computed transitively tracks that signal through the getter and re-fires whenever Material flips completion. hasError is a plain property setter on CdkStep, NOT a Signal - a hasError write that is not paired with a completed change does not re-trigger this computed. In practice Material wizards write the two together (step.hasError = true; step.completed = false in error-handler patterns and inside Material's own error-state matchers) so the limitation is benign for the documented usage pattern.
• errorAggregator - points at the shared NO_ERROR_AGGREGATOR constant.