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Journey

Send Pipeline

Source file: packages/core/src/journey-machine/send.ts

This file turns an incoming event into either:

  • a committed transition
  • a committed navigation fallback
  • a terminal status change
  • or a non-transitioning result with optional error information

How It Works

Section titled “How It Works”
  1. executeSend(...) starts by checking that the machine is still "running" and emits transition.start. If the runtime has already been disposed, the surrounding queue resolves a non-transitioning result with JourneyDisposedError instead of throwing.
  2. handleHeadlessSend(...) short-circuits omitted-transition definitions:
    • goToStepById validates the target step and commits a direct step transition
    • goToNextStep and custom events resolve as no-ops
    • terminal events and goToPreviousStep still continue through the normal pipeline
  3. resolveTransitionsForSend(...) then handles the graph/linear goToStepById special case by filtering to only matching declared goToStepById transitions for the requested target step.
  4. selectTransitionForSend(...) calls selectTransition(...) from helpers.ts. While async guards are running, it updates snapshot.async through the async-state controller and passes a run-scoped AbortSignal into the guard args.
  5. If transition selection throws or times out, the file records step error state, emits transition.error, and resolves the send result with error instead of rejecting.
  6. If no transition matches, handleNoTransitionMatch(...) applies the built-in fallbacks:
    • goToPreviousStep falls back to history navigation
    • goToNextStep can auto-complete the journey when requireExplicitCompletion is not set and no explicit next-step transition was declared
    • everything else becomes a non-transitioning result
  7. If a transition matched, resolveNextContext(...) runs its synchronous updateContext callback, applies timeout protection to async guard work, and returns the next context or an error result.
  8. When the async work is done, the file clears the source step’s async loading state, resolves the target, and delegates the actual snapshot commit to navigation:
    • terminal targets go through commitTerminalTransition(...)
    • step targets go through commitStepTransition(...)

What This File Does Not Do

Section titled “What This File Does Not Do”

This separation is what keeps transition selection, snapshot commits, and async bookkeeping independently readable.

Section titled “Recommended Reading”