feat: add type safety for skippable step dependencies

[jumski]

Add Type Safety for Skippable Step Dependencies

This PR enhances the Flow DSL's type system to properly handle skippable steps. When a step has whenUnmet: 'skip' or whenFailed: 'skip', dependent steps now receive that step's output as an optional property in their dependencies object.

Key improvements:

• Added a StepMeta interface to track both output type and skippability status
• Modified StepInput to make dependencies optional when they come from skippable steps
• Added comprehensive type tests to verify correct behavior in various scenarios
• Ensured type narrowing works properly after existence checks

This change improves type safety by preventing runtime errors when accessing potentially undefined outputs from skipped steps. Developers will now get proper TypeScript errors if they try to access properties on skippable dependencies without first checking for their existence.

Example usage:

flow.step({ slug: 'risky', whenFailed: 'skip' }, () => ({ result: 42 }))
    .step({ slug: 'dependent', dependsOn: ['risky'] }, (deps) => {
      // TypeScript now requires a null check before accessing properties
      if (deps.risky) {
        return { value: deps.risky.result };
      }
      return { value: 0 };
    });

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[jumski]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• fix: improve type safety for skip-cascade mode in flow steps #593
• refactor: rename condition_pattern to required_input_pattern and condition_not_pattern to forbidden_input_pattern #587
• feat: add whenUnmet and whenFailed condition modes to flow shapes #585
• feat: add ifNot condition pattern for negative condition checks #584
• feat: improve type safety for flow step outputs and skippable dependencies #583
• feat: add type safety for skippable step dependencies #582 👈 (View in Graphite)
• feat: add ContainmentPattern type for JSON condition matching #576
• feat: add whenFailed option for error handling after retries exhausted #575
• feat: add conditional step execution with skip/fail behavior #573
• feat: add conditional step execution with skip infrastructure #572 : 1 other dependent PR (#594 )
• main

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[nx-cloud]

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☁️ Nx Cloud last updated this comment at 2026-01-20 09:44:29 UTC

[jumski]

Folded into #572 (squashed conditional steps PR)