[Feature Request] Validate step references at flow load time

[ameet]

Problem

In One CLI flows, code steps can reference $.steps.X where step X either doesn't exist or is declared after the referencing step. No error is raised at flow load or validation time — the reference silently resolves to undefined at runtime.

How We Discovered This

We found 7 flows where buildCacheEntry referenced $.steps.buildResult, but buildResult was declared AFTER buildCacheEntry in the steps array:

{
  "steps": [
    { "id": "buildCacheEntry", "type": "code", "code": { "source": "var result = $.steps.buildResult ? $.steps.buildResult.output : null; ..." } },
    { "id": "writeCacheFile", "type": "file-write", ... },
    { "id": "buildResult", "type": "code", ... }
  ]
}

Since One CLI executes steps sequentially by declaration order, buildCacheEntry always sees $.steps.buildResult as undefined. The quality gate if (!result) return null always triggers, and caching silently never works. Every flow invocation re-computes expensive LLM calls that should have been cached.

This affected 7 flows in our codebase and went undetected until we wrote a custom static analysis script.

Proposed Solutions

Option A (best): At one flow execute time, before execution begins, scan all code step sources for $.steps.X references and validate:

1. Step X exists in the flow's step list
2. Step X is declared before the referencing step (or flag as "forward reference — may be undefined at runtime")

Option B: Add a one flow validate command (or enhance existing validation) that performs static step reference analysis and reports warnings.

Option C: At runtime, when a code step accesses $.steps.X and X hasn't executed yet, log a warning: "Step 'buildCacheEntry' references 'buildResult' which hasn't executed yet — value will be undefined."

Impact

Forward-reference bugs cause silent failures (caching broken, data missing, quality gates bypassed) that are extremely difficult to debug because no error is raised. Seven flows in our 88-flow codebase had this bug, potentially wasting significant LLM compute on every invocation.