vant-flow-runtime

name	vant-flow-runtime
description	Renderer, frm scripting, validation, actions, and host integration guidance for Vant Flow. Use when working on VfRenderer, VfFormContext, client-script behavior, metadata-driven logic, action buttons, link field loading, media handlers, or runtime field and section state.

Vant Flow Runtime

Use this skill for changes that happen after a schema is already authored and being executed.

Start Here

1. Read references/runtime-api-matrix.md.
2. Read references/host-integration-checklist.md if the task touches renderer inputs, host callbacks, media handlers, or remote link loading.
3. Inspect:
   • projects/vant-flow/src/lib/components/form-renderer/form-renderer.component.ts
   • projects/vant-flow/src/lib/services/form-context.ts
   • projects/vant-flow/src/lib/components/form-field.component.ts

Runtime Design Rules

• Put per-field UI behavior in VfField.
• Put form lifecycle, payload packing, full-form validation, and host-facing outputs in VfRenderer.
• Put script APIs and runtime state mutation in VfFormContext.
• Prefer host inputs and callbacks for page-level workflow state. Prefer frm for dynamic in-form reactions.

Validation Rules

• Preserve built-in required and regex validation unless the task explicitly changes those semantics.
• If scripts call frm.validate() during the validate hook, maintain the non-recursive fallback behavior.
• If stepper behavior changes, verify both full-form and per-step validation paths.

Action Rules

• Renderer header actions are not the same as field-level Button fields.
• Custom action behavior should stop emission when the callback or action returns false.
• Keep formAction payloads consistent: action, buttonName, packed data, rawData, frm, and source.

Link And Media Rules

• Keep Link as a full-object selection model, not an ID-only control.
• Keep uploads and downloads application-owned through mediaHandler and mediaResolver.
• Keep request/observer contracts stable when extending async field behavior.

Done Criteria

• Script behavior, renderer lifecycle, and host integration rules all still agree.
• Related runtime specs were updated.
• Docs changed if a host integration contract or public runtime API changed.