Refactor: extract shared iac.provider discovery + grouping helper used by plan and apply

[intel352]

Background

Surfaced by Copilot's review of PR #528 (W-3b): cmd/wfctl/infra_plan_provider.go::computePlanForInfraSpecs duplicates the iac.provider discovery + grouping logic in cmd/wfctl/infra_apply.go::applyInfraModules. Both walk cfg.Modules, filter by iac.provider, group resource specs by provider ref, count provider types for the fallback heuristic, etc.

Why this exists today: apply was the original; plan was added in W-3b mirroring it intentionally so the v2 dispatch path (W-3b T3.6b) could honestly emit Replace actions before apply. The duplication was accepted in-PR to keep W-3b scope-locked (per workspace memory feedback_implementer_scope_bleed).

Risk

Plan and apply can drift over time on:

• env-var resolution rules
• disabled-provider handling
• grouping order
• provider-type-counts fallback heuristic
• error wrapping of plugin-load failures

Drift here is silent and only surfaces when an operator's plan and apply produce different action sets for the same input.

Proposed shape

Extract a shared helper in cmd/wfctl/infra_provider_dispatch.go (or similar):

// resolveProviderDefs walks cfg.Modules, filters `iac.provider`
// modules, expands env vars in cfg, and returns provType -> providerDef.
func resolveProviderDefs(cfg *engine.Config, envName string) (map[string]providerDef, error)

// groupSpecsByProviderRef walks resource specs, looks up the matching
// providerDef via `cfg.provider` field, and returns moduleRef ->
// planGroup{ moduleRef, provType, provCfg, specs[] } in stable order.
func groupSpecsByProviderRef(specs []interfaces.ResourceSpec, defs map[string]providerDef) ([]string, map[string]*planGroup, error)

// loadProvidersForGroups iterates groups in order, calls
// resolveIaCProvider per group, and returns map[moduleRef]*loadedProvider
// (with closer + error). Caller decides whether to fail-fast or
// surface partial results.
func loadProvidersForGroups(ctx context.Context, groups map[string]*planGroup) (map[string]*loadedProvider, error)

Then computePlanForInfraSpecs and applyInfraModules both call into these helpers, eliminating the duplication.

Acceptance

• Single helper used by both plan and apply paths
• Existing test coverage migrated (no test deletion)
• New unit test asserts plan and apply produce the same provider grouping for the same input config
• No behavior change for v1 plugins (grouping output identical)

Source

Copilot inline comment on PR #528 round 5: #528 (comment)