fix(diff): VPC/Droplet/AppPlatform Diff now compares region (#70)

[intel352]

Summary

Closes #70. Adds region comparison to VPCDriver, DropletDriver, AppPlatformDriver Diff functions.

Surfaced by core-dump TC2 staging cutover (run) where the cascade-replace plan-shape assertion expected 5 replace actions but got 1 (Volume only). Without the gate, apply would have left VPC + Droplet in nyc3 while moving App + Volume to nyc1 — half-migrated state requiring manual cleanup.

Changes

File	Δ	Why
internal/drivers/vpc.go	+13	VPCDriver.Diff: add region check, ForceNew on drift
internal/drivers/droplet.go	+13	DropletDriver.Diff: same pattern
internal/drivers/app_platform.go	+28	AppPlatformDriver.Diff: same pattern + add region to appOutput so Diff has a current-side value to compare
internal/drivers/vpc_test.go	+59	RegionChangeForcesReplace + RegionEmptyCurrentSkipped
internal/drivers/droplet_test.go	+71	same pattern
internal/drivers/app_platform_test.go	+71	same pattern
CHANGELOG.md	+3	[Unreleased] fixed entry

Total: 6 source files + CHANGELOG, 266 insertions.

Pattern

All three drivers now follow VolumeDriver.Diff's canonical region block (lines 165-173):

if region := strFromConfig(desired.Config, "region", ""); region != "" {
    curRegion, _ := current.Outputs["region"].(string)
    if curRegion != "" && curRegion != region {
        changes = append(changes, interfaces.FieldChange{
            Path: "region", Old: curRegion, New: region, ForceNew: true,
        })
        needsReplace = true
    }
}

The curRegion != "" guard is the upgrade-safe path: resources in state from earlier plugin versions (when their output functions didn't include region) don't false-positive on the first plan after upgrade — they'll Read on next apply to populate the field naturally.

Validation

$ GOWORK=off go build ./...
# clean

$ GOWORK=off go test -count=1 ./internal/drivers/
ok  	github.com/GoCodeAlone/workflow-plugin-digitalocean/internal/drivers	6.151s

$ GOWORK=off go test -count=1 ./...
ok  	github.com/GoCodeAlone/workflow-plugin-digitalocean	1.448s
ok  	github.com/GoCodeAlone/workflow-plugin-digitalocean/internal	2.046s
ok  	github.com/GoCodeAlone/workflow-plugin-digitalocean/internal/drivers	6.151s

Scope discipline

Only the 3 Diff fixes + their regression tests + the appOutput.region addition + CHANGELOG entry. No other Diff changes; no public API changes; no .github/workflows touch.

Test plan

• Local validation
• CI green
• Copilot review pass
• Admin-merge → tag v0.10.2

Downstream

After v0.10.2 ships, core-dump's .wfctl-lock.yaml + wfctl.yaml bump v0.10.1 → v0.10.2 in a follow-up PR. Re-dispatching tc2-cutover.yml will then emit the expected 5-resource cascade.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes a planning blind spot in the DigitalOcean IaC provider by ensuring Diff detects region drift for VPCs, Droplets, and App Platform apps, and marks those changes as replace-only (ForceNew). This prevents incomplete “region migration” plans that would otherwise leave some resources in the old region while dependents move.

Changes:

• Add region comparisons to VPCDriver.Diff, DropletDriver.Diff, and AppPlatformDriver.Diff, emitting FieldChange{ForceNew: true} on drift.
• Extend appOutput to include Outputs["region"] so App Platform diffs have a current-side value to compare.
• Add regression tests for “region change forces replace” and “missing current region is skipped” cases, plus a CHANGELOG entry.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/drivers/vpc.go	Adds region drift detection in VPCDriver.Diff and marks drift as ForceNew.
internal/drivers/vpc_test.go	Adds tests covering replace-on-region-drift and upgrade-safe empty-current behavior for VPCs.
internal/drivers/droplet.go	Adds region drift detection in DropletDriver.Diff and marks drift as ForceNew.
internal/drivers/droplet_test.go	Adds tests covering replace-on-region-drift and upgrade-safe empty-current behavior for Droplets.
internal/drivers/app_platform.go	Adds region drift detection to Diff (replace-only) and includes region in appOutput.
internal/drivers/app_platform_test.go	Adds tests covering replace-on-region-drift and upgrade-safe empty-current behavior for App Platform.
CHANGELOG.md	Documents the fix under [Unreleased].

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.