Add render-and-diff scripts for debugging chart changes

[mhotan]

Summary

• scripts/render-and-diff.sh — Renders helm templates at two git refs (tags, branches, SHAs) using temporary worktrees and diffs the output. Accepts arbitrary --values flags to mirror ArgoCD's exact values layering.
• scripts/compare-manifests.py — Structural diff engine that parses multi-document YAML, matches resources by (kind, name), and deep-diffs ConfigMap data by full key path. Dashboard ConfigMaps are flagged as changed without dumping giant JSON blobs.
• README section documenting usage

Usage

# Compare a release tag against main
./scripts/render-and-diff.sh controlplane-2026.4.7 main

# With terraform-generated values (any number of --values)
./scripts/render-and-diff.sh controlplane-2026.4.7 main \
  --values /path/to/values.yaml \
  --values /path/to/values-union.yaml

# Dataplane chart
./scripts/render-and-diff.sh dataplane-2026.4.7 main --chart dataplane

# Full text diff or all-resource structural diff
./scripts/render-and-diff.sh controlplane-2026.4.7 main --text
./scripts/render-and-diff.sh controlplane-2026.4.7 main --all

Test plan

• Verified render-and-diff.sh with default test fixture (controlplane.aws.yaml)
• Verified multiple --values flags work correctly
• Verified dashboard ConfigMaps show "CHANGED" without dumping JSON
• Verified --text mode falls back to diff -u

🤖 Generated with Claude Code

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[davidmirror-ops]

Maybe I'm doing smth wrong but I tried this with my values but got an error

./scripts/render-and-diff.sh dataplane-2026.4.7 main --chart dataplane --values $HOME/code/byok-testing/onprem-values.yaml

Rendering dataplane chart...
  old: dataplane-2026.4.7
  new: main

./scripts/render-and-diff.sh: line 141: chart_args[@]: unbound variable

[mhotan]

/aviator cancel

[aviator-app]

This pull request (or associated stack) has been cancelled and is no longer ready-to-merge.