/arn-infra-change-plan

name: arn-infra-change-plan
description: >-
  This skill should be used when the user says "plan infra change",
  "arn-infra-change-plan", "infra change plan", "plan this infrastructure change",
  "create infra plan", "arn infra plan", "plan the infra spec",
  "infrastructure implementation plan", "infra plan from spec",
  "generate infra plan", "plan infrastructure", or wants to generate a
  phased implementation plan from an infrastructure change specification,
  structured by provisioning order, blast radius, rollback checkpoints,
  and environment promotion gates.
version: 1.0.0

Arness Infra Change Plan

Generate a phased implementation plan from an infrastructure change specification by invoking the `arn-infra-change-planner` agent. The plan is written to disk as a PLAN_PREVIEW file, presented to the user for review, and iteratively refined based on feedback until approved. The approved plan then feeds into `/arn-infra-save-plan` for structuring into phases, tasks, and reports.

This skill plans in infrastructure terms -- phases are ordered by provisioning dependency, blast radius classification, rollback checkpoint placement, and environment promotion gates -- not by application development concepts.

Pipeline position: arn-infra-init -> arn-infra-change-spec -> [arn-infra-change-plan] -> arn-infra-save-plan -> arn-infra-execute-change -> arn-infra-review-change -> arn-infra-document-change

Prerequisites

Read `## Arness` from the project's CLAUDE.md. If no `## Arness` section exists or Arness Infra fields are missing, inform the user: "Arness Infra is not configured for this project yet. Run `/arn-infra-wizard` to get started — it will set everything up automatically." Do not proceed without it.

Check the **Deferred** field. If `Deferred: yes`, inform the user: "Infrastructure is in deferred mode. Change planning is not available until infrastructure is fully configured. Run `/arn-infra-assess` to un-defer." Stop.

Extract:

• **Infra specs directory** -- path where INFRA_CHANGE_*.md specs are stored (default: `.arness/infra-specs`)
• **Infra plans directory** -- path where plans are stored (default: `.arness/infra-plans`)
• **Experience level** -- derived from user profile. Read `~/.arness/user-profile.yaml` (or `.claude/arness-profile.local.md` if it exists — project override takes precedence). Apply the experience derivation mapping from `${CLAUDE_PLUGIN_ROOT}/skills/arn-infra-ensure-config/references/experience-derivation.md`. If no profile exists, check for legacy `Experience level` in `## Arness` as fallback.
• **Providers** -- which cloud providers are configured
• **Environments** -- which environments exist and their promotion order

If `Infra plans directory` is not configured, use the default `.arness/infra-plans`. If the directory does not exist, create it: `mkdir -p <infra-plans-dir>`.

---

Workflow

Step 1: Find the Change Specification

The user may provide a spec name as an argument (e.g., "plan infra change migrate-database-managed" or "arn infra plan INFRA_CHANGE_vpc-restructure").

**If an argument was provided:**

• Look for `<infra-specs-dir>/<argument>.md` (exact match)
• If not found, try `<infra-specs-dir>/INFRA_CHANGE_<argument>.md`
• If not found, try matching files in `<infra-specs-dir>/` that contain the argument text in their filename
• If still not found, list available specs and ask the user to choose

**If no argument was provided:**

• List all `INFRA_CHANGE_*.md` files in `<infra-specs-dir>/`
• If only one exists, use it automatically
• If multiple exist, show the list sorted by modification date (most recent first) and ask the user to choose
• If none exist, inform the user: "No infrastructure change specifications found in `<infra-specs-dir>/`. Run `/arn-infra-change-spec` to create one first."

---

Step 2: Load Context

Read these files: 1. The selected specification file (INFRA_CHANGE_*.md) 2. The blast radius guide for classification reference: > Read `${CLAUDE_PLUGIN_ROOT}/skills/arn-infra-change-spec/references/blast-radius-guide.md`

If the spec file cannot be read, inform the user and stop.

---

Step 3: Invoke the Change Planner Agent

Derive the spec name from the spec filename (strip prefix and extension):

• `INFRA_CHANGE_migrate-database-managed.md` -> `migrate-database-managed`
• `INFRA_CHANGE_vpc-restructure.md` -> `vpc-restructure`

The output file path is: `<infra-plans-dir>/PLAN_PREVIEW_INFRA_<spec-name>.md`

**Check for existing PLAN_PREVIEW:** If a PLAN_PREVIEW file already exists at that path, inform the user: "A plan preview already exists for this spec: `<path>`."

Ask (using `AskUserQuestion`):

**"A plan preview already exists. What would you like to do?"**

Options: 1. **Regenerate** -- Generate a new plan from scratch 2. **Review** -- Review the existing plan

If **Review**, skip to Step 4. If **Regenerate**, proceed.

Invoke the `arn-infra-change-planner` agent via the Task tool, passing the model from `.arness/agent-models/infra.md` as the `model` parameter (see `plugins/arn-infra/skills/arn-infra-ensure-config/references/ensure-config.md` "Dispatch convention" for fallback). Context:

You are generating a phased infrastructure implementation plan for the following change specification.

**Specification:** <spec-name>
**Spec file:** <infra-specs-dir>/<spec-filename>

--- CHANGE SPEC ---
[full spec file content]
--- END CHANGE SPEC ---

--- PROVIDER CONFIG ---
Providers: [from ## Arness]
Default IaC tool: [from ## Arness, if configured]
--- END PROVIDER CONFIG ---

--- ENVIRONMENT CONFIG ---
Environments: [from ## Arness]
Promotion order: [from ## Arness or from the spec's Environment Scope section]
--- END ENVIRONMENT CONFIG ---

--- OUTPUT INSTRUCTIONS ---
Output file: <infra-plans-dir>/PLAN_PREVIEW_INFRA_<spec-name>.md

Generate a phased implementation plan structured by:
1. Provisioning dependency order (network before compute, compute before application)
2. Blast radius clas