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 classification per phase (lowest to highest where possible)
3. Rollback checkpoint placement (before data-involved phases, before network changes, before cross-environment promotions)
4. Environment promotion gates (sequential: dev -> staging -> production, with explicit gates)
5. Cost budgeting per phase (estimated delta, cumulative tracking)
6. Parallel execution opportunities (independent resources within the same environment)

Include `Spec: <infra-specs-dir>/<spec-filename>` near the top for linkage.

Write the plan to the output file.
--- END OUTPUT INSTRUCTIONS ---

Step 4: Present Plan and Feedback Loop

After the planner agent completes:

1. Read the generated plan from <infra-plans-dir>/PLAN_PREVIEW_INFRA_<spec-name>.md
2. Present a structured summary to the user, adapted by experience level:

Expert: Concise summary with phase table:

Intermediate: Phase list with brief descriptions and key decisions:

"Phase [N]: [title]

• Environment: [env]
• Blast radius: [classification]
• Resources: [list]
• Rollback checkpoint: [yes/no -- what is checkpointed]
• Cost: [delta]"

Beginner: Narrative walkthrough explaining each phase in plain language, what it does, and why it is ordered this way.

3. Ask: "Does this plan look right, or would you like to change anything?"

If the user approves (e.g., "looks good", "approved", "yes", "proceed"): Go to Step 5.

If the user provides feedback (e.g., "combine phases 2 and 3", "add a rollback checkpoint before phase 4", "move the DNS change to a separate phase"): Go to Step 4b.

Step 4b: Iterate with Feedback

Invoke a fresh 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 (the current plan and user feedback):

You are revising an existing infrastructure implementation plan based on user feedback.

**Current plan file:** <infra-plans-dir>/PLAN_PREVIEW_INFRA_<spec-name>.md
**Spec file:** <infra-specs-dir>/<spec-filename>

--- USER FEEDBACK ---
[user's feedback verbatim]
--- END USER FEEDBACK ---

Read the current plan from the plan file, apply the user's feedback, and write
the updated plan to the same file. S