itx-plan-build

name	itx:plan-build
description	Create high-level implementation plan with product output and technical details
argument-hint	<issue-number>

name: itx:plan-build

Implementation Planning (Build Phase)

Create a high-level implementation plan for a GitHub issue with product output and technical details.

Instructions

1. Fetch Issue: Get full issue details

   gh issue view <number> --json number,title,body,labels,comments
   

2. Explore Codebase: Understand the scope

   • Identify affected files and modules
   • Review related code patterns
   • Check for existing tests
   • Note any dependencies

3. Create Plan: Structure the implementation approach

   • Break down into logical steps
   • Identify files to modify/create
   • Define test strategy
   • Note potential risks

4. Decide on Subtasks:

   • Simple issue (< 3 files, single concern): No subtasks needed
   • Complex issue (multiple files, multiple concerns): Create subtasks

5. If Subtasks Needed: Create subtask issues and link as sub-issues

   # Create subtask
   CHILD_URL=$(gh issue create \
     --title "[Parent #<parent>] <subtask description>" \
     --label "ready" \
     --body "<subtask details>")
   CHILD_NUM=$(basename $CHILD_URL)
   
   # Link as sub-issue using GraphQL
   gh api graphql -f query='
     mutation($parentId: ID!, $childId: ID!) {
       addSubIssue(input: {issueId: $parentId, subIssueId: $childId}) {
         issue { number }
         subIssue { number }
       }
     }' \
     -f parentId=$(gh api graphql -f query='query($owner: String!, $repo: String!, $issue: Int!) { repository(owner: $owner, name: $repo) { issue(number: $issue) { id } } }' -f owner=OWNER -f repo=REPO -F issue=$PARENT_NUM | jq -r '.data.repository.issue.id') \
     -f childId=$(gh api graphql -f query='query($owner: String!, $repo: String!, $issue: Int!) { repository(owner: $owner, name: $repo) { issue(number: $issue) { id } } }' -f owner=OWNER -f repo=REPO -F issue=$CHILD_NUM | jq -r '.data.repository.issue.id')
   

6. Post Plan: Add plan as comment on parent issue

   ## Implementation Plan
   
   ### Overview
   <brief description of approach>
   
   ### Files to Modify
   - `path/to/file.py` - <what changes>
   
   ### Steps
   1. <step>
   2. <step>
   
   ### Test Strategy
   - <how to verify>
   
   ### Subtasks
   - #<subtask1> - <description>
   - #<subtask2> - <description>
   (or "None - single task execution")
   
   ---
   
   <details>
   <summary>Prompt Log</summary>
   

Stage: planning Skill: /itx:plan-build Timestamp: Model:

<original user prompt that triggered planning>

```

7. Update Labels:

   gh issue edit <number> --remove-label "planning" --add-label "planned"
   

8. Return: Plan summary and any subtask issue numbers

Subtask Guidelines

• Each subtask should be independently executable
• Subtasks should have clear boundaries
• Order subtasks by dependency (execute first → last)
• Subtask title format: [Parent #N] <action verb> <target>

Notes

• Use expensive models (Opus/Sonnet) for planning - this is where thinking matters
• Execution can use cheaper models (Haiku)
• Plans should be detailed enough that any developer can execute