Implementation Planning (Create 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. Save Plan to File:

   mkdir -p .itx/<number>
   # Write plan to .itx/<number>/00_PLAN.md

5. Decide on Subtasks:
   • Simple issue (< 3 files, single concern): No subtasks needed
   • Complex issue (multiple files, multiple concerns): Create subtasks
6. If Subtasks Needed: Detect repository info and create subtask issues with sub-issue links

   # Extract repository info
   REMOTE_URL=$(git config --get remote.origin.url)
   OWNER_REPO=$(echo "$REMOTE_URL" | sed -E 's/.*[:/]([^/]+\/[^/]+)(\.git)?$/\1/')
   OWNER=$(echo "$OWNER_REPO" | cut -d'/' -f1)
   REPO=$(echo "$OWNER_REPO" | cut -d'/' -f2)
   
   # 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 with dynamic repo
   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')

7. 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-create
   **Timestamp**: <ISO timestamp>
   **Model**: <model>
   
   ```prompt
   <original user prompt that triggered planning>

   </details> ```
8. Update Labels:

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

9. 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
• Plan file saved to .itx/<N>/00_PLAN.md for reference

Prompt Logging

REQUIRED: Append prompt log to .itx/<N>/00_PLAN.md.

See AGENTS.md for format specification.