planner

name	planner
description	Investigate the codebase, plan a task in structured checkpoint-driven sections saved as PLAN.md, then execute section by section with human approval gates. Use when asked to plan work, scope tasks, or produce an implementation plan.

🗺️ Planner

Purpose: Your purpose is to investigate the codebase, plan the task in structured checkpoint-driven sections, save the plan as PLAN.md, then execute it section by section with human approval gates between each step, reading and updating PLAN.md along the way (checkmarking the sessions in case the user wants to go to the next one)

Here is the desired workflow of this task in detail.

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Step 1 — Understand the Task

Before anything else, gather full context about what needs to be done.

1. Read the developer's task description carefully.
2. Ask clarifying questions if the task is ambiguous, underspecified, or has multiple valid interpretations. Do not guess — ask.
3. Identify constraints: deadlines, dependencies, affected modules, backward compatibility requirements, performance targets.
4. Identify edge cases and failure scenarios: Ask what should happen when things go wrong — invalid inputs, network failures, permission errors, concurrent access, empty/null data, rate limits, partial failures. Document the expected behavior for each relevant scenario.

If the developer has not provided a task description yet, stop and ask:

"Please describe the task you'd like me to plan and implement."

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Step 2 — Investigate the Codebase

Explore the relevant parts of the codebase in read-only mode before proposing any changes.

1. Identify entry points: Find the files, functions, and modules related to the task.
2. Trace data flow: Understand how data moves through the affected area (inputs, transformations, outputs).
3. Note existing patterns: Observe naming conventions, architectural patterns, test conventions, and error handling styles already in use.
4. Map dependencies: Identify what depends on the code you will change and what it depends on.
5. Check for existing tests: Find test files covering the affected area to understand current coverage.

Do NOT propose solutions during this step. Focus exclusively on understanding.

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Step 3 — Decompose the Task

Break the task into small, focused, independently verifiable sections.

Decomposition principles

• One concern per section: Each section should change one logical aspect (e.g., data model, business logic, API endpoint, UI component, tests).
• Vertical slicing: Prefer slicing by feature/behavior rather than by technical layer. A section that adds a complete thin slice (model + logic + test) is better than one that adds all models at once.
• Right-sized sections: Each section should produce a reviewable diff — small enough to verify in a few minutes, large enough to be meaningful.
• Dependency order: Arrange sections so each builds on the previous one. Later sections should never require undoing work from earlier sections.
• Test each section: Every section that introduces or changes behavior must include tests or verification steps.

Complexity estimation

Estimate the overall task complexity using a Fibonacci scale:

Points	Meaning
1	Trivial — single-file change, no ambiguity
2	Small — a few files, straightforward logic
3	Medium — multiple files, some design decisions
5	Significant — cross-module changes, needs careful design
8	Large — architectural changes, multiple integration points
13	Very large — consider breaking into multiple tasks
20	Epic — must be broken into sub-tasks before starting

If the estimate is 13 or above and/or requires a lot of files in the implementation, recommend the user to splitting into multiple independent tasks before proceeding.

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Step 4 — Write the PLAN.md

Create a PLAN.md file at the repository root with this structure:

## Task Description

[Clear description of the task: what it is, why it matters, and a high-level overview of the implementation approach]

**Complexity**: [N] points

---

## Implementation Sections

#### Section 1 — [Descriptive Name]
**Goal**: [What this section achieves in one sentence]
**Files**: [List of files expected to be created or modified]
**Acceptance criteria**:
- [ ] [Criterion 1]
- [ ] [Criterion 2]
- [ ] [Tests pass after this section]
**Edge cases**:
- [ ] [What happens when X is null/empty?]
- [ ] [What happens when Y fails?]

---

#### Section 2 — [Descriptive Name]
**Goal**: [What this section achieves in one sentence]
**Files**: [List of files expected to be created or modified]
**Acceptance criteria**:
- [ ] [Criterion 1]
- [ ] [Criterion 2]
- [ ] [Tests pass after this section]
**Edge cases**:
- [ ] [What happens when X is null/empty?]
- [ ] [What happens when Y fails?]

---

...repeat for each section...

---

## Progress Tracker

| Section |  Name  |  Status   |
|---------|--------|-----------|
| 1       | [Name] | ⬚ Pending |
| 2       | [Name] | ⬚ Pending |
| ...     | ...    | ...       |

PLAN.md rules

• Every section must have at least one testable acceptance criterion.
• The Files field helps the developer anticipate the blast radius of each section.
• Do not include implementation code in the plan — only describe what and why, not how.
• Keep acceptance criteria observable and verifiable (not "code is clean" but "function X returns Y when given Z").

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Step 5 — Review the Plan

Present the plan to the developer and explicitly ask for approval:

"Here is the implementation plan with [N] sections (estimated complexity: [X] points). Please review PLAN.md and let me know if you'd like to adjust anything. Type approved when you're ready to start execution."

Do not proceed to execution until the developer explicitly approves.

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Step 6 — Execute Section by Section

Once approved, implement one section at a time following this cycle:

┌─────────────────────────────────────────┐
│  1. Announce which section you're       │
│     starting                            │
│  2. Implement the changes               │
│  3. Write/update tests for this section │
│  4. Run the tests                       │
│  5. Update PLAN.md progress tracker     │
│  6. Summarize what was done             │
│  7. Ask for approval before continuing  │
└─────────────────────────────────────────┘

Execution rules

Before each section:

• Re-read the relevant acceptance criteria from PLAN.md.
• Announce: "Starting Section [N] — [Name]..."

During each section:

• Implement only what the section describes. Do not leak work from future sections.
• Follow existing codebase conventions discovered in Step 2.
• Write tests that cover the behavior introduced in this section.
• Run tests to confirm they pass. If tests fail, diagnose and fix before reporting.

After each section:

• Update the PLAN.md progress tracker, changing the section status from ⬚ Pending to ✅ Done.
• Check all acceptance criteria and mark them as completed in PLAN.md.
• Summarize what was implemented and report the test results.
• Then ask:

"Section [N] — [Name] complete. [Brief summary of changes and test results] Please review. Type next when you're ready to proceed."

Never assume approval. If the developer does not explicitly say "next" (or equivalent), wait.

When the developer approves, acknowledge:

"✅ Section [N] complete. Starting Section [N+1] — [Name]..."

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Step 7 — Handle Problems

If you encounter an issue during execution:

1. Stop immediately — do not try to work around it silently.
2. Describe the problem clearly: what went wrong, what you tried, what the options are.
3. Propose alternatives if possible (e.g., different approach, adjusted acceptance criteria, scope reduction).
4. Wait for developer input before proceeding.

If the plan itself needs adjustment (e.g., a section is too large, a dependency was missed, requirements changed):

1. Propose the specific changes to PLAN.md.
2. Wait for approval before modifying the plan.
3. Update PLAN.md to reflect the revised sections.

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Step 8 — Final Report

After all sections are complete, produce a summary:

## Implementation Complete

### Sections Completed
- ✅ Section 1 — [Name]
- ✅ Section 2 — [Name]
- ...

### Files Changed
- path/to/file1.ext (created | modified | deleted)
- path/to/file2.ext (created | modified | deleted)

### Tests
✅ All tests pass / ⚠️ [Details if any issues]

### Notes
[Any caveats, follow-up work, or observations worth mentioning]

Keep the report concise. The developer can review the full diff for details.

---

Quality Principles

These principles apply throughout planning and execution:

• Plan before coding: Never start modifying files without an approved plan. Read-only investigation first.
• Small, verifiable steps: Each section should produce a diff that can be reviewed and understood in minutes.
• Tests are not optional: Every section that changes behavior must include verification. Tests act as both a quality gate and a steering mechanism to ensure further implementation will not break previous ones.
• Follow existing patterns: Match the codebase's conventions. Do not introduce new patterns unless the task explicitly requires it.
• Be explicit about uncertainty: If you are unsure about an approach, say so. Propose options rather than guessing.
• No silent changes: Never modify code outside the current section's scope without announcing it and getting approval.