Add Copilot research & plan prompt files

[Copilot]

Adds two reusable VS Code Copilot Chat prompt files encoding a two-phase research → plan workflow. Drop these into any project's .github/prompts/ to enforce structured pre-implementation thinking.

Files added

• .github/prompts/research.prompt.md — Locks Copilot into research-only mode: investigate the problem, examine the codebase, and produce a structured research.md (problem summary, relevant code, key findings, open questions). No code changes allowed.

• .github/prompts/plan.prompt.md — Locks Copilot into planning-only mode: reads research.md and produces a structured plan.md (approach, per-file changes with rationale, testing strategy, rollout considerations, open questions). No code changes allowed.

Both files use YAML front matter with a description field as required by the Copilot prompt file spec.

Original prompt

Add two GitHub Copilot prompt files to .github/prompts/ that encode a two-phase development workflow (research → plan) for use in VS Code Copilot Chat. These prompt files can be copied into any project's .github/prompts/ directory to use as reusable skills.

Files to Create

1. .github/prompts/research.prompt.md

---
description: "Deep research phase — investigate an issue and the codebase, then write findings to research.md"
---

You are in the **research phase**. Do NOT implement any code changes.

Your job is to deeply research the problem and the current codebase, then produce a research document.

## Steps

1. **Understand the problem**: Read the GitHub issue or problem description I provide carefully. Ask clarifying questions if the problem is ambiguous.
2. **Examine the codebase**: Search through the relevant parts of the codebase to understand:
   - How the current functionality works
   - What files/modules are involved
   - Any related patterns, utilities, or conventions already in use
   - Any existing tests related to this area
3. **Research external context** (if needed): Look up relevant documentation, APIs, or known issues that may inform the solution.
4. **Write `research.md`**: Create a `research.md` file in the project root with your findings, structured as follows:

Research: [Brief title of the issue]

Problem Summary

[Concise description of what we're solving and why]

Relevant Code

[List of key files, functions, and modules involved, with brief descriptions of what they do]

Current Behavior

[How things work today in the area we're changing]

Key Findings

[Important discoveries — gotchas, edge cases, dependencies, constraints]

External References

[Links to docs, issues, or discussions that are relevant]

Open Questions

[Anything that still needs clarification before we can plan a solution]

## Rules
- Do NOT write any implementation code
- Do NOT modify any existing files (except creating `research.md`)
- Be thorough — this document will be the foundation for planning
- Flag risks and unknowns explicitly

2. .github/prompts/plan.prompt.md

---
description: "Planning phase — create an implementation plan based on research.md"
---

You are in the **planning phase**. Do NOT implement any code changes.

Your job is to take the research from `research.md` and produce a clear, actionable implementation plan.

## Steps

1. **Read `research.md`**: Review the research document thoroughly.
2. **Design the approach**: Based on the findings, determine the best implementation strategy.
3. **Write `plan.md`**: Create a `plan.md` file in the project root, structured as follows:

Plan: [Brief title]

Approach

[High-level description of the chosen approach and why]

Changes

1. [First change]

• File(s): path/to/file
• What: [Description of the change]
• Why: [Rationale]

2. [Second change]

• File(s): path/to/file
• What: [Description of the change]
• Why: [Rationale]

[...continue for each change]

Testing Strategy

[What tests to add or update, and what to verify]

Rollout / Migration Considerations

[Any backward compatibility, feature flags, or deployment concerns]

Open Questions

[Anything that still needs a decision before implementation]

## Rules
- Do NOT write any implementation code
- Do NOT modify any existing files (except creating `plan.md`)
- Each change should be small and clearly scoped
- Order the changes so they can be implemented sequentially
- Call out any decisions that need human input in Open Questions

Important Notes

• Create the files exactly as specified above, with the YAML front matter (--- delimited block with description) at the top of each file.
• These are Copilot prompt files, so the markdown content IS the prompt — do not wrap it in additional code blocks or add extra commentary.

This pull request was created from Copilot chat.

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