implement

name	implement
description	Implement the next pending task in the current sprint phase. Follows TDD: write tests first (RED), then implement (GREEN), verify all tests pass, update docs, commit. Use when user says "implement", "next task", "work on task", "start task", "do the task", or when the user wants to pick up the next piece of work in an active sprint. Also trigger when user says "implement task N" to target a specific task.
allowed-tools	Bash, Read, Write, Edit, Grep, Glob, Agent

Implement Task

Find and implement the next pending task in the current sprint phase. Follow TDD strictly. Stop and report if architecture is compromised.

Protocol

1. Find the current task

Read docs/STATUS.md to find the active sprint and current phase.

If there's no active sprint, or no current phase, or the phase has no task files — tell the user there's nothing to implement and stop.

Read the sprint's sprint.md from docs/sprints/NNN-slug/ and the phase's task files from tasks/. Find the first task with status: pending. That's what we're implementing.

If all tasks are done — tell the user the phase is complete and stop. Don't start the next phase — that requires /plan-phase.

2. Update status

Mark the task as in-progress:

In the task file, change:

`pending` → `in_progress`

Update docs/STATUS.md to reflect what we're working on:

**Phase:** N — <Phase Name> (task M in progress) — <date>

3. Read the task and review relevant code

Read the full task file. Understand:

• What tests to write (from "Tests First" section)
• What to implement (from "Implementation" section)
• Acceptance criteria

Then read the code areas that will be affected. Understand the current state before changing anything.

4. Architectural check

Before writing any code, verify the foundation is solid. Look for:

• DRY violations in the area you're about to modify — will your changes make copy-paste worse?
• Hardcoded game data in Python that should be YAML — will you add more hardcoding on top?
• Mixed responsibilities — is the function/class you're extending already doing too much?
• Giant functions — will your changes push a 150-line method to 250?

If you find a problem that your task would make worse:

Stop. Report to the user:

• What the problem is
• Why proceeding would make it worse
• Proposed fix (quick refactor, separate task, or phase restructure)

Don't implement on a bad foundation just to close the task. A stopped task with a clear report is better than a "done" task that introduced technical debt.

5. TDD — RED phase

Write the tests described in the task's "Tests First" section.

Product-level tests. Test game behavior, not code structure. Long chains through real logic, mocking only external boundaries (I/O, LLM, random/dice).

Run the tests. They should be RED (failing). If they pass before implementation — either the feature already exists (re-evaluate the task) or the tests are too weak (rewrite them).

uv run pytest <test_file> -v

If the task's tests live under tests/integration/, they need the docker stack to run — uv run pytest against them won't work without a live backend. Write them now, but their RED/GREEN verification happens in step 7b via docker, not here.

6. TDD — GREEN phase

Implement the minimum code to make the tests pass. Follow the task's "Implementation" section as a guide, but use judgment — the task plan may not account for everything you discovered during code review.

Principles during implementation:

• Minimum viable change. Don't gold-plate. Don't add features the task didn't ask for.
• Respect existing patterns. Match the style and structure of surrounding code.
• No hardcoded game data in Python. If you need new game data — it goes in YAML under content/ or in frozen dataclass definitions in core/.
• Rules stay pure. No I/O, no state, no side effects in rules/.
• Layers depend down. Don't import from layers above or from service/adapters in core/rules/layers.

7. Verification

Run the full test suite:

make check

This runs the full local gate: backend (lint + typecheck + tests) and frontend (eslint + typecheck + vitest) — the same checks CI runs, minus integration. Everything must pass. (Integration is not in make check — if this task touched it, see step 7b.)

If new tests fail

Debug and fix. This is normal TDD iteration.

If OLD tests fail

Do not blindly fix old tests to make them pass. Old tests existed for a reason. Analyze:

1. What contract changed? Identify the exact interface or behavior that shifted.
2. Was the contract change intentional? Does the task require this change, or did we accidentally break something?
3. If intentional — update the old tests to reflect the new contract. Document what changed and why in the task's developer notes.
4. If accidental — fix the implementation, not the tests. The old tests are telling you something is wrong.
5. If unclear — ask the user. "These 3 tests in test_combat.py fail because we changed the Attack dataclass. The task requires this change because X. Should I update them or rethink the approach?"

7b. Run integration tests if this task added or changed any

make check does not run integration tests. If this task touched tests/integration/, run them now via docker (don't defer to /close-phase):

make test-integration 2>&1 | tee /tmp/integration.log

The whole suite must be green, not just your new test. Treat failures like any other: fix to root cause before commit.

8. Update docs and commit

Update the task file:

## Status

`done`

## Developer Notes

<What actually happened. Key decisions, surprises, problems encountered.
If old tests were modified — explain why. If you deviated from the plan — explain why.
Keep it brief but informative for future context recovery.>

Update docs/STATUS.md — note the completed task:

**Phase:** N — <Phase Name> (task M done, M+1 pending) — <date>

Commit:

git add <changed files> docs/STATUS.md
git commit -m "sprint NNN phase N task M: <what was done>"

Stage specific files — don't git add -A. Do NOT push.

9. Report

Task M: <title> — done
  Tests: N new, M modified, K total passing
  Files changed: <list>
  Notes: <anything notable>
Next: Task M+1 — <title>