Task Execution Loop
For each task in priority order:
while (tasks remain):
- Mark task as in-progress
- Read any referenced files from the plan or discovered during Phase 0
- **If the unit's work is already present and matches the plan's intent** (files exist with the expected capability, or the unit's `Verification` criteria are already satisfied by the current code), the work has likely shipped on a prior branch or session. Verify it matches, mark the task complete, and move on. Do not silently reimplement.
- Look for similar patterns in codebase
- Find existing test files for implementation files being changed (Test Discovery — see below)
- Implement following existing conventions
- Add, update, or remove tests to match implementation changes (see Test Discovery below)
- Run System-Wide Test Check (see below)
- Run tests after changes
- Assess testing coverage: did this task change behavior? If yes, were tests written or updated? If no tests were added, is the justification deliberate (e.g., pure config, no behavioral change)?
- Mark task as completed
- Evaluate for incremental commit (see below)
When a unit carries an Execution note, honor it. For test-first units, write the failing test before implementation for that unit. For characterization-first units, capture existing behavior before changing it. For units without an Execution note, proceed pragmatically.
Guardrails for execution posture:
- Do not write the test and implementation in the same step when working test-first
- Do not skip verifying that a new test fails before implementing the fix or feature
- Do not over-implement beyond the current behavior slice when working test-first
- Skip test-first discipline for trivial renames, pure configuration, and pure styling work
Test Discovery — Before implementing changes to a file, find its existing test files (search for test/spec files that import, reference, or share naming patterns with the implementation file). When a plan specifies test scenarios or test files, start there, then check for additional test coverage the plan may not have enumerated. Changes to implementation files should be accompanied by corresponding test updates — new tests for new behavior, modified tests for changed behavior, removed or updated tests for deleted behavior.
Test Scenario Completeness — Before writing tests for a feature-bearing unit, check whether the plan's Test scenarios cover all categories that apply to this unit. If a category is missing or scenarios are vague (e.g., "validates correctly" without naming inputs and expected outcomes), supplement from the unit's own context before writing tests:
| Category | When it applies | How to derive if missing |
|---|
| Happy path | Always for feature-bearing units | Read the unit's Goal and Approach for core input/output pairs |
| Edge cases | When the unit has meaningful boundaries (inputs, state, concurrency) | Identify boundary values, empty/nil inputs, and concurrent access patterns |
| Error/failure paths | When the unit has failure modes (validation, external calls, permissions) | Enumerate invalid inputs the unit should reject, permission/auth denials it should enforce, and downstream failures it should handle |
| Integration | When the unit crosses layers (callbacks, middleware, multi-service) | Identify the cross-layer chain and write a scenario that exercises it without mocks |
System-Wide Test Check — Before marking a task done, pause and ask:
| Question | What to do |
|---|
| What fires when this runs? Callbacks, middleware, observers, event handlers — trace two levels out from your change. | Read the actual code (not docs) for callbacks on models you touch, middleware in the request chain, after_* hooks. |
| Do my tests exercise the real chain? If every dependency is mocked, the test proves your logic works in isolation — it says nothing about the interaction. | Write at least one integration test that uses real objects through the full callback/middleware chain. No mocks for the layers that interact. |
| Can failure leave orphaned state? If your code persists state (DB row, cache, file) before calling an external service, what happens when the service fails? Does retry create duplicates? | Trace the failure path with real objects. If state is created before the risky call, test that failure cleans up or that retry is idempotent. |
| What other interfaces expose this? Mixins, DSLs, alternative entry points (Agent vs Chat vs ChatMethods). | Grep for the method/behavior in related classes. If parity is needed, add it now — not as a follow-up. |
| Do error strategies align across layers? Retry middleware + application fallback + framework error handling — do they conflict or create double execution? | List the specific error classes at each layer. Verify your rescue list matches what the lower layer actually raises. |
When to skip: Leaf-node changes with no callbacks, no state persistence, no parallel interfaces. If the change is purely additive (new helper method, new view partial), the check takes 10 seconds and the answer is "nothing fires, skip."
When this matters most: Any change that touches models with callbacks, error handling with fallback/retry, or functionality exposed through multiple interfaces.
Incremental Commits
After completing each task, evaluate whether to create an incremental commit:
| Commit when... | Don't commit when... |
|---|
| Logical unit complete (model, service, component) | Small part of a larger unit |
| Tests pass + meaningful progress | Tests failing |
| About to switch contexts (backend → frontend) | Purely scaffolding with no behavior |
| About to attempt risky/uncertain changes | Would need a "WIP" commit message |
Heuristic: "Can I write a commit message that describes a complete, valuable change? If yes, commit. If the message would be 'WIP' or 'partial X', wait."
If the plan has Implementation Units, use them as a starting guide for commit boundaries — but adapt based on what you find during implementation. A unit might need multiple commits if it's larger than expected, or small related units might land together. Use each unit's Goal to inform the commit message.
Commit workflow:
git add <files related to this logical unit>
git commit -m "feat(scope): description of this unit"
Handling merge conflicts: If conflicts arise during rebasing or merging, resolve them immediately. Incremental commits make conflict resolution easier since each commit is small and focused.
Note: Incremental commits use clean conventional messages without attribution footers. The final Phase 4 commit/PR includes the full attribution.
Parallel subagent mode: Commit ownership is split by isolation mode (see Phase 1 Step 4):
- Worktree-isolated: subagents may stage and commit inside their own worktree branch; the orchestrator merges those branches in dependency order after the batch.
- Shared-directory fallback: subagents do not commit; the orchestrator stages and commits each unit after the entire parallel batch completes.
Simplify as You Go
After completing a cluster of related implementation units (or every 2-3 units), review recently changed files for simplification opportunities — consolidate duplicated patterns, extract shared helpers, and improve code reuse and efficiency. This is especially valuable when using subagents, since each agent works with isolated context and can't see patterns emerging across units.
Don't simplify after every single unit — early patterns may look duplicated but diverge intentionally in later units. Wait for a natural phase boundary or when you notice accumulated complexity.
If ce-simplify-code is available, invoke it at phase boundaries (especially before Phase 3 when the diff is >=30 lines). Otherwise, review the changed files yourself for reuse and consolidation opportunities.