# Plan: Per-task model override via MCP + cheapest-model prompt guidance

Spec: `docs/superpowers/specs/2026-06-09-per-task-model-override-design.md`

TDD, one focused commit per task. Build with `-c Release` per project; run
`ClaudeDo.Worker.Tests` (and `Data.Tests` if touched).

## Task 1 — ModelRegistry: cost ordering + alias validation

- Add `ByCostAscending = ["haiku","sonnet","opus"]`.
- Add `string? NormalizeAlias(string? model)`: trim; null/blank → null;
  case-insensitive match against `Aliases` → canonical lowercase; else throw
  `ArgumentException($"Unknown model '{model}'. Allowed: {join(Aliases)}.")`.
- Tests (Data.Tests): "sonnet"/"OPUS"/" haiku " → normalized; ""/null/"  " →
  null; "gpt4" → throws.

## Task 2 — CreateChildAsync accepts model

- `TaskRepository.CreateChildAsync`: add `string? model = null` (before the
  trailing `CancellationToken ct = default`); set
  `child.Model = ModelRegistry.NormalizeAlias(model)`.
- Update the two existing callers to compile (named pass-through added in
  Tasks 3–4; keep default null here).

## Task 3 — Planning + improvement MCP tools forward model

- `PlanningMcpService.CreateChildTask`: add `string? model` param after
  `commitType`; pass to `CreateChildAsync`. Extend `[Description]` to document
  the model arg (haiku/sonnet/opus; cheapest capable).
- `TaskRunMcpService.SuggestImprovement`: add `string? model` param after
  `description`; pass to `CreateChildAsync`. Extend `[Description]`.
- Tests: each tool persists the model; invalid value throws.

## Task 4 — External AddTask forwards model

- `ExternalMcpService.AddTask`: add `string? model = null` param (before the
  trailing `CancellationToken`); `entity.Model = ModelRegistry.NormalizeAlias(model)`.
  Extend `[Description]`.
- Test: AddTask persists model; invalid value rejected.

## Task 5 — Prompt guidance

- `PromptFiles.PlanningSystemDefault`: add a short paragraph — assign each
  subtask the cheapest model that does it well, with ordering haiku < sonnet <
  opus and the heuristic; pass it as `CreateChildTask(model=...)`.
- `PromptFiles.SystemDefault` Out-of-scope section: when filing via
  `SuggestImprovement`, pass the cheapest capable `model`.
- `PromptFiles.ImprovementChildDefault`: one-line minimality reminder.
- No test (static prompt text); verify build only.

## Task 6 — Verify

- Build App + Worker `-c Release`; run Worker.Tests + Data.Tests.
- Update `ClaudeDo.Worker/CLAUDE.md` (ConfigMcpTools/creation-tool notes) and
  `ClaudeDo.Data/CLAUDE.md` (ModelRegistry) if needed.