---
name: oat-project-design
version: 2.2.0
description: Use when discovery is complete and implementation-ready decisions are needed. Runs a collaborative, selective collaborative, or draft-and-review design flow, confirms requirements and produces both `spec.md` and `design.md`, and commits artifacts before the user-review gate.
disable-model-invocation: true
user-invocable: true
allowed-tools: Read, Write, Bash(git:*), Glob, Grep, AskUserQuestion
---

# Design Phase

Transform specification requirements into a detailed technical design with architecture, components, and implementation strategy.

## Prerequisites

**Required:** Completed discovery (`discovery.md` with `oat_status: complete`). Specification is optional — this skill folds requirements confirmation into its flow and produces `spec.md` as a byproduct (see Step 2). If the user already ran `oat-project-spec` standalone, that spec is reused.

## Principles

- **YAGNI ruthlessly** — remove unnecessary features from all designs.
  If a section drafts a capability the spec doesn't require, cut it.
  If a component boundary is there "in case we need it later", cut it.

## Progress Indicators (User-Facing)

When executing this skill, provide lightweight progress feedback so the user can tell what’s happening after they confirm.

- Print a phase banner once at start using horizontal separators, e.g.:

  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  OAT ▸ DESIGN
  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

- Before multi-step work, print step indicators, e.g.:
  - `[1/5] Validating spec + reading context…`
  - `[2/5] Drafting architecture overview…`
  - `[3/5] Designing components + data models…`
  - `[4/5] Reviewing design with user…`
  - `[5/5] Updating state + committing…`

## Process

### Step 0: Resolve Active Project

OAT stores active project context in `.oat/config.local.json` (`activeProject`, local-only).

```bash
PROJECT_PATH=$(oat config get activeProject 2>/dev/null || true)
PROJECTS_ROOT="${OAT_PROJECTS_ROOT:-$(oat config get projects.root 2>/dev/null || echo ".oat/projects/shared")}"
PROJECTS_ROOT="${PROJECTS_ROOT%/}"
```

**If `PROJECT_PATH` is missing/invalid:**

- Ask the user for `{project-name}`
- Set `PROJECT_PATH` to `${PROJECTS_ROOT}/{project-name}`
- Write it for future phases:
  ```bash
  mkdir -p .oat
  oat config set activeProject "$PROJECT_PATH"
  ```

**If `PROJECT_PATH` is valid:** derive `{project-name}` as the directory name (basename of the path).

### Step 1: Check Specification Complete

Specification is OPTIONAL in the default workflow. This skill folds requirements confirmation into Step 2 below and produces `spec.md` as a byproduct.

If `"$PROJECT_PATH/spec.md"` already exists (e.g., the user ran the standalone `oat-project-spec` skill first), validate it and reuse it:

```bash
if [ -f "$PROJECT_PATH/spec.md" ]; then
  cat "$PROJECT_PATH/spec.md" | head -10 | grep "oat_status:"
fi
```

**If `spec.md` exists, required frontmatter:**

- `oat_status: complete`
- `oat_ready_for: oat-project-design`

**If `spec.md` exists but is incomplete:** Block and ask user to finish the standalone spec skill first, OR delete the draft and let this skill regenerate it from discovery.

**If `spec.md` does not exist:** That is the default path. Skip to Step 1.5 (mode resolution); Step 2 (Requirements Confirmation) will produce it from `discovery.md`.

### Step 1.5: Resolve Interaction Mode

Resolve whether to run the design phase in Collaborative (section-by-section), Selective Collaborative (section-by-section only for sections that need eyes), or Draft-and-review (full draft up front) mode. Argument precedes env var. An **explicit** non-interactive signal forces draft. Persisted config preference is consulted before prompting the user.

> **Tool availability is not the same as interactivity.** If the structured `AskUserQuestion` tool is unavailable but the assistant can still exchange normal chat messages with the user, run Collaborative mode using plain chat prompts. Use Draft-and-review only for explicit non-interactive execution (`OAT_NON_INTERACTIVE=1`) or when no user-response channel exists at all (e.g., a CI job with stdin fully redirected from `/dev/null` and no agent-side user turn).

```bash
# 1. Check for explicit override (argument wins over env var — FR1)
DESIGN_MODE="${ARG_MODE:-${OAT_DESIGN_MODE:-}}"

# 2. If no override, check for EXPLICIT non-interactive signals only.
#    Lack of a structured question tool (e.g., AskUserQuestion unavailable)
#    is NOT a non-interactive signal by itself — if normal chat with the
#    user is available, the session is still interactive.
if [ -z "$DESIGN_MODE" ]; then
  if [ "${OAT_NON_INTERACTIVE:-}" = "1" ] || no_user_response_channel_exists; then
    DESIGN_MODE="draft"
    echo "Non-interactive context detected. Falling back to draft-and-review mode."
  else
    # 3. Consult persisted preference (FR15 / Component 14) before prompting
    CONFIG_MODE=$(oat config get workflow.designMode 2>/dev/null || echo "")
    if [ "$CONFIG_MODE" = "collaborative" ] || [ "$CONFIG_MODE" = "selective" ] || [ "$CONFIG_MODE" = "draft" ]; then
      DESIGN_MODE="$CONFIG_MODE"
      echo "Using workflow.designMode = ${DESIGN_MODE} from config."
    else
      # 4. Interactive: run the selective preflight, then prompt the user.
      #    The preflight uses references/selective-review-pass.md to classify
      #    sections and determine whether Selective Collaborative is
      #    recommended, available, available-not-recommended, or unavailable.
      #    Default recommendation is Collaborative when in doubt; Draft is
      #    never the default recommendation from the picker.
      #
      #    - Prefer AskUserQuestion for structured multi-choice when it is
      #      available.
      #    - If AskUserQuestion is unavailable, ask the same question as a
      #      plain chat message and wait for the user's reply. Do NOT switch
      #      to draft mode just because the structured tool is missing.
      #
      #    Question: "How would you like to work through the design?
      #       1. Collaborative — section-by-section, every section confirmed
      #       2. Selective collaborative — agent drafts routine sections silently
      #          and walks you through high-risk sections live; before drafting,
      #          you'll see which sections will be presented and why
      #       3. Draft-and-review — full draft up front, you review the committed file"
      #    Mark exactly one option "(recommended for this design)". Hide or
      #    label Selective unavailable when grounding is broadly absent:
      #    - Recommended: "Selective collaborative (recommended for this design)"
      #    - Available: "Selective collaborative (available)"
      #    - Available-not-recommended: "Selective collaborative (available, not recommended)"
      #    - Unavailable: "Selective collaborative (unavailable — insufficient grounding context)"
      #    If Selective is recommended, add one sentence explaining the section
      #    count and adequate grounding.
      #
      # Result populates DESIGN_MODE
      :
    fi
  fi
fi

echo "Running in ${DESIGN_MODE} mode."
```

**Resolution order (FR1 + FR15):**

1. `--mode` argument (`ARG_MODE`)
2. `OAT_DESIGN_MODE` env var
3. **Explicit** non-interactive signal (`OAT_NON_INTERACTIVE=1`, or the runtime truly cannot pause for any user response) → forces `draft`
4. `workflow.designMode` from effective config
5. Interactive prompt (default: Collaborative)

Runtime/context signals always outrank persisted preferences. **Missing `AskUserQuestion` is not a non-interactive signal** — fall through to the plain-chat prompt path instead.

**Selective recommendation states:** `recommended` when grounding is adequate and at least 3 sections (or about 30-40% of sections) classify as routine; `available` when it can run but Collaborative is safer; `available-not-recommended` when savings are marginal; `unavailable` when grounding is broadly absent. Do not offer Selective Collaborative from quick-start — this mode is only for full `oat-project-design`.

**Recovery — draft mode entered by mistake:** If the agent drafted and committed the full design in draft mode because `AskUserQuestion` was unavailable but normal chat was available, do **not** mark the design complete. Treat the committed draft as a starting point and walk it section by section with the user via plain chat — present each section, ask for confirmation or changes, revise and commit on feedback, then move to the next section. Only after the section-by-section pass approves the full artifact should Step 6's user-review gate be considered satisfied.

### Step 2: Requirements Confirmation (folded spec authoring)

<!--
Requirements-confirmation sub-step.
The authoring logic below duplicates oat-project-spec Steps 6-16.
When updating the requirements-authoring prose, update BOTH files.
-->

**If `spec.md` already exists with `oat_status: complete`** (produced by the optional standalone `oat-project-spec` skill): read it to understand Problem Statement, FRs/NFRs, Constraints, Dependencies, High-Level Design, Success Metrics, Requirement Index. Then skip to Step 2.5 (Approach Reaffirmation).

**Otherwise** (default path — no `spec.md` yet): author `spec.md` inline by formalizing requirements from `discovery.md`, following the steps below (ported from `oat-project-spec` Steps 6-16).

**Step 2a: Read discovery**

Read `"$PROJECT_PATH/discovery.md"` and extract:

- **Initial Request** → Core problem
- **Clarifying Questions** → Context and nuances
- **Key Decisions** → Scope boundaries, FR seeds
- **Success Criteria** → Goals and NFR seeds
- **Constraints** → Constraints section
- **Out of Scope** → Non-Goals

**Step 2b: Initialize spec.md from template**

Copy `.oat/templates/spec.md` → `"$PROJECT_PATH/spec.md"`. Update frontmatter:

```yaml
---
oat_status: in_progress
oat_ready_for: null
oat_blockers: []
oat_last_updated: { today }
oat_generated: false
oat_template: false
---
```

**Step 2c: Draft Problem Statement**

Transform from discovery: Initial Request → Core problem; Clarifying Questions → Context; Key Decisions → Scope boundaries. Write 2-4 paragraphs clearly describing the problem being solved.

**Step 2d: Define Goals and Non-Goals**

**Primary Goals:** Must-have outcomes (from Key Decisions + Success Criteria).
**Secondary Goals:** Nice-to-have outcomes (Success Criteria marked optional).
**Non-Goals:** Copy from discovery "Out of Scope", adding explicit boundaries and related work intentionally excluded.

**Step 2e: Draft Requirements**

Transform Key Decisions and Success Criteria into structured requirements.

**Functional Requirements (FR):**

```markdown
**FR1: {Requirement Name}**

- **Description:** {What the system must do}
- **Acceptance Criteria:**
  - {Testable criterion 1}
  - {Testable criterion 2}
- **Priority:** P0 / P1 / P2
```

**Non-Functional Requirements (NFR):**

```markdown
**NFR1: {Requirement Name}**

- **Description:** {Performance, security, usability requirement}
- **Acceptance Criteria:**
  - {Measurable criterion}
- **Priority:** P0 / P1 / P2
```

**Priorities:**

- **P0:** Must have — blocks launch
- **P1:** Should have — important but not blocking
- **P2:** Nice to have — future enhancement

**Step 2f: Iterate with user (collaborative and selective modes only)**

```
IF DESIGN_MODE == "collaborative" || DESIGN_MODE == "selective":
  Present draft requirements list to user.
  Ask (AskUserQuestion): "Are these requirements complete? Anything missing or unclear?"
  Update spec.md with refinements; update oat_last_updated.
  Repeat until user confirms completeness.

IF DESIGN_MODE == "draft":
  Commit the drafted requirements as part of the one-pass draft.
  The user reviews them holistically at the user-review gate (Step 6).
```

**Focus areas:** Acceptance criteria testable; priorities clear; edge cases covered; dependencies identified.

**Step 2g: Document Constraints and Dependencies**

Copy from discovery "Constraints" and enrich with technical constraints from knowledge base (architecture.md, concerns.md), business/timeline/resource constraints. Identify dependencies: external systems (integrations.md), existing components (architecture.md), third-party libraries, infrastructure.

**Step 2h: Draft High-Level Design in spec.md**

Transform discovery "Options Considered" into design proposal:

```markdown
## High-Level Design (Proposed)

{2-3 paragraph overview of chosen approach}

**Key Components:**

- {Component 1} — {Brief description}

**Alternatives Considered:**

- {Alternative 1} — {Why rejected}

**Open Questions:**

- {Question needing resolution}
```

Keep high-level — detailed design comes in `design.md` below.

**Guardrail:** Do not name specific scripts/files/functions here. Describe components and responsibilities only.

**Step 2i: Define Success Metrics**

Transform "Success Criteria" into measurable metrics (performance, quality, user, business).

**Step 2j: Populate Requirement Index**

Create traceability matrix in spec.md "Requirement Index" section:

| Column        | Content                                       |
| ------------- | --------------------------------------------- |
| ID            | FR1, FR2, NFR1, etc. (sequential)             |
| Description   | Brief 1-sentence summary                      |
| Priority      | P0/P1/P2 from requirement                     |
| Verification  | `method: pointer` — how this will be verified |
| Planned Tasks | Leave as "TBD - see plan.md"                  |

**Verification column format:** `method: pointer` — method is `unit` / `integration` / `e2e` / `manual` / `perf`; pointer is a brief scope hint (e.g., `unit: auth token validation`).

**Step 2k: Quality Gate (merged into Step 5 self-review)**

The prior standalone-spec quality gate (completeness / quality / boundary checks) now merges into Step 5 (Design Self-Review) — those checks run once against both `spec.md` and `design.md` together rather than twice.

**Step 2l: Mark spec.md complete and commit**

Update spec.md frontmatter:

```yaml
oat_status: complete
oat_ready_for: oat-project-design
oat_last_updated: { today }
```

Commit separately (keeps history clean; lets reviewers fetch spec independently):

```bash
git add "$PROJECT_PATH/spec.md"
git commit -m "docs: confirm requirements for {project-name}"
```

### Step 2.5: Approach Reaffirmation (one divergent moment)

This is the sole divergent-thinking moment in the skill. After requirements are confirmed and before drafting begins, reaffirm the approach-level direction. Do this exactly once per run.

```
Read "$PROJECT_PATH/discovery.md" — look for "## Solution Space" section
with a "### Chosen Direction" sub-section.

IF Chosen Direction exists:
  Present to user:
    "Based on discovery, we're designing around [Approach N — one-line summary].
     Confirming this is still the right direction before I draft the design?"
  Use AskUserQuestion:
    1. Yes — proceed with this approach
    2. Revisit — I want to explore alternatives again
  If "Revisit": invoke the 2-3-approaches block below.

IF no Chosen Direction (or Solution Space section absent):
  Invoke the 2-3-approaches pattern inline:

    > Propose 2-3 different approaches with trade-offs.
    > Present options conversationally with your recommendation and reasoning.
    > Lead with your recommended option and explain why.

  Ask user to choose. Document the chosen approach in design.md's
  Overview section before section drafting begins.

Record confirmed approach in design.md §Overview before Step 4 (section iterator).
```

**Key points:**

- One divergent moment per run — not per section. Section-level divergence happens organically when the user pushes back on a drafted section (see Step 4).
- Reaffirmation, not re-derivation: if discovery already chose a direction, confirm and move on.
- The 2-3-approaches block handles the case where discovery skipped solution-space exploration (well-understood request).

### Step 3: Read Knowledge Base for Design Context

Read for architectural context and conventions:

- `.oat/repo/knowledge/project-index.md` - Overview
- `.oat/repo/knowledge/architecture.md` - Existing patterns
- `.oat/repo/knowledge/stack.md` - Technologies available
- `.oat/repo/knowledge/conventions.md` - Code patterns to follow
- `.oat/repo/knowledge/integrations.md` - External services
- `.oat/repo/knowledge/concerns.md` - Issues to avoid

**Purpose:** Ensure design aligns with existing architecture and follows established patterns.

### Step 4: Section Iterator

Draft `design.md` section-by-section (Collaborative mode) or in a single pass (Draft-and-review mode). The section list and per-section templates are shared between both branches.

**Shared section list (in order):**

1. **Overview + Architecture** — System context (how this fits into existing architecture, components it interacts with, boundaries of this change); Key Components (main components, responsibilities, relationships); Data Flow (how data moves through the system, entry/exit points, transformation steps).
2. **Component Design** — For each component: Purpose (single responsibility), Responsibilities (specific tasks), Interfaces (code signatures following `conventions.md`), Dependencies, Design Decisions (why this approach). Follow patterns from `conventions.md`; use `stack.md` technologies.
3. **Data Models** — For each entity/model: Schema (fields, types, validation, storage from `architecture.md`); Considerations (align with existing models; follow naming from `conventions.md`; address NFRs).
4. **API Design** — For each API/interface: Method and path, Request/response schemas, Error handling, Authorization; Considerations (follow API patterns from `architecture.md`; align with `integrations.md`; address security NFRs).
5. **Security Considerations** — Authentication, Authorization, Data protection (encryption, PII), Input validation, Threat mitigation. Reference `conventions.md` and `concerns.md`.
6. **Performance Considerations** — Scalability, Caching, Database optimization, Resource limits. Reference `concerns.md`.
7. **Error Handling** — Error categories and handling, Retry logic, Logging approach (follow `conventions.md`).
8. **Testing Strategy (with Requirement-to-Test Mapping)** —
   - **Step a (Requirement-to-Test Mapping):** Pull from spec.md Requirement Index and expand into a table with `ID | Verification | Key Scenarios`. For each requirement: copy the ID, copy the **method** (left side of `method: pointer`) into Verification, use the **pointer** (right side) to seed Key Scenarios, expand scenarios based on component design decisions, note if multiple test levels apply.
   - **Step b (Test Levels):** Unit tests (scope and coverage target), Integration tests (key scenarios and test environment), E2E tests (critical user paths). Follow `testing.md`.
   - **Why mapping matters:** Every requirement gets a verification plan; feeds `oat-project-plan` task breakdown; prevents untested-requirement gaps.
9. **Deployment Strategy** — Build process (from `stack.md`), Deployment steps, Rollback plan, Configuration, Monitoring and alerts.
10. **Migration Plan** — Database migrations, Data migrations, Breaking changes handling, Rollback strategy. If not applicable, state as a single sentence.
11. **Implementation Phases** — Break work into manageable phases (1-3 days each). Per-phase structure: Goal, Tasks (high-level), Verification.
12. **Risks and Mitigation** — For each significant risk: Probability | Impact; Mitigation; Contingency.

### Step 4a: Selective Review Pass

If `DESIGN_MODE == "selective"`, classify every section before drafting and present the Section Review Plan to the user. Use `.agents/skills/oat-project-design/references/selective-review-pass.md` for the full signal set, grounding rules, edge cases, and dogfood notes.

The pass returns a table with `Section | Classification | Reason | Signals hit`. Classifications are `routine` or `needs-eyes`. Bias is conservative: any one needs-eyes signal marks the section `needs-eyes`. `Overview + Architecture`, `Security Considerations`, `Performance Considerations`, `Error Handling`, and `Migration Plan` are high-risk-by-default and always `needs-eyes`; if no section is marked `needs-eyes`, force `Overview + Architecture` to `needs-eyes` so the user sees the framing.

Before drafting, print `## Section Review Plan` followed by `Section | Classification | Reason | Signals hit`.

Then ask: "Proceed with this section review plan, or elevate any routine sections to needs-eyes?" If the user elevates sections, update the plan. If every section is `needs-eyes`, say "All sections flagged for review — running as full collaborative" and use the Collaborative branch.

**YAGNI check per section:** If the section would draft a capability `spec.md` doesn't require, cut it. If a component boundary is speculative ("in case we need it later"), cut it.

**Collaborative branch:**

```
IF DESIGN_MODE == "collaborative":
  Read spec.md for requirements context; read knowledge base.

  Do NOT create or write to design.md yet — sections are drafted in
  context and shown to the user inline. design.md is assembled and
  written to disk only after all sections are approved (see end of
  this branch). Writing per-section to file is wrong in collaborative
  mode; it bypasses the per-section review and produces a committed
  artifact the user never read.

  For SECTION in [
    "Overview + Architecture",
    "Component Design",
    "Data Models",
    "API Design",
    "Security Considerations",
    "Performance Considerations",
    "Error Handling",
    "Testing Strategy (with Requirement-to-Test Mapping)",
    "Deployment Strategy",
    "Migration Plan",
    "Implementation Phases",
    "Risks and Mitigation"
  ]:
    Draft section content from spec.md + knowledge base. Scale each
      section to its complexity: a few sentences if straightforward,
      up to 200-300 words if nuanced.
    Not-applicable sections: state as a single sentence, not empty
      (e.g., "No database migrations required.").

    STEP A — emit the section content as a plain assistant message.
      Show the full drafted text, not a summary. Do NOT put the section
      content inside an AskUserQuestion prompt — the question widget is
      for the confirmation choices only.

    STEP B — ask for approval (separate message, via AskUserQuestion
      when available, or as a plain chat message when it is not; do
      not downgrade to draft mode just because AskUserQuestion is
      missing):
      "Does this look right, or should we adjust before continuing?"

    On feedback: revise the draft in context. Re-emit the revised
      section if the change is substantive. Only the final approved
      text gets written to design.md.
    Mark section approved. Move to next.

  Track which sections have been approved so re-runs don't redo
  finalized sections. Divergent thinking during sections happens
  organically in response to user feedback — there is no scripted
  per-section "present 2-3 options" step (that happened once at
  Step 2.5 Approach Reaffirmation).

  Once ALL sections are approved:
    Copy `.oat/templates/design.md` → `"$PROJECT_PATH/design.md"`.
    Write each approved section into the corresponding template
    section. Update frontmatter:
      oat_status: in_progress
      oat_ready_for: null
      oat_blockers: []
      oat_last_updated: {today}
      oat_generated: false
      oat_template: false
    Continue to Step 5 (Self-Review) and Step 6 (User-Review Gate).
```

**Selective Collaborative branch:**

```
IF DESIGN_MODE == "selective":
  Read spec.md for requirements context; read knowledge base.
  Run Step 4a if not already run during the picker.

  Do NOT create or write to design.md yet. Draft routine sections
  silently in memory; present needs-eyes sections inline using the
  Collaborative approval mechanics.

  For SECTION in shared section list:
    Draft section content from spec.md + knowledge base.
    Apply the same YAGNI and not-applicable rules as Collaborative mode.

    IF SECTION classification == "routine":
      Store the drafted section in the approved-section buffer.
      Track SECTION in SILENT_SECTIONS for Step 6.

    IF SECTION classification == "needs-eyes":
      Emit the full section content as a plain assistant message.
      Ask: "Does this look right, should we adjust, or should I walk
      through every remaining section?"
      If user chooses walk-through: mark every remaining section
        needs-eyes and continue like Collaborative mode.
      On feedback: revise in context; only final approved text gets
        written to design.md.

  Once ALL sections are approved or silently accepted:
    Copy `.oat/templates/design.md` → `"$PROJECT_PATH/design.md"`.
    Write each section into the corresponding template section.
    Update frontmatter as in Collaborative mode.
    Continue to Step 5 (Self-Review) and Step 6 (User-Review Gate).
```

**Draft-and-review branch:**

```
IF DESIGN_MODE == "draft":
  Read spec.md for requirements context; read knowledge base.

  Initialize design.md now (draft-and-review writes first, user
  reviews the committed file):
    Copy `.oat/templates/design.md` → `"$PROJECT_PATH/design.md"`.
    Update frontmatter:
      oat_status: in_progress
      oat_ready_for: null
      oat_blockers: []
      oat_last_updated: {today}
      oat_generated: false
      oat_template: false

  Draft all applicable sections in one pass using the same section
    list above. Apply the same "scale each section to its complexity"
    principle. Not-applicable sections get a single-sentence statement.
  Do NOT fire per-section validation prompts — this is a one-pass draft.
  Append a banner to design.md when non-interactive:
    "Ran in draft-and-review mode — no interactive user present.
     Review manually before plan generation." (FR9 — applies when the
    mode was selected via non-interactive fallback, not when the user
    explicitly chose draft mode interactively.)
  Write the complete design.md.
  Continue to Step 5 (Self-Review) and Step 6 (User-Review Gate).
  The user-review gate is the sole point of user interaction in draft mode.
```

### Step 5: Design Self-Review

Silent agent-side quality pass — no user prompt fires here. After all sections are drafted (in either mode), look at `design.md` and `spec.md` with fresh eyes and run four named checks. Fix issues inline; do not recurse on self-review.

1. **Placeholder scan** — Search `design.md` and `spec.md` for `TBD`, `TODO`, `FIXME`, `...`, and placeholder sections that just say "Not applicable" without elaboration. Fix inline.
2. **Internal consistency** — Does the architecture description match the component design? Do the API request/response shapes match the data models? Does the testing strategy cover the requirements? Fix inline.
3. **Scope check** — Did the design grow beyond what discovery scoped? If out-of-scope items crept in, move them to discovery.md "Deferred Ideas". If genuine multi-subsystem scope surfaces, escalate to the user — they may want to split into multiple projects (follow-up split-escape-hatch work, not this skill's responsibility).
4. **Ambiguity check** — Could any requirement or design statement be interpreted two ways? Pick one and make it explicit.

Apply fixes inline. Do not re-run self-review. Continue to Step 6 (User-Review Gate).

### Step 6: User-Review Gate (commit-first ordering)

By the time Step 6 runs, `design.md` already exists on disk regardless of mode:

- **Collaborative**: written at the end of the Step 4 approval loop, after all sections were confirmed in chat.
- **Selective Collaborative**: written at the end of the Step 4 selective loop, after `needs-eyes` sections were confirmed and `routine` sections were silently accepted.
- **Draft-and-review**: written in Step 4 as the one-pass draft.

Step 6 commits the file and then (if a HiLL gate is configured) presents the user-review prompt. This keeps the "written and committed" prompt wording literally accurate.

**Step 6a: Commit drafted artifacts (before user-review gate)**

Even when no HiLL checkpoint is configured, the artifact is committed — consistent behavior across HiLL-on / HiLL-off configurations. "Committed" no longer means "approved" — it means "written to disk and tracked."

```bash
# Update design.md frontmatter for the draft commit:
#   oat_status: in_progress
#   oat_ready_for: null
#   oat_last_updated: {today}

git add "$PROJECT_PATH/spec.md" "$PROJECT_PATH/design.md" "$PROJECT_PATH/state.md"
git diff --cached --quiet || git commit -m "docs: draft design for {project-name} (awaiting review)"
```

**Step 6b: Read state.md frontmatter**

Read `"$PROJECT_PATH/state.md"`:

- `oat_hill_checkpoints`
- `oat_hill_completed`

**Step 6c: If no HiLL gate configured, skip prompt (artifact still committed)**

If neither `"design"` nor `"spec"` is in `oat_hill_checkpoints`: no user-review prompt fires; artifact is committed. Skip to Step 7.

**Step 6d: If HiLL gate configured, present the user-review prompt**

If `"design"` is in `oat_hill_checkpoints` (or `"spec"` is in `oat_hill_checkpoints` and was not already completed via the standalone `oat-project-spec` skill):

```
Prompt (required wording):

  > "Design written and committed to {design.md path}.
  >  spec.md (with confirmed requirements) is at {spec.md path}.
  >  Please review them and let me know if you want to make any changes
  >  before we move to planning.
  >
  >  Optional: run `oat-project-review-provide artifact design` for an
  >  independent reviewer pass first."

If `DESIGN_MODE == "selective"` and `SILENT_SECTIONS` is non-empty, append: "Drafted without live confirmation: {SILENT_SECTIONS}. Please review those sections especially carefully in the committed file."

Wait for user response:

- Approval → continue to Step 7.
- Change requests → revise the relevant section(s), re-run Step 5
  (Self-Review), then MAKE A NEW COMMIT:
    git add "$PROJECT_PATH/spec.md" "$PROJECT_PATH/design.md"
    git commit -m "docs: revise design after user review feedback"
  Re-present this prompt.
- If user does not approve yet (wants to pause without explicit change
  requests): keep design frontmatter as oat_status: in_progress /
  oat_ready_for: null; do not append "design" to oat_hill_completed;
  stop and report: "Design draft committed; awaiting HiLL approval."
```

### Step 7: Approval — Mark Design Complete and Update HiLL State

On approval (either explicit user approval when HiLL gate fired, or automatic when no HiLL gate is configured):

**Step 7a: Mark design.md complete**

Update `design.md` frontmatter:

```yaml
---
oat_status: complete
oat_ready_for: oat-project-plan
oat_blockers: []
oat_last_updated: { today }
---
```

**Step 7b: Update project state.md**

Update `"$PROJECT_PATH/state.md"`:

**Frontmatter updates:**

- `oat_current_task: null`
- `oat_last_commit: {commit_sha_from_step_6a_or_revision}`
- `oat_blockers: []`
- `oat_phase: design`
- `oat_phase_status: complete`
- `oat_project_state_updated: "{ISO 8601 UTC timestamp}"`
- **If** `"design"` is in `oat_hill_checkpoints`: append `"design"` to `oat_hill_completed` array.
- **If** `"spec"` is in `oat_hill_checkpoints` and not previously completed via the standalone spec skill: append `"spec"` too (folded HiLL — a single approval covers both).

**Note:** Only append to `oat_hill_completed` when the phase is configured as a HiLL gate.

Update content:

```markdown
## Current Phase

Design - Ready for implementation planning

## Progress

- ✓ Discovery complete
- ✓ Specification complete (folded into design)
- ✓ Design complete
- ⧗ Awaiting implementation plan
```

**Step 7c: Commit the approval-side metadata**

```bash
git add "$PROJECT_PATH/design.md" "$PROJECT_PATH/state.md"
git diff --cached --quiet || git commit -m "chore(oat): mark design complete for {project-name}"
```

### Step 8: Output Summary

```
Design phase complete for {project-name}.

Architecture:
- {N} components defined
- {N} data models specified
- {N} API endpoints designed

Next: Create implementation plan with the oat-project-plan skill
```

### Gate Execution

Before reporting this skill as complete, run the configured gate as the final
step:

1. Resolve the gate for this skill:

   ```bash
   oat gate resolve <this-skill> --json
   ```

   If the command returns JSON `null`, no gate is configured; the skill is
   complete.

2. Export the resolved project path into the command shell:

   ```bash
   export PROJECT_PATH
   ```

   If the resolved command invokes `oat gate review`, the configured review
   command must already include `--project "$PROJECT_PATH"` and must not include
   `--target <id>`. A valid reusable shape is
   `oat gate review --project "$PROJECT_PATH" ...`. If the declaration is
   missing, stop and migrate the stored gate command; do not inject or append
   arguments at execution time.

3. Execute the resolved command exactly as configured. Capture stdout, stderr,
   the exit code, and the structured JSON result. A zero exit code means the
   review passed its threshold, but it does not by itself authorize artifact
   receipt or complete the handoff.

4. Review-artifact handoff:
   - Parse the structured gate result. An exit code or artifact path alone never
     authorizes `oat-project-review-receive`.
   - Invoke receive only when all three conditions hold: `status` is `ok` or
     `blocked`, the envelope explicitly sets `receiveEligible: true`, and a
     non-null `handoff` confirms the artifact was corroborated.
   - `receiveEligible: false` is a hard stop even when `artifactPath` is present.
     Never receive `targeting_correlation_failed`; correct the project/run
     routing and run a new gate.
   - Keep `artifact_validation_failed` outside receive until the artifact is
     corrected and the gate successfully revalidates it. Treat `review_failed`,
     unknown statuses, null handoffs, and contradictory eligibility fields as
     operational failures.
   - `blocked` exits nonzero but is receive-eligible; `ok` exits zero and still
     requires durable receive disposition. Route by structured status and
     eligibility, not by exit code.

5. If the command exits nonzero, use `description` to orient the next steps and
   handle `onFailure`:
   - `block`: read gate feedback, remediate, and re-run the gate up to
     `maxAttempts` attempts (default `2`). If attempts are exhausted, escalate
     to the human with accumulated feedback and append that feedback to
     `implementation.md`. Treat a launch failure, missing CLI, or no eligible
     runtime as escalation-biased and do not spend it as a remediation attempt.
   - `prompt`: surface the gate failure and ask the human how to proceed.
   - `warn`: record the gate failure and continue.

6. Runtime selection note (V1): the step runs the gate `command` as-is and reads
   no OAT runtime env var. By default, `oat gate review` and
   `oat gate cross-provider-exec` resolve the current host from built-in
   `hostDetectionCommand`s and avoid the same runtime when no exact target is
   supplied. Reusable lifecycle skill-gate commands must not include
   `--target <id>` so independent review stays provider-neutral. Use explicit
   targets only for manual/debug commands or deliberate local/user-specific
   overrides; do not hardcode provider/model targets in bundled skill guidance
   or shared lifecycle gate examples.

When `OAT_AUTONOMOUS=1`, perform eligible review receive immediately and apply
the autonomy contract's `onFailure` semantics without prompting: `warn`
continues with provenance, `block` stops after bounded attempts, and `prompt`
is a reported boundary. Unresolved Critical review findings always stop
autonomous design progression, regardless of a less restrictive gate failure
setting; record the blocker and leave the project resumable. Important findings
follow the configured gate policy. When autonomy is inactive, the interactive
behavior above is unchanged.

## Success Criteria

- Architecture aligns with existing patterns (from architecture.md)
- Components follow conventions (from conventions.md)
- All functional requirements addressed
- All non-functional requirements addressed
- Testing strategy covers success metrics
- Implementation phases are clear and manageable
- Risks identified with mitigation strategies
- User confirmed design is complete
