Technical Plans: Bridging Specification and Implementation

Introduction: The Missing Bridge

You have an approved specification scoring \geq75/100 defining WHAT to build. But there's a gap before creating executable tasks. You need to answer HOW : Which components are required? How do they interact? What database changes are needed? Which existing code do we integrate with? This is the technical plan - the bridge between specification and task decomposition.

The SDD Workflow

text ┌────────────────────────────────────────────────────────────────┐ │ 📋 PRD \to 📝 Specification (WHAT) \to 🏗️ Technical Plan (HOW) │ │ ◄── CURRENT LESSON │ │ \to ✅ Task Decomposition \to 💻 Implementation 📝 │ └────────────────────────────────────────────────────────────────┘ ┌────────────────────────────────────────────────────────────────┐ │ 📋 PRD \to 📝 Specification (WHAT) \to 🏗️ Technical Plan (HOW) │ │ ◄── CURRENT LESSON │ │ \to ✅ Task Decomposition \to 💻 Implementation 📝 │ └────────────────────────────────────────────────────────────────┘ A technical plan translates functional requirements into concrete technical decisions. It has 7 key sections.

1. Architecture (Component Interactions)

Markdown## Architecture: Task Comments Component Flow: Client → API Endpoint → CommentService → CommentRepository → Database Data Flow: 1. Client sends POST /api/tasks/{id}/comments with JWT 2. API validates token, calls `CommentService.create_comment()` 3. Service validates: user owns task, content length valid 4. Service calls CommentRepository.create() 5. Repository persists via SQLAlchemy, returns Comment 6. API transforms to CommentSchema, returns 201## Architecture: Task Comments Component Flow: Client → API Endpoint → CommentService → CommentRepository → Database Data Flow: 1. Client sends POST /api/tasks/{id}/comments with JWT 2. API validates token, calls `CommentService.create_comment()` 3. Service validates: user owns task, content length valid 4. Service calls CommentRepository.create() 5. Repository persists via SQLAlchemy, returns Comment 6. API transforms to CommentSchema, returns 201 Why: Prevents conflicting assumptions about layer responsibilities, duplicate validation, and architectural drift. Common mistakes: Reversed dependencies (Service→API), skipping layers (API→DB), ambiguous validation location. How to decide: Start from entry point → follow data transformations → identify decision points → validate against CLAUDE.md.

2. Data Model (Database Schema)

Markdown ## Data Model: Comment Table: comments - `id`: UUID, primary key, default=uuid4 - `task_id`: UUID, FK to tasks.id, NOT NULL - `user_id`: UUID, FK to users.id, NOT NULL - `content`: String(5000), NOT NULL - `created_at`: DateTime, default=utcnow, NOT NULL Relationships: - task: relationship to Task (backref="comments") - author: relationship to User (backref="comments") Indexes: - (`task_id`, `created_at`) for chronological listing ## Data Model: Comment Table: comments - `id`: UUID, primary key, default=uuid4 - `task_id`: UUID, FK to tasks.id, NOT NULL - `user_id`: UUID, FK to users.id, NOT NULL - `content`: String(5000), NOT NULL - `created_at`: DateTime, default=utcnow, NOT NULL Relationships: - task: relationship to Task (backref="comments") - author: relationship to User (backref="comments") Indexes: - (`task_id`, `created_at`) for chronological listing Why: Prevents N+1 queries, missing constraints, orphaned records, and performance issues. Common mistakes: No indexes, missing NOT NULL, undefined relationships, ambiguous column types. How to decide: Indexes for query patterns, NOT NULL for required data, relationships for navigation, FKs for referential integrity.

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text

┌────────────────────────────────────────────────────────────────┐
│  📋 PRD → 📝 Specification (WHAT) → 🏗️ Technical Plan (HOW)     │
│                                      ◄── CURRENT LESSON        │
│  → ✅ Task Decomposition → 💻 Implementation        📝          │
└────────────────────────────────────────────────────────────────┘

Markdown

## Architecture: Task Comments

Component Flow:
Client → API Endpoint → CommentService → CommentRepository → Database

Data Flow:
1. Client sends POST /api/tasks/{id}/comments with JWT
2. API validates token, calls `CommentService.create_comment()`
3. Service validates: user owns task, content length valid
4. Service calls CommentRepository.create()
5. Repository persists via SQLAlchemy, returns Comment
6. API transforms to CommentSchema, returns 201

Markdown

## Data Model: Comment

Table: comments
- `id`: UUID, primary key, default=uuid4
- `task_id`: UUID, FK to tasks.id, NOT NULL
- `user_id`: UUID, FK to users.id, NOT NULL
- `content`: String(5000), NOT NULL
- `created_at`: DateTime, default=utcnow, NOT NULL

Relationships:
- task: relationship to Task (backref="comments")
- author: relationship to User (backref="comments")

Indexes:
- (`task_id`, `created_at`) for chronological listing

Markdown

## API Implementation

POST `/api/tasks/{task_id}/comments`
- Router: src/api/comments.py, async def `create_comment()`
- Dependencies: `current_user`, `comment_service`
- Response: 201 with CommentSchema
- Errors: 400/401/403/404
- Error handling: Catch service exceptions → HTTPException

GET `/api/tasks/{task_id}/comments`
- Query params: skip (0), limit (50)
- Response: 200 with List[CommentSchema]

DELETE `/api/comments/{comment_id}`
- Authorization: comment owner OR task owner
- Response: 204 No Content

## API Implementation

POST `/api/tasks/{task_id}/comments`
- Router: src/api/comments.py, async def `create_comment()`
- Dependencies: `current_user`, `comment_service`
- Response: 201 with CommentSchema
- Errors: 400/401/403/404
- Error handling: Catch service exceptions → HTTPException

GET `/api/tasks/{task_id}/comments`
- Query params: skip (0), limit (50)
- Response: 200 with List[CommentSchema]

DELETE `/api/comments/{comment_id}`
- Authorization: comment owner OR task owner
- Response: 204 No Content

Markdown

## Module Structure

New Files:
- `src/models/comment.py`
- `src/repositories/comment_repository.py`
- `src/services/comment_service.py`
- `src/schemas/comment.py`
- `src/api/comments.py`

Test Files:
- `tests/unit/test_comment_{model,repository,service}.py`
- `tests/integration/test_comment_api.py`

Modified Files:
- `src/models/task.py` (add comments relationship)
- `src/api/__init__.py` (register router)
- `alembic/versions/XXXX_add_comments_table.py`

## Module Structure

New Files:
- `src/models/comment.py`
- `src/repositories/comment_repository.py`
- `src/services/comment_service.py`
- `src/schemas/comment.py`
- `src/api/comments.py`

Test Files:
- `tests/unit/test_comment_{model,repository,service}.py`
- `tests/integration/test_comment_api.py`

Modified Files:
- `src/models/task.py` (add comments relationship)
- `src/api/__init__.py` (register router)
- `alembic/versions/XXXX_add_comments_table.py`

Markdown

## Integration Points

Use Existing Code:
1. Task Model (src/models/task.py) - validate `task_id`, check ownership
2. User Model (src/models/user.py) - foreign key for author
3. Authentication (src/api/auth.py) - `get_current_user` dependency
4. Database Session (src/database.py) - `get_db` dependency
5. Repository Pattern (CLAUDE.md) - all DB access through repositories
6. Error Handling (CLAUDE.md) - HTTPException with status codes

## Integration Points

Use Existing Code:
1. Task Model (src/models/task.py) - validate `task_id`, check ownership
2. User Model (src/models/user.py) - foreign key for author
3. Authentication (src/api/auth.py) - `get_current_user` dependency
4. Database Session (src/database.py) - `get_db` dependency
5. Repository Pattern (CLAUDE.md) - all DB access through repositories
6. Error Handling (CLAUDE.md) - HTTPException with status codes

Markdown

## Testing Strategy

Unit Tests (Mocked):
- `test_comment_repository.py`: create, get, list, delete (95%+)
- `test_comment_service.py`: validation, authorization logic (90%+)

Integration Tests (TestClient):
- `test_comment_api.py`: all endpoints, auth, errors (85%+)

Overall Target: 90%+

## Testing Strategy

Unit Tests (Mocked):
- `test_comment_repository.py`: create, get, list, delete (95%+)
- `test_comment_service.py`: validation, authorization logic (90%+)

Integration Tests (TestClient):
- `test_comment_api.py`: all endpoints, auth, errors (85%+)

Overall Target: 90%+

Markdown

## Security

Authorization:
- Verify user owns task before comment creation
- DELETE: Allow comment owner OR task owner

Input Validation:
- Content: 1-5000 characters
- Use SQLAlchemy ORM (no raw SQL)

Data Leaks:
- Use Pydantic schemas for responses (never raw ORM)
- Only return comments for user's tasks

## Security

Authorization:
- Verify user owns task before comment creation
- DELETE: Allow comment owner OR task owner

Input Validation:
- Content: 1-5000 characters
- Use SQLAlchemy ORM (no raw SQL)

Data Leaks:
- Use Pydantic schemas for responses (never raw ORM)
- Only return comments for user's tasks

Aspect	Specification	Technical Plan
Audience	Product team + developers	Developers only
Focus	User behavior, validation	Components, files, patterns
Example	"Comments: 1-5000 chars"	"CommentService validates, raises ValidationError"

Markdown

Given approved specification (specs/task-comments/specification.md),
generate technical plan for TaskMaster.

Context: Review CLAUDE.md, analyze existing code
Stack: Python 3.11, FastAPI, SQLAlchemy, PostgreSQL

Required: Architecture, Data Model, API, Module Structure, 
Integration Points, Testing, Security

Constraints: Repository pattern, DI, type hints, HTTPException

Given approved specification (specs/task-comments/specification.md),
generate technical plan for TaskMaster.

Context: Review CLAUDE.md, analyze existing code
Stack: Python 3.11, FastAPI, SQLAlchemy, PostgreSQL

Required: Architecture, Data Model, API, Module Structure, 
Integration Points, Testing, Security

Constraints: Repository pattern, DI, type hints, HTTPException

Markdown

## API Implementation

POST `/api/tasks/{task_id}/comments`
- Router: src/api/comments.py, async def `create_comment()`
- Dependencies: `current_user`, `comment_service`
- Response: 201 with CommentSchema
- Errors: 400/401/403/404
- Error handling: Catch service exceptions → HTTPException

GET `/api/tasks/{task_id}/comments`
- Query params: skip (0), limit (50)
- Response: 200 with List[CommentSchema]

DELETE `/api/comments/{comment_id}`
- Authorization: comment owner OR task owner
- Response: 204 No Content

Markdown

## Module Structure

New Files:
- `src/models/comment.py`
- `src/repositories/comment_repository.py`
- `src/services/comment_service.py`
- `src/schemas/comment.py`
- `src/api/comments.py`

Test Files:
- `tests/unit/test_comment_{model,repository,service}.py`
- `tests/integration/test_comment_api.py`

Modified Files:
- `src/models/task.py` (add comments relationship)
- `src/api/__init__.py` (register router)
- `alembic/versions/XXXX_add_comments_table.py`

Markdown

## Integration Points

Use Existing Code:
1. Task Model (src/models/task.py) - validate `task_id`, check ownership
2. User Model (src/models/user.py) - foreign key for author
3. Authentication (src/api/auth.py) - `get_current_user` dependency
4. Database Session (src/database.py) - `get_db` dependency
5. Repository Pattern (CLAUDE.md) - all DB access through repositories
6. Error Handling (CLAUDE.md) - HTTPException with status codes

Markdown

## Testing Strategy

Unit Tests (Mocked):
- `test_comment_repository.py`: create, get, list, delete (95%+)
- `test_comment_service.py`: validation, authorization logic (90%+)

Integration Tests (TestClient):
- `test_comment_api.py`: all endpoints, auth, errors (85%+)

Overall Target: 90%+

Markdown

## Security

Authorization:
- Verify user owns task before comment creation
- DELETE: Allow comment owner OR task owner

Input Validation:
- Content: 1-5000 characters
- Use SQLAlchemy ORM (no raw SQL)

Data Leaks:
- Use Pydantic schemas for responses (never raw ORM)
- Only return comments for user's tasks

Markdown

Given approved specification (specs/task-comments/specification.md),
generate technical plan for TaskMaster.

Context: Review CLAUDE.md, analyze existing code
Stack: Python 3.11, FastAPI, SQLAlchemy, PostgreSQL

Required: Architecture, Data Model, API, Module Structure, 
Integration Points, Testing, Security

Constraints: Repository pattern, DI, type hints, HTTPException

Introduction: The Missing Bridge

The SDD Workflow

1. Architecture (Component Interactions)

2. Data Model (Database Schema)

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3. API Implementation (Endpoints)

4. Module Structure (Files)

5. Integration Points (Existing Code)

6. Testing Strategy (Coverage)

7. Security Considerations

Technical Plan vs Specification

How Detailed Should It Be?

Validation & Usage

Summary