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2025-07-06 20:40:08 -05:00
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+# TermTodo Architecture Document
+
+## Introduction
+
+This document outlines the overall project architecture for TermTodo, including backend systems, shared services, and non-UI specific concerns. Its primary goal is to serve as the guiding architectural blueprint for AI-driven development, ensuring consistency and adherence to chosen patterns and technologies.
+
+**Relationship to Frontend Architecture:**
+If the project includes a significant user interface, a separate Frontend Architecture Document will detail the frontend-specific design and MUST be used in conjunction with this document. Core technology stack choices documented herein (see "Tech Stack") are definitive for the entire project, including any frontend components.
+
+### Starter Template or Existing Project
+
+N/A - This is a greenfield Rust CLI project with no starter template.
+
+### Change Log
+
+| Date       | Version | Description                                | Author              |
+| ---------- | ------- | ------------------------------------------ | ------------------- |
+| 2025-07-07 | 1.0     | Initial architecture based on TermTodo PRD | Winston (Architect) |
+
+## High Level Architecture
+
+### Technical Summary
+
+TermTodo is a monolithic, single-binary CLI application built with Rust, utilizing embedded SQLite for ACID-compliant local storage. The architecture employs clean architecture principles with clear separation between CLI parsing, business logic, and data persistence layers. Performance-critical design choices including synchronous execution, prepared statement caching, and minimal dependencies ensure sub-100ms command execution. The system implements repository and command patterns to maintain testability while delivering a zero-configuration tool that integrates seamlessly into developer workflows.
+
+### High Level Overview
+
+**Architectural Style:** Monolithic Single Binary
+
+- All functionality compiled into one executable for instant startup
+- No network dependencies or service discovery overhead
+- Embedded SQLite database with local file storage
+
+**Repository Structure:** Monorepo
+
+- Single repository containing all code, tests, and documentation
+- Simplified dependency management and atomic commits
+- Unified CI/CD pipeline for all components
+
+**Service Architecture:** Monolith
+
+- Single process handling all operations
+- Synchronous execution model (no async runtime needed)
+- Direct database access without network layers
+
+**Primary Data Flow:**
+
+1. User invokes `todo` command with arguments
+2. CLI parser validates and routes to appropriate command handler
+3. Command handler orchestrates business logic operations
+4. Repository layer manages SQLite transactions
+5. Formatted output returned to terminal
+
+**Key Architectural Decisions:**
+
+- **Synchronous Model**: Eliminates async runtime overhead for faster cold starts
+- **Embedded Database**: Zero configuration, portable data storage
+- **Static Linking**: Single binary distribution with no runtime dependencies
+- **Clean Architecture**: Testable layers despite monolithic structure
+
+### High Level Project Diagram
+
+```mermaid
+graph TB
+    User[Terminal User]
+
+    subgraph "TermTodo Binary"
+        CLI[CLI Parser<br/>clap v4]
+        CMD[Command Handlers]
+        BL[Business Logic]
+        REPO[Repository Layer]
+        DB[(SQLite DB)]
+        CONFIG[Config Manager<br/>TOML]
+    end
+
+    subgraph "File System"
+        DBFILE[todo.db]
+        CFGFILE[config.toml]
+    end
+
+    User -->|todo add/list/etc| CLI
+    CLI -->|Parsed Commands| CMD
+    CMD -->|Operations| BL
+    BL -->|Data Access| REPO
+    REPO -->|SQL| DB
+    DB -.->|File I/O| DBFILE
+    CONFIG -.->|Read/Write| CFGFILE
+
+    style User fill:#e1f5fe
+    style CLI fill:#fff3e0
+    style CMD fill:#fff3e0
+    style BL fill:#f3e5f5
+    style REPO fill:#e8f5e9
+    style DB fill:#e8f5e9
+```
+
+### Architectural and Design Patterns
+
+- **Clean Architecture:** Separation of concerns with CLI, Application, Domain, and Infrastructure layers - _Rationale:_ Enables 80%+ test coverage requirement by isolating business logic from I/O operations
+
+- **Repository Pattern:** Abstract SQLite operations behind trait-based interfaces - _Rationale:_ Allows in-memory repositories for unit tests and potential future database migrations
+
+- **Command Pattern:** Each CLI subcommand as a discrete handler with execute method - _Rationale:_ Simplifies testing and follows clap's natural structure for maintainable command routing
+
+- **Builder Pattern:** Fluent interfaces for constructing complex queries and task filters - _Rationale:_ Provides readable API for combining multiple filter criteria while maintaining performance
+
+- **Result/Option Monads:** Explicit error handling using Rust's type system - _Rationale:_ Prevents runtime panics and enables graceful error messages as required by NFR13
+
+## Tech Stack
+
+This is the DEFINITIVE technology selection for TermTodo. All implementation must use these exact versions and technologies.
+
+### Cloud Infrastructure
+
+- **Provider:** Local-only (No cloud requirements)
+- **Key Services:** N/A
+- **Deployment Regions:** N/A
+
+### Technology Stack Table
+
+| Category               | Technology     | Version | Purpose                       | Rationale                                                                 |
+| ---------------------- | -------------- | ------- | ----------------------------- | ------------------------------------------------------------------------- |
+| **Language**           | Rust           | 1.78.0  | Primary development language  | Zero-cost abstractions, memory safety, single binary output               |
+| **Database**           | SQLite         | 3.45.0  | Embedded database             | ACID compliance, zero configuration, excellent performance                |
+| **CLI Framework**      | clap           | 4.5.4   | Command-line argument parsing | Automatic help generation, shell completion, strong typing                |
+| **ORM/Query Builder**  | sqlx           | 0.7.4   | Database operations           | Compile-time checked queries, async support (if needed later), migrations |
+| **Date Parsing**       | chrono         | 0.4.38  | Date/time handling            | Comprehensive timezone support, widely adopted                            |
+| **Human Date Parsing** | chrono-english | 0.1.7   | Natural language dates        | Parses "tomorrow", "next friday" as required                              |
+| **Serialization**      | serde          | 1.0.197 | JSON/CSV export               | De facto standard, excellent performance                                  |
+| **Configuration**      | toml           | 0.8.12  | Config file parsing           | Human-readable, simple for users                                          |
+| **Terminal Colors**    | termcolor      | 1.4.1   | Colored output                | Respects NO_COLOR, cross-platform                                         |
+| **Error Handling**     | anyhow         | 1.0.82  | Application errors            | Simplified error handling with context                                    |
+| **Error Types**        | thiserror      | 1.0.58  | Custom error types            | Derive macro for error enums                                              |
+| **Testing**            | built-in       | std     | Unit/integration tests        | Rust's excellent built-in test framework                                  |
+| **Benchmarking**       | criterion      | 0.5.1   | Performance testing           | Statistical benchmarking for CI regression detection                      |
+| **Logging**            | env_logger     | 0.11.3  | Debug logging                 | Simple, runtime-configurable via RUST_LOG                                 |
+
+## Data Models
+
+### Task
+
+**Purpose:** Core entity representing a single todo item with all associated metadata
+
+**Key Attributes:**
+
+- `id`: i64 - Unique identifier (SQLite ROWID)
+- `description`: String - Task description (up to 1000 chars)
+- `status`: TaskStatus - Enum (Incomplete/Complete)
+- `project`: Option<String> - Optional project grouping
+- `priority`: Priority - Enum (High/Medium/Low), defaults to Medium
+- `due_date`: Option<DateTime> - Optional due date with timezone
+- `created_at`: DateTime - Creation timestamp
+- `updated_at`: DateTime - Last modification timestamp
+- `completed_at`: Option<DateTime> - Completion timestamp
+
+**Relationships:**
+
+- Has many Tags (many-to-many via task_tags table)
+- Belongs to one Project (denormalized for performance)
+
+### Tag
+
+**Purpose:** Flexible categorization system for tasks
+
+**Key Attributes:**
+
+- `id`: i64 - Unique identifier
+- `name`: String - Tag name (alphanumeric + dash/underscore)
+- `created_at`: DateTime - First use timestamp
+
+**Relationships:**
+
+- Has many Tasks (many-to-many via task_tags table)
+- Cascade delete orphaned tags
+
+### TaskTag
+
+**Purpose:** Junction table for many-to-many task-tag relationship
+
+**Key Attributes:**
+
+- `task_id`: i64 - Foreign key to tasks
+- `tag_id`: i64 - Foreign key to tags
+
+**Relationships:**
+
+- Composite primary key (task_id, tag_id)
+- ON DELETE CASCADE for both foreign keys
+
+## Components
+
+### CLI Parser
+
+**Responsibility:** Parse command-line arguments, validate inputs, and route to appropriate command handlers
+
+**Key Interfaces:**
+
+- `parse_args()` - Main entry point parsing std::env::args()
+- `generate_completions()` - Shell completion script generation
+- Subcommand routing to handlers
+
+**Dependencies:** clap v4 for parsing, command handlers for execution
+
+**Technology Stack:** Pure Rust with clap derive macros for type-safe parsing
+
+### Command Handlers
+
+**Responsibility:** Orchestrate business logic for each CLI subcommand (add, list, complete, etc.)
+
+**Key Interfaces:**
+
+- `execute(&self, app: &Application) -> Result<()>` - Common trait for all commands
+- Command-specific structs with validated parameters
+- Output formatting for terminal display
+
+**Dependencies:** Application service layer, terminal output formatters
+
+**Technology Stack:** Rust structs implementing Command trait, termcolor for output
+
+### Application Service
+
+**Responsibility:** Core business logic and workflow orchestration independent of I/O concerns
+
+**Key Interfaces:**
+
+- `add_task(desc: &str, opts: AddOptions) -> Result<Task>`
+- `list_tasks(filters: FilterOptions) -> Result<Vec<Task>>`
+- `complete_tasks(ids: &[i64]) -> Result<usize>`
+- `search_tasks(query: &str) -> Result<Vec<Task>>`
+
+**Dependencies:** Repository interfaces (traits), domain models
+
+**Technology Stack:** Pure Rust business logic with Result-based error handling
+
+### Repository Layer
+
+**Responsibility:** Abstract data persistence operations with SQLite implementation
+
+**Key Interfaces:**
+
+- `TaskRepository` trait with CRUD operations
+- `TagRepository` trait for tag management
+- `Transaction` support for atomic operations
+- Migration runner for schema updates
+
+**Dependencies:** sqlx for database access, domain models
+
+**Technology Stack:** sqlx with compile-time checked queries, connection pooling
+
+### Configuration Manager
+
+**Responsibility:** Load, validate, and provide access to user configuration
+
+**Key Interfaces:**
+
+- `load_config() -> Result<Config>` - Load from XDG directory
+- `save_config(&Config) -> Result<()>` - Persist changes
+- `get_default_project()` - Typed config access
+
+**Dependencies:** toml for parsing, serde for serialization
+
+**Technology Stack:** TOML files with serde deserialization
+
+### Database Manager
+
+**Responsibility:** SQLite connection lifecycle, migrations, and performance optimization
+
+**Key Interfaces:**
+
+- `connect() -> Result<SqlitePool>` - Initialize connection pool
+- `run_migrations() -> Result<()>` - Apply schema updates
+- Prepared statement caching
+- PRAGMA optimizations
+
+**Dependencies:** sqlx SQLite driver, migration files
+
+**Technology Stack:** SQLite with WAL mode, connection pool size of 1
+
+### Component Diagram
+
+```mermaid
+graph LR
+    subgraph "Presentation Layer"
+        CLI[CLI Parser]
+        FMT[Output Formatter]
+    end
+
+    subgraph "Application Layer"
+        CMD[Command Handlers]
+        APP[Application Service]
+    end
+
+    subgraph "Domain Layer"
+        MODELS[Domain Models]
+        TRAITS[Repository Traits]
+    end
+
+    subgraph "Infrastructure Layer"
+        REPO[SQLite Repository]
+        CONFIG[Config Manager]
+        DB[Database Manager]
+    end
+
+    CLI --> CMD
+    CMD --> APP
+    CMD --> FMT
+    APP --> TRAITS
+    TRAITS --> REPO
+    REPO --> DB
+    APP --> MODELS
+    CONFIG --> APP
+
+    style CLI fill:#fff3e0
+    style CMD fill:#fff3e0
+    style APP fill:#f3e5f5
+    style REPO fill:#e8f5e9
+    style DB fill:#e8f5e9
+```
+
+## External APIs
+
+This project does not require any external API integrations. All operations are performed locally with no network dependencies.
+
+## Core Workflows
+
+### Add Task Workflow
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant CLI
+    participant CMD as AddCommand
+    participant APP as Application
+    participant REPO as Repository
+    participant DB as SQLite
+
+    User->>CLI: todo add "Review PR" -p work -P high +review
+    CLI->>CMD: parse_add_command()
+    CMD->>CMD: validate_description_length()
+    CMD->>APP: add_task(desc, options)
+    APP->>APP: parse_tags_from_description()
+    APP->>REPO: begin_transaction()
+    REPO->>DB: BEGIN TRANSACTION
+    APP->>REPO: insert_task(task)
+    REPO->>DB: INSERT INTO tasks...
+    DB-->>REPO: task_id = 42
+    APP->>REPO: insert_tags(task_id, tags)
+    REPO->>DB: INSERT INTO tags...
+    REPO->>DB: INSERT INTO task_tags...
+    APP->>REPO: commit()
+    REPO->>DB: COMMIT
+    APP-->>CMD: Task { id: 42, ... }
+    CMD->>User: ✓ Added task #42
+```
+
+### List Tasks with Filters Workflow
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant CLI
+    participant CMD as ListCommand
+    participant APP as Application
+    participant REPO as Repository
+    participant DB as SQLite
+    participant FMT as Formatter
+
+    User->>CLI: todo list -p work -P high --due
+    CLI->>CMD: parse_list_command()
+    CMD->>APP: list_tasks(filters)
+    APP->>REPO: find_tasks_with_filters(filters)
+    REPO->>REPO: build_query_with_filters()
+    REPO->>DB: SELECT ... WHERE project=? AND priority=? AND due_date IS NOT NULL
+    DB-->>REPO: Vec<TaskRow>
+    REPO->>REPO: load_tags_for_tasks(task_ids)
+    REPO->>DB: SELECT ... FROM task_tags WHERE task_id IN (...)
+    DB-->>REPO: Vec<TagRow>
+    REPO-->>APP: Vec<Task>
+    APP-->>CMD: Vec<Task>
+    CMD->>FMT: format_task_list(tasks)
+    FMT->>User: ID  Description           Project  Priority  Due        Tags<br/>42  Review PR            work     !!!       tomorrow   #review
+```
+
+### Complete Task with Toggle Workflow
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant CLI
+    participant CMD as CompleteCommand
+    participant APP as Application
+    participant REPO as Repository
+    participant DB as SQLite
+
+    User->>CLI: todo complete 42 43
+    CLI->>CMD: parse_complete_command()
+    CMD->>APP: complete_tasks([42, 43])
+
+    loop For each task_id
+        APP->>REPO: find_task_by_id(task_id)
+        REPO->>DB: SELECT ... WHERE id = ?
+        DB-->>REPO: Task
+
+        alt Task exists
+            APP->>APP: toggle_status(task)
+            APP->>REPO: update_task_status(id, new_status)
+            REPO->>DB: UPDATE tasks SET status=?, completed_at=?
+            DB-->>REPO: 1 row affected
+        else Task not found
+            APP->>APP: record_error(task_id)
+        end
+    end
+
+    APP-->>CMD: CompletionResult { success: 2, failed: 0 }
+    CMD->>User: ✓ Completed tasks: #42, #43
+```
+
+## Database Schema
+
+```sql
+-- Enable foreign key constraints
+PRAGMA foreign_keys = ON;
+
+-- Enable Write-Ahead Logging for better concurrency
+PRAGMA journal_mode = WAL;
+
+-- Optimize for fast reads
+PRAGMA synchronous = NORMAL;
+PRAGMA temp_store = MEMORY;
+PRAGMA mmap_size = 30000000000;
+
+-- Tasks table: Core entity
+CREATE TABLE tasks (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    description TEXT NOT NULL CHECK(length(description) <= 1000),
+    status TEXT NOT NULL DEFAULT 'incomplete' CHECK(status IN ('incomplete', 'complete')),
+    project TEXT,
+    priority TEXT NOT NULL DEFAULT 'medium' CHECK(priority IN ('high', 'medium', 'low')),
+    due_date DATETIME,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    completed_at DATETIME
+);
+
+-- Indexes for common query patterns
+CREATE INDEX idx_tasks_status ON tasks(status);
+CREATE INDEX idx_tasks_project ON tasks(project) WHERE project IS NOT NULL;
+CREATE INDEX idx_tasks_priority ON tasks(priority);
+CREATE INDEX idx_tasks_due_date ON tasks(due_date) WHERE due_date IS NOT NULL;
+CREATE INDEX idx_tasks_created_at ON tasks(created_at);
+
+-- Composite index for common filter combinations
+CREATE INDEX idx_tasks_filters ON tasks(status, project, priority);
+
+-- Tags table
+CREATE TABLE tags (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    name TEXT NOT NULL UNIQUE CHECK(name REGEXP '^[a-zA-Z0-9][a-zA-Z0-9_-]*$'),
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Junction table for many-to-many relationship
+CREATE TABLE task_tags (
+    task_id INTEGER NOT NULL,
+    tag_id INTEGER NOT NULL,
+    PRIMARY KEY (task_id, tag_id),
+    FOREIGN KEY (task_id) REFERENCES tasks(id) ON DELETE CASCADE,
+    FOREIGN KEY (tag_id) REFERENCES tags(id) ON DELETE CASCADE
+);
+
+-- Index for tag lookups
+CREATE INDEX idx_task_tags_tag_id ON task_tags(tag_id);
+
+-- Full-text search virtual table
+CREATE VIRTUAL TABLE tasks_fts USING fts5(
+    description,
+    project,
+    content=tasks,
+    content_rowid=id
+);
+
+-- Triggers to keep FTS index in sync
+CREATE TRIGGER tasks_fts_insert AFTER INSERT ON tasks
+BEGIN
+    INSERT INTO tasks_fts(rowid, description, project)
+    VALUES (new.id, new.description, new.project);
+END;
+
+CREATE TRIGGER tasks_fts_update AFTER UPDATE ON tasks
+BEGIN
+    UPDATE tasks_fts
+    SET description = new.description, project = new.project
+    WHERE rowid = old.id;
+END;
+
+CREATE TRIGGER tasks_fts_delete AFTER DELETE ON tasks
+BEGIN
+    DELETE FROM tasks_fts WHERE rowid = old.id;
+END;
+
+-- Update trigger for updated_at timestamp
+CREATE TRIGGER tasks_update_timestamp AFTER UPDATE ON tasks
+BEGIN
+    UPDATE tasks SET updated_at = CURRENT_TIMESTAMP WHERE id = NEW.id;
+END;
+
+-- Migration tracking table
+CREATE TABLE IF NOT EXISTS schema_migrations (
+    version INTEGER PRIMARY KEY,
+    applied_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+```
+
+## Source Tree
+
+```plaintext
+termtodo/
+├── Cargo.toml                 # Project manifest with dependencies
+├── Cargo.lock                # Locked dependency versions
+├── build.rs                   # Build script for embedding resources
+├── .github/
+│   └── workflows/
+│       ├── ci.yml            # Test, lint, build on all platforms
+│       └── release.yml       # Build and publish binaries on tag
+├── src/
+│   ├── main.rs              # Entry point, CLI setup
+│   ├── cli/
+│   │   ├── mod.rs           # CLI module exports
+│   │   ├── parser.rs        # Clap command definitions
+│   │   ├── commands/        # Command handlers
+│   │   │   ├── mod.rs
+│   │   │   ├── add.rs       # Add command implementation
+│   │   │   ├── list.rs      # List command with formatting
+│   │   │   ├── complete.rs  # Complete/uncomplete logic
+│   │   │   ├── delete.rs    # Delete command
+│   │   │   ├── search.rs    # Full-text search
+│   │   │   └── config.rs    # Config management commands
+│   │   └── output.rs        # Terminal output formatting
+│   ├── app/
+│   │   ├── mod.rs           # Application layer exports
+│   │   ├── service.rs       # Main application service
+│   │   ├── filters.rs       # Filter builder and logic
+│   │   └── errors.rs        # Application error types
+│   ├── domain/
+│   │   ├── mod.rs           # Domain model exports
+│   │   ├── task.rs          # Task entity and value objects
+│   │   ├── tag.rs           # Tag entity
+│   │   └── types.rs         # Enums (Status, Priority)
+│   ├── infra/
+│   │   ├── mod.rs           # Infrastructure exports
+│   │   ├── db/
+│   │   │   ├── mod.rs       # Database module
+│   │   │   ├── connection.rs # Connection pool setup
+│   │   │   ├── migrations.rs # Migration runner
+│   │   │   └── queries.rs   # SQL query constants
+│   │   ├── repos/
+│   │   │   ├── mod.rs       # Repository traits
+│   │   │   ├── task_repo.rs # Task repository impl
+│   │   │   └── tag_repo.rs  # Tag repository impl
+│   │   └── config/
+│   │       ├── mod.rs       # Config module
+│   │       └── manager.rs   # Config file handling
+│   └── utils/
+│       ├── mod.rs           # Utility exports
+│       ├── dates.rs         # Date parsing helpers
+│       └── result.rs        # Result extensions
+├── tests/
+│   ├── integration/         # Integration tests
+│   │   ├── cli_tests.rs     # End-to-end CLI tests
+│   │   ├── db_tests.rs      # Database integration
+│   │   └── helpers/         # Test utilities
+│   └── fixtures/            # Test data files
+├── benches/
+│   └── performance.rs       # Criterion benchmarks
+├── migrations/              # SQL migration files
+│   ├── 001_initial.sql
+│   └── 002_add_fts.sql
+└── docs/
+    ├── architecture.md      # This document
+    ├── prd.md              # Product requirements
+    └── README.md           # User documentation
+```
+
+## Infrastructure and Deployment
+
+### Infrastructure as Code
+
+- **Tool:** Not applicable (local application)
+- **Location:** N/A
+- **Approach:** Single binary deployment
+
+### Deployment Strategy
+
+- **Strategy:** Direct binary distribution
+- **CI/CD Platform:** GitHub Actions
+- **Pipeline Configuration:** `.github/workflows/release.yml`
+
+### Environments
+
+- **Development:** Local developer machine with debug builds
+- **Testing:** CI environment with all platforms (Linux, macOS, Windows)
+- **Production:** User's local machine with release binary
+
+### Environment Promotion Flow
+
+```text
+Development (local) -> CI Testing -> GitHub Release -> User Installation
+                         ↓
+                    Failed tests
+                         ↓
+                    Fix & retry
+```
+
+### Rollback Strategy
+
+- **Primary Method:** Previous version binary installation
+- **Trigger Conditions:** User-reported critical bugs, data corruption
+- **Recovery Time Objective:** < 5 minutes (download previous release)
+
+## Error Handling Strategy
+
+### General Approach
+
+- **Error Model:** Result<T, Error> for all fallible operations
+- **Exception Hierarchy:** anyhow::Error for applications, custom types for libraries
+- **Error Propagation:** ? operator with context via .context()
+
+### Logging Standards
+
+- **Library:** env_logger 0.11.3
+- **Format:** `[TIMESTAMP] [LEVEL] [MODULE] Message`
+- **Levels:** ERROR, WARN, INFO, DEBUG, TRACE
+- **Required Context:**
+  - Correlation ID: Not needed (single-user CLI)
+  - Service Context: Module path automatically included
+  - User Context: Never log user data or task content
+
+### Error Handling Patterns
+
+#### External API Errors
+
+- **Retry Policy:** No external APIs
+- **Circuit Breaker:** Not applicable
+- **Timeout Configuration:** Not applicable
+- **Error Translation:** Not applicable
+
+#### Business Logic Errors
+
+- **Custom Exceptions:**
+  - `TaskNotFound(id)`
+  - `InvalidTaskDescription(reason)`
+  - `DuplicateTag(name)`
+  - `ConfigError(path, reason)`
+- **User-Facing Errors:** Clear, actionable messages via Display trait
+- **Error Codes:** Not used - descriptive messages preferred
+
+#### Data Consistency
+
+- **Transaction Strategy:** Explicit transactions for multi-table operations
+- **Compensation Logic:** Not needed with ACID SQLite
+- **Idempotency:** Complete/uncomplete operations are naturally idempotent
+
+## Coding Standards
+
+These standards are MANDATORY for AI agents and define project-specific conventions.
+
+### Core Standards
+
+- **Languages & Runtimes:** Rust 1.78.0 (edition 2021)
+- **Style & Linting:** rustfmt with default config, clippy with pedantic lints
+- **Test Organization:** Unit tests in `#[cfg(test)]` modules, integration tests in tests/
+
+### Naming Conventions
+
+| Element   | Convention      | Example               |
+| --------- | --------------- | --------------------- |
+| Structs   | PascalCase      | `TaskFilter`          |
+| Functions | snake_case      | `parse_due_date`      |
+| Constants | SCREAMING_SNAKE | `MAX_DESCRIPTION_LEN` |
+| Modules   | snake_case      | `task_repo`           |
+
+### Critical Rules
+
+- **No unwrap() in production code:** Use expect() with clear message or proper error handling
+- **All public functions must have doc comments:** Include examples for complex APIs
+- **SQL queries must use parameterized statements:** Never concatenate user input
+- **Benchmark new features:** Add criterion benchmarks for any performance-critical code
+- **Check Task description length:** Enforce 1000 character limit at CLI parsing layer
+
+## Test Strategy and Standards
+
+### Testing Philosophy
+
+- **Approach:** Test-after development with comprehensive coverage
+- **Coverage Goals:** 80% overall, 90% for business logic
+- **Test Pyramid:** 70% unit, 25% integration, 5% e2e
+
+### Test Types and Organization
+
+#### Unit Tests
+
+- **Framework:** Rust built-in testing
+- **File Convention:** Tests in same file as code under `#[cfg(test)]` module
+- **Location:** Bottom of each source file
+- **Mocking Library:** Manual test doubles (traits make this easy)
+- **Coverage Requirement:** 90% for domain and app layers
+
+**AI Agent Requirements:**
+
+- Generate tests for all public methods
+- Cover edge cases and error conditions
+- Follow AAA pattern (Arrange, Act, Assert)
+- Mock all external dependencies
+
+#### Integration Tests
+
+- **Scope:** Database operations, CLI parsing, file I/O
+- **Location:** `tests/integration/`
+- **Test Infrastructure:**
+  - **Database:** In-memory SQLite for speed
+  - **File System:** tempfile crate for isolated testing
+  - **CLI:** assert_cmd for command execution tests
+
+#### End-to-End Tests
+
+- **Framework:** assert_cmd 2.0.14
+- **Scope:** Full command execution with real database
+- **Environment:** Isolated temp directory per test
+- **Test Data:** Fixtures in tests/fixtures/
+
+### Test Data Management
+
+- **Strategy:** Builder pattern for test objects
+- **Fixtures:** `tests/fixtures/` for import/export tests
+- **Factories:** TaskBuilder, TagBuilder in test modules
+- **Cleanup:** Automatic via tempfile cleanup
+
+### Continuous Testing
+
+- **CI Integration:** Run on every push (test, clippy, fmt)
+- **Performance Tests:** Criterion benchmarks with 5% regression threshold
+- **Security Tests:** cargo audit in CI pipeline
+
+## Security
+
+### Input Validation
+
+- **Validation Library:** Built-in Rust type system + manual checks
+- **Validation Location:** CLI parsing layer before any processing
+- **Required Rules:**
+  - All external inputs MUST be validated
+  - Validation at API boundary before processing
+  - Whitelist approach preferred over blacklist
+
+### Authentication & Authorization
+
+- **Auth Method:** Not applicable (local single-user application)
+- **Session Management:** Not applicable
+- **Required Patterns:**
+  - File permissions rely on OS user permissions
+  - XDG directory compliance for proper isolation
+
+### Secrets Management
+
+- **Development:** No secrets required
+- **Production:** No secrets required
+- **Code Requirements:**
+  - NEVER hardcode secrets
+  - Access via configuration service only
+  - No secrets in logs or error messages
+
+### API Security
+
+Not applicable - no network APIs exposed
+
+### Data Protection
+
+- **Encryption at Rest:** Relies on OS disk encryption
+- **Encryption in Transit:** Not applicable (local only)
+- **PII Handling:** Task descriptions may contain PII - never log
+- **Logging Restrictions:** Never log task content, only IDs and metadata
+
+### Dependency Security
+
+- **Scanning Tool:** cargo audit
+- **Update Policy:** Monthly dependency updates
+- **Approval Process:** Review changelog for breaking changes
+
+### Security Testing
+
+- **SAST Tool:** cargo clippy with security lints
+- **DAST Tool:** Not applicable
+- **Penetration Testing:** Not required for local CLI
+
+## Checklist Results Report
+
+To be completed after architecture review.
+
+## Next Steps
+
+### Developer Handoff
+
+Begin implementation with the following:
+
+- Reference this architecture document and coding standards throughout development
+- Start with Epic 1, Story 1.1: Project Setup and Infrastructure
+- Key technical decisions to follow:
+  - Use Rust 1.78.0 with 2021 edition
+  - Implement clean architecture layers as specified
+  - All commands must complete in < 100ms
+  - Use synchronous code (no async/await)
+  - Follow the defined error handling patterns