# ADR-006: Nim for Worker Coordination CLI

## Status

Accepted

## Context

The multi-agent orchestration system needs a CLI tool (`worker`) for:
- Spawning worker workspaces with git worktrees
- State machine transitions (ASSIGNED → WORKING → IN_REVIEW → APPROVED → COMPLETED)
- Heartbeat monitoring for stuck agent detection
- SQLite-based message bus for coordination
- Review-gate integration for quality enforcement

Requirements:
- Fast startup (<10ms) for CLI commands run frequently
- Single static binary for deployment simplicity
- SQLite with WAL mode for concurrent access
- Background thread for heartbeat without shared state complexity
- Easy iteration during development

## Decision

Use **Nim** with ORC memory management for the worker CLI.

### Core Dependencies

| Package | Purpose |
|---------|---------|
| `tiny_sqlite` | SQLite wrapper with RAII, statement caching |
| `cligen` | Auto-generates CLI from proc signatures |
| `std/json` | JSON parsing for context files |

### Why Nim

**Performance:**
- ~1ms startup time (vs ~50ms Python, ~20ms Go)
- Compiles to native binary via C backend
- No runtime initialization overhead

**Developer Experience:**
- Python-like syntax, low learning curve
- REPL available for prototyping (`nim secret`)
- Compile-time checks catch errors early
- Excellent error messages

**Memory Management:**
- ORC (Ownership + Reference Counting) handles cycles automatically
- No manual memory management needed
- Deterministic cleanup via destructors
- Thread-safe without shared state via channels

**SQLite Integration:**
- `tiny_sqlite` provides clean RAII semantics
- Statement caching for performance
- Proper NULL handling via Option types
- WAL mode works correctly with multiple connections

**CLI Generation:**
- `cligen` generates CLI from proc signatures
- Help text from doc comments
- Type-safe argument parsing
- Subcommands via `dispatchMulti`

Example:
```nim
proc spawn(taskId: string, description = "", fromBranch = "origin/integration") =
  ## Create a new worker workspace
  ...

when isMainModule:
  dispatchMulti(
    [spawn, help = {"taskId": "Task identifier"}]
  )
```

### Alternatives Considered

**Python:**
- Slow startup (~50ms) unacceptable for frequent CLI calls
- Packaging complexity (venv, dependencies)
- Would work for prototype but not production

**Go:**
- Faster startup than Python (~20ms) but still slower than Nim
- More verbose syntax
- Good SQLite support via mattn/go-sqlite3
- Reasonable choice but Nim is more pleasant to write

**Rust:**
- Excellent performance and safety
- Steep learning curve slows iteration
- Borrow checker friction for exploratory code
- Good for later rewrite if needed

**Bash:**
- Used for review-gate (simpler requirements)
- Inadequate for state machine and SQLite operations
- Error handling is painful

### Build Configuration

```nim
# config.nims
switch("mm", "orc")           # Memory management
switch("threads", "on")       # Background heartbeat thread
switch("d", "release")        # Optimizations
switch("opt", "size")         # Smaller binary
switch("passL", "-lsqlite3")  # Link SQLite
```

Build command:
```bash
nim c -d:release src/worker.nim
```

### Architecture

```
src/
├── worker.nim        # CLI dispatch, command implementations
└── worker/
    ├── types.nim     # Shared types, constants, error types
    ├── db.nim        # SQLite operations, message bus
    ├── state.nim     # State machine transitions
    ├── git.nim       # Worktree operations
    ├── context.nim   # Worker context file handling
    ├── heartbeat.nim # Background heartbeat thread
    ├── review.nim    # Review-gate integration
    └── utils.nim     # Common helpers
```

## Consequences

### Positive

- Sub-millisecond startup enables responsive CLI
- Single binary simplifies deployment
- ORC eliminates memory management burden
- `cligen` reduces CLI boilerplate to near-zero
- Python-like syntax enables fast iteration
- Type safety catches bugs at compile time

### Negative

- Smaller ecosystem than Python/Go/Rust
- Fewer developers familiar with Nim
- Some library quality variance
- Compiler occasionally has edge case bugs

### Mitigations

- Pin Nim version (2.2.x) for stability
- Use well-maintained libraries (tiny_sqlite, cligen)
- Keep modules small and focused for maintainability
- Document patterns for future contributors

## References

- [Nim Manual](https://nim-lang.org/docs/manual.html)
- [tiny_sqlite](https://github.com/GULPF/tiny_sqlite)
- [cligen](https://github.com/c-blake/cligen)
- [ORC Memory Management](https://nim-lang.org/blog/2020/10/15/introduction-to-arc-orc-in-nim.html)