## Why

OpenCode is an AI-powered terminal-based development environment that provides a web interface for interactive development. It demonstrates the platform's extensibility beyond standard tools like code-server. As a POC, it validates the manifest-driven spawn system with a non-trivial runtime that requires web terminal forwarding.

## What Changes

- **OpenCode manifest**: Define the tool with terminal web interface, workspace mounts, and health checks
- **Container image**: Reference to OpenCode image with built-in web terminal
- **Health reporting**: Endpoint that reports tool health to the platform
- **Spawn integration**: Reuse the spawn flow from FN-010 but with OpenCode-specific configuration
- **Web terminal**: Support for browser-based terminal access

## Capabilities

### New Capabilities
- `opencode-manifest`: OpenCode tool manifest with web terminal config
- `web-terminal`: Support for browser-based terminal interfaces
- `health-reporting`: Tool health status reporting mechanism

### Modified Capabilities
- None (reuses spawn infrastructure from FN-010)

## Impact

- **apps/api/app/tools/manifests/opencode.yml**: Updated manifest
- **apps/api/app/services/spawn.py**: Minor updates for OpenCode-specific mounts
- **apps/web/src/**: OpenCode appears in tool selection UI
- **Docker images**: Uses official OpenCode image