Plugins¶

Plugins extend agents with reusable skills, commands, agents, hooks, and MCP servers. They live in workspace/plugins/ and are managed with the plugin CLI (scripts/tri-onyx-plugin.py).

How plugins reach agents¶

Agent definition declares plugins in frontmatter:
```
plugins:
  - newsagg
```
Gateway (sandbox.ex) adds FUSE read paths for each plugin:
/plugins/ (parent directory, for readdir)
/plugins/<name>/** (all files in the plugin)

Agent runner passes plugin paths to the Claude Agent SDK:

plugins=[{"type": "local", "path": "/workspace/plugins/newsagg"}]

SDK passes --plugin-dir /workspace/plugins/newsagg to the bundled Claude Code CLI, which discovers the plugin manifest and registers components (skills, commands, hooks, etc.).
Skill invocations use the /<plugin>:<skill> syntax (e.g., /newsagg:fetchnews). The CLI expands the skill's SKILL.md into the prompt and sends it to the model.

Plugin directory structure¶

Each plugin follows the Claude Code plugin convention:

newsagg/
├── .claude-plugin/
│   └── plugin.json          # Plugin manifest (name is required)
├── skills/                  # Auto-discovered by convention
│   └── fetchnews/
│       └── SKILL.md         # Skill definition
├── commands/                # Slash commands (optional)
├── agents/                  # Subagent definitions (optional)
├── hooks/                   # Event handlers (optional)
│   └── hooks.json
├── .mcp.json                # MCP servers (optional)
└── ...                      # Plugin-specific files

plugin.json¶

Minimal manifest — only name is required:

{
  "name": "newsagg",
  "description": "News aggregation and formatting plugin",
  "version": "0.2.0"
}

Component directories (skills/, commands/, agents/, hooks/) are auto-discovered at their default locations. You only need to declare them in plugin.json if they live at non-standard paths.

Path rules (important)¶

The Claude Code CLI enforces strict path rules for plugin manifests:

All custom paths must start with ./ — relative to the plugin root. Paths starting with ../ are invalid and will cause the CLI to silently fail to load the plugin.
Default directories are auto-discovered — skills/, commands/, agents/, hooks/ don't need to be declared in plugin.json.
Custom paths supplement defaults — declaring a custom skills path adds to the default skills/ directory, it doesn't replace it.

Example of what NOT to do:

{
  "name": "newsagg",
  "skills": "../skills/"
}

This fails silently because ../skills/ doesn't start with ./. Since skills/ is auto-discovered anyway, the fix is to omit the field entirely.

Gateway: system command handling¶

Messages starting with / are intercepted by the gateway's SystemCommand module before reaching agents. Known commands (e.g., /restart) are executed directly. Unknown commands return an error.

Skill invocations use colons (/newsagg:fetchnews) to distinguish themselves from system commands. The parser detects the : and passes the message through to the agent instead of intercepting it:

# system_command.ex — parse/1
:error ->
  if String.contains?(name, ":") do
    :not_a_command        # Skill — pass through to agent
  else
    {:command, :unknown, ["/" <> name]}  # Unknown system command — error
  end

Debugging plugin loading¶

If a skill invocation returns 0 turns, check these in order:

Is the plugin loaded? Look at the SDK SystemMessage init data in container logs. The plugins array should contain your plugin, and slash_commands should list <plugin>:<skill>.
Is the manifest valid? Ensure .claude-plugin/plugin.json has valid JSON and no paths starting with ../.
Is the FUSE policy correct? The agent definition must list the plugin in plugins:. Check that /plugins/<name>/** appears in the FUSE read policy (/etc/tri_onyx/fs-policy.json inside the container).
Is the gateway passing the message through? Messages with : in the command name should reach the agent. Check gateway logs if the agent never receives the prompt.
Check container logs directly:
```
docker logs <container-name> 2>&1 | grep -i "plugin\|skill\|denied"
```
Unhandled SDK message types (including SystemMessage) are logged as warnings by the agent runner.

Managing plugins¶

# Install a plugin from a git repo
uv run scripts/tri-onyx-plugin.py add <git-url> [--name NAME]

# List installed plugins
uv run scripts/tri-onyx-plugin.py list

# Upgrade a plugin
uv run scripts/tri-onyx-plugin.py upgrade <name>

# Remove a plugin
uv run scripts/tri-onyx-plugin.py remove <name>

Plugin metadata is recorded in workspace/plugins.yaml. When installed from git, the .git/ directory is stripped so files become mutable workspace content.