Design Agent

"An agent is a role, not a god -- it owns a boundary, delegates within it, and never crosses it."

Design a plugin agent with complete frontmatter, role definition, skill assignments, execution flows, and operating principles. Prominently enforces the plugin subagent constraint: agents in plugins cannot use hooks, mcpServers, or permissionMode.

CRITICAL: Plugin Subagent Constraints

Plugin agents are subagents with restricted capabilities. The following fields are FORBIDDEN in plugin agent frontmatter:

Attempting to use these fields will cause runtime errors or silent failures. This constraint is enforced by the Claude Code runtime and cannot be circumvented.

Procedure

Step 1 -- Define Role and Boundary

• Define the agent's role in one sentence following the pattern: "This agent {verb} {scope} by {method}."
• Establish the boundary: what the agent owns vs. what it delegates.
• Determine if this is the plugin's primary agent or a secondary specialist.
• Tag: [DOC] for role definition, [CONFIG] for boundary rules.

Step 2 -- Draft Frontmatter

Draft the YAML frontmatter using ALL supported fields for plugin subagents:

Use tools OR disallowedTools, never both. If both are present, disallowedTools is ignored.

Step 3 -- Map Skills to Agent

• List all skills this agent manages from the architecture plan.
• For each skill, specify:
  • Whether the agent invokes it directly or delegates to a sub-agent.
  • The typical invocation order (sequential, parallel, conditional).
  • Any shared data or state between skills.
• Verify skill names match the architecture plan. [CODIGO]

Step 4 -- Design Execution Flows

• For each command the agent handles, document the execution flow:

  /prefix:command
  1. Agent receives request
  2. Runs skill-a
  3. If condition: runs skill-b, else: runs skill-c
  4. Collects results
  5. Presents to user

• Include error handling: what happens if a skill fails.
• Include quality gate checks between movements.
• Use Mermaid flowcharts for complex flows. [DOC]

Step 5 -- Write Operating Principles

• Define 4-7 operating principles that govern the agent's behavior.
• Each principle must be:
  • Specific to this agent (not generic "be careful" advice).
  • Actionable (describes a behavior, not a value).
  • Verifiable (an observer can determine if it was followed).
• Common patterns:
  • "Read first, write never" (for analysis agents).
  • "Cite file + line" (for audit agents).
  • "Fail fast on CRITICAL" (for validation agents).
  • "Propose before creating" (for design agents).

Step 6 -- Set maxTurns

• Estimate maxTurns based on:
  • Number of skills managed: roughly 3-5 turns per skill.
  • Complexity of execution flows: add 5 turns for complex routing.
  • User interaction points: add 2 turns per decision point.
• Formula: maxTurns = (skills * 4) + (complexity_bonus) + (interaction_points * 2)
• Round up to nearest 5 for headroom.
• Document the calculation. [INFERENCIA]

Step 7 -- Validate Against Constraints

• Verify the designed agent does NOT include forbidden fields (hooks, mcpServers, permissionMode).
• Verify tools listed are available in the Claude Code environment.
• Verify skill names exist or are planned in the architecture.
• Cross-reference with the constraint matrix in references/agent-constraint-matrix.md. [CONFIG]

Step 8 -- Compose Agent Body

• Structure the agent markdown body:

  # Agent Name
  **Role**: {one-sentence role description}
  ## Responsibilities
  ## Skills Assigned
  ## Execution Flows
  ## Operating Principles
  ## Delegation Criteria (if multi-agent plugin)

• Target length: 60-120 lines depending on complexity.
• Present for review. Write file only on user confirmation.

Quality Criteria

• Agent frontmatter contains NO forbidden fields (hooks, mcpServers, permissionMode). [CONFIG]
• Every skill listed in the agent body exists in the architecture plan. [CODIGO]
• Execution flows cover all commands the agent handles. [DOC]
• Operating principles are specific, actionable, and verifiable. [DOC]
• maxTurns calculation is documented with rationale. [INFERENCIA]
• Tool selection follows least privilege -- no unnecessary tools. [CONFIG]

Assumptions & Limits

• This skill produces an agent design document, not the final .md file. The output is a specification for review before spec-agent-command produces the deployable artifact.
• The forbidden fields list (hooks, mcpServers, permissionMode) reflects the current Claude Code runtime. If future versions allow these for plugin subagents, this constraint must be updated.
• The maxTurns formula is a heuristic estimate. Actual turn usage depends on task complexity, user interaction, and model behavior at runtime.
• Cannot validate that operating principles will actually be followed by the LLM -- they are prompt-level guidance, not enforced constraints.
• Agent skill assignments assume the architecture plan is finalized. If skills are added or removed after agent design, the agent must be redesigned.

Good vs Bad

Bad agent design:

---
name: my-agent
description: Handles things
hooks:
  PreToolUse: [...]
---
# My Agent
This agent does validation.

Missing: forbidden hooks field, no tool allowlist, no skills assigned, no execution flows, no operating principles.

Good agent design:

---
name: plugin-qa-engineer
description: >
  Orchestrates validation, audit, and reporting for plugin quality assurance.
  Trigger: qa engineer, run validation, audit plugin.
tools:
  - Read
  - Glob
  - Grep
  - Bash
maxTurns: 45
---
# Plugin QA Engineer
**Role**: This agent validates plugin quality by orchestrating 9 QA skills across 4 movements.
## Skills Assigned
| Skill | Movement | Invocation |
|-------|----------|------------|
| validate-structure | VALIDATE | Sequential, first |
| validate-manifest | VALIDATE | Sequential, second |
## Operating Principles
1. Read first, write never -- this agent only reads and reports.
2. Cite file + line for every finding.

Includes: no forbidden fields, tool allowlist, maxTurns, structured body, skill table, operating principles.

Anti-Patterns

1. Including hooks in agent frontmatter (forbidden for plugin subagents -- causes runtime error).
2. Setting maxTurns too low (agent stops mid-execution) or too high (wastes resources).
3. Creating an agent that manages only one skill (merge the agent's logic into the skill).
4. Defining tools AND disallowedTools simultaneously (disallowedTools is silently ignored).
5. Writing operating principles that are generic platitudes instead of specific behavioral rules.
6. Omitting delegation criteria in a multi-agent plugin (ambiguous handoffs).

Edge Cases

1. Plugin has only one agent -- the agent IS the plugin orchestrator. Include all skills.
2. Agent needs to invoke skills from another plugin -- currently not supported. Document the limitation.
3. Agent handles a command that spans multiple movements with quality gates -- document the gate check in the execution flow.
4. Agent should have different tool access for different skills -- use allowed-tools at the skill level to restrict per-skill.
5. Agent needs background context from reference files -- use the background field with the reference file path.