[feat] New agent: architect

[lugassawan]

Goal

An architect subagent handles multi-system design work — ADRs, RFCs, cross-service contract design — distinct from senior-engineer's in-codebase advisory scope.

Motivation

senior-engineer operates within a codebase: it reads files, traces call graphs, and advises on design decisions visible in the code. There is no agent for cross-system, multi-service architecture decisions where the "code" doesn't exist yet (greenfield design, service decomposition, API contracts between teams). This gap leaves architects without a principled agent to consult.

Surface

• Subagent

Sketch (optional)

File: agents/architect.md

Scope:

• Multi-system and cross-service design
• Architecture Decision Records (ADRs): when to write, how to structure
• RFC drafting for cross-team API contracts
• Service decomposition and boundary decisions
• Technology selection frameworks

Wired principles: principle-distributed-systems, principle-clean-architecture, principle-api-design

Not in scope: in-codebase file edits, PR review (that's senior-engineer and reviewer).

Acceptance (optional)

• agents/architect.md exists with valid frontmatter and tools list
• scripts/validate.py passes
• Agent is registered in plugin.json
• Principle skills wired via Skill invocations