New command: /onboard - Quick codebase summary for new projects

[avifenesh]

Summary

Add an /onboard command that generates a quick codebase summary to help developers get oriented in unfamiliar projects.

Motivation

Onboarding to a new codebase is painful. We already have /repo-map for AST-based symbol mapping, but there's no user-facing command that synthesizes a high-level "what is this project and how does it work" overview.

Proposed Scope

• Generate a concise project overview (purpose, tech stack, architecture)
• Identify key entry points and main workflows
• Surface important patterns and conventions
• Highlight getting-started steps (build, test, run)
• Leverage existing infrastructure: repo-map, lib/discovery, lib/patterns

Output

A structured summary a developer can read in a few minutes to understand:

• What the project does
• How it's organized
• Where to start reading code
• How to build/test/run

Prior Art

• Suggested by GLM-5 (zai) via /consult as a high-value gap in the current 12 commands
• Codex also identified setup/readiness gaps in its consultation

Checklist

• Read checklists/new-command.md before starting
• Read checklists/cross-platform-compatibility.md
• Works across Claude Code, OpenCode, and Codex

[avifenesh]

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