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MANDATORY recipe for every Caffeine build that sends email through the user's own Gmail account. The ONLY supported path is the `googlemail-client` mops package (Gmail REST API) combined with the `google-oauth` mops package (token exchange + refresh + PKCE). Hand-rolling `ic.http_request` calls to `oauth2.googleapis.com` or `gmail.googleapis.com` is a FORBIDDEN anti-pattern — it bypasses bearer auth, replication-cost safeguards, and the `google-oauth` library's percent-encoding and JSON parsing. Load this skill whenever the user, spec, or any prior task mentions sending email, Gmail, "notify via email", "forward results by email", or any equivalent phrasing — and BEFORE writing any code that touches a Google endpoint.

Refactor and polish recently modified code for improved clarity and consistency.

Layered architecture framework for scalable Flutter apps with strict separation of concerns.

Automated UI code review against Vercel's Web Interface Guidelines.

Visual plan and diff review UI with structured feedback, annotation, and auto-save to Obsidian or Bear Notes.

Create modern Angular standalone components following v20+ best practices. Use for building UI components with signal-based inputs/outputs, OnPush change detection, host bindings, content projection, and lifecycle hooks. Triggers on component creation, refactoring class-based inputs to signals, adding host bindings, or implementing accessible interactive components.