Parent: #6853
Related: #6856

Objective

Implement P2 developer-experience helper surfaces for extension output and logging.

Proposal IDs covered

• P2-1 Standard output helpers
• P2-2 Structured logging

In scope

• Output utility APIs for common extension UX patterns.
• Structured logging helpers with context propagation support.
• Tests for verbosity/format behavior and logging semantics.

Out of scope

• Security utility APIs (handled in Extension framework P2 security utilities (P2-3..P2-4) #6947).
• Runtime process/shell/file helpers (handled in Extension framework P3 runtime utilities (P3-1..P3-5) #6948).

Deliverables

• Output helper API definitions + implementation.
• Structured logging API + implementation.
• Behavior tests (quiet/debug/interactive/non-interactive scenarios).
• Usage examples and migration notes.

Verification checklist

• API usage is additive and predictable.
• Logging semantics are documented (fields, levels, propagation behavior).
• mage preflight passes.

Definition of done

• P2-1 and P2-2 are complete, tested, and documented.