Firstmate exposes canary for context rot

This is not a product launch, but it is a useful operator pattern: context health needs behavioral checks, not just token counters.

• –A simple sentinel instruction can reveal when an agent stops respecting high-priority context.
• –The trick is crude but practical for catching drift before outputs become visibly wrong.
• –It points to a broader need for agent observability around instruction adherence, compaction quality, and memory decay.
• –Developers should treat this as a canary, not a full eval; an agent can remember "captain" while still losing task-critical context.