cache-hygiene

name	cache-hygiene
description	Prompt cache cost optimization. Generates periodic conversation turns to keep the 5-minute prompt cache warm during idle gaps. TRIGGER immediately after any Bash or Agent call with `run_in_background=true` on the official Anthropic runtime, or when the user says "cache keep-alive".
allowed-tools	["ScheduleWakeup"]
compatibility	Claude Code

Cache Hygiene

Prompt cache cost optimization protocol. The prompt cache has a 5-minute TTL. A cache miss costs 1.25x vs 0.1x for a hit — keeping the cache warm saves ~1.15P per avoided miss.

When to Use

• Auto-triggered (via hook): after launching a background task (Bash or Agent) on the official Anthropic runtime.
• Manual (user types /cache-hygiene): user signals they will be away. Start the keep-alive loop after ending the current response.

Keep-Alive Protocol

Start a keep-alive loop:

/loop Cache keep-alive. Idle tick 1/10.

Each tick:

1. Monitor background tasks. Resolve stucks.
2. Call ScheduleWakeup with delaySeconds=270. Pass the same prompt, incrementing N/10. Reset to 1/10 when user requests or there are background-task running this turn.
3. End your response with a single space character if nothing to report.

Stop (omit ScheduleWakeup) when N would exceed 10.

Beyond 10 ticks (45 minutes), cumulative keep-alive cost (10 × 0.1P) exceeds the one-time cache miss penalty (1.15P).

Key Pitfalls

Always set up schedule at <5 minutes delay, otherwise prompt cache (5-min TTL) would costly invalidate.

Never block a single tool call for >4 minutes (timeout argument in Bash, TaskOutput, Monitor). The cache TTL ticks during blocking calls — a 4-minute block plus response overhead can bust the 5-minute window. The keep-alive protocol prevents misses between turns; this cap prevents misses within turns.

Never start multiple keep-alive loops in parallel. Reset existing keep-alive loop to 1/10 instead.