Cache prefix stability for subagents
Skill ychampion/cskill-agents/agents/claude-code/skills/cache-prefix-stability-for-subagents
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What its author says it does
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Preserve cache-critical request fields when a child agent must share the parent's prompt prefix for cache hits.
SKILL.md
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SKILL: Cache Prefix Stability For Subagents
Domain: agentic-loop Trigger: Apply when a subagent should share the parent's cached prompt prefix instead of recomputing a divergent request shape. Source Pattern: Distilled from reviewed subagent orchestration, isolation, and lifecycle implementations.
Core Method
Treat prompt-cache compatibility as an explicit contract when building child agent options. Preserve the cache-critical fields that define the API request prefix, including the merged tool pool, thinking configuration, query source, and content-replacement state, instead of letting child defaults drift away from the parent request. This keeps forked or exact-tool subagents eligible for the same cached prefix while still allowing non-cache-sensitive options to vary.
Key Rules
- Only inherit cache-critical request fields when the child is intentionally sharing the parent's prefix, such as the use exact tools path.
- Keep the resolved tool list, thinking configuration, and content-replacement state aligned with the parent request so cache keys do not diverge accidentally.
- Preserve the recursive-fork guard inputs like query source when they are part of the cached request prefix contract.
- Do not inherit unrelated defaults blindly; share only the fields that stabilize the prefix and let other child-specific behavior vary intentionally.
Example Application
If a forked review agent must reuse the parent’s prompt cache, build its options from the parent’s tool list and thinking config instead of resetting them to child defaults; the child can then reuse cached request prefixes while still emitting its own downstream messages.
Anti-Patterns (What NOT to do)
- Do not disable thinking or rebuild the tool pool for a cache-sharing child unless you also accept losing cache alignment.
- Do not rely on accidental structural similarity between parent and child requests; explicitly carry forward the fields that define the cache prefix.