Context after prompt breaks cache

“On the first request of a session, Claude Code places session-invariant context after the user's first prompt.”

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I hit this bug: rapsheet.dev/sheets/claude-code/issues/585/file
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Session-invariant context sent after first prompt, forcing prompt cache rewrites. Every new session with a distinct first prompt pays a full cache write for content that is byte-identical across sessions.

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Where: Prompt cache
Versions: 0.3.284
How bad: Breaks a normal workflow.

Part of: Prompt cache misses and re-writes11 bugs

Interactive sessions get 5m cache TTL18 people
Sleep re-sends full agent context4 people
Warm prompt cache fully missed2 people
Resume re-writes prompt cache3 people
CLAUDE.md cache not shared3 people
Cross-session prompt cache misses2 people
Prompt cache misses after system message3 people
Subagent prompt cache expires2 people
Background agent summary requests12 people
Subagent resume cache miss4 people

Original reports1, newest first

Sep 30, 2026Session-invariant context (skill/agent listings, deferred tools, CLAUDE.md) is sent after the first user prompt, so every new session and subagent rewrites it to the prompt cache#98513