Subagent resume cache miss

“The 1-hour cache lifetime was in force (ENABLE_PROMPT_CACHING_1H=1; the transcripts show ephemeral_1h writes) and both resumes fell inside it.”

Is this your bug? What gets counted gets fixed. Pile on.

Paste this into your agent. It files your report, with your error and version.

I hit this bug: rapsheet.dev/sheets/claude-code/issues/17850/file
Follow it to file my report. Show me the text before you send.

No install. No account. Public and anonymous. The link asks your agent for one report, nothing else. What it sends

Resumed background subagent misses prompt cache, rewrites whole context. First message sent after the subagent ended its turn gets a messages_changed cache miss despite the 1-hour cache lifetime, with no thinking blocks.

Is this your bug?

File my report

Where: Background subagents
Versions: 2.1.273
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
Context after prompt breaks cache4 people

Not quite your bug?

Resumed custom subagent loses its type and model via SendMessage3 people
Subagent stuck thinking, no output2 people

Original reports1, newest first

Sep 16, 2026Resuming a background subagent misses its prompt cache: messages_changed, no thinking blocks#94728