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feat(context): remind the model of changed blocks without busting the prompt cache (#2089) - #2405
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threepointone merged 3 commits intoSep 28, 2026
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… prompt cache (#2089) A block declared whenChanged: "remind" is re-read each turn. While its rendering no longer appears in the frozen prompt, ContextBlocks.reminder() returns its current value, and Think adds it to the last user message of the model request without persisting it. refreshSystemPrompt() promotes the value and ends the reminders. Co-authored-by: Cursor <cursoragent@cursor.com>
…n is exact Co-authored-by: Cursor <cursoragent@cursor.com>
…ply continuation Co-authored-by: Cursor <cursoragent@cursor.com>
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Closes #2089.
Problem
A frozen system prompt keeps the provider's prefix cache warm, but it also freezes context that changes between turns: the date, workspace state, project instructions. Today the only way to update it is
refreshSystemPrompt(), which throws away the cached prefix.Change
whenChanged: "remind".ContextBlocks.reminder()re-reads those blocks and returns the current value of any whose rendering no longer appears in the frozen prompt.refreshSystemPrompt()promotes the value. Think already refreshes after a compaction.Edge cases:
Tests
context.test.tscovers promotion, restart through a shared prompt store, and the edge-change and emptiness cases, each with the block first and last. It also checks thatinit()is not called again.prompt-cache.test.tsruns six turns and shows that the system message stays byte-identical, reminders appear only while the value differs, the only prefix break before the refresh is the previous user message, and the refresh busts the cache once. It fails without the Think wiring.