🤖 fix: improve compaction prompt for better model compliance #912
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Added tests to verify that compaction messages include word count instructions:
- Verify word count derived from maxOutputTokens (4096 tokens / 1.3 ≈ 3151 words)
- Verify default word target (2000 words) when maxOutputTokens not specified
Investigation found NO regression - the word count has been consistently present
in prepareCompactionMessage() since the feature was added. The message sent to
the model includes 'Use approximately {targetWords} words.' where:
- targetWords = maxOutputTokens / 1.3 (when specified)
- targetWords = 2000 (default from DEFAULT_COMPACTION_WORD_TARGET)
Note: The UI displays '/compact' for UX simplicity, but the actual message
sent to the model includes the full compaction prompt with word count guidance.
…del compliance
Expanded the compaction prompt to help models better respect the word count
target and produce more useful summaries. The new prompt:
- Emphasizes word count importance ('aim to be within 10% of this target')
- Provides structured guidance on what to include:
- User's overall goal and current task
- Key decisions and rationale
- Current state of work
- Important technical details
- Errors encountered and resolutions
- Unresolved issues/blockers
- Explicitly lists what NOT to include
- Requests factual, dense writing style
This addresses reports of certain models not properly respecting the word
count guidance in the previous simpler prompt.
Updated: desktop, mobile, mock scenarios, and tests.
ammario
approved these changes
Dec 4, 2025
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Summary
Improves the compaction prompt to help models better respect the word count target and produce more useful summaries.
Changes
The new prompt provides structured guidance:
What to include:
What NOT to include:
Style: Factual, dense writing where every sentence conveys essential context.
Implementation
buildCompactionPrompt()intosrc/common/constants/ui.tsas a shared functionGenerated with
mux