Replace the old '[CONTEXT SUMMARY]:' prefix on compressed summaries
with a Codex-inspired handoff framing that tells the model what happened
and how to use the summary.
What changes:
1. New SUMMARY_PREFIX constant — the text prepended to every
compressed summary:
[CONTEXT COMPACTION] An earlier part of this conversation was
summarized to preserve context space. Below is the summary — use
it to build on the work already done and avoid duplicating effort:
2. _with_summary_prefix() helper — normalizes model output by stripping
any legacy '[CONTEXT SUMMARY]:' prefix the summarization model may
have produced, then prepends the new SUMMARY_PREFIX.
3. System message annotation updated — the note appended to the system
prompt on first compression now says 'compacted into a handoff
summary' and instructs 'build on that summary rather than re-doing
work' instead of the old generic note.
Why this is better:
The old prefix ('[CONTEXT SUMMARY]: <raw text>') gave the model no
context about what the summary is or how to use it. The new prefix
explicitly frames it as a context compaction event and instructs the
model to build on prior work rather than re-doing it. This reduces
redundant tool calls and file re-reads after compression.
What does NOT change:
- The compression algorithm (positional protection, boundary alignment)
- The role alternation logic (summary role adapts to avoid consecutive
same-role messages)
- The summarization model or trigger thresholds
- LEGACY_SUMMARY_PREFIX is exported for backward compatibility
Inspired by PR #776 by @kshitijk4poor and the research in #499.
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