Batch delegation returned each subagent's full final_response verbatim
into the parent's context. A fan-out of N children could dump 60k+ tokens
at once, blowing the parent's context window and — on rate-limited
providers — triggering a compression/429 death spiral (429 misread as
context-too-large -> window step-down -> retry loop -> conversation dies).
Cap each summary against the parent's *remaining* context headroom split
across the batch (not a magic char count). When trimming, mirror the
web_extract convention: spill the full text to cache/delegation (mounted
into remote backends via credential_files._CACHE_DIRS) and return a
head+tail window (75/25, line-snapped) plus a footer with the exact
read_file offset to page the omitted middle. Both the subagent's opening
AND its closing (outcomes / files-changed / issues, which live at the end)
survive in-context, and nothing is lost — the parent can read_file the
full version on any backend.
delegation.max_summary_chars (default 24000) is a static ceiling layered
on top as belt-and-suspenders for models that ignore 'be concise'; 0
disables it. Child prompt tightened to lead with outcomes / bullets.
Co-authored-by: rc-int <rcint@klaith.com>
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