Context Is the Bottleneck (Harness Design, Part 2)

Deep End Era. Engineering with Sankalp · Oct 12, 2026 · 54m

Ines finds that more than half her agent's failed runs never wrote a line: they overflowed the context window. With Gideon she works through why the history fills up, context rot, lossy versus lossless compaction, and the five tiers in Fan, Zhang et al. (arXiv:2609.20804). On SWE-Bench Verified, managing context was worth 35.7 points at a 32k window but only 2.7 at 128k, and almost all of that came from stopping overflow (78.7% of unmanaged runs overflowed at 32k, versus zero for managed runs). Eliding first and summarising later was the cheapest policy. Recoverable recall was rarely called…