X-12Observation Compression

Shape tool output before it enters the window: the errors, the tail, the counts, and a pointer to the rest.

Key insight

Previous actions and observations are the largest slice of a mature agent’s window — bigger than the system prompt, the tools and the retrievals combined. Shaping them is the highest-leverage context work available, and it is harness code, not prompting.

Failure mode

Blind truncation to a character limit. It cuts mid-traceback and keeps the passing tests, which is the exact inverse of what the agent needed.

X-12Observation Compression

Elsewhere in the atlas