Context files (AGENTS.md, CLAUDE.md, .hermes.md, .cursorrules, SOUL.md) were
hard-capped at a flat 20K chars before head/tail truncation. Among the agent
harnesses we track, only Codex caps project docs at all (32 KiB); Claude Code,
OpenCode, and Cline load them whole. The flat 20K predates large context
windows and silently truncates real-world AGENTS.md files.
B — dynamic cap: when context_file_max_chars is unset (now the shipped
default), the cap scales with the model's context window
(ctx_tokens * 4 * 0.06, floor 20K, ceiling 500K). Small-context models stay at
the historical 20K; a 200K model gets 48K; large models stop truncating real
docs. An explicit context_file_max_chars still wins. Context length is resolved
once per conversation (stable -> prompt cache untouched).
C — when truncation does happen, the marker now names the concrete file path
and tells the agent to read_file it for the full content.
Validation: 154 targeted tests + full agent/ + hermes_cli/ + test_config
(0 failures); E2E against a real 60K AGENTS.md confirms small windows truncate
with the path-bearing marker, large windows load whole, and the system prompt
is byte-stable across rebuilds.
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