Salvage of #26860 (hunk 2, ported \u2014 the PR's base predates the current
gateway layout by ~11.9K commits). Messaging platforms can set
gateway.platforms.<key>.skip_context_files: true to skip the
filesystem-heavy context-file discovery (SOUL.md, AGENTS.md,
.cursorrules walks) during AIAgent construction \u2014 10-100x slower
stat()/walk costs on Windows made this a real per-turn tax. Soul
identity is still loaded (single small file), so the persona survives.
The flag participates in _agent_config_signature so toggling it
rebuilds the cached agent instead of silently reusing a prompt built
under the other setting (prompt-cache correctness).
The PR's hunk 1 (mtime-caching the per-turn dotenv reload) was dropped:
df51ad797 mtime-cached load_config/read_raw_config and c2eda92fd
removed the per-turn deepcopies, capturing most of that win; the
function has since gained a multiplex early-return and managed-scope
overlay that the original whole-function skip would have bypassed.
314574126