The automatic MCP reload added in #1474 watches config.yaml's mcp_servers
section every 5s and reloads on any change. Every reload rebuilds the agent
tool surface and INVALIDATES the provider prompt cache — the next message
re-sends the full input prefix, which is expensive on long-context /
high-reasoning models. When config.yaml is rewritten frequently (external
tooling, multiple Hermes instances, or a flapping MCP server that rewrites
config), this causes silent, repeated cache-breaking reloads.
Add `mcp.auto_reload_on_config_change` (default: true, backward compatible).
When set to false:
- The config change is still DETECTED (watcher keeps running).
- No automatic reload happens.
- The user is told the config changed, that new settings are NOT yet
applied, and how to apply them on their own terms with /reload-mcp —
including the explicit warning that /reload-mcp invalidates the prompt
cache.
Manual /reload-mcp is unaffected and still works for users who want to
apply changes deliberately.
Tests: extend TestMCPConfigWatch with test_optout_disables_auto_reload.
Co-authored-by: Turgut Kural <turgut.kural@gmail.com>
Turgut Kural
5c2d098bb0