fix(config): retain the MCP dispatcher storage key

Preserve mcp.server_definitions as the established literal JSON-text key consumed and persisted by the stdio dispatcher. Unknown nested TOML writes remain rejected before mutation.

Validation: all 3 real CLI MCP proxy integration tests pass, including spawned tools/resources and missing-child reporting. npm test: 66 wrapper, 9 SDK, 446 web passed; check:web passed with 0 errors and 2 existing warnings. Formatting and diff checks passed. The previous full sweep stopped at this regression and will restart on the corrected head.

Author: CodeWhale Bot

crates/config/src/lib.rs

@@ -3202,7 +3202,9 @@ impl ConfigToml {
                     .get_or_insert_with(HookSinksToml::default)
                     .unix_socket_path = Some(PathBuf::from(value));
             }
-            _ if key.contains('.') => {
+            // The MCP stdio dispatcher persists this established literal key
+            // as JSON text; it is not a nested TOML setting.
+            _ if key.contains('.') && key != "mcp.server_definitions" => {
                 let (table, field) = key.rsplit_once('.').expect("dotted key");
                 bail!(
                     "`config set` does not support nested key `{key}`; edit `{field}` in the [{table}] table of config.toml instead (use a TOML value of the documented type). No value was changed."