You'll noticeTier: how much it should matter to you
4Useful: my rating, 1 to 5
0Signal: worth watching, 1 to 5
MCPArea: what it touches
New FeaturesKind: in v2.1.219,
What probably matters to youSection of the release
What
Servers passed via --mcp-config that fail validation are no longer silently absent; they are collected, surfaced on the SDK init message, and printed to stderr on a TTY.
Details
Validation warnings carrying mcpErrorMetadata.skipReason and a server name are collected, and servers that ended up unregistered are recorded
A new optional mcp_server_errors array on the system/init payload lists each skipped entry with name, a stable type category (unknown_type, url_missing_type, invalid_config, reserved_name) and a message, filtered to servers with no live client
On a TTY the same list is printed to stderr as a control-character-scrubbed warning
Affected servers no longer appear only as gaps in mcp_servers[], so CI can fail on a non-empty list
Also new on init: fast_mode_disabled_reason
Neither the collection nor the init-message field existed in 2.1.218
Evidence
MCP server config entries from --mcp-config that failed validation and were skipped, skipped due to invalid config
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
