You'll noticeTier: how much it should matter to you
2Useful: my rating, 1 to 5
1Signal: worth watching, 1 to 5
MCPArea: what it touches
ImprovementsKind: in v2.1.246,
ImprovementsSection of the release
What
When a tool call issued through the SDK control channel is interrupted, the handler now returns an error naming the MCP server instead of a normal, empty-looking content response.
Details
The message is built at runtime from the fixed text "mcp_call cancelled by client: " followed by the server name.
Triggered by an interrupted field on the tool result; unconditional for control-channel MCP calls.
Evidence
mcp_call cancelled by client:
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
