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MCP servers using a newer protocol era no longer get custom notification handlers, and you see a warning.
Protocol-era-aware notification handling only applies when MCP era negotiation flags are on.
What's wrong with this entry?
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What
Registering a handler for an unsolicited custom notification is refused when the connection negotiated a modern protocol era, because there is no delivery path for it.
Details
- Emits a warning naming the server, the method and the negotiated revision.
- In 2.1.220 the handler was always registered;
getProtocolEradoes not appear in that build. - Only reachable when era negotiation is on, see the tengu_mcp_protocol_negotiation_* flags.
Evidence
which has no delivery path for unsolicited custom notifications
Strings lifted out of the shipped bundle, so the claim above can be checked against them.