Last-Event-ID is ignored — streams are not resumable

How to fix this

Ignore the `Last-Event-ID` header. Streams are not resumable in this revision, so the header is inert — but rejecting a request that carries it breaks clients that still send it.

How the validator checks this

Probe P5.4, against a streamable-http server on the modern protocol. What it reports:

pass

Last-Event-ID was ignored — streams are not resumable

warn

Rejected a request carrying Last-Event-ID (HTTP …); it should simply be ignored

Quoted from the probe that runs this check, so it cannot drift from what the validator actually reports.

This rule is checked deterministically: a fail here is a certain violation, not an inference.

Check your own server against this rule

The validator makes real protocol requests and reports this rule as pass, warn or fail alongside the other 78. Validate a server or read how the check works.

Other Statelessness and session removal rules

• MCP-STL-001Server never mints or echoes Mcp-Session-Id
• MCP-STL-002A client-supplied Mcp-Session-Id is ignored, not required
• MCP-STL-003A cold modern request succeeds with no prior handshake
• MCP-STL-004Server does not rely on prior requests over the same connection
• MCP-STL-005GET on the MCP endpoint returns 405
• MCP-STL-006DELETE on the MCP endpoint returns 405
• MCP-STL-008tools/list does not vary per connection