Never test a system against itself. Driving mcpx’s own server/discover against mcpx proved both halves agreed, not that either was right — they shared the same wrong field name. Test against the schema, the spec, or a reference implementation.
The signature defect is declared but not delivered (#177): a flag parsed and dropped, a capability advertised and never sent, a setting read but inert. consumed_test.go proves a setting is read, not that reading it changes anything.
The daemon is keyed by its config file set. Three separate bugs came from this; environment differences that should produce different daemons do not.
On macOS /tmp is a symlink to /private/tmp and the product canonicalises paths, so a test using os.MkdirTemp("/tmp", …) passes on Linux CI and fails on every Mac.
nix build’s checkPhase has had a hand-maintained package list that drifted from the packages that have tests. CI runs go test ./... and does not.
The official conformance suite ships its own fixture server. Running it against a different server measures nothing. A falling score can mean the code got more correct — it has, twice.
Under parallel agents, load averages above 150 push internal/e2e past its default timeout. Raise -timeout; do not read it as a failure.