server: restore Service compatibility and fix API check

[Rememorio]

Summary

• remove ServiceName() from the public server.Service interface
• keep ServiceName() available on the built-in service implementation
• verify that custom services implementing the original three-method interface remain valid
• align the API compatibility check with trpc-group/trpc-agent-go by using joelanford/go-apidiff against the PR merge base

API check root cause

imjasonh/apidiff-action@v0.0.3 passed the base and head Git SHAs directly to apidiff. The tool interpreted those SHAs as Go package import paths and failed to load them. The action swallowed that error and reported that no breaking changes were detected. It also could not post its PR comment because fork pull requests receive a read-only token.

The replacement follows the trpc-agent-go workflow: it calculates the merge base with the target branch and passes that revision to joelanford/go-apidiff. There is no exception or allowlist. Breaking API changes fail the check.

Compatibility

Adding a method to an exported Go interface prevents existing third-party implementations from compiling. This restores the server.Service contract from v1.0.3 without changing built-in service behavior.

This intentionally prioritizes compatibility with existing custom server.Service implementations. Code introduced against v1.0.4 that calls server.New(...).ServiceName() directly must instead use an optional interface assertion:

if namer, ok := service.(interface{ ServiceName() string }); ok {
    name := namer.ServiceName()
    _ = name
}

The corrected API check reports this removal as incompatible and is expected to fail on this PR.

Testing

• go test ./...
• GOTOOLCHAIN=go1.19.13 go test ./server
• actionlint
• verified joelanford/go-apidiff exits non-zero and reports Service.ServiceName: removed against the PR merge base

[Flash-LHR]

LGTM