Why: the resolver refactor replaced the explicit `omp` branch with an
unconditional `return resolveOmpSessionFile(...)`. That is behaviour-identical
today, but a future member of NativeChatTranscriptAgent would silently scan
OMP's session root with a foreign session id, and the tail return stays
well-typed so nothing fails the build.
Restore the explicit branch and add a `satisfies never` check so adding an
agent is a compile error at this line instead of a wrong resolve at runtime.
OrcaWin
8ffed254a4