refactor(sketch): tighten review feedback

- workspace-routing best-effort probe: catch ONLY SessionNotFound
  (was Effect.catch(() => undefined) which swallowed all E-channel
  errors, broader than the prior catchDefect-only behavior). Drop the
  now-redundant catchDefect since session.get fails typed instead of
  throwing.
- trace.ts: TODO(typed-errors) marker on the legacy Hono shim so it
  greps as a known retirement target.
- httpapi-parity.test.ts: drop stale FIXME comment above the now-
  passing reproducer.