Monadic transformation is broken

[W95Psp]

* Error 54 at Sandwich.Tunnel.Tls.fsti(383,22-397,94):
  - Core.Ops.Control_flow.t_ControlFlow (Core.Result.t_Result Prims.unit Sandwich.Error.t_Error)
      (Prims.bool & Prims.bool) is not a subtype of the expected type Prims.bool & Prims.bool

1 error was reported (see above)

Action item:

• throw an error instead of trying to transform, with hints to how to rewrite
• fix the transformation

[franziskuskiefer]

Most cases should be covered by what's doing in #393. Let's assess if this is still needed when that's done.

[github-actions]

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[W95Psp]

We still need this phase: rewrite control flow introduces too many deduplication in certain case.