Quick fix/workaround is the following patch, simply overwriting the
wrapped trezor_agent.py with the real thing.

live well,
  vagrant

commit ef39a4dc42dcd2daaa7a626c923f1115f8540091
Author: Vagrant Cascadian <vagrant@debian.org>
Date:   Fri Feb 8 03:23:14 2019 +0000

    trezor-agent: Overwrite trezor_agent.py wrapper with real thing.

diff --git a/gnu/packages/finance.scm b/gnu/packages/finance.scm
index 035f6f5965..88b365dfb7 100644
--- a/gnu/packages/finance.scm
+++ b/gnu/packages/finance.scm
@@ -805,6 +805,17 @@ Then set the environment variable GNUPGHOME to
        (sha256
         (base32
          "144657c7bn0a667dq5fv5r6j7iilxf3h9agj29v1m2qpq40g0az8"))))
+    (arguments
+     ;; Tests fail with "AttributeError: module 'attr' has no attribute 's'".
+     `(#:phases
+       (modify-phases %standard-phases
+         (add-after 'wrap 'fixup-agent-py
+           (lambda* (#:key inputs outputs #:allow-other-keys)
+             (let* ((out (assoc-ref outputs "out")))
+               ;; overwrite the wrapper with the real thing.
+               (install-file "./trezor_agent.py"
+                             (string-append out "/bin/"))
+             #t))))))
     (build-system python-build-system)
     (inputs
      `(("python-trezor" ,python-trezor)