ci: Test build dir with spaces #35356

In theory this is already tested by setting the scratch dir to scratch_ ₿🧪_ in the CI:

https://github.com/bitcoin/bitcoin/blob/b9f0040caf45355c4621e792df09fffabf23495e/ci/test/00_setup_env.sh#L26

However, this doesn't cover everything, because on Linux, the build dir will contain symlinks to the Python functional tests, which will drop the space when they are resolved. So the subprocess.h may not see spaces in the command.

In theory, this can be fixed by moving the CI root dir to something with spaces, but this breaks other stuff (like depends).

So, only test subprocess.h handling of paths with spaces on Windows, which creates copies instead of symlinks to Python scripts.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35356.

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Concept ACK.

[420](https://github.com/bitcoin/bitcoin/actions/runs/26286704505/job/77376033170#step:14:3421)
 test  2026-05-22T12:47:14.418896Z TestFramework (ERROR): Unexpected exception: 
                                   Traceback (most recent call last):
                                     File "D:\a\bitcoin\bitcoin\build_ _\test\functional\test_framework\test_framework.py", line 143, in main
                                       self.run_test()
                                       ~~~~~~~~~~~~~^^
                                     File "D:\a\bitcoin\bitcoin\build_ _\test\functional\wallet_signer.py", line 58, in run_test
                                       self.test_valid_signer()
                                       ~~~~~~~~~~~~~~~~~~~~~~^^
                                     File "D:\a\bitcoin\bitcoin\build_ _\test\functional\wallet_signer.py", line 71, in test_valid_signer
                                       self.nodes[1].createwallet(wallet_name='hww', disable_private_keys=True, external_signer=True)
                                       ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                     File "D:\a\bitcoin\bitcoin\build_ _\test\functional\test_framework\coverage.py", line 50, in __call__
                                       return_val = self.auth_service_proxy_instance.__call__(*args, **kwargs)
                                     File "D:\a\bitcoin\bitcoin\build_ _\test\functional\test_framework\authproxy.py", line 153, in __call__
                                       raise JSONRPCException(response['error'], status)
                                   test_framework.authproxy.JSONRPCException: {'code': -1, 'message': "RunCommandParseJSON error: process(C:\\hostedtoolcache\\windows\\Python\\3.14.5\\x64\\python.exe D:\\a\\bitcoin\\bitcoin\\build_ _\\test\\functional\\mocks\\signer.py enumerate) returned 2: C:\\hostedtoolcache\\windows\\Python\\3.14.5\\x64\\python.exe: can't open file 'D:\\\\a\\\\bitcoin\\\\bitcoin\\\\build_': [Errno 2] No such file or directory\r\n"} [http_status=200]
 test  2026-05-22T12:47:14.424669Z TestFramework (DEBUG): Closing down network thread

The Windows CI fails, as expected. To reproduce on Linux:

# ./bld-cmake/test/functional/wallet_signer.py 
2026-05-22T13:25:49.297591Z TestFramework (INFO): PRNG seed is: 1399337446465493161
2026-05-22T13:25:49.349357Z TestFramework (INFO): Initializing test directory /tmp/bitcoin_func_test_txcy4g9y
2026-05-22T13:25:50.900451Z TestFramework (ERROR): Unexpected exception:
Traceback (most recent call last):
  File "/root/ ₿🧪_/test/functional/test_framework/test_framework.py", line 143, in main
    self.run_test()
    ~~~~~~~~~~~~~^^
  File "/root/ ₿🧪_/./bld-cmake/test/functional/wallet_signer.py", line 58, in run_test
    self.test_valid_signer()
    ~~~~~~~~~~~~~~~~~~~~~~^^
  File "/root/ ₿🧪_/./bld-cmake/test/functional/wallet_signer.py", line 71, in test_valid_signer
    self.nodes[1].createwallet(wallet_name='hww', disable_private_keys=True, external_signer=True)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/ ₿🧪_/test/functional/test_framework/coverage.py", line 50, in __call__
    return_val = self.auth_service_proxy_instance.__call__(*args, **kwargs)
  File "/root/ ₿🧪_/test/functional/test_framework/authproxy.py", line 153, in __call__
    raise JSONRPCException(response['error'], status)
test_framework.authproxy.JSONRPCException: {'code': -1, 'message': "RunCommandParseJSON error: process(/usr/bin/python3 /root/ ₿🧪_/test/functional/mocks/signer.py enumerate) returned 1: /usr/bin/python3: can't find '__main__' module in '/root/'\n"} [http_status=200]
2026-05-22T13:25:50.955938Z TestFramework (INFO): Not stopping nodes as test failed. The dangling processes will be cleaned up later.
2026-05-22T13:25:50.956328Z TestFramework (WARNING): Not cleaning up dir /tmp/bitcoin_func_test_txcy4g9y
2026-05-22T13:25:50.956531Z TestFramework (ERROR): Test failed. Test logging available at /tmp/bitcoin_func_test_txcy4g9y/test_framework.log
2026-05-22T13:25:50.956800Z TestFramework (ERROR): 
2026-05-22T13:25:50.957103Z TestFramework (ERROR): Hint: Call /root/ ₿🧪_/test/functional/combine_logs.py '/tmp/bitcoin_func_test_txcy4g9y' to consolidate all logs
2026-05-22T13:25:50.957270Z TestFramework (ERROR): 
2026-05-22T13:25:50.957401Z TestFramework (ERROR): If this failure happened unexpectedly or intermittently, please file a bug and provide a link or upload of the combined log.
2026-05-22T13:25:50.957595Z TestFramework (ERROR): https://github.com/bitcoin/bitcoin/issues
2026-05-22T13:25:50.957724Z TestFramework (ERROR): 
[node 1] Cleaning up leftover process
[node 0] Cleaning up leftover process



# history 
    4  git clone https://github.com/bitcoin/bitcoin.git  --depth=1 "./ ₿🧪_" && cd "./ ₿🧪_"
    5  cmake -B ./bld-cmake    -DCMAKE_C_COMPILER='clang' -DCMAKE_CXX_COMPILER='clang++' --preset=dev-mode
    9  cmake --build ./bld-cmake --parallel  $(nproc) 
   10  ./bld-cmake/test/functional/wallet_signer.py 

(failure happens on Linux, before and after 2706758dc38c7a4e271d9df5ea3104b7135974f3)