fix: use existing executable or unversioned python

[zimeg]

Summary

This PR uses the existing executable or an unversioned python command otherwise. Fixes #70.

Testing

WIP.

Special notes

These changes shouldn't break the experience for Unix, despite the python3 alias being somewhat common. I understand that this option is most relevant when creating a virtual environment, but afterward all aliases point to the same version it seems:

(.venv) $ ls .venv/bin
python -> python3.13*
python3 -> python3.13*
python3.13 -> /opt/homebrew/opt/python@3.13/bin/python3.13*

Windows setups don't include aliases from what I find:

(.venv) PS C:> ls .\.venv\Scripts
python.exe
(.venv) PS C:> python --version
Python 3.14.0

We might make additional changes to the upstream init command if this seems correct as well:

https://github.com/slackapi/slack-cli/blob/a2df7c635e6ba442f51220f6a88c57ed9b64b521/internal/runtime/python/hooks.json#L3

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run ./scripts/install_and_run_tests.sh after making the changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.73%. Comparing base (b53cab3) to head (c4d5644).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #96      +/-   ##
==========================================
+ Coverage   94.68%   94.73%   +0.05%     
==========================================
  Files          11       11              
  Lines         207      209       +2     
==========================================
+ Hits          196      198       +2     
  Misses         11       11              

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[zimeg]

🔍 From a Windows machine:

[2026-02-26 10:08:36] starting hook command: python -m slack_cli_hooks.hooks.get_hooks
[2026-02-26 10:08:37] {"hooks": {"get-manifest": "'C:\\Users\\user\\programming\\slack-cli\\strange-orca-513\\.venv\\Scripts\\python.exe' -m slack_cli_hooks.hooks.get_manifest", "start": "'C:\\Users\\user\\programming\\slack-cli\\strange-orca-513\\.venv\\Scripts\\python.exe' -X dev -m slack_cli_hooks.hooks.start", "check-update": "'C:\\Users\\user\\programming\\slack-cli\\strange-orca-513\\.venv\\Scripts\\python.exe' -m slack_cli_hooks.hooks.check_update", "doctor": "'C:\\Users\\user\\programming\\slack-cli\\strange-orca-513\\.venv\\Scripts\\python.exe' -m slack_cli_hooks.hooks.doctor"}, "config": {"protocol-version": ["message-boundaries", "default"], "sdk-managed-connection-enabled": true, "watch": {"app": {"filter-regex": "\\.py$", "paths": ["."]}, "manifest": {"paths": ["manifest.json"]}}}, "runtime": "python"}
[2026-02-26 10:08:37] finished hook command: python -m slack_cli_hooks.hooks.get_hooks
[2026-02-26 10:08:37] initialized SDK CLI config: {Runtime:python Hooks:{BuildProject:{Command: Name:BuildProject} CheckUpdate:{Command:'C:\Users\user\programming\slack-cli\strange-orca-513\.venv\Scripts\python.exe' -m slack_cli_hooks.hooks.check_update Name:CheckUpdate} Deploy:{Command: Name:Deploy} Doctor:{Command:'C:\Users\user\programming\slack-cli\strange-orca-513\.venv\Scripts\python.exe' -m slack_cli_hooks.hooks.doctor Name:Doctor} GetHooks:{Command:python -m slack_cli_hooks.hooks.get_hooks Name:GetHooks} GetManifest:{Command:'C:\Users\user\programming\slack-cli\strange-orca-513\.venv\Scripts\python.exe' -m slack_cli_hooks.hooks.get_manifest Name:GetManifest} GetTrigger:{Command: Name:GetTrigger} InstallUpdate:{Command: Name:InstallUpdate} Start:{Command:'C:\Users\user\programming\slack-cli\strange-orca-513\.venv\Scripts\python.exe' -X dev -m slack_cli_hooks.hooks.start Name:Start}} Config:{Watch:{FilterRegex: Paths:[]} SDKManagedConnection:true TriggerPaths:[] SupportedProtocols:[message-boundaries default]} WorkingDirectory:}
[2026-02-26 10:08:37] initialize runtime from hooks.json: Python (python)

And:

> Failed to get app manifest details. Please check your manifest file. (invalid_manifest)
   Error running 'GetManifest' command: exit status 1 (sdk_hook_invocation_failed)
   Suggestion: Run `slack.exe doctor` to check that your system dependencies are up-to-date.

   At line:1 char:81
   + ... mming\slack-cli\strange-orca-513\.venv\Scripts\python.exe' -m slack_c ...
   +                                                                ~~
   Unexpected token '-m' in expression or statement.
   At line:1 char:84
   + ... env\Scripts\python.exe' -m slack_cli_hooks.hooks.get_manifest --sourc ...
   +                                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Unexpected token 'slack_cli_hooks.hooks.get_manifest' in expression or statement.
       + CategoryInfo          : ParserError: (:) [], ParentContainsErrorRecordException
       + FullyQualifiedErrorId : UnexpectedToken

[zimeg]

🤖 Goodness gracious the laptop I have is out of battery. Will continue testing this later.