[python] update python emitter install with helpful 401 error output

[JennyPng]

closes Azure/azure-sdk-for-python#46964

Because the python emitter's install.ts may use uv pip to install packages, it can run into authentication errors if a package version isn't cached in our central feed service, which we now default to pulling from instead of PyPI (see Azure/azure-sdk-for-python#46281 )

updates the error point to link to python repo's authentication docs

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-client-python@10720

commit: 62fb7bb

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-client-python

Show changes

@typespec/http-client-python - internal ✏️

When python emitter install fails due to 401 error, output informative instructions linking to resolution steps in the Python SDK's repo docs.

[azure-sdk-automation]

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[Copilot]

Pull request overview

Improves the Python http-client emitter’s installation experience by surfacing more actionable diagnostics when package installation fails, particularly for authentication-related (401) failures against the Azure feed.

Changes:

• Switch install_packages to capture subprocess output and include it in raised errors.
• Add special-case guidance (linking to Azure SDK for Python contributing/auth docs) when failure output indicates a 401/Unauthorized.
• Add a Chronus entry documenting the internal change.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
packages/http-client-python/eng/scripts/setup/package_manager.py	Capture pip/uv install output and enhance errors with 401-specific guidance.
.chronus/changes/cfs-error-message-2026-4-18-15-8-34.md	Add changelog entry describing the improved 401 failure messaging.