fix(vm): fall back on invalid image alias doc

[rohan-patnaik]

Fixes #33162

Summary

This makes az vm image list fall back to the bundled image alias document when the remote alias document returns HTTP 200 but the body is not valid JSON.

Why

Today that path raises a raw JSONDecodeError, which makes the command fail with a Python traceback. If the alias endpoint is intercepted or returns a small error body, the CLI should behave like the existing fetch-failure paths and use the local alias copy instead.

Test plan

• PYTHONPATH=src/azure-cli:src/azure-cli-core .venv/bin/python -m py_compile src/azure-cli/azure/cli/command_modules/vm/_actions.py src/azure-cli/azure/cli/command_modules/vm/tests/latest/test_vm_image.py
• git diff --check

Note: I also tried the focused pytest for the new test, but the local venv is missing vcr, required by azure-cli-testsdk during test collection.

[azure-client-tools-bot-prd]

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[azure-client-tools-bot-prd]

Hi @rohan-patnaik,
Since the current milestone time is less than 7 days, this pr will be reviewed in the next milestone.

[azure-client-tools-bot-prd]

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[microsoft-github-policy-service]

Thank you for your contribution @rohan-patnaik! We will review the pull request and get back to you soon.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a fallback to the local VM image alias doc when the remote alias document returns invalid JSON, and introduces a regression test to cover that scenario.

Changes:

• Handle invalid JSON from the remote alias doc by logging a warning and falling back to the embedded local alias doc.
• Add a unit test that mocks a 200 response with non-JSON content and verifies the fallback behavior.

Reviewed changes

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

File	Description
src/azure-cli/azure/cli/command_modules/vm/_actions.py	Adds JSON parsing error handling and local-copy fallback when remote content is not valid JSON.
src/azure-cli/azure/cli/command_modules/vm/tests/latest/test_vm_image.py	Adds a test ensuring invalid JSON from the alias doc endpoint falls back to local aliases.

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[yonzhan]

vm

[yonzhan]

Thank you for your contribution! We will review the pull request and get back to you soon.

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