[Bryan Chen (bryanchen-d)]

Please make sure the code is following contribution guidelines in CONTRIBUTING.md

• : This PR has a corresponding issue open in the Repository. Fixes [Feature Request] Retry transient failures in 'az artifacts universal download' (tooling lookup and download) #1534
• : Approach is signed off on the issue. (Opened as a draft until the approach is confirmed on [Feature Request] Retry transient failures in 'az artifacts universal download' (tooling lookup and download) #1534.)

What

az artifacts universal download / publish look up the latest Universal Packages tooling (ArtifactTool) release before every run. That lookup is a single request with no retry, so one transient error (for example Read timed out) fails the whole command with Failed to update Universal Packages tooling, even when a working ArtifactTool is already cached on disk.

This change, scoped to artifacttool_updater.py:

• Retries the release lookup twice with a short backoff (2s, 5s).
• If every attempt fails and no AZURE_DEVOPS_EXTENSION_ARTIFACTTOOL_OVERRIDE_VERSION is set, falls back to the newest cached ArtifactTool_* release (compared numerically by version) that contains the artifacttool binary, and logs a warning.
• Still raises the existing CLIError when nothing usable is cached, or when a specific version was requested.

The --retries option suggested in #1534 is left for a follow-up.

Tests

New azext_devops/tests/latest/common/test_artifacttool_updater.py (unittest + mock.patch, temp tool root, time.sleep patched):

• lookup succeeds on the third attempt
• persistent failure falls back to the cached release
• the newest cached version is picked numerically (0.2.576 over 0.2.99), skipping dirs without the binary
• persistent failure with nothing cached still raises CLIError
• no fallback when a version override is set

python -m unittest azext_devops.tests.latest.common.test_artifacttool_updater: 5 passed. flake8 --max-line-length 120 is clean on both files.

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