[Agents extension] Filter our model query by the supported hosted agents regions

[trangevi]

Fixes #8516

[github-actions]

📋 Prioritization Note

Thanks for the contribution! The linked issue isn't in the current milestone yet.
Review may take a bit longer — reach out to @rajeshkamal5050 or @kristenwomack if you'd like to discuss prioritization.

[Copilot]

Pull request overview

This PR updates the Azure AI Agents extension init flows so that “all regions” model catalog queries are constrained to the hosted-agents supported region allowlist (addressing issue #8516), preventing users from being offered models in regions where hosted agents can’t run.

Changes:

• Introduces newModelSelector(...) and updates InitAction.getModelSelector(ctx) to eagerly fetch and cache the hosted-agents supported regions list.
• Applies the supported-region allowlist to model catalog queries that previously used “all regions” (ListModels / PromptAiModel).
• Adds tests covering selector construction, memoization behavior, and context-cancellation propagation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cli/azd/extensions/azure.ai.agents/internal/cmd/init.go	Adds a supportedRegions field to modelSelector, plus a constructor and context-aware memoized getter.
cli/azd/extensions/azure.ai.agents/internal/cmd/init_models.go	Uses the supported-region allowlist in “all models” catalog queries and updates some user-facing strings.
cli/azd/extensions/azure.ai.agents/internal/cmd/init_models_test.go	Adds unit tests validating supported-regions population, memoization, and cancellation behavior.
cli/azd/extensions/azure.ai.agents/internal/cmd/init_from_code.go	Switches recovery path selector construction to newModelSelector(...) so it also respects supported regions.
cli/azd/extensions/azure.ai.agents/internal/cmd/init_foundry_resources_helpers.go	Documents agentModelFilter behavior regarding nil/empty locations and supported-regions filtering expectations.

Comments suppressed due to low confidence (1)

cli/azd/extensions/azure.ai.agents/internal/cmd/init_models.go:862

• The prompt copy has been updated to "supported regions", but the wrapped error message still says "across all regions". Aligning this wording will make troubleshooting less confusing.

				}

				return nil, "", exterrors.FromPrompt(err, "failed to prompt for model selection across all regions")
			}

[therealjohn]

I will confirm if the models a hosted agent uses need to be limited to the regions you can deploy a hosted agent too - I do not think they are linked.

I believe a model deployment can technically be in a different region (supported or not of HA) of hosted agent.

[trangevi]

Confirmed, no such restriction