Auto-install missing project extensions before command execution

[Copilot]

Project commands reported unsupported service hosts before offering to install the extensions needed by azure.yaml. Auto-install also handled only one missing extension and ignored requiredVersions and custom provisioning providers.

Changes

• Preflight extension discovery

  • Runs before project commands such as up, provision, deploy, and infra generate.
  • Detects all missing extensions required by service targets and provisioning providers.
  • Rebuilds the command tree once after installation.

• Required extensions

  • Honors requiredVersions.extensions and its version constraints.
  • Installs explicit requirements before inferred ones.
  • Supports extension packs; dependencies installed by a pack are skipped during subsequent inferred processing.

• Provider compatibility

  • Restricts installation candidates to versions that provide the requested capability.
  • Deduplicates extensions needed by multiple services or providers.
  • Retains deterministic ordering across multiple requirements.

Behavior at a glance

Scenario	Before	After
Multiple custom service hosts	Installs one, then command fails on the next	Discovers and offers every missing extension
requiredVersions.extensions	Ignored outside initialization	Installed with the declared constraint
Custom infra.provider	No auto-install	Matching provisioning extension is discovered
Extension pack	Not considered	Pack installs first; inferred dependencies are skipped
Unsupported service host	Error shown before install prompt	Extension preflight runs before command execution

• Fixes Improve UX for install experience of missing extensions #8999

[azure-pipelines]

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