agentHost: Own SDK auto-download preference

[TylerLeonhardt]

Fixes #334675.

Summary

• Offer the Agent Host SDK download whenever the SDK is missing, independent of GitHub sign-in, entitlement resolution, or the signed-out experiment.
• Persist each SDK's download-on-use consent in the Agent Host's agent-host-storage.json, on the machine that owns the SDK cache.
• Record consent only when the user clicks Download or an agent turn actually starts a lazy SDK download; never infer consent from cache presence.
• Never prefetch an SDK at Agent Host startup: remembered consent suppresses repeat prompting, and the download begins only when an agent turn actually needs the SDK.
• Serialize setup initialization, consent, explicit downloads, lazy completion, and reload refreshes through one Sequencer and one download-activity state; duplicate explicit requests short-circuit before entering the queue.
• Keep status publication inside the setup channel: providers request a fresh serialized probe instead of publishing previously computed SDK-readiness values.
• Failed downloads return to the explicit offer without retrying in a loop; the workbench only renders host-reported setup state and sends explicit requests.

Testing

• npm run transpile-client

• npm run typecheck-client

• npm run eslint -- <changed TypeScript files>

• .\scripts\test.bat --run src\vs\platform\agentHost\test\common\agentSdkSetup.test.ts --run src\vs\platform\agentHost\test\node\agentSdkSetupChannel.test.ts --run src\vs\platform\agentHost\test\node\agentConfigurationService.test.ts --run src\vs\platform\agentHost\test\node\agentSdkDownloader.test.ts --run src\vs\platform\agentHost\test\node\agentHostServices.test.ts (64 passing)

• .\scripts\test.bat --run src\vs\platform\agentHost\test\node\claudeAgent.test.ts --run src\vs\platform\agentHost\test\node\codex\codexModelRefresh.test.ts --grep "agent SDK setup channel" (18 passing)

• .\scripts\test.bat --run src\vs\platform\agentHost\test\node\codex\codexModelRefresh.test.ts --grep "restored model waits|queues a fresh model refresh" (2 passing)

• .\scripts\test.bat --run src\vs\workbench\contrib\chat\test\browser\agentSessions\agentHostSdkSetupNotification.test.ts (36 passing)

• .\scripts\test-integration.bat --run src\vs\platform\agentHost\test\node\claudeAgent.integrationTest.ts (5 passing)rnrnFull npm run compile remains locally blocked by an unrelated stale @vscode/markdown-editor API mismatch; main-source typecheck and transpilation pass.

SDK notification follow-up

Fixes #334668. Includes the notification fix from #334672.

• Explain that users can click Download or send a message when models are available for the agent.
• Update the visible notification as models appear or disappear, while preserving the required-download wording when no models are available and always keeping Download.

Follow-up validation: 45 targeted SDK setup notification and session target picker tests passed, along with transpilation, ESLint, and hygiene checks.

[Copilot]

Copilot review overview

🟡 Changes recommended

Existing session and window gates still prevent signed-out users from reaching the offer when the experiment is disabled.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review tier: Balanced
Findings: 1

New issues introduced by this change (1)

Severity	Finding
	src/​vs/​workbench/​contrib/​chat/​browser/​agentSessions/​agentHost/​agentHostSdkSetupNotification.ts — This does not make the offer independent of the signed-out experiment end to end. The notification…

What changed in this PR

Moves Agent Host SDK download offers ahead of sign-in, entitlement, and experiment checks.

Changes:

• Offers missing SDK downloads to all users.
• Keeps missing-account guidance behind existing signed-out checks.
• Adds state-transition tests.

File	Description
agentHostSdkSetupNotification.ts	Reorders setup-state decisions.
agentHostSdkSetupNotification.test.ts	Tests independent download offers.

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[github-actions]

Base: d4471383 Current: 168a976a

No screenshot changes.

[TylerLeonhardt]

I also ran a full build and verified this did what it should