Agents: Cloud session type pill appears interactive when no alternative is available

[meganrogge]

Type of Issue

Bug

Description

In the Agents window new-session picker, selecting a GitHub repository that is not local shows a Cloud session type pill. Because Cloud is the only session type available for that repository, activating the pill does nothing and no picker opens.

The pill should remain visible to communicate the selected session type, but it should be rendered as disabled when there are no alternatives. If another session type becomes available, it should become interactive again.

Steps to Reproduce

1. Open the Agents window.
2. Start a new session.
3. Select a GitHub repository that is not available locally.
4. Observe the Cloud session type pill.
5. Try to activate it.

Expected

The sole Cloud session type is visible but disabled.

Actual

The pill appears interactive, but activating it has no effect.

[vs-code-engineering]

Sharing media and context from merged PR #333603 for verification:

Summary

• keep the sole session type pill visible when a selected repository supports no alternatives
• render the pill as disabled and remove it from keyboard navigation
• restore interaction automatically when another session type becomes available

Testing

• npm run transpile-client
• ./scripts/test.sh --run src/vs/sessions/contrib/chat/test/browser/sessionTypePicker.test.ts (26 passing)

Source PR: #333603

[vritant24]

verified, but found a slight accessibility issue #333879