Experiment: surface connection state in the Connections tree via FileDecorationProvider

Summary

Experiment with using a FileDecorationProvider to surface connection state for clusters in the Connections tree (and potentially the Discovery tree) in general.

Today a user cannot tell at a glance which clusters are currently connected and which are not. A decoration provider could attach a small badge/color overlay to each cluster node reflecting its live state (e.g. connected, disconnected, connecting, error), adding value without replacing the node icon.

Motivation

• At-a-glance visibility of which clusters have an active session/connection.
• Non-intrusive: decorations overlay the existing icon instead of replacing it, so the DocumentDB cluster icon stays intact.
• Came out of the PR #621 Kubernetes discovery UX review (§9.6 option B), where a reachability badge for ClusterIP / port-forwarded targets was considered. Generalizing it to all connections is more broadly useful than a Kubernetes-only badge.

Scope of the experiment

• Prototype a FileDecorationProvider registered for the Connections view that maps cluster nodes (by a stable URI scheme/resourceUri) to a decoration reflecting connection state.
• Define the connection-state model and where it is sourced from (credential cache / active client presence / port-forward tunnel status).
• Evaluate UX: badge glyph vs. color, light/dark/high-contrast themes, and accessibility (the state must also be conveyed via tooltip/description, not color alone).
• Decide whether to extend to the Discovery tree (e.g. Kubernetes reachability) once the general mechanism works.

Out of scope

• Final visual design / string wording (decide after the prototype).
• Replacing existing node icons.

Notes

• Decorations require nodes to expose a resourceUri; confirm the tree items can carry one without breaking existing treeId/clusterId behavior.
• Accessibility: never rely on color alone — mirror the state in the tooltip and/or description (see the a11y guidance in the repo).

Filed for the 0.10.0 milestone as a follow-up from the Kubernetes discovery UX review (PR #621).

Start with the Connections tree entry point, the VS Code FileDecorationProvider API, and the Kubernetes discovery UX discussion in PR #621. Inspect whether tree items can expose a stable resourceUri without breaking treeId or clusterId behavior, then prototype connection-state mapping and evaluate tooltip, theme, and accessibility behavior before deciding whether Discovery should also be covered.