backstage release v3.19.0

(agent-platform) Say on a model’s page when no context window is configured by @marians — A model’s page under Customize’s Models tab says No context window is configured for this model and whom to ask, when agentPlatform.models.contextWindows names none for it. Created shows a relative time, with the full date on hover.
(agent-platform) Show your actual model cost on Your sessions by @marians — Usage’s Your sessions view shows Cost: what your own model calls actually cost, in total and per agent, from the LLM gateway’s per-user figures. Where those cannot be read it falls back to Est. cost, with the reason.
(agent-platform) Export a session from its actions menu by @marians — The session page’s actions menu has Export session, which saves the whole session, every message and tool call as kagent stores it, as a JSON file.

(app) Let the notification inbox’s toasts go on their own after 6 s by @marians — Agent Platform notification toasts, for waiting sessions, failed or finished turns and MCP sign-ins, disappear on their own after 6 seconds, counted from when the window has focus. The notification bell keeps them.
(muster) A connector still connecting with the portal sign-in reads Connecting by @teemow — Right after you sign in, a connector muster is still connecting with your portal sign-in reads Connecting in Customize’s Connectors tab, and reaches its state without a reload.
(muster) Never ask a sign-in of an SSO connector, and say when one cannot connect by @marians — Connectors that use your portal sign-in are no longer listed as needing your sign-in, not even briefly while the portal opens. One that refuses your sign-in reads Cannot connect, and its page says <connector> cannot connect for you and what an administrator has to change.

Full Changelog: https://github.com/giantswarm/backstage/compare/v3.18.0...v3.19.0