feat(desktop): harden connection session lifecycle

- add a visible connection session summary for ready/testing/demo/retry states
- prevent stale live connection tests from overwriting a newer active DB selection
- include the missing frontend helpers already referenced by App.tsx so the branch builds cleanly

Co-Authored-By: Paperclip <noreply@paperclip.ing>

plans/2026-03-31-hac-28-connection-context-lifecycle.md

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+# HAC-28 Connection Context Lifecycle
+
+Date: 2026-03-31
+Owner: Senior Frontend Engineer
+Issue: HAC-28
+
+## Goal
+
+Harden connection-context and session-state clarity without changing backend contracts or pulling next-phase scope into `desktop-v1`.
+
+## Scope
+
+- keep connection status copy consistent between the header, connection cards, and the active-session summary
+- make ready, checking, demo, and retry-needed states visibly distinct in the utility rail
+- prevent a finished live connection test from yanking the current active DB after the operator has already switched to another connection
+- keep retry guidance explicit when a live test fails
+- add focused frontend tests around the connection-session helper
+
+## Non-Goals
+
+- no Add Key expansion
+- no delete execution
+- no non-string editing
+- no visual refresh
+- no backend contract changes
+
+## Delivery Shape
+
+1. Add a shared connection-session helper for:
+   - connection test state transitions
+   - consistent status and connection-card copy
+   - visible active-session summary copy
+2. Update `apps/desktop/src/App.tsx` so:
+   - the utility rail shows a clear active connection session card
+   - the test button distinguishes active-scope testing from another in-flight connection test
+   - live test completion only reapplies the returned DB scope when the same connection is still active
+3. Revalidate frontend tests and production build.
+
+## Acceptance
+
+- connection session state is visible as ready, testing, demo fallback, or retry needed
+- connection-card detail and header status use the same wording model
+- switching to another connection during a live test does not silently replace the current active DB when the earlier test returns
+- failed live tests leave a clear retry path in visible UI copy
+- `pnpm --filter @redis-gui/desktop test` passes
+- `pnpm run desktop:build` passes