Extends the previous describeApiError rollout to the rest of the UI.
Two symptom classes covered:
- Bare e.message / err.message in toast descriptions would render
"undefined" on Spring error bodies (plain objects without a proper
Error prototype). Affected: OidcConfigPage (save/test/delete),
ClaimMappingRulesModal (save + test), AgentHealth (dismiss),
RouteControlBar (route action + replay).
- Inline {String(error)} on load-failure banners would render
"[object Object]". Affected: InboxPage, RulesListPage, SilencesPage,
OutboundConnectionsPage.
Not touched: auth-store, AppsTab, UsersTab — they already guard with
`e instanceof Error` and fall back to a static string; replacing the
fallback with describeApiError would be a behavioral change best
evaluated separately.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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