A render error in one viewer or gate widget unmounted the whole React root
(white screen). Add a reusable ErrorBoundary (class component, no new dep) with
resetKeys + an on-brand fallback, and wire it at two surfaces:
- WidgetHost: isolates the gate widget (reset on descriptor id) so a malformed
gate payload no longer blanks the conversation
- SessionDocumentsPanel: wraps each document (reset on doc key/content) so one
crashing viewer degrades only its section; siblings and the panel survive
The observed crash: a schema-linking doc that parses but lacks `candidates`
makes SchemaLinkingViewer throw. Verified live via Playwright against the mock
backend. TDD throughout; tsc clean, 123/123 vitest (+8 new tests).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
marcopanandClaude Fable 5
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