Why: A rejected result-reference request could discard the user text or uploads after the composer cleared.
Evidence: 286 frontend tests, TypeScript and the unchanged unused-export gate pass; mixed-input browser regression preserves the draft.
Impact: Validate incompatible inputs before clearing, retain failed pending input with its request identity, and require explicit retry while other messages can continue.
Refs: feature/workbench-flow-completion review frontend-races finding
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