isStreamingUpstreamError used a key-presence check (parsed.error != null)
which false-positives on benign values some backends emit on every chunk
({}, '', false, 0). When opencode issues a tool-call turn, the upstream SSE
opens with role-only frames (no recognized content) and a later chunk that
carries real tool_calls content PLUS a benign empty error field. The error
gate runs BEFORE content recognizers, so that single frame short-circuits
to 'error' -> 502 'streaming upstream error'. Same combo via kilocode works
because its wire format never emits the empty error field.
Fix: isSubstantiveError() helper — only treat error as real when it carries
non-empty string, non-empty object, or explicit true. Empty object {}, empty
string '', false, and 0 are benign.
TDD: tests/unit/quality-validation-benign-error.test.ts proves tool_calls
chunk with error:{} or error:'' is valid (was 502), while a real error
{message, code} still correctly fails.
69647b3b94