The AI city forecast hook still owned stream queueing and in-flight request dedupe after the first request-client pass. Moving that policy into scanTerminalClient keeps network concurrency, queued progress, and requestKey reuse in the request layer while leaving the hook responsible only for cached UI state and progress rendering.
Constraint: Preserve existing two-stream concurrency limit and queued user-facing progress copy.
Rejected: Move localStorage cache at the same time | cache policy should be separated from stream transport policy to keep this refactor reviewable.
Confidence: high
Scope-risk: narrow
Reversibility: clean
Tested: npm run build
Not-tested: Live multi-city SSE under production latency.
The scan terminal hooks were each carrying their own fetch, SSE parsing, error normalization, previous-data handling, and market request behavior. This adds a small scanTerminalClient plus RemoteData helpers so terminal data, city detail, market scans, and AI city streams share one request boundary without introducing React Query.
Constraint: Do not add dependencies or change backend API contracts.
Rejected: Introduce React Query immediately | too broad for this release and would force larger UI state rewrites.
Rejected: Move localStorage caches in the same pass | safer to first isolate network and stream IO before cache policy migration.
Confidence: high
Scope-risk: moderate
Reversibility: clean
Tested: npm run build
Not-tested: Live SSE cancellation against production latency.
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