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.
City-card fallback reads now stop using stale METAR or official observations as strong live anchors. A stale observation no longer forces high/low revisions, and both backend and browser AI cache keys include the observation fingerprint so updated report times, receipt times, temperatures, or stale status invalidate old AI text.
Constraint: Cached city AI reads must not survive a material observation update
Rejected: Let stale METAR trigger observed-break revisions | stale reports can be older than the active temperature path
Confidence: high
Scope-risk: moderate
Tested: pytest tests/test_web_observability.py -q
Tested: npm run build
City AI can return a partially streamed JSON string when the provider truncates output. The fallback previously kept an unfinished clause such as '但TAF显示', which made the forecast explanation look broken even though earlier evidence was usable.
Constraint: Provider JSON can be truncated after useful fields have already streamed
Rejected: Drop all partial AI text | would lose valid METAR interpretation already returned before truncation
Confidence: high
Scope-risk: narrow
Tested: pytest city AI truncation regression tests
Tested: npm run build
Not-tested: Live DeepSeek provider response
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