worldmonitor/todos/178-pending-p2-aborontroller-on-rapid-region-pill-clicks.md

status, priority, issue_id, tags, dependencies

status	priority	issue_id	tags	dependencies
pending	p2	178	code-review phase-0 regional-intelligence performance frontend	179

refetchForRegion missing AbortController - rapid clicks fire wasted RPCs

Problem Statement

src/components/ForecastPanel.ts:318-331 uses a sequence counter to discard stale UI updates, but every click still fires a full RPC. Clicking MENA → East Asia → Europe issues 3 full HTTP calls. Each hits getCachedJson(REDIS_KEY) in get-forecasts.ts:17 with no in-process memoization, so each is a fresh Redis GET + filter + ~50KB response. The 1st-2nd responses are silently discarded.

Compounded by P2 #179 (server has no cachedFetchJson coalescing), the user can trigger an order of magnitude more Redis traffic than necessary.

Findings

• src/components/ForecastPanel.ts:318-331 — regionFetchSeq guard discards stale results but does not abort in-flight requests.

Proposed Solutions

Option 1: AbortController

Thread signal through fetchForecasts → IntelligenceServiceClient.getForecasts. Verify the generated proto-ts client supports options.abort.

Pros: Explicit cancellation; reduces server work; idiomatic fetch pattern. Cons: Requires verifying proto-ts client signal support and threading it through. Effort: Small. Risk: Low.

Option 2: Debounce 150ms before issuing the RPC

Wait 150ms after last click before fetching.

Pros: Single-line change. Cons: Adds delay on first click; doesn't help the already-fired request; degrades perceived responsiveness. Effort: Small. Risk: Low.

Option 3: Client-side cache

Add a Map<regionId, Forecast[]> keyed on region. Instant back-navigation.

Pros: Zero server trips for revisits; instant UI. Cons: Stale until panel re-opens; needs a TTL or invalidation trigger. Effort: Small. Risk: Low.

Recommended Action

Option 1 + Option 3. Together they prevent server work and give instant return navigation. Option 2 is a fallback if proto-ts signal support is absent.

Technical Details

Proto-ts clients generated by make generate typically accept an AbortSignal through an options bag — confirm via the generated IntelligenceServiceClient interface before wiring. If the signal path isn't plumbed, wrap the call in a native fetch-level abort at the client edge.

Cache shape: Map<regionId, { data: Forecast[]; ts: number }> with a 60-second TTL matching server cache. Invalidate on visibility change + explicit refresh button.

Acceptance Criteria

• Clicking 5 region pills rapidly issues at most 1 in-flight RPC.
• Stale RPCs are explicitly aborted (not just UI-discarded).
• Returning to a previously-fetched region serves from client cache.
• Cache entries honor a TTL and refresh on visibility change.

Work Log

Resources

• PR #2942
• Spec: docs/internal/pro-regional-intelligence-upgrade.md