worldmonitor/todos/179-pending-p2-getforecasts-handler-no-cachedfetchjson.md

status, priority, issue_id, tags, dependencies

status	priority	issue_id	tags	dependencies
pending	p2	179	code-review phase-0 regional-intelligence performance redis cache-stampede

getForecasts RPC handler lacks cachedFetchJson coalescing (cache stampede risk)

Problem Statement

server/worldmonitor/forecast/v1/get-forecasts.ts:17 calls getCachedJson(REDIS_KEY) directly. Per CLAUDE.md ("Cache Stampede: Use cachedFetchJson"), RPC handlers with shared cache should use cachedFetchJson to coalesce concurrent misses. With 8 region pills and a user clicking quickly, multiple concurrent edge function invocations could each miss the in-process cache and hit Upstash with the same key.

Findings

• server/worldmonitor/forecast/v1/get-forecasts.ts:17 — uses getCachedJson directly without cachedFetchJson wrapper.
• CLAUDE.md "Cache Stampede: Use cachedFetchJson (Critical Pattern)" — established rule for all RPC handlers with shared cache.

Proposed Solutions

Option 1: Wrap in cachedFetchJson

Wrap the read in cachedFetchJson with a 30-60s in-process TTL keyed by forecast:predictions:v2.

Pros: Matches project convention; concurrent identical requests share one Redis round-trip; documented pattern; minimal diff. Cons: None significant. Effort: Small. Risk: Low.

Recommended Action

Option 1. Separate from PR #2942 scope but highlighted by it — the forecast panel's region pills (see #178) multiply concurrent reads, making the stampede window measurably hit.

Technical Details

cachedFetchJson (in server/_shared/redis.ts) coalesces concurrent cache misses via an in-process Map<key, Promise>. The first request issues the Redis GET; parallel requests await the same promise. When the promise resolves, all waiters receive the result without additional Redis traffic.

Per CLAUDE.md:

1. Wrap in try-catch for stale/backup fallback.
2. Await stale/backup cache writes (Edge runtimes may terminate isolate).

Cache key: forecast:predictions:v2 (match the Redis key). In-process TTL: 30-60s is the canonical window used by other handlers in this directory.

Acceptance Criteria

• get-forecasts.ts uses cachedFetchJson per the CLAUDE.md cache stampede rule.
• Concurrent identical RPC requests share a single in-flight Redis read.
• Stale/backup fallback path is exercised via try-catch.
• Test: 10 parallel identical RPC calls produce 1 Redis GET.

Work Log

Resources

• PR #2942
• Spec: docs/internal/pro-regional-intelligence-upgrade.md
• CLAUDE.md: "Cache Stampede: Use cachedFetchJson (Critical Pattern)"