fix(fuel): enable week-on-week price diff computation

[koala73]

Summary

• Remove observedAt guard in WoW computation that silently skipped nearly all countries when the EU XLSX source date didn't change between weekly runs
• Only rotate current data to :prev snapshot when existing prev is 6+ days old, preventing fresh backfill data from being overwritten

Context

The fuel prices panel has had wowAvailable: false since launch. Root cause: the observedAt !== prev.observedAt check on lines 656/665 required different source observation dates between runs. The EU Oil Bulletin XLSX (covering 27 countries) often publishes the same observation date across consecutive weekly updates, causing WoW to be skipped for the majority of countries.

The prevAge check (6-day minimum) already prevents stale comparisons, and the 15% anomaly threshold catches data bugs, making the observedAt guard both redundant and harmful.

Additionally, the extraKeys unconditionally overwrote :prev on every run, which meant running a backfill followed by the seeder would immediately clobber the backfill data.

Verification

Manually backfilled March 23 EU prices from the EC historical XLSX, ran the fixed seeder: 27/32 countries now show WoW arrows in production.

Test plan

• Verified wowAvailable: true in Redis after seeder run
• 27/32 countries have wowPct values (missing: MY gasoline=0, MX API down, BR/NZ/UK no prev)
• Anomaly threshold correctly flags MY diesel (-90.94%)
• npm run typecheck passes

[vercel]

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
worldmonitor	Ignored	Preview	Apr 2, 2026 4:05pm

[greptile-apps]

Greptile Summary

This PR fixes two root causes that kept wowAvailable: false since launch: (1) the observedAt !== prev.observedAt guard silently skipped WoW for the 27 EU countries because the EC Oil Bulletin XLSX reuses the same observation date across consecutive weekly publishes, and (2) extraKeys unconditionally overwrote :prev on every run, clobbering any manually backfilled historical snapshot. The new shouldRotatePrev flag (!hasPrevData || !prevTooRecent) correctly skips the rotation only when a fresh prev snapshot already exists (< 6 days old), preserving backfill data for the next scheduled run. Logic has been verified in production with 27/32 countries now showing WoW arrows.

Confidence Score: 5/5

• Safe to merge — both changes are logically correct and production-verified.
• All remaining findings are P2 (readability). The core logic of removing the observedAt guard and the shouldRotatePrev gate is sound: the three state cases (no prev, prev too recent, prev old enough) are all handled correctly, and the 6-day minimum age + 15% anomaly threshold provide adequate data-quality protection in place of the removed guard.
• No files require special attention.

Important Files Changed

Filename	Overview
scripts/seed-fuel-prices.mjs	Removes the over-restrictive observedAt guard on WoW computation and adds a shouldRotatePrev gate to prevent fresh backfill snapshots from being overwritten; logic is correct and verified in production.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Seeder starts\nreads CANONICAL_KEY:prev] --> B{hasPrevData?}
    B -- No --> C[wowAvailable = false\nshouldRotatePrev = true]
    B -- Yes --> D{prevTooRecent?\nprevAge < 6 days}
    D -- Yes\nbackfill guard --> E[wowAvailable = false\nshouldRotatePrev = false]
    D -- No\nnormal weekly run --> F[wowAvailable = true\nshouldRotatePrev = true]
    F --> G[Compute WoW per country\nguarded by 15% anomaly threshold]
    G --> H[Write data to CANONICAL_KEY\nWrite data to :prev]
    C --> I[Write data to CANONICAL_KEY\nWrite data to :prev\nseed initial snapshot]
    E --> J[Write data to CANONICAL_KEY\nPreserve :prev backfill]

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_{Reviews (1): Last reviewed commit: "fix(fuel): enable week-on-week price dif..." | Re-trigger Greptile}

[greptile-apps]

Readability of shouldRotatePrev expression

The expression !hasPrevData || !prevTooRecent is a double-negation that requires a moment to parse. It is equivalent to !(hasPrevData && prevTooRecent) — i.e., "rotate unless we have fresh prev data." A brief inline comment (or a positive rewrite) would make the intent immediately clear to the next reader.

Suggested change

	const shouldRotatePrev = !hasPrevData || !prevTooRecent;
	const shouldRotatePrev = !hasPrevData || !prevTooRecent; // rotate unless prev exists AND is too recent (backfill guard)

_{Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!}