Stop serving economy results cached with ×100 decile relative changes #4025

What's wrong

Since the simulation API moved to .py 4.x, it has returned decile.relative, and for the UK wealth_decile.relative, as percentages (multiplied by 100) instead of fractions. Production economy results have carried these values since 2026-06-29, when the Public API started requesting .py 4.18.3. The simulation API bug is PolicyEngine/policyengine-sim-api#827, and its fix, which divides these values by 100 when the decile output is built, is PolicyEngine/policyengine-sim-api#904.

Why the Public API also needs a change

The Public API caches economy results in Redis for 30 days. A later request finds a cached result by its scope (country, policy pair, region, dataset and period), the economy cache version, and the options hash. None of these change when only the simulation API's code changes. So once #904 is deployed, results already cached for the current .py version (6.7.5) would keep being served with the multiplied-by-100 values until they expire.

What to change

Raise RUNTIME_CACHE_SCHEMA_VERSIONS["economy_impact"] in policyengine_api/constants.py from 3 to 4. get_economy_impact_cache_version builds the economy cache version from it, so lookups stop finding results stored under version 3 and those results are recomputed. The budget-window cache key uses the same version, so budget-window results are recomputed too.

The change should be merged only after PolicyEngine/policyengine-sim-api#904 is merged and deployed to the simulation app the Public API uses (policyengine-simulation-py6-7-5 today). Merging earlier would recompute results that still carry the multiplied-by-100 values.

Not covered

Report outputs already saved to v1 report records keep the multiplied-by-100 values. Correcting them needs a separate follow-up.