Cast time_period to string before posting to simulation gateway

The policyengine-api-v2 simulation gateway (PR #458, deployed in v42 on
2026-04-26) tightened its request schema to require time_period as
Optional[str]. The locally-installed policyengine PyPI package
(PolicyEngine/policyengine.py, commit 29f2c1a 2025-01-28) declares
TimePeriodType = int on SimulationOptions.time_period, so
model_validate() coerces incoming string years to int and model_dump()
re-emits them as int. The gateway then 422s every economy-comparison
request.

Cast time_period to str on the dict produced by model_dump() right
before passing to simulation_api.run(), without changing the
SimulationOptions schema. This is the minimum-surface fix on the
caller side; downstream simulation code that consumes time_period as
int is unaffected because that work happens after the gateway has
deserialized the body.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: DTrim99

changelog.d/fix-cast-time-period-string-for-gateway.fixed.md

@@ -0,0 +1 @@
+Cast time_period to string before posting to the simulation gateway. The gateway's request schema (policyengine-api-v2 PR #458) requires Optional[str], but the local policyengine package's SimulationOptions.TimePeriodType is int and model_dump re-emits int, which the gateway 422s.

policyengine_api/services/economy_service.py

@@ -511,6 +511,15 @@ def _handle_create_impact(
         }
         sim_params["_telemetry"] = telemetry
 
+        # The simulation gateway (policyengine-api-v2 PR #458) requires
+        # ``time_period`` as a string, but the upstream ``policyengine``
+        # package (``TimePeriodType = int``) coerces the value to int during
+        # ``model_validate`` and ``model_dump`` re-emits it as int. Cast back
+        # to str at the request boundary so the gateway's strict schema
+        # validates instead of returning 422.
+        if sim_params.get("time_period") is not None:
+            sim_params["time_period"] = str(sim_params["time_period"])
+
         sim_api_execution = simulation_api.run(sim_params)
         execution_id = simulation_api.get_execution_id(sim_api_execution)
         run_id = getattr(sim_api_execution, "run_id", None) or telemetry["run_id"]