create_model: default max_consumption into fixed_params

The runtime-upper-bound change requires every caller to supply
`max_consumption` via `fixed_params`; estimation tasks (e.g.
`task_simulate_aca`) hit a `KeyError` mid-pipeline because they
construct the model from data-derived `fixed_params` that have no
reason to mention a grid bracket. Centralise the default in both
`baseline.model.create_model` and `aca.model.create_model` so
existing callers keep working with the prior 300k bracket and only
opt-in callers need to override.

Author: hmgaudecker

src/aca_model/aca/model.py

@@ -11,6 +11,7 @@
 
 from aca_model.aca import PolicyVariant
 from aca_model.aca.regimes import build_all_regimes
+from aca_model.baseline.model import _with_max_consumption_default
 from aca_model.baseline.regimes import RegimeId
 from aca_model.config import GRID_CONFIG, MODEL_CONFIG, GridConfig
 
@@ -51,6 +52,7 @@ def create_model(
         stop=MODEL_CONFIG.end_age - 1,
         step="Y",
     )
+    fixed_params = _with_max_consumption_default(fixed_params)
     regimes = build_all_regimes(
         policy=policy,
         grid_config=grid_config,
@@ -63,6 +65,6 @@ def create_model(
         ages=ages,
         regime_id_class=RegimeId,
         description=f"Structural retirement model ({policy.name})",
-        fixed_params=fixed_params or {},
+        fixed_params=fixed_params,
         derived_categoricals=derived_categoricals,
     )

src/aca_model/baseline/model.py

@@ -18,6 +18,11 @@
 from aca_model.baseline.regimes import RegimeId, build_all_regimes
 from aca_model.config import GRID_CONFIG, MODEL_CONFIG, GridConfig
 
+_DEFAULT_MAX_CONSUMPTION: float = 300_000.0
+"""Upper bound of the consumption grid in $/year. Brackets the unconstrained
+CRRA optimum for the highest-asset, highest-income agents in the state space.
+Callers can override by passing `max_consumption` in `fixed_params`."""
+
 
 def create_model(
     *,
@@ -59,6 +64,7 @@ def create_model(
         stop=MODEL_CONFIG.end_age - 1,
         step="Y",
     )
+    fixed_params = _with_max_consumption_default(fixed_params)
     regimes = build_all_regimes(
         grid_config,
         fixed_params=fixed_params,
@@ -71,6 +77,15 @@ def create_model(
         ages=ages,
         regime_id_class=RegimeId,
         description="Baseline structural retirement model (pre-ACA)",
-        fixed_params=fixed_params or {},
+        fixed_params=fixed_params,
         derived_categoricals=derived_categoricals,
     )
+
+
+def _with_max_consumption_default(
+    fixed_params: Mapping[str, Any] | None,
+) -> dict[str, Any]:
+    """Return a copy of `fixed_params` with `max_consumption` defaulted."""
+    out = dict(fixed_params or {})
+    out.setdefault("max_consumption", _DEFAULT_MAX_CONSUMPTION)
+    return out