fix: use num_ib_patches_max_namelist in Python toolchain for patch_ib limit

NIB and the case_validator both now reference num_ib_patches_max_namelist
(50000) instead of num_ib_patches_max (2050000). This constant is the
actual namelist limit; particle beds grow patch_ib beyond it at runtime
but those entries are never specified in the namelist. The fallback values
match the constant, ensuring Homebrew installs (which lack m_constants.fpp)
use the correct limit.

Author: sbryngelson

toolchain/mfc/case_validator.py

@@ -601,10 +601,10 @@ def check_ibm(self):
             ib and num_ibs <= 0 and not has_particle_beds,
             "num_ibs must be >= 1 when ib is enabled (or specify at least one particle_bed with num_particles > 0)",
         )
-        num_ib_patches_max = get_fortran_constants().get("num_ib_patches_max", 100000)
+        num_ib_patches_max = get_fortran_constants().get("num_ib_patches_max_namelist", 50000)
         self.prohibit(
             ib and num_ibs > num_ib_patches_max,
-            f"num_ibs must be <= {num_ib_patches_max} (num_ib_patches_max in m_constants.fpp)",
+            f"num_ibs must be <= {num_ib_patches_max} (num_ib_patches_max_namelist in m_constants.fpp)",
         )
         self.prohibit(not ib and num_ibs > 0, "num_ibs is set, but ib is not enabled")
         self.prohibit(ib_state_wrt and not ib, "ib_state_wrt requires ib to be enabled")

toolchain/mfc/params/definitions.py

@@ -31,7 +31,7 @@ def _fc(name: str, default: int) -> int:
 NPR = _fc("num_probes_max", 10)  # probe, acoustic, integral
 NB = _fc("num_bc_patches_max", 10)  # patch_bc
 NUM_PATCHES_MAX = _fc("num_patches_max", 10)  # patch_icpp (Fortran array bound)
-NIB = _fc("num_ib_patches_max", 50000)   # patch_ib (Fortran array bound)
+NIB = _fc("num_ib_patches_max_namelist", 50000)  # patch_ib namelist limit (patch_ib grows beyond this for particle beds)
 NPB = _fc("num_particle_beds_max", 10)  # particle_bed (Fortran array bound)
 # Enumeration limits for families not yet converted to IndexedFamily.
 # These are smaller than the Fortran array bounds to keep the registry compact.
@@ -1184,9 +1184,8 @@ def _load():
         _r(f"bub_pp%{a}", REAL, {"bubbles"}, math=sym)
 
     # patch_ib (immersed boundaries) — registered as indexed family for O(1) lookup.
-    # max_index is None so the parameter registry stays compact (no enumeration).
-    # The Fortran-side upper bound (num_ib_patches_max in m_constants.fpp) is parsed
-    # and enforced by the case_validator, not by max_index here.
+    # max_index=NIB enforces the namelist limit (num_ib_patches_max_namelist); particle beds can
+    # grow patch_ib beyond this at runtime, but those entries are never in the namelist.
     _ib_tags = {"ib"}
     _ib_attrs: Dict[str, tuple] = {}
     for a in ["geometry", "moving_ibm"]: