State trgeometry as a reference geometry and a temporal pose in the type registry

docs/cross-repo-handoff.md

@@ -57,11 +57,13 @@ results across all three platforms using the bare names only.
 - **`cbuffer`, `npoint`, `pose`, `rgeo` are full user-facing temporal
   types**, covered like every other type; they are never excluded from a
   parity headline.
-- **One base type carries several temporal types.** A geometry is the base of
-  `tgeompoint` and `tgeometry`, a geography of `tgeogpoint` and `tgeography`,
-  a pose of `tpose` and `trgeometry`. `typeRelations.byBase[...].temporal` is a
-  list for that reason, one entry or several, so a consumer reads one shape;
-  taking a single name loses three types MEOS has.
+- **The instants of several temporal types store one base type.** Those of
+  `tgeompoint` and `tgeometry` store a geometry, of `tgeogpoint` and `tgeography`
+  a geography, of `tpose` and `trgeometry` a pose. `typeRelations.byBase[...].temporal`
+  is a list for that reason, one entry or several, so a consumer reads one shape;
+  taking a single name loses three types MEOS has. A `trgeometry` is not
+  `Temporal<pose>`: it is the concatenation of a reference geometry and a temporal
+  pose, its value at an instant the geometry the stored pose places.
 - **A surface that speaks MF-JSON reads the type token from
   `temporalTypes[...].mfjson`.** It differs per type and MEOS states it in one
   place, `temptype_as_mfjson_sb`. A type the switch does not name carries no

parser/typerelations.py

@@ -8,9 +8,13 @@
 and resolving through the names yields, for each base type name, the names of
 its set, span, span set and temporal types.
 
-``Temporal<T>`` is the one template a base instantiates more than once, so the
-``temporal`` role is a list: a geometry carries ``tgeompoint`` and ``tgeometry``,
-a pose carries ``tpose`` and ``trgeometry``.
+The ``temporal`` role names every temporal type whose instants store a value of the
+base, the inverse of ``temptype_basetype``, so it is a list: the instants of
+``tgeompoint`` and ``tgeometry`` store a geometry, and those of ``tpose`` and
+``trgeometry`` a pose. A ``trgeometry`` is not ``Temporal<pose>``: it is the
+concatenation of a reference geometry and a temporal pose, each instant storing the
+pose that places the geometry, so its value at an instant is a geometry while
+``getValue`` reads the stored pose.
 
 This is the static metadata a binding generator needs to pick the concrete
 collection type of a value-domain result — ``SpanSet<float>`` is ``floatspanset``
@@ -135,8 +139,9 @@ def attach_type_relations(idl: dict, src_root: Path | None) -> dict:
                 related[role][meos_type] = fields[forward]
             if inverse in fields:
                 related[role][fields[inverse]] = meos_type
-        # A base names no temporal type of its own, and one base carries SEVERAL of them: a
-        # geometry is the base of tgeompoint and tgeometry, a pose of tpose and trgeometry. So
+        # A base names no temporal type of its own, and the instants of SEVERAL may store it:
+        # those of tgeompoint and tgeometry a geometry, those of tpose and trgeometry (a
+        # reference geometry and a temporal pose) a pose. So
         # the temporal role is the inverse of temptype_basetype, and it is every type naming
         # that base, in MeosType order. Keeping one of them drops the others from the registry
         # entirely, and a generator projecting the temporal types out of it then emits a