BL18: build modules found through their build seats' holders on the seat list

The builder finds a build module as the indexer's seed does: the build seat whose acting rule
`build` has an `on` matching the artifact's language or kind:image, and that seat's holder, read
from the seat list's definitions and the claims of the catalog half's manifests. Task.Module, every
lane key, the unpublished modules, the toolchain sources, the ends watched, the sayer and
builder_stuck (through `<seat>.steps`) derive from it; the floor's sources are the holders of the
seats git and mesh-catalog. buildrun.GoBuildModule, NodeBuildModule, LanguageOf,
buildstep.BuildModuleOf use, build.ImageBuildModule and StuckBuildModules are gone from the builder
(the checker keeps its own names in two small files until its part reads them from the list).

Builds: design 47 G §7, §428, §704, §204, A-82
Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

modules/mesh-delivery-builder/module.json

@@ -13,6 +13,8 @@
   ],
   "tools": [
     "builder_announce_again",
+    "builder_seat_list",
+    "builder_seat_list_again",
     "builder_ask_again",
     "builder_bounds",
     "builder_build_again",
@@ -51,6 +53,8 @@
     "go-package-registry.removed",
     "mesh-artifact-sweep.artifacts-gone",
     "mesh-catalog.manifest-accepted",
+    "mesh-catalog.seat-definition-changed",
+    "mesh-catalog.seat-definition-removed",
     "mesh-catalog.version-released",
     "mesh-catalog.versions-filled",
     "mesh-conditions.condition-cleared",
@@ -96,6 +100,7 @@
     "mesh-delivery-assigner.assigner_read_assignments",
     "seat:mesh-catalog.entry",
     "seat:mesh-catalog.registrations",
+    "seat:mesh-catalog.seat-definitions",
     "seat:mesh-catalog.revision",
     "seat:mesh-delivery.source"
   ],
@@ -134,9 +139,9 @@
     { "name": "build-log", "max-age-days": 30, "max-mib": 3072 }
   ],
   "reads": [
-    "mesh-build-go.steps",
-    "mesh-build-image.steps",
-    "mesh-build-node.steps",
+    "node-build-go.steps",
+    "node-build-image.steps",
+    "node-build-node.steps",
     "mesh-delivery-assigner.assignments",
     "mesh-delivery-gate.source"
   ],