Register R237: assign's answer agrees with plan right after the act (hq issue 237)

Rebase of #81 (a020f60) onto main after #80 (R358) merged into the same
spot in register.go. The R237 block is byte-identical to the one approved
at a020f60; only its place in the file differs, now after R358.

Proved with go run ./cmd/prove R237: fails on mesh-controller #253's commit
before (72edb45), passes on the fix (5facd8b, mesh-controller #253).
TestReplay237 needs MESH_TEST_POSTGRES (inventory.ForTest raises a throwaway
database), same as the controller's other store-backed replays.

replays/register.go

@@ -327,6 +327,21 @@ var Register = []Replay{
 			"and the account that could have made it",
 		Package: "./internal/apply", Test: "TestAParentSwappedForALinkLeavesItsTargetUntouched",
 		Files: []string{"internal/apply/replay358_test.go"}},
+	// assign said two things that could not both be true (2026-10-04): a workstation already ran a module
+	// contributing node-hotkeys, and the module holding that seat was assigned to it; the answer said in
+	// order that the seat was now held, then that the node was left out of the rest of the mesh for lack
+	// of it, naming the assignment just made as the remedy. `plan` for the node right after resolved. A
+	// test in the controller, written with only what it had before its fix — register, assign's command,
+	// planFor — laid over the commit before. Needs a store: raised by inventory.ForTest against
+	// MESH_TEST_POSTGRES, same as the controller's other store-backed replays. Fix is the merge of its
+	// pull request (mesh-controller #253).
+	{ID: "R237", Issue: 237, Kind: InRepository, Repository: "mesh-controller", Fix: "5facd8b08e245545fb7656dd4af11280d9306a08",
+		What: "assign on a workstation already running a module that contributed node-hotkeys, after " +
+			"assigning the module holding that seat, said the seat was now held and then that the node was " +
+			"left out of the mesh for lack of it, naming the assignment just made as the remedy",
+		Asserts: "every line of assign's answer is derived from one resolution of the node taken after the " +
+			"write committed, and agrees with plan for the node run right after the act",
+		Package: "./cmd/mesh-controller", Test: "TestReplay237", Files: []string{"cmd/mesh-controller/replay237_test.go"}},
 	// Not a core incident, and the first of its kind: a module's. The crash loop was found by a person
 	// reading the agent server's log for another reason (issue 268); research 032 measured it, and ADR
 	// 0240 makes the node-engine judge it and the gate fail it.