Keep assignments in the assignments bucket and move the rows there at start (issue 1093)

Once chain_moved records the kind, Assign, Unassign and Assigned write and read the keys <node>.<module>, and every join of the store that read assignments is made from the bucket: where a module runs, what is behind, what a machine awaits, a given value due for replacement, taking a module, and whether a module may be forgotten (refused while a standing assignment names it). An unassignment ends the key with a marker and keeps its earlier values, as it removed the row; no ended or pending mark is written yet. The generation rises with each change, and a seat held by an assignment goes with it: the foreign key from seat_holding is dropped by migration 0104 and the controller says both. The provisioner's plan is kept in the values by a pass of the tick that writes that one field by compare-and-set; the assignment-changed event is said from what the bucket holds, whoever wrote it. The start moves the rows with what each machine was last sent, keeping a plan the mirror put in a value.

internal/inventory/sends_test.go

@@ -22,9 +22,8 @@ func generationNow(t *testing.T, inv *Inventory) int64 {
 	return g
 }
 
-// **Every change to what is assigned where raises the generation, in its own transaction** — an
-// assignment, an unassignment, and one taken by the machine's removal, which no writer in Go makes — and
-// a repeated assignment, which changes nothing, does not.
+// **Every change to what is assigned where raises the generation** — an assignment and an unassignment — and a repeated
+// assignment, which changes nothing, does not.
 func TestEveryAssignmentChangeRaisesTheGeneration(t *testing.T) {
 	inv, node := aNodeWithModules(t, "postgres", "web")
 	ctx := t.Context()
@@ -52,16 +51,8 @@ func TestEveryAssignmentChangeRaisesTheGeneration(t *testing.T) {
 	if unassigned <= assigned {
 		t.Fatalf("an unassignment left the generation at %d", unassigned)
 	}
-	if _, err := inv.Assign(ctx, node, "web"); err != nil {
-		t.Fatal(err)
-	}
-	before := generationNow(t, inv)
-	if _, err := inv.RemoveNodeForTest(ctx, node); err != nil {
-		t.Fatal(err)
-	}
-	if removed := generationNow(t, inv); removed <= before {
-		t.Errorf("a machine's removal took its assignments and left the generation at %d", removed)
-	}
+	// A machine's removal, which no verb makes, is read from the machines the store knows: an assignment on a machine it
+	// does not know is none (assignments in the bucket have no key of the store to cascade through).
 }
 
 // **The generation never goes down, and is raised past what a machine applied when the mesh's own counter
@@ -175,22 +166,6 @@ func TestASendRecordThatCannotBeWrittenLeavesTheMachinesRecord(t *testing.T) {
 	}
 }
 
-// **An update that leaves an assignment as it was raises nothing** (the trigger's WHEN).
-func TestAnUpdateThatChangesNoAssignmentRaisesNothing(t *testing.T) {
-	inv, node := aNodeWithModules(t, "web")
-	ctx := t.Context()
-	if _, err := inv.Assign(ctx, node, "web"); err != nil {
-		t.Fatal(err)
-	}
-	before := generationNow(t, inv)
-	if _, err := inv.store.Pool().Exec(ctx, `update assignment set module = module`); err != nil {
-		t.Fatal(err)
-	}
-	if after := generationNow(t, inv); after != before {
-		t.Errorf("an update that changed nothing moved the generation from %d to %d", before, after)
-	}
-}
-
 // **A machine that reads a generation is recorded from its reports**, and one rolled back says so no longer.
 func TestWhetherAMachineReadsAGenerationIsItsLatestWord(t *testing.T) {
 	inv, node := aNodeWithModules(t)