Keep rollouts and the merges they answer in the rollouts bucket (issue 1092)

Once chain_moved records the kind, a plan is a key of the rollouts bucket under its id and the open batch is the same key in state assembling. A save refuses a copy another save moved since (the plan's own Revision, kept in its value, counts saves) and keeps the merges the record holds, so a copy read before a merge moved cannot lay it back. The merges a batch or walk answers are the record's held field, with the columns the table had; a merge no plan answers stays, flagged, in the record that held it last, or in the record kept for those. A merge moved to a plan is written to the receiving record first and then taken from the giving one; one found in both is read from the one it entered last and repaired at the next cut. Plans and merges are read from a view kept by one watch of the bucket. A bus that does not answer, a lease lost and a key moved are now not-now like the store being away, so a merge whose plan could not be written is held and handed over again, never acknowledged. The start moves release_plan and batched_merge into the bucket, one kind, counted against both tables.

internal/inventory/chain.go

@@ -19,9 +19,14 @@ import (
 
 // The kinds of the chain, as chain_moved names them.
 const (
-	KindBuilds = "builds"
+	KindBuilds   = "builds"
+	KindRollouts = "rollouts"
 )
 
+// testChains are the chains in memory a test made for its store, by the store's address: every inventory opened on that
+// store is given the same chain, as every process of a mesh is on the same bus. Empty outside a test.
+var testChains sync.Map
+
 // ErrNoChain is a kind moved to the bus read by an inventory that has no chain attached: a process that did not
 // open the bus. Refused loudly, never answered from the tables the move left behind.
 var ErrNoChain = errors.New("this kind of record lives on the bus, and this process has not opened the bus")
@@ -32,6 +37,10 @@ type movedKinds struct {
 	mu   sync.Mutex
 	kind map[string]bool
 	open ChainOpener
+	// view is the rollouts bucket kept in memory by one watch (issue 1092); pending are the merges added to a plan that
+	// is not saved yet.
+	view    *rolloutView
+	pending map[string]pendingMerge
 }
 
 // ChainOpener opens the chain on the bus when a process first needs it: a command that reads and never moved anything has
@@ -51,6 +60,10 @@ func (i *Inventory) UseChain(c *chain.Chain) {
 	i.moved.mu.Lock()
 	defer i.moved.mu.Unlock()
 	i.chain = c
+	if i.moved.view != nil {
+		i.moved.view.stop()
+		i.moved.view = nil
+	}
 }
 
 // attached is the chain this inventory has, nil when none.