Write into a marked block of a text file instead of over it, so a shared hosts file keeps every line that is not the mesh's (hq issue 128)

internal/store/store.go

@@ -84,7 +84,7 @@ type Applied struct {
 	Reads map[string]string `json:"reads,omitempty"`
 }
 
-// Into is what a file written into held before the mesh's keys.
+// Into is what a file written into held before the mesh's keys, or before the mesh's block.
 type Into struct {
 	Format  string                     `json:"format"`
 	Before  map[string]json.RawMessage `json:"before,omitempty"`
@@ -94,6 +94,19 @@ type Into struct {
 	// to the machine's list — never a member that was already there. Undeclared, only these go,
 	// and drift is judged on these alone (novox/hq ADR 0102).
 	Added map[string][]json.RawMessage `json:"added,omitempty"`
+
+	// Region is, for a file written into a block (novox/hq issue 128), what the lines between the
+	// mesh's markers held before the mesh wrote them — nil when there was no region, which is
+	// different from a region that was there and empty. Undeclared, a recorded region is put back
+	// and an unrecorded one is taken out, markers and all. It is the block's "what each key held
+	// before": the one thing the host needs to give the file back.
+	Region *string `json:"region,omitempty"`
+	// Separated says the host put a blank line between the region and the machine's lines when it
+	// added the region — before it at the end, after it at the start, as At says — so taking the
+	// region out takes that line with it and nothing of the operator's.
+	Separated bool `json:"separated,omitempty"`
+	// At is where the host added the region: "start", or empty for the end.
+	At string `json:"at,omitempty"`
 }
 
 // State is the whole of what a node knows about what it has done.