Read a rebuild of an unchanged source as no move, whatever image digest it made (hq issue 280)

An image is not byte-reproducible, so ADR 0236's 'same artifacts is no move'
never held for one: a catalogue merge that did not touch the bus rebuilt it,
and every send to the control node waited for a planned bus upgrade.

The builder now records a source fingerprint per build (module tree, context
trees, bases and toolchains by digest). A rebuild with the fingerprint of the
build it repeats is registered with that build's artifacts, handed to modules
standing on it, holds no push, demands no bus step, and a plan sends and
gates nothing for it. Identical artifacts remain a second way to be no move.

cmd/mesh-controller/release_plan.go

@@ -620,6 +620,20 @@ func advanceOnce(ctx context.Context, open *stores, p *inventory.Plan,
 		if err != nil {
 			return false, err
 		}
+		// **A build whose source is unchanged is never a move** (novox/hq issue 280): made from the source
+		// of the build every machine running it was sent, it is registered with that build's artifacts —
+		// nothing to send, and nothing for a gate to judge.
+		if state.FirstAt == nil {
+			if same, err := unchangedOnEvery(ctx, inv, m, state.Build, running); err != nil {
+				return false, err
+			} else if same {
+				now := time.Now().UTC()
+				state.SentAt = &now
+				state.Why = "no move: made from the source every machine running it runs"
+				fmt.Printf("%s: %s built from the source every machine running it runs: no move, nothing sent\n", p.ID, m)
+				continue
+			}
+		}
 		policy, err := inv.UpgradeOf(ctx, m)
 		if err != nil {
 			return false, err