Move no module whose fingerprint is unchanged, and let a key's build stand on the held build-agent build of the same digests at the switch (issue 1851, A9)

internal/inventory/source.go

@@ -2,6 +2,8 @@ package inventory
 
 import (
 	"context"
+	"encoding/json"
+	"strings"
 
 	"github.com/novox/mesh-controller/internal/chain"
 )
@@ -43,6 +45,11 @@ func (i *Inventory) sourceRows(ctx context.Context, module string) (map[string][
 
 // standing is, of a module's builds newest first, the index of the build that stands for the build at
 // `from`: the oldest of the unbroken run of builds behind it with its source fingerprint.
+//
+// **Across the switch to the new form** (novox/hq ADR 0453 §6, ADR 0499; R4e A9): a build of the new form (`src2:`, taken
+// from the builder's key) continues the run of the build before it of the old form (`src1:` or none, build-agent's)
+// when every artifact of the two has the same digest: the fingerprints cannot be compared, the programs can, and equal
+// digests are no move. Past it the run goes on by the old fingerprint.
 func standing(builds []sourceRow, from int) int {
 	at := from
 	fp := builds[from].fingerprint
@@ -50,14 +57,53 @@ func standing(builds []sourceRow, from int) int {
 		return at
 	}
 	for j := from + 1; j < len(builds); j++ {
-		if builds[j].fingerprint != fp || builds[j].failedGate {
+		if builds[j].failedGate {
 			break
 		}
+		if builds[j].fingerprint != fp {
+			if !newForm(fp) || newForm(builds[j].fingerprint) || !sameDigests(builds[at].made, builds[j].made) {
+				break
+			}
+			fp = builds[j].fingerprint
+		}
 		at = j
 	}
 	return at
 }
 
+// newForm says a source fingerprint is of the new form (ADR 0453 §6).
+func newForm(fp string) bool { return strings.HasPrefix(fp, "src2:") }
+
+// sameDigests says two builds' artifacts, as recorded (JSON of []Artifact), are the same programs: the same names, each
+// with the same digest, wherever each was pushed. A build naming an artifact with no digest is never the same.
+func sameDigests(a, b []byte) bool {
+	digests := func(raw []byte) map[string]string {
+		var made []Artifact
+		if json.Unmarshal(raw, &made) != nil || len(made) == 0 {
+			return nil
+		}
+		out := map[string]string{}
+		for _, m := range made {
+			d := digestIn(m.Reference)
+			if d == "" {
+				return nil
+			}
+			out[m.Name] = d
+		}
+		return out
+	}
+	da, db := digests(a), digests(b)
+	if da == nil || db == nil || len(da) != len(db) {
+		return false
+	}
+	for name, d := range da {
+		if db[name] != d {
+			return false
+		}
+	}
+	return true
+}
+
 // StandingBuild is the build that stands for a module's build (novox/hq issue 280): the oldest build of
 // the unbroken run of builds with its source fingerprint, at or before it — itself when its fingerprint
 // is empty or it starts the run. Answers its id and the manifest it was recorded with; empty when the