Project sequence origins onto appended indexes

docs/roadmap/implementation.md

@@ -291,6 +291,21 @@ Scope: composition evidence, not import acquisition.
 Validation: composition/provenance/path tests and `./scripts/check.sh`.
 Completion: correct trees and effective origins share the same record ordering.
 
+Completion evidence: composition origins now traverse each source document with
+separate local and effective semantic paths. Stage 2's source ranges shift list
+items and descendants to assigned indexes while retaining each field's physical
+location and contributor order at sequence containers; conflict claims remain
+source-local. Tests cover a later source's local index zero becoming effective
+index one, mounted and escaped/numeric-key paths, multiple collections, and
+detached origins, claims, ranges, and input trees. These checks passed with Go
+`go1.26.9 linux/amd64`:
+
+- `GOTOOLCHAIN=local GOPROXY=off go test ./internal/engine -run 'Compose|Provenance|Path' -count=1`
+- `GOTOOLCHAIN=local ./scripts/check.sh`
+- `git diff --check`
+
+No environmental limitation affected validation; checks ran on Linux/amd64.
+
 ## Stage 4 — Preserve append history and whole-list tier replacement
 
 Scope: private history operations, replay, and precedence handoff.

internal/engine/compose.go

@@ -116,7 +116,7 @@ func composeDocumentsWithPolicy(policy sequencePolicy, inputs ...*document.Node)
 	for _, input := range inputs {
 		applications = append(applications, historyApplication{layer: LayerBase, value: input})
 	}
-	origins := compositionOrigins(collected.ordered)
+	origins := projectedCompositionOrigins(inputs, ranges)
 	completeCompositionOrigins(root, Path{}, origins)
 	return &composedDocument{
 		root:           root,
@@ -337,18 +337,51 @@ func documentEntryIndex(entries []document.Entry, key string) int {
 	return -1
 }
 
-func compositionOrigins(claims []compositionClaim) map[string]Origin {
-	origins := make(map[string]Origin, len(claims))
-	for _, claim := range claims {
-		pointer := claim.path.String()
-		origin := origins[pointer]
-		origin.Layer = LayerBase
-		origin.Locations = append(origin.Locations, claim.location)
-		origins[pointer] = origin
+func projectedCompositionOrigins(inputs []*document.Node, ranges []sequenceRange) map[string]Origin {
+	origins := make(map[string]Origin)
+	rangeBySourcePath := make(map[sequenceRangeKey]int, len(ranges))
+	for index, assigned := range ranges {
+		rangeBySourcePath[sequenceRangeKey{sourceIndex: assigned.sourceIndex, path: assigned.path.String()}] = index
+	}
+	for sourceIndex, input := range inputs {
+		collectProjectedCompositionOrigins(input, Path{}, Path{}, sourceIndex, ranges, rangeBySourcePath, origins)
 	}
 	return origins
 }
 
+type sequenceRangeKey struct {
+	sourceIndex int
+	path        string
+}
+
+// Keep local paths for matching Stage 2 ranges and effective paths for emitted
+// evidence. The paths are transformed segment by segment; pointer strings are
+// only used as map keys after projection is complete.
+func collectProjectedCompositionOrigins(node *document.Node, localPath, effectivePath Path, sourceIndex int, ranges []sequenceRange, rangeBySourcePath map[sequenceRangeKey]int, origins map[string]Origin) {
+	pointer := effectivePath.String()
+	origin := origins[pointer]
+	origin.Layer = LayerBase
+	origin.Locations = append(origin.Locations, publicLocation(node.Location))
+	origins[pointer] = origin
+
+	switch node.Kind {
+	case document.Mapping:
+		for _, entry := range node.Mapping {
+			collectProjectedCompositionOrigins(entry.Value, localPath.Key(entry.Key), effectivePath.Key(entry.Key), sourceIndex, ranges, rangeBySourcePath, origins)
+		}
+	case document.Sequence:
+		start := 0
+		if rangeIndex, ok := rangeBySourcePath[sequenceRangeKey{sourceIndex: sourceIndex, path: localPath.String()}]; ok {
+			start = ranges[rangeIndex].start
+		}
+		for index, child := range node.Sequence {
+			localChild := localPath.Index(index)
+			effectiveChild := effectivePath.Index(start + index)
+			collectProjectedCompositionOrigins(child, localChild, effectiveChild, sourceIndex, ranges, rangeBySourcePath, origins)
+		}
+	}
+}
+
 func applyCompositionOrigins(decoded *decodedConfiguration, origins map[string]Origin) {
 	for pointer, origin := range origins {
 		if _, present := decoded.presence[pointer]; present {

internal/engine/compose_test.go

@@ -220,6 +220,96 @@ func TestComposeDocumentsAppendsRegisteredSequencesAndReturnsRanges(t *testing.T
 	}
 }
 
+func TestComposeDocumentsProjectsSequenceOriginsToAssignedIndexes(t *testing.T) {
+	first := parseCompositionDocument(t, "source-1", `mounted:
+  records:
+    - id: first
+      name: first-name
+escaped/~:
+  "7":
+    - id: escaped-first
+      name: escaped-first-name
+`)
+	second := parseCompositionDocument(t, "source-2", `mounted:
+  records:
+    - id: second
+      name: second-name
+escaped/~:
+  "7":
+    - id: escaped-second
+      name: escaped-second-name
+`)
+	firstBefore, secondBefore := document.Clone(first), document.Clone(second)
+	policy := sequencePolicy{identityFields: map[string]string{
+		Keys("mounted", "records").String(): "id",
+		Keys("escaped/~", "7").String():     "id",
+	}}
+
+	composed, diagnostics := composeDocumentsWithPolicy(policy, first, second)
+	if len(diagnostics) != 0 {
+		t.Fatalf("composeDocumentsWithPolicy() diagnostics = %#v", diagnostics)
+	}
+	for _, test := range []struct {
+		path Path
+		want Location
+	}{
+		{path: Keys("mounted", "records").Index(1).Key("name"), want: Location{SourceID: "source-2", Line: 4, Column: 13}},
+		{path: Keys("escaped/~", "7").Index(1).Key("name"), want: Location{SourceID: "source-2", Line: 8, Column: 13}},
+	} {
+		path, want := test.path, test.want
+		origin, ok := composed.origins[path.String()]
+		if !ok || !reflect.DeepEqual(origin.Locations, []Location{want}) {
+			t.Errorf("origin at %s = %#v, want source-specific location %#v", path, origin, want)
+		}
+	}
+	for _, test := range []struct {
+		path        Path
+		wantSources []string
+	}{
+		{path: Keys("mounted", "records"), wantSources: []string{"source-1", "source-2"}},
+		{path: Keys("escaped/~", "7"), wantSources: []string{"source-1", "source-2"}},
+	} {
+		path, wantSources := test.path, test.wantSources
+		origin := composed.origins[path.String()]
+		gotSources := make([]string, len(origin.Locations))
+		for index, location := range origin.Locations {
+			gotSources[index] = location.SourceID
+		}
+		if !reflect.DeepEqual(gotSources, wantSources) {
+			t.Errorf("container origin at %s = %#v, want contributors %#v", path, gotSources, wantSources)
+		}
+	}
+	if !reflect.DeepEqual(first, firstBefore) || !reflect.DeepEqual(second, secondBefore) {
+		t.Fatal("composition projection mutated an input")
+	}
+
+	copy := cloneComposedDocument(composed)
+	copy.origins[Keys("mounted", "records").Index(1).Key("name").String()].Locations[0].SourceID = "changed"
+	for index := range copy.claims {
+		if copy.claims[index].path.String() == "/mounted/records" {
+			copy.claims[index].path.segments[0].key = "changed"
+			break
+		}
+	}
+	copy.sequenceRanges[0].path.segments[0].key = "changed"
+	if got := composed.origins[Keys("mounted", "records").Index(1).Key("name").String()].Locations[0].SourceID; got != "source-2" {
+		t.Fatalf("copied origin mutation changed source evidence: %q", got)
+	}
+	foundClaim := false
+	for _, claim := range composed.claims {
+		if claim.path.String() == "/mounted/records" {
+			foundClaim = true
+			break
+		}
+	}
+	if !foundClaim {
+		t.Fatal("copied claim mutation changed source path")
+	}
+	if got := composed.sequenceRanges[0].path.String(); got != "/mounted/records" {
+		t.Fatalf("copied range mutation changed assigned path: %q", got)
+	}
+}
+
 func TestComposeDocumentsValidatesRegisteredSequenceSingletons(t *testing.T) {
 	tests := []struct {
 		name     string