feat(topdata): parts autogen from CDN part.yml channel (Phase 2) (#25)

Phase 2 of the parts-row autogen design — Crucible (sow-tools) side only.

Resolves parts 2DA rows from the immutable \`part.yml\` published with the asset HAK release, over the anonymous Bunny CDN channel, with the parts consumer **required** (no fail-open).

## Changes
- **Resolver (T3):** generalize \`resolveCDNChannelManifest\` — derive manifest basename + provenance label from config; drop hardcoded \`assets/vfxs.yml\` so \`part.yml\` resolves through the same path. VFX behavior unchanged.
- **Parts filter (T4):** \`filterCDNChannelEntries\` dispatches on consumer mode; new \`filterPartsCDNChannelEntries\` implements the inventory contract — \`restype: mdl\` under \`part/<supported-cat>/\`, row id from trailing digits, dedup l/r/race/gender variants by (category,rowID), sort by source, **zero accepted rows = hard fail**, reject row id 0 / non-numeric / malformed / no-assets.
- **Category (T5):** add \`hand\` + \`parts/hand\` mapping (12 datasets; \`leg→legs\` already present).
- **Pipeline (T6):** native build runs one explicit augment → normalize → override sequence under the configured \`parts_rows\` policy; overrides may update an existing/discovered row but **never synthesize** one (orphan override now errors).
- **Validation (T7):** reject more than one \`parts_rows\` consumer.

## Tests
9 new tests: parts filter contract, 12-dataset coverage, offline manifest-basename, orphan-override reject + discovered-row update, and a parity guard proving a bare CDN-only parts build needs no wrapper/token/NWN_ROOT/checkout.

Gate green: \`go test ./internal/topdata/... ./internal/project/...\` + full \`go build ./... && go test ./...\`.

## Scope / ordering
Phase 2 is inert until **Phase 1** (sow-assets-manifest publishes \`part.yml\`) ships and the operational **Gate** (release publish/promote) runs, then **Phase 3** enables the sow-topdata consumer. Do not enable the consumer against a channel whose current release predates \`part.yml\`.

Plan: \`sow-topdata/docs/superpowers/plans/2026-06-25-topdata-parts-autogen-channel.md\`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #25
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

internal/project/project.go

@@ -1581,6 +1581,15 @@ func validateAutogenConfig(cfg AutogenConfig) []error {
 
 func validateAutogenConsumerSources(consumers []AutogenConsumerConfig) []error {
 	var failures []error
+	partsRows := 0
+	for _, c := range consumers {
+		if strings.TrimSpace(c.Mode) == "parts_rows" {
+			partsRows++
+		}
+	}
+	if partsRows > 1 {
+		failures = append(failures, fmt.Errorf("at most one autogen consumer may use mode parts_rows; found %d (override precedence would be ambiguous)", partsRows))
+	}
 	for _, c := range consumers {
 		if strings.TrimSpace(c.Source.Kind) != "cdn_channel" {
 			continue

internal/project/project_test.go

@@ -1864,6 +1864,20 @@ func TestValidateAutogenConsumerSourcesCDNChannel(t *testing.T) {
 	}
 }
 
+func TestValidateRejectsMultiplePartsRowsConsumers(t *testing.T) {
+	consumers := []AutogenConsumerConfig{
+		{ID: "parts-a", Mode: "parts_rows"},
+		{ID: "parts-b", Mode: "parts_rows"},
+	}
+	if failures := validateAutogenConsumerSources(consumers); len(failures) == 0 {
+		t.Fatal("expected error for two parts_rows consumers")
+	}
+	single := []AutogenConsumerConfig{{ID: "parts", Mode: "parts_rows"}}
+	if failures := validateAutogenConsumerSources(single); len(failures) != 0 {
+		t.Fatalf("single parts_rows consumer must validate, got %v", failures)
+	}
+}
+
 func loadAndValidate(root string) error {
 	proj, err := Load(root)
 	if err != nil {

internal/topdata/autogen.go

@@ -299,23 +299,34 @@ func resolveCDNChannelManifest(p *project.Project, consumer project.AutogenConsu
 		progress = func(string) {}
 	}
 
-	// 1. Offline / air-gapped override: a vfxs.yml path or a manifest-repo
+	// Manifest basename + provenance label are derived from config, not hardcoded,
-	//    checkout root containing assets/vfxs.yml. Skips the network entirely.
+	// so the same resolver serves vfxs.yml (accessory VFX) and part.yml (parts).
+	manifestBase := filepath.Base(filepath.FromSlash(strings.TrimSpace(src.ManifestPath)))
+	if manifestBase == "." || manifestBase == "" || manifestBase == string(filepath.Separator) {
+		manifestBase = "manifest.yml"
+	}
+	label := strings.TrimSpace(consumer.ID)
+	if label == "" {
+		label = "autogen"
+	}
+
+	// 1. Offline / air-gapped override: a manifest file path or a manifest-repo
+	//    checkout root containing assets/<manifestBase>. Skips the network entirely.
 	if envName := strings.TrimSpace(src.OfflineOverrideEnv); envName != "" {
 		if override := strings.TrimSpace(os.Getenv(envName)); override != "" {
-			vfxsPath := override
+			manifestPath := override
 			if info, err := os.Stat(override); err == nil && info.IsDir() {
-				vfxsPath = filepath.Join(override, "assets", "vfxs.yml")
+				manifestPath = filepath.Join(override, "assets", manifestBase)
 			}
-			raw, err := os.ReadFile(vfxsPath)
+			raw, err := os.ReadFile(manifestPath)
 			if err != nil {
-				return nil, fmt.Errorf("offline vfxs override %s: %w", vfxsPath, err)
+				return nil, fmt.Errorf("offline %s override %s: %w", manifestBase, manifestPath, err)
 			}
 			entries, err := filterCDNChannelEntries(raw, consumer)
 			if err != nil {
 				return nil, err
 			}
-			progress(fmt.Sprintf("Using offline vfxs override for %s from %s...", consumer.ID, vfxsPath))
+			progress(fmt.Sprintf("Using offline %s override for %s from %s...", manifestBase, consumer.ID, manifestPath))
 			return &autogenManifest{ID: consumer.Producer, Ref: "local", Entries: entries}, nil
 		}
 	}
@@ -359,13 +370,13 @@ func resolveCDNChannelManifest(p *project.Project, consumer project.AutogenConsu
 	if tag == "" {
 		return nil, unavailableAutogenManifest(fmt.Errorf("channel %q absent in channels.json (%s)", channel, channelsURL))
 	}
-	progress(fmt.Sprintf("Accessory VFX: channel %s -> tag %s", channel, tag))
+	progress(fmt.Sprintf("%s: channel %s -> tag %s", label, channel, tag))
 
-	// 5. vfxs.yml for the tag.
+	// 5. per-tag manifest for the tag.
 	manifestURL := join(src.ManifestPath, tag)
 	vstatus, vbody, err := httpGetStatus(manifestURL)
 	if err != nil {
-		return nil, unavailableAutogenManifest(fmt.Errorf("vfxs.yml unreachable %s: %w", manifestURL, err))
+		return nil, unavailableAutogenManifest(fmt.Errorf("%s unreachable %s: %w", manifestBase, manifestURL, err))
 	}
 	switch vstatus {
 	case http.StatusOK:
@@ -377,27 +388,103 @@ func resolveCDNChannelManifest(p *project.Project, consumer project.AutogenConsu
 		if marker := strings.TrimSpace(src.ReleaseMarkerPath); marker != "" {
 			markerURL := join(marker, tag)
 			if mstatus, _, merr := httpGetStatus(markerURL); merr == nil && mstatus == http.StatusOK {
-				return nil, fmt.Errorf("release %s has %s but no vfxs.yml (%s) — accessory rows would silently vanish; backfill/republish vfxs.yml for %s", tag, marker, manifestURL, tag)
+				return nil, fmt.Errorf("release %s has %s but no %s (%s) — rows would silently vanish; backfill/republish %s for %s", tag, marker, manifestBase, manifestURL, manifestBase, tag)
 			}
 		}
-		return nil, unavailableAutogenManifest(fmt.Errorf("vfxs.yml 404 %s (no published release for %s)", manifestURL, tag))
+		return nil, unavailableAutogenManifest(fmt.Errorf("%s 404 %s (no published release for %s)", manifestBase, manifestURL, tag))
 	default:
-		return nil, unavailableAutogenManifest(fmt.Errorf("vfxs.yml HTTP %d %s", vstatus, manifestURL))
+		return nil, unavailableAutogenManifest(fmt.Errorf("%s HTTP %d %s", manifestBase, vstatus, manifestURL))
 	}
 
 	entries, err := filterCDNChannelEntries(vbody, consumer)
 	if err != nil {
-		return nil, err // malformed vfxs.yml = HARD fail
+		return nil, err // malformed manifest = HARD fail
 	}
-	progress(fmt.Sprintf("Accessory VFX: resolved %d model entries from %s", len(entries), manifestURL))
+	progress(fmt.Sprintf("%s: resolved %d model entries from %s", label, len(entries), manifestURL))
 	return &autogenManifest{ID: consumer.Producer, Ref: tag, Entries: entries}, nil
 }
 
-// filterCDNChannelEntries parses vfxs.yml and keeps restype==mdl assets under
+// filterCDNChannelEntries dispatches per-tag manifest parsing on the consumer
+// mode. parts_rows consumes part.yml (the parts inventory contract); every other
+// mode consumes vfxs.yml (the accessory-VFX contract).
+func filterCDNChannelEntries(raw []byte, consumer project.AutogenConsumerConfig) ([]autogenManifestEntry, error) {
+	switch strings.TrimSpace(consumer.Mode) {
+	case "parts_rows":
+		return filterPartsCDNChannelEntries(raw)
+	default:
+		return filterVFXCDNChannelEntries(raw, consumer)
+	}
+}
+
+// filterPartsCDNChannelEntries parses part.yml and keeps restype==mdl assets
+// under part/<supported-category>/.../<stem><digits>.mdl. The asset category is
+// the path segment after part/; the row ID is the trailing decimal of the
+// filename stem. Body/race/gender/left-right variants dedup by (category,rowID).
+// Zero accepted rows is a HARD fail (silent-drop guard).
+func filterPartsCDNChannelEntries(raw []byte) ([]autogenManifestEntry, error) {
+	var manifest struct {
+		Assets *[]struct {
+			Path    string `yaml:"path"`
+			Restype string `yaml:"restype"`
+		} `yaml:"assets"`
+	}
+	if err := yaml.Unmarshal(raw, &manifest); err != nil {
+		return nil, fmt.Errorf("malformed part.yml (cannot parse): %w", err)
+	}
+	if manifest.Assets == nil {
+		return nil, fmt.Errorf("malformed part.yml (no assets array)")
+	}
+	seen := map[string]struct{}{}
+	var entries []autogenManifestEntry
+	for _, a := range *manifest.Assets {
+		if a.Restype != "mdl" {
+			continue
+		}
+		path := filepath.ToSlash(strings.TrimSpace(a.Path))
+		if !strings.HasPrefix(path, "part/") {
+			continue
+		}
+		rel := strings.TrimPrefix(path, "part/")
+		segs := strings.Split(rel, "/")
+		if len(segs) < 2 {
+			continue
+		}
+		category := segs[0]
+		if !isSupportedPartCategory(category) {
+			continue // ignores _masters, cloak, head, helm, tail, wings
+		}
+		stem := strings.TrimSuffix(segs[len(segs)-1], ".mdl")
+		match := trailingNumberRegex.FindString(stem)
+		if match == "" {
+			return nil, fmt.Errorf("part.yml: supported-category model %q has no trailing row number", path)
+		}
+		rowID, err := strconv.Atoi(match)
+		if err != nil || rowID == 0 {
+			return nil, fmt.Errorf("part.yml: supported-category model %q resolves to invalid row id %q", path, match)
+		}
+		key := category + "/" + strconv.Itoa(rowID)
+		if _, dup := seen[key]; dup {
+			continue
+		}
+		seen[key] = struct{}{}
+		entries = append(entries, autogenManifestEntry{
+			Source: rel, Group: category, ModelStem: stem, RowID: rowID,
+		})
+	}
+	if len(entries) == 0 {
+		return nil, fmt.Errorf("part.yml: zero supported part rows after filtering")
+	}
+	slices.SortFunc(entries, func(a, b autogenManifestEntry) int {
+		return strings.Compare(a.Source, b.Source)
+	})
+	return entries, nil
+}
+
+// filterVFXCDNChannelEntries parses vfxs.yml and keeps restype==mdl assets under
 // vfxs/<group>/ for the consumer's 4 accessory groups, stripping the leading
 // vfxs/ from each source path. A present-but-malformed manifest (unparseable, or
 // no assets array) is an error; an empty assets array yields zero entries.
-func filterCDNChannelEntries(raw []byte, consumer project.AutogenConsumerConfig) ([]autogenManifestEntry, error) {
+func filterVFXCDNChannelEntries(raw []byte, consumer project.AutogenConsumerConfig) ([]autogenManifestEntry, error) {
 	var manifest struct {
 		Assets *[]struct {
 			Path    string `yaml:"path"`

internal/topdata/autogen_cdn_channel_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"os"
 	"path/filepath"
 	"testing"
 
@@ -194,6 +195,35 @@ func TestResolveCDNChannelOfflineOverride(t *testing.T) {
 	}
 }
 
+// TestResolveCDNChannelOfflineUsesManifestBasename proves the resolver derives
+// the offline checkout filename from manifest_path's basename (part.yml here),
+// not a hardcoded assets/vfxs.yml, and routes parts_rows through the parts filter.
+func TestResolveCDNChannelOfflineUsesManifestBasename(t *testing.T) {
+	root := testProjectRoot(t)
+	dir := filepath.Join(root, "manifest-checkout")
+	if err := os.MkdirAll(filepath.Join(dir, "assets"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	writeFile(t, filepath.Join(dir, "assets", "part.yml"),
+		"assets:\n  - {path: part/belt/m/pfa0_belt017.mdl, restype: mdl}\n")
+	t.Setenv("SOW_PART_MANIFEST", dir)
+
+	c := projectPartsConsumer()
+	c.Source = project.AutogenSourceConfig{
+		Kind:               "cdn_channel",
+		ManifestPath:       "releases/haks/{tag}/part.yml",
+		OfflineOverrideEnv: "SOW_PART_MANIFEST",
+	}
+
+	m, err := resolveCDNChannelManifest(testProject(root), c, c.Source, nil)
+	if err != nil {
+		t.Fatalf("resolve: %v", err)
+	}
+	if len(m.Entries) != 1 || m.Entries[0].RowID != 17 || m.Entries[0].Group != "belt" {
+		t.Fatalf("unexpected entries: %+v", m.Entries)
+	}
+}
+
 func errorIsUnavailable(err error) bool {
 	return errors.Is(err, errAutogenManifestUnavailable)
 }

internal/topdata/native.go

@@ -460,7 +460,15 @@ func buildNativeUnchecked(p *project.Project, opts NativeBuildOptions, progress
 	if err != nil {
 		return BuildResult{}, err
 	}
-	collected, err = applyPartOverrides(sourceDir, collected)
+	// Single explicit parts sequence: augment (inside applyAutogenConsumers) ->
+	// normalize -> apply overrides exactly once, all under the one configured
+	// parts_rows consumer's policy.
+	partsCfg := partsRowsConfigForProject(p)
+	collected, err = normalizePartsRowsACBonus(collected, partsCfg)
+	if err != nil {
+		return BuildResult{}, err
+	}
+	collected, err = applyPartOverridesWithConfig(sourceDir, collected, partsCfg)
 	if err != nil {
 		return BuildResult{}, err
 	}

internal/topdata/parity_guard_test.go

@@ -1,6 +1,8 @@
 package topdata
 
 import (
+	"os"
+	"path/filepath"
 	"testing"
 
 	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/project"
@@ -54,3 +56,45 @@ func TestParityGuardCDNChannelProducesAccessoryRows(t *testing.T) {
 		t.Fatalf("PARITY GUARD: expected lock id for %s, got %#v", wantKey, got[0].LockData)
 	}
 }
+
+// PARITY GUARD (parts): a bare project whose only parts source is the offline
+// CDN-equivalent (SOW_PART_MANIFEST -> a part.yml), with no NWN_ROOT, no token,
+// no asset checkout, must produce parts rows from the filtered inventory. If
+// parts resolution ever drifts back into a wrapper, this fails.
+func TestParityGuardCDNChannelProducesPartsRows(t *testing.T) {
+	root := testProjectRoot(t)
+	checkout := filepath.Join(root, "manifest-checkout")
+	if err := os.MkdirAll(filepath.Join(checkout, "assets"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	writeFile(t, filepath.Join(checkout, "assets", "part.yml"),
+		"assets:\n  - {path: part/belt/m/pfa0_belt017.mdl, restype: mdl}\n  - {path: part/belt/m/pfa0_belt018.mdl, restype: mdl}\n")
+	t.Setenv("SOW_PART_MANIFEST", checkout)
+	t.Setenv("NWN_ROOT", "")
+
+	c := projectPartsConsumer()
+	c.Source = project.AutogenSourceConfig{
+		Kind:               "cdn_channel",
+		ChannelsPath:       "releases/haks/channels.json",
+		ManifestPath:       "releases/haks/{tag}/part.yml",
+		ReleaseMarkerPath:  "releases/haks/{tag}/haks.json",
+		OfflineOverrideEnv: "SOW_PART_MANIFEST",
+	}
+
+	p := testProject(root)
+	p.Config.Autogen.Consumers = []project.AutogenConsumerConfig{c}
+
+	collected := []nativeCollectedDataset{partsDatasetWithIDs("parts/belt", nil)}
+
+	got, err := applyAutogenConsumers(p, collected, nil)
+	if err != nil {
+		t.Fatalf("applyAutogenConsumers failed: %v", err)
+	}
+	ids := map[int]bool{}
+	for _, row := range got[0].Rows {
+		ids[row["id"].(int)] = true
+	}
+	if !ids[17] || !ids[18] {
+		t.Fatalf("PARITY GUARD: expected belt rows 17 and 18 from inventory, got %#v", got[0].Rows)
+	}
+}

internal/topdata/parts_cdn_channel_test.go

@@ -0,0 +1,87 @@
+package topdata
+
+import (
+	"testing"
+
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/project"
+)
+
+func projectPartsConsumer() project.AutogenConsumerConfig {
+	return project.AutogenConsumerConfig{ID: "parts", Producer: "parts", Mode: "parts_rows"}
+}
+
+const partYML = `assets:
+  - {path: part/belt/m/pfa0_belt017.mdl, restype: mdl}
+  - {path: part/hand/m/pfh0_handl105.mdl, restype: mdl}
+  - {path: part/hand/m/pfh0_handr105.mdl, restype: mdl}
+  - {path: part/leg/m/pfa0_legl001.mdl, restype: mdl}
+  - {path: part/leg/m/pfa0_legr001.mdl, restype: mdl}
+  - {path: part/cloak/m/cloak001.mdl, restype: mdl}
+  - {path: part/belt/m/readme.txt, restype: txt}
+`
+
+func TestFilterPartsKeepsSupportedDedupsVariants(t *testing.T) {
+	consumer := projectPartsConsumer()
+	entries, err := filterCDNChannelEntries([]byte(partYML), consumer)
+	if err != nil {
+		t.Fatalf("filter: %v", err)
+	}
+	inv := autogenPartsInventory(entries)
+	if _, ok := inv["belt"][17]; !ok {
+		t.Errorf("missing belt 17")
+	}
+	if len(inv["hand"]) != 1 {
+		t.Errorf("hand should dedup l/r to 1 row, got %d", len(inv["hand"]))
+	}
+	if _, ok := inv["hand"][105]; !ok {
+		t.Errorf("missing hand 105")
+	}
+	if len(inv["leg"]) != 1 {
+		t.Errorf("leg should dedup l/r to 1 row, got %d", len(inv["leg"]))
+	}
+	if _, ok := inv["cloak"]; ok {
+		t.Errorf("cloak must be ignored")
+	}
+}
+
+func TestFilterPartsRejectsZeroAccepted(t *testing.T) {
+	_, err := filterCDNChannelEntries([]byte("assets:\n  - {path: part/cloak/m/cloak001.mdl, restype: mdl}\n"), projectPartsConsumer())
+	if err == nil {
+		t.Fatal("expected hard error on zero accepted part rows")
+	}
+}
+
+func TestFilterPartsRejectsRowZeroAndNonNumeric(t *testing.T) {
+	for _, doc := range []string{
+		"assets:\n  - {path: part/belt/m/pfa0_belt000.mdl, restype: mdl}\n",
+		"assets:\n  - {path: part/belt/m/pfa0_belt.mdl, restype: mdl}\n",
+	} {
+		if _, err := filterCDNChannelEntries([]byte(doc), projectPartsConsumer()); err == nil {
+			t.Fatalf("expected error for %q", doc)
+		}
+	}
+}
+
+func TestFilterPartsRejectsMalformedAndMissingAssets(t *testing.T) {
+	if _, err := filterCDNChannelEntries([]byte("assets:\n  - path: [unterminated"), projectPartsConsumer()); err == nil {
+		t.Fatal("expected malformed error")
+	}
+	if _, err := filterCDNChannelEntries([]byte("other: 1\n"), projectPartsConsumer()); err == nil {
+		t.Fatal("expected no-assets error")
+	}
+}
+
+func TestSupportedPartCategoriesCoverTwelveDatasets(t *testing.T) {
+	want := []string{"belt", "bicep", "chest", "foot", "forearm", "hand", "leg", "neck", "pelvis", "robe", "shin", "shoulder"}
+	for _, c := range want {
+		if !isSupportedPartCategory(c) {
+			t.Errorf("category %q not supported", c)
+		}
+	}
+	if partDatasetToAssetCategory["hand"] != "hand" {
+		t.Errorf("parts/hand must map to asset category hand")
+	}
+	if partDatasetToAssetCategory["legs"] != "leg" {
+		t.Errorf("parts/legs must map to asset category leg")
+	}
+}

internal/topdata/parts_discovery.go

@@ -21,6 +21,7 @@ var supportedPartCategories = []string{
 	"chest",
 	"foot",
 	"forearm",
+	"hand",
 	"leg",
 	"neck",
 	"pelvis",
@@ -35,6 +36,7 @@ var partDatasetToAssetCategory = map[string]string{
 	"chest":    "chest",
 	"foot":     "foot",
 	"forearm":  "forearm",
+	"hand":     "hand",
 	"legs":     "leg",
 	"neck":     "neck",
 	"pelvis":   "pelvis",
@@ -390,6 +392,18 @@ func applyPartOverrides(sourceDir string, collected []nativeCollectedDataset) ([
 	return applyPartOverridesWithConfig(sourceDir, collected, project.PartsRowsConfig{})
 }
 
+// partsRowsConfigForProject returns the PartsRows policy of the single configured
+// parts_rows autogen consumer, or the zero value if none. Project validation
+// guarantees at most one parts_rows consumer, so the first match is canonical.
+func partsRowsConfigForProject(p *project.Project) project.PartsRowsConfig {
+	for _, c := range p.Config.Autogen.Consumers {
+		if strings.TrimSpace(c.Mode) == "parts_rows" {
+			return c.PartsRows
+		}
+	}
+	return project.PartsRowsConfig{}
+}
+
 func applyPartOverridesWithConfig(sourceDir string, collected []nativeCollectedDataset, cfg project.PartsRowsConfig) ([]nativeCollectedDataset, error) {
 	result := make([]nativeCollectedDataset, len(collected))
 	copy(result, collected)
@@ -430,9 +444,7 @@ func applyPartOverridesWithConfig(sourceDir string, collected []nativeCollectedD
 			}
 			row, ok := rowByID[rowID]
 			if !ok {
-				row = createDefaultPartRowForDataset(rowID, dataset.Dataset.Name, dataset.Columns, cfg)
+				return nil, fmt.Errorf("parts/%s override %d targets row id %d which is neither a baseline row nor a discovered model row; author the row in data/parts/%s.json instead", category, index, rowID, category)
-				rows = append(rows, row)
-				rowByID[rowID] = row
 			}
 			for field, value := range override {
 				if field == "id" {

internal/topdata/parts_override_test.go

@@ -0,0 +1,51 @@
+package topdata
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/project"
+)
+
+func partsDatasetWithIDs(name string, ids []int) nativeCollectedDataset {
+	rows := make([]map[string]any, 0, len(ids))
+	for _, id := range ids {
+		rows = append(rows, map[string]any{"id": id, "COSTMODIFIER": "0", "ACBONUS": "0.00"})
+	}
+	return nativeCollectedDataset{
+		Dataset: nativeDataset{Name: name, Kind: nativeDatasetBase},
+		Columns: []string{"COSTMODIFIER", "ACBONUS"},
+		Rows:    rows,
+	}
+}
+
+func TestApplyPartOverridesRejectsOrphan(t *testing.T) {
+	dir := t.TempDir()
+	if err := os.MkdirAll(filepath.Join(dir, "data", "parts", "overrides"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	writeFile(t, filepath.Join(dir, "data", "parts", "overrides", "belt.json"),
+		`{"overrides": [{"id": 999, "COSTMODIFIER": "5"}]}`)
+	collected := []nativeCollectedDataset{partsDatasetWithIDs("parts/belt", []int{17})}
+	if _, err := applyPartOverridesWithConfig(dir, collected, project.PartsRowsConfig{}); err == nil {
+		t.Fatal("expected orphan override to fail, not synthesize a row")
+	}
+}
+
+func TestApplyPartOverridesUpdatesDiscoveredRow(t *testing.T) {
+	dir := t.TempDir()
+	if err := os.MkdirAll(filepath.Join(dir, "data", "parts", "overrides"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	writeFile(t, filepath.Join(dir, "data", "parts", "overrides", "belt.json"),
+		`{"overrides": [{"id": 17, "COSTMODIFIER": "5"}]}`)
+	collected := []nativeCollectedDataset{partsDatasetWithIDs("parts/belt", []int{17})}
+	out, err := applyPartOverridesWithConfig(dir, collected, project.PartsRowsConfig{})
+	if err != nil {
+		t.Fatalf("override: %v", err)
+	}
+	if got := out[0].Rows[0]["COSTMODIFIER"]; got != "5" {
+		t.Fatalf("row 17 COSTMODIFIER want 5, got %v", got)
+	}
+}