fix(nwsync): stream emit so peak memory tracks the largest resource (#76) (#78)

Closes #76. Part of #54.

`nwsync emit` held roughly 5× the artifact size in RAM, so ovh-main (7 GB, no swap) OOM-killed it on any hak over ~1.4 GB. That blocked the backfill in sow-assets-manifest and would have killed the next release rebuilding a large hak.

## What it does

- `erf.ReadIndex` / `erf.ReadPayload` — parse the header and resource table only, read one payload on demand. `erf.Read` keeps its shape but returns payloads as subslices of the buffer instead of fresh copies, which removes one full copy for the `pipeline` callers too. Callers must not mutate `Resource.Data`; the doc comment says so and no caller does.
- `nwsync.Emit` opens the artifact, hashes it by streaming for the key check (through a section reader, so the file offset stays put), then hashes, compresses and stores one resource at a time. The archive is never resident. Shadowed duplicate resrefs are now never read at all.
- Bounds checks in `ReadIndex` moved to `int64`, so key/resource-list offsets can no longer overflow.

## Not in the issue, but memory-motivated

The zstd blob encoder ran at the default concurrency, which is one encoder per CPU, each holding a window-sized history — about 200 MB of live heap doing nothing on a 24-core runner. `EncodeAll` is single-threaded per call, so concurrency 1 costs nothing. `TestSingleThreadedEncoderMatchesDefault` pins the claim that blobs come out byte-identical.

## Measured

Peak heap during emit, sampled 1 ms:

| hak | before | after |
|-----|--------|-------|
| 8 MB | 155 MB | 21 MB |
| 64 MB | 289 MB | 22 MB |

Flat, as the acceptance asks. `TestEmitPeakMemoryDoesNotScaleWithArtifactSize` fails if the 64 MB fixture costs more than the 8 MB one plus 24 MB of slack.

## Gaps

- The regression check measures Go heap, not RSS, and its largest fixture is 64 MB — a multi-GB run was not done here. A 2.15 GB hak now needs about the same ~22 MB the 64 MB one does, so the 5 GB budget is not close, but that is inference from the flat curve, not a measurement.
- mmap was suggested in the issue and skipped. Payload buffers are still anonymous, but they are one resource each (≤15 MiB), so making them file-backed buys nothing now.

🤖 Generated with [Claude Code](https://claude.com/claude-code)Reviewed-on: #78
Reviewed-by: xtul <mpiasecki720@protonmail.com>
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>

README.md

@@ -19,6 +19,7 @@ Crucible is how the artifact repos turn source into artifacts.
 | `crucible-depot`   | `crucible depot`   | content-addressed depot blob verify/move        |
 | `crucible-hak`     | `crucible hak`     | ERF/HAK pack/unpack + hak manifests             |
 | `crucible-module`  | `crucible module`  | build/extract/validate/compare the `.mod`       |
+| `crucible-nwsync`  | `crucible nwsync`  | NWSync blob emit + manifest assemble            |
 | `crucible-topdata` | `crucible topdata` | compile 2da/tlk topdata + packages              |
 | `crucible-wiki`    | `crucible wiki`    | render + deploy mechanical wiki pages           |
 

cmd/crucible-nwsync/main.go

@@ -0,0 +1,11 @@
+// Command crucible-nwsync is the standalone nwsync builder (equivalent to
+// `crucible nwsync`). A single-token binary keeps consumer wrapper scripts simple.
+package main
+
+import (
+	"os"
+
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/dispatch"
+)
+
+func main() { os.Exit(dispatch.RunBuilder("nwsync", os.Args[1:])) }

docs/command-surface.md

@@ -34,11 +34,71 @@ aliases.
 | `depot` | `verify` | Existence sweep plus sampled download re-hash. |
 | `depot` | `get` | Fetch one blob with sha re-verify. |
 | `depot` | `pull` | Incremental verified pull of every referenced blob. |
+| `nwsync` | `emit` | Explode one artifact into NWSync blobs plus its own NSYM manifest. |
+| `nwsync` | `assemble` | Merge per-artifact NSYM manifests into one merged manifest. |
 
 `depot status` and `depot get` pick their backend either with `--out DIR`, a
 depot tree on disk, or with `--target bunny|cdn`, a remote backend. The two
 flags are mutually exclusive.
 
+`nwsync emit` runs where an artifact is born (a `.hak`/`.erf`, or a loose file
+such as the TLK); `nwsync assemble` runs at module release and reads only the
+small per-artifact indexes. Both take **depot keys**: an artifact's index lives
+beside the artifact itself with the extension replaced, so `emit` and
+`assemble` agree on where it is without being told.
+
+```
+nwsync emit     [--as NAME] [--out DIR] <artifact-key> <file>
+nwsync assemble --group-id N [--tlk-key KEY] [--out DIR] <artifact-key>...
+```
+
+Both verbs upload by default; nothing bulky is ever written to the runner's
+disk. `--out DIR` writes a local repository tree instead, which is the
+conformance path against upstream `nwn_nwsync_write`. The zone comes from
+`NWSYNC_STORAGE_ZONE` and `NWSYNC_STORAGE_PASSWORD`, with the host from
+`BUNNY_STORAGE_HOST` — NWSync data is a separate zone from the asset depot.
+
+`assemble`'s artifact keys are in `Mod_HakList` order, highest priority first: a
+resref in more than one artifact resolves to the earliest one, the way the game
+resolves it. `--tlk-key` has its own slot because the TLK shadows nothing.
+`--group-id` is per channel — 1 is current, 2 is testing, and 0 leaves the field
+out of the sidecar.
+
+`emit` uploads blobs first and the index last, so the presence of an index is
+the publication marker: an artifact whose emit died halfway leaves real blobs in
+the zone and no index. Blob names are content hashes, so re-running skips
+whatever already landed, and `assemble` fails closed on an artifact with no
+index rather than publishing a manifest that is missing a hak.
+
+### What an emitted tree looks like
+
+`--out DIR` produces the same tree `emit` would upload, which makes it the way
+to check a zone by hand without touching one:
+
+```
+<artifact-sha>.nsym          binary index
+<artifact-sha>.nsym.json     the same index, readable
+data/sha1/a7/4a/a74aa84a...  one blob per resource, two-level fanout
+```
+
+A blob's name is the SHA-1 of the resource's **original** bytes, but the file on
+disk is not those bytes: each blob is wrapped in NWCompressedBuffer framing, a
+24-byte `NSYC` header followed by a zstd frame. Hashing the file directly will
+not match its name, which is the obvious
+first thing to try and the obvious first thing to be confused by. Strip the
+header first:
+
+```
+tail -c +25 <blob> | zstd -dc | sha1sum   # == the blob's filename
+```
+
+The header carries the uncompressed length as a little-endian `uint32` at offset
+12, so the decompressed size is checkable without decompressing. Compression is
+worth roughly a 4:1
+saving on hak content: a 250 MB hak emitted 2296 blobs totalling 59 MB on disk
+against 249 MB of resources, as recorded in the sidecar's `on_disk_bytes` and
+`total_bytes`.
+
 ## Hidden compatibility aliases
 
 Existing scripts may continue using these names indefinitely. They are accepted

flake.nix

@@ -22,12 +22,13 @@
             pname = "crucible";
             inherit version;
             src = ./.;
-            vendorHash = "sha256-hm6mrNAtXv0LidzHUfz4eukTFZouizGtxkZ8gKJFUVI=";
+            vendorHash = "sha256-0I8j7On9YGD2GK9xbj/KkgBrlkMJ6Y6XQv+KCLTgBBU=";
             subPackages = [
               "cmd/crucible"
               "cmd/crucible-depot"
               "cmd/crucible-hak"
               "cmd/crucible-module"
+              "cmd/crucible-nwsync"
               "cmd/crucible-topdata"
               "cmd/crucible-wiki"
             ];

go.mod

@@ -6,3 +6,5 @@ require (
 	golang.org/x/text v0.35.0
 	gopkg.in/yaml.v3 v3.0.1
 )
+
+require github.com/klauspost/compress v1.19.1

go.sum

@@ -1,3 +1,5 @@
+github.com/klauspost/compress v1.19.1 h1:VsB4HPswih7mmZ8WleSFQ75c/Ui1M4trX5oAsJnhSlk=
+github.com/klauspost/compress v1.19.1/go.mod h1:cwPg85FWrGar70rWktvGQj8/hthj3wpl0PGDogxkrSQ=
 golang.org/x/text v0.35.0 h1:JOVx6vVDFokkpaq1AEptVzLTpDe9KGpj5tR4/X+ybL8=
 golang.org/x/text v0.35.0/go.mod h1:khi/HExzZJ2pGnjenulevKNX1W67CUy0AsXcNubPGCA=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=

internal/depot/keystore.go

@@ -0,0 +1,121 @@
+package depot
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+)
+
+// KeyStore is the zone addressed by object key rather than by depot sha. The
+// depot names every object after the sha256 of its contents; NWSync does not —
+// a blob is named after the sha1 of its *uncompressed* bytes while the body
+// uploaded is the compressed form, and a per-artifact index is named after its
+// artifact. Both addressing modes want the same transport, retry and probe
+// discipline, so the sha-addressed Backend rides on this rather than the other
+// way round.
+type KeyStore interface {
+	// ProbeKey returns the existence state of one key. transient=true means a
+	// retry might change the answer — never read it as "missing, re-upload".
+	ProbeKey(ctx context.Context, key string) (state ProbeState, transient bool, err error)
+	// PutReader uploads size bytes read from r to key. checksum is the
+	// uppercase hex sha256 of those bytes, which Bunny verifies server-side.
+	PutReader(ctx context.Context, key string, r io.Reader, size int64, checksum string) error
+	// GetKey fetches the whole object at key. Small objects only — it holds
+	// the body in memory and does no hash check, because a key is not always
+	// a content hash.
+	GetKey(ctx context.Context, key string) ([]byte, error)
+}
+
+// NewKeyStore returns a KeyStore for cfg's storage zone. Fails closed on a
+// missing host or read key, matching NewBackend.
+func NewKeyStore(cfg Config) (KeyStore, error) {
+	if cfg.StorageHost == "" {
+		return nil, errors.New("storage backend requires a storage host")
+	}
+	if cfg.StorageZone == "" {
+		return nil, errors.New("storage backend requires a storage zone")
+	}
+	if cfg.ReadKey == "" {
+		return nil, errors.New("storage backend requires a read key")
+	}
+	return &httpBackend{name: "bunny", client: newHTTPClient(cfg), cfg: cfg}, nil
+}
+
+// keyURL is the storage URL of one object key.
+func (b *httpBackend) keyURL(key string) string {
+	host := b.cfg.StorageHost
+	// StorageHost is normally a bare host ("storage.bunnycdn.com"); allow a
+	// full scheme (used by tests against httptest.NewServer) to pass through
+	// unchanged.
+	if !strings.Contains(host, "://") {
+		host = "https://" + host
+	}
+	return fmt.Sprintf("%s/%s/%s", strings.TrimSuffix(host, "/"), b.cfg.StorageZone, key)
+}
+
+func (b *httpBackend) ProbeKey(ctx context.Context, key string) (ProbeState, bool, error) {
+	return b.rangeProbe(ctx, b.keyURL(key), map[string]string{"AccessKey": b.cfg.ReadKey})
+}
+
+func (b *httpBackend) PutReader(ctx context.Context, key string, r io.Reader, size int64, checksum string) error {
+	if b.name == "cdn" {
+		return errors.New("cdn backend is read-only")
+	}
+	if b.cfg.WriteKey == "" {
+		return errors.New("storage backend requires a write key to write")
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPut, b.keyURL(key), r)
+	if err != nil {
+		return err
+	}
+	req.ContentLength = size
+	req.Header.Set("AccessKey", b.cfg.WriteKey)
+	// Bunny defines Checksum as sha256 of the body and rejects a mismatch, so
+	// this is server-side integrity checking, not decoration.
+	req.Header.Set("Checksum", strings.ToUpper(checksum))
+
+	resp, err := b.client.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	_, _ = io.Copy(io.Discard, resp.Body)
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("put %s: unexpected status %d", key, resp.StatusCode)
+	}
+	return nil
+}
+
+func (b *httpBackend) GetKey(ctx context.Context, key string) ([]byte, error) {
+	resp, err := b.get(ctx, b.keyURL(key), map[string]string{"AccessKey": b.cfg.ReadKey})
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		_, _ = io.Copy(io.Discard, resp.Body)
+		return nil, fmt.Errorf("get %s: unexpected status %d", key, resp.StatusCode)
+	}
+	return io.ReadAll(resp.Body)
+}
+
+// putFile uploads the file at src to key, streaming it. checksum is the
+// uppercase hex sha256 of the file's bytes.
+func (b *httpBackend) putFile(ctx context.Context, key, src, checksum string) error {
+	f, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	info, err := f.Stat()
+	if err != nil {
+		return err
+	}
+	return b.PutReader(ctx, key, f, info.Size(), checksum)
+}

internal/depot/remote.go

@@ -10,7 +10,6 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
-	"strings"
 	"time"
 )
 
@@ -71,16 +70,7 @@ type httpBackend struct {
 
 func (b *httpBackend) Name() string { return b.name }
 
-func (b *httpBackend) storageURL(sha string) string {
+func (b *httpBackend) storageURL(sha string) string { return b.keyURL(BlobKey(sha)) }
-	host := b.cfg.StorageHost
-	// StorageHost is normally a bare host ("storage.bunnycdn.com"); allow a
-	// full scheme (used by tests against httptest.NewServer) to pass through
-	// unchanged.
-	if strings.Contains(host, "://") {
-		return fmt.Sprintf("%s/%s/%s", strings.TrimSuffix(host, "/"), b.cfg.StorageZone, BlobKey(sha))
-	}
-	return fmt.Sprintf("https://%s/%s/%s", host, b.cfg.StorageZone, BlobKey(sha))
-}
 
 func (b *httpBackend) cdnURL(sha string) string {
 	return fmt.Sprintf("%s/%s", b.cfg.CDNBase, BlobKey(sha))
@@ -140,7 +130,8 @@ func (b *httpBackend) Probe(ctx context.Context, sha string) (ProbeState, bool,
 	return b.rangeProbe(ctx, b.storageURL(sha), map[string]string{"AccessKey": b.cfg.ReadKey})
 }
 
-// Put uploads src for sha. cdn is read-only.
+// Put uploads src for sha. cdn is read-only. A depot object is named after the
+// sha256 of its own bytes, so the key's sha doubles as the Checksum header.
 func (b *httpBackend) Put(ctx context.Context, sha, src string) error {
 	if b.name == "cdn" {
 		return errors.New("cdn backend is read-only")
@@ -157,30 +148,7 @@ func (b *httpBackend) Put(ctx context.Context, sha, src string) error {
 		return nil
 	}
 
-	f, err := os.Open(src)
+	return b.putFile(ctx, BlobKey(sha), src, sha)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	req, err := http.NewRequestWithContext(ctx, http.MethodPut, b.storageURL(sha), f)
-	if err != nil {
-		return err
-	}
-	req.Header.Set("AccessKey", b.cfg.WriteKey)
-	req.Header.Set("Checksum", strings.ToUpper(sha))
-
-	resp, err := b.client.Do(req)
-	if err != nil {
-		return err
-	}
-	defer resp.Body.Close()
-	_, _ = io.Copy(io.Discard, resp.Body)
-
-	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
-		return fmt.Errorf("bunny put %s: unexpected status %d", sha, resp.StatusCode)
-	}
-	return nil
 }
 
 // Get fetches sha into dest via temp file + rename, re-hashing and deleting

internal/dispatch/dispatch.go

@@ -21,6 +21,7 @@ import (
 	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/buildinfo"
 	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/depot"
 	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/menu"
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/nwsync"
 )
 
 // Exit codes follow the sysexits(3) convention so CI can distinguish
@@ -104,6 +105,16 @@ var Registry = []Builder{
 		},
 		Wired: true,
 	},
+	{
+		Name:    "nwsync",
+		Bin:     "crucible-nwsync",
+		Summary: "publish NWSync blobs and manifests (emit/assemble)",
+		Commands: []Command{
+			{Name: "emit", Summary: "explode one artifact into blobs plus its own NSYM manifest", Usage: "crucible nwsync emit <artifact> --out DIR"},
+			{Name: "assemble", Summary: "merge per-artifact NSYM manifests into one", Usage: "crucible nwsync assemble --order NAMES --entries DIR --out DIR [--group-id N]"},
+		},
+		Wired: true,
+	},
 	{
 		Name:    "assets",
 		Bin:     "crucible-assets",
@@ -241,7 +252,7 @@ var Registry = []Builder{
 					"2da-to-module [flags] <input.2da> [output.json]",
 					"json-to-2da <input.json> <output.2da>",
 				},
-				Aliases:    []CommandAlias{{Name: "convert-topdata"}},
+				Aliases: []CommandAlias{{Name: "convert-topdata"}},
 			},
 		},
 		Wired: true,
@@ -392,7 +403,7 @@ func runBuilder(name string, args []string, out, errw io.Writer) int {
 		}
 	}
 	if b.Wired {
-		// depot and assets are self-contained builders: they parse their own
+		// depot, assets and nwsync are self-contained builders: they parse their own
 		// subcommands and own their exit contract, bypassing the
 		// b.Commands/delegateLegacy legacy routing entirely.
 		switch b.Name {
@@ -400,6 +411,8 @@ func runBuilder(name string, args []string, out, errw io.Writer) int {
 			return depot.Run(args, out, errw, os.Getenv)
 		case "assets":
 			return assets.Run(args, out, errw, os.Getenv)
+		case "nwsync":
+			return nwsync.Run(args, out, errw)
 		}
 	}
 	if !b.Wired {

internal/dispatch/dispatch_test.go

@@ -148,6 +148,10 @@ func TestBuilderHelpIsOK(t *testing.T) {
 	}
 }
 
+// selfContained builders parse their own subcommands instead of delegating to
+// the legacy internal/app surface.
+var selfContained = map[string]bool{"depot": true, "assets": true, "nwsync": true}
+
 func TestCanonicalCommandSurface(t *testing.T) {
 	want := map[string][]string{
 		"depot":   {"status", "push", "verify", "get", "pull"},
@@ -156,6 +160,7 @@ func TestCanonicalCommandSurface(t *testing.T) {
 		"module":  {"build", "extract", "validate", "compare", "manifest"},
 		"topdata": {"validate", "build", "package", "compare", "convert"},
 		"wiki":    {"build", "deploy"},
+		"nwsync":  {"emit", "assemble"},
 	}
 	for _, builder := range Registry {
 		got := builder.subcommands()
@@ -173,10 +178,10 @@ func TestRegistryCommandNamesAndAliasesAreUnambiguous(t *testing.T) {
 	for _, builder := range Registry {
 		seen := map[string]bool{}
 		for _, command := range builder.Commands {
-			// depot and assets parse their own subcommands and bypass AppCommand
+			// depot, assets and nwsync parse their own subcommands and bypass
-			// routing entirely (see the self-contained-builder branch in
+			// AppCommand routing entirely (see the self-contained-builder branch
-			// runBuilder), so their Commands carry no AppCommand.
+			// in runBuilder), so their Commands carry no AppCommand.
-			requireAppCommand := builder.Name != "depot" && builder.Name != "assets"
+			requireAppCommand := !selfContained[builder.Name]
 			if command.Name == "" || command.Summary == "" || command.Usage == "" || (requireAppCommand && command.AppCommand == "") {
 				t.Errorf("%s has incomplete command metadata: %#v", builder.Name, command)
 			}

internal/erf/erf.go

@@ -311,63 +311,110 @@ func Write(w io.Writer, archive Archive) error {
 	return nil
 }
 
+// IndexEntry locates one resource inside an archive without holding its
+// payload. Streaming callers read one payload at a time from these, so peak
+// memory tracks the largest resource instead of the whole archive.
+type IndexEntry struct {
+	Name   string
+	Type   uint16
+	Offset int64
+	Size   int64
+}
+
+// Index is the header plus the resource table of an ERF: everything except the
+// payloads.
+type Index struct {
+	FileType string
+	Version  string
+	Entries  []IndexEntry
+}
+
+// ReadIndex parses the tables of an ERF of the given size, reading only the
+// header, the key list and the resource list.
+func ReadIndex(r io.ReaderAt, size int64) (Index, error) {
+	if size < headerSize {
+		return Index{}, fmt.Errorf("erf file too small: %d bytes", size)
+	}
+
+	var hdr header
+	if err := binary.Read(io.NewSectionReader(r, 0, headerSize), binary.LittleEndian, &hdr); err != nil {
+		return Index{}, fmt.Errorf("decode erf header: %w", err)
+	}
+
+	if int64(hdr.KeyListOffset)+int64(hdr.EntryCount)*24 > size {
+		return Index{}, fmt.Errorf("erf key list exceeds file bounds")
+	}
+	keys := make([]keyEntry, hdr.EntryCount)
+	keyReader := io.NewSectionReader(r, int64(hdr.KeyListOffset), int64(hdr.EntryCount)*24)
+	if err := binary.Read(keyReader, binary.LittleEndian, &keys); err != nil {
+		return Index{}, fmt.Errorf("decode key list: %w", err)
+	}
+
+	if int64(hdr.ResourceListOffset)+int64(hdr.EntryCount)*8 > size {
+		return Index{}, fmt.Errorf("erf resource list exceeds file bounds")
+	}
+	entries := make([]resourceEntry, hdr.EntryCount)
+	entryReader := io.NewSectionReader(r, int64(hdr.ResourceListOffset), int64(hdr.EntryCount)*8)
+	if err := binary.Read(entryReader, binary.LittleEndian, &entries); err != nil {
+		return Index{}, fmt.Errorf("decode resource list: %w", err)
+	}
+
+	index := Index{
+		FileType: string(hdr.FileType[:]),
+		Version:  string(hdr.Version[:]),
+		Entries:  make([]IndexEntry, 0, hdr.EntryCount),
+	}
+	for position, key := range keys {
+		entry := entries[position]
+		if int64(entry.Offset)+int64(entry.Size) > size {
+			return Index{}, fmt.Errorf("resource %d exceeds file bounds", position)
+		}
+		index.Entries = append(index.Entries, IndexEntry{
+			Name:   string(bytes.TrimRight(key.ResRef[:], "\x00")),
+			Type:   key.ResourceType,
+			Offset: int64(entry.Offset),
+			Size:   int64(entry.Size),
+		})
+	}
+	return index, nil
+}
+
+// ReadPayload returns one resource's bytes.
+func ReadPayload(r io.ReaderAt, entry IndexEntry) ([]byte, error) {
+	payload := make([]byte, entry.Size)
+	if _, err := r.ReadAt(payload, entry.Offset); err != nil {
+		return nil, fmt.Errorf("read resource %q: %w", entry.Name, err)
+	}
+	return payload, nil
+}
+
+// Read materialises a whole archive. Payloads are subslices of the buffer the
+// archive was read into, so nothing is copied twice: a caller must not mutate
+// Data. Callers that only need one resource at a time should use ReadIndex
+// instead, which never holds the archive at all.
 func Read(r io.Reader) (Archive, error) {
 	data, err := io.ReadAll(r)
 	if err != nil {
 		return Archive{}, fmt.Errorf("read erf: %w", err)
 	}
-	if len(data) < headerSize {
+	index, err := ReadIndex(bytes.NewReader(data), int64(len(data)))
-		return Archive{}, fmt.Errorf("erf file too small: %d bytes", len(data))
+	if err != nil {
+		return Archive{}, err
 	}
 
-	var hdr header
+	resources := make([]Resource, 0, len(index.Entries))
-	if err := binary.Read(bytes.NewReader(data[:headerSize]), binary.LittleEndian, &hdr); err != nil {
+	for _, entry := range index.Entries {
-		return Archive{}, fmt.Errorf("decode erf header: %w", err)
-	}
-
-	keyStart := int(hdr.KeyListOffset)
-	keyEnd := keyStart + int(hdr.EntryCount)*24
-	if keyEnd > len(data) {
-		return Archive{}, fmt.Errorf("erf key list exceeds file bounds")
-	}
-	keys := make([]keyEntry, hdr.EntryCount)
-	if err := binary.Read(bytes.NewReader(data[keyStart:keyEnd]), binary.LittleEndian, &keys); err != nil {
-		return Archive{}, fmt.Errorf("decode key list: %w", err)
-	}
-
-	resourceStart := int(hdr.ResourceListOffset)
-	resourceEnd := resourceStart + int(hdr.EntryCount)*8
-	if resourceEnd > len(data) {
-		return Archive{}, fmt.Errorf("erf resource list exceeds file bounds")
-	}
-	entries := make([]resourceEntry, hdr.EntryCount)
-	if err := binary.Read(bytes.NewReader(data[resourceStart:resourceEnd]), binary.LittleEndian, &entries); err != nil {
-		return Archive{}, fmt.Errorf("decode resource list: %w", err)
-	}
-
-	resources := make([]Resource, 0, hdr.EntryCount)
-	for index, key := range keys {
-		entry := entries[index]
-		start := int(entry.Offset)
-		end := start + int(entry.Size)
-		if end > len(data) {
-			return Archive{}, fmt.Errorf("resource %d exceeds file bounds", index)
-		}
-
-		resref := string(bytes.TrimRight(key.ResRef[:], "\x00"))
-		payload := make([]byte, entry.Size)
-		copy(payload, data[start:end])
 		resources = append(resources, Resource{
-			Name: resref,
+			Name: entry.Name,
-			Type: key.ResourceType,
+			Type: entry.Type,
-			Data: payload,
+			Data: data[entry.Offset : entry.Offset+entry.Size],
-			Size: int64(entry.Size),
+			Size: entry.Size,
 		})
 	}
 
 	return Archive{
-		FileType:  string(hdr.FileType[:]),
+		FileType:  index.FileType,
-		Version:   string(hdr.Version[:]),
+		Version:   index.Version,
 		Resources: resources,
 	}, nil
 }

internal/nwsync/assemble.go

@@ -0,0 +1,128 @@
+package nwsync
+
+import (
+	"crypto/sha1"
+	"encoding/json"
+	"fmt"
+	"path"
+)
+
+// AssembleOptions describes one merged manifest.
+type AssembleOptions struct {
+	// ArtifactKeys are the depot keys of the artifacts to merge, in
+	// Mod_HakList order — highest priority first. Each one's index is read
+	// from the key beside it.
+	ArtifactKeys []string
+	TLKKey       string // the TLK's key, if the manifest carries one
+	OutDir       string // write locally instead of uploading — the conformance path
+	GroupID      int    // 1 = current, 2 = testing; 0 means absent
+	ModuleName   string
+	Description  string
+	Sink         sink // test seam; nil means OutDir or the zone
+}
+
+// AssembleResult reports what one assemble run produced.
+type AssembleResult struct {
+	SHA1         string
+	ManifestPath string
+	Entries      int
+}
+
+// Assemble merges the per-artifact NSYM manifests named by Order into one
+// manifest. It reads no bulk data at all — only the small index files.
+//
+// Merge rule is resref shadowing, not concatenation: a resref present in more
+// than one artifact resolves to the earliest artifact in Order, which is how
+// the game resolves it (upstream's resman adds haks in reverse and lets the
+// last one win). Get this backwards and the wrong texture ships silently.
+func Assemble(options AssembleOptions) (AssembleResult, error) {
+	if len(options.ArtifactKeys) == 0 {
+		return AssembleResult{}, fmt.Errorf("assemble: no artifact keys given")
+	}
+
+	target, err := openSink(options.OutDir, options.Sink)
+	if err != nil {
+		return AssembleResult{}, err
+	}
+
+	// The TLK carries no precedence — it is not a hak and shadows nothing —
+	// so it merges last, after every hak has had its say.
+	keys := append([]string{}, options.ArtifactKeys...)
+	if options.TLKKey != "" {
+		keys = append(keys, options.TLKKey)
+	}
+
+	merged := make([]Entry, 0, 1024)
+	winner := make(map[Identity]bool, 1024)
+	var onDiskBytes int64
+
+	for _, artifactKey := range keys {
+		key, err := resolveIndexKey(artifactKey, options.OutDir)
+		if err != nil {
+			return AssembleResult{}, err
+		}
+		data, sidecarBody, err := target.getIndex(key)
+		if err != nil {
+			// An artifact with no index is an artifact whose emit never
+			// finished. Publishing a manifest without it would ship a release
+			// missing a hak, so this fails closed.
+			return AssembleResult{}, fmt.Errorf("assemble: no index for %s: %w", artifactKey, err)
+		}
+		entries, err := readManifest(data)
+		if err != nil {
+			return AssembleResult{}, fmt.Errorf("%s: %w", target.describe(key), err)
+		}
+		sidecar, err := parseSidecar(target.describe(key), sidecarBody)
+		if err != nil {
+			return AssembleResult{}, err
+		}
+		// Two producers of blobs means a skewed emitter can write blobs the
+		// merged manifest quietly disagrees with. Refuse to merge across
+		// mismatched emitter versions.
+		if sidecar.EmitterVersion != emitterVersion {
+			return AssembleResult{}, fmt.Errorf(
+				"assemble: emitter version mismatch: %s was emitted by emitter %q, this is emitter %q",
+				artifactKey, sidecar.EmitterVersion, emitterVersion)
+		}
+		// on_disk_bytes overcounts by the handful of cross-artifact
+		// duplicates. It is a display statistic; no dedupe pass for it.
+		onDiskBytes += sidecar.OnDiskBytes
+
+		for _, entry := range entries {
+			identity := entry.identity()
+			if winner[identity] {
+				continue
+			}
+			winner[identity] = true
+			merged = append(merged, entry)
+		}
+	}
+
+	if len(merged) == 0 {
+		return AssembleResult{}, fmt.Errorf("assemble: merged manifest is empty")
+	}
+
+	data, err := writeManifest(merged)
+	if err != nil {
+		return AssembleResult{}, err
+	}
+	sha1Hex := fmt.Sprintf("%x", sha1.Sum(data))
+	manifestKey := path.Join("manifests", sha1Hex)
+	sidecar := Sidecar{
+		ModuleName:  options.ModuleName,
+		Description: options.Description,
+		GroupID:     options.GroupID,
+	}
+	if err := putManifestPair(target, manifestKey, data, merged, onDiskBytes, sidecar); err != nil {
+		return AssembleResult{}, err
+	}
+	return AssembleResult{SHA1: sha1Hex, ManifestPath: target.describe(manifestKey), Entries: len(merged)}, nil
+}
+
+func parseSidecar(where string, data []byte) (Sidecar, error) {
+	var sidecar Sidecar
+	if err := json.Unmarshal(data, &sidecar); err != nil {
+		return Sidecar{}, fmt.Errorf("%s: %w", where, err)
+	}
+	return sidecar, nil
+}

internal/nwsync/compressedbuf.go

@@ -0,0 +1,80 @@
+package nwsync
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+
+	"github.com/klauspost/compress/zstd"
+)
+
+// NWCompressedBuffer framing, as upstream's neverwinter/compressedbuf.nim
+// writes it for NWSync blobs. All fields are little-endian uint32:
+//
+//	magic "NSYC", version 3, algorithm 2 (zstd), uncompressed size,
+//	zstd header version 1, dictionary 0, then the raw zstd frame.
+const (
+	blobMagic       = 0x4359534E // "NSYC" little-endian
+	blobVersion     = 3
+	algorithmZstd   = 2
+	zstdHeaderVer   = 1
+	zstdDictionary  = 0
+	blobHeaderBytes = 24
+)
+
+// EncodeAll/DecodeAll are single-threaded per call, so the default pool of one
+// encoder per CPU only buys idle memory: each holds a window-sized history, so
+// on a 24-core runner that is ~200 MB of live heap doing nothing. Concurrency 1
+// produces byte-identical output.
+var (
+	blobEncoder, _ = zstd.NewWriter(nil, zstd.WithEncoderConcurrency(1))
+	blobDecoder, _ = zstd.NewReader(nil, zstd.WithDecoderConcurrency(1))
+)
+
+// compressBlob wraps data in NWCompressedBuffer framing.
+func compressBlob(data []byte) []byte {
+	var out bytes.Buffer
+	header := []uint32{blobMagic, blobVersion, algorithmZstd, uint32(len(data)), zstdHeaderVer, zstdDictionary}
+	for _, field := range header {
+		_ = binary.Write(&out, binary.LittleEndian, field)
+	}
+	out.Write(blobEncoder.EncodeAll(data, nil))
+	return out.Bytes()
+}
+
+// decompressBlob unwraps NWCompressedBuffer framing. It exists so a blob this
+// package wrote — or one upstream wrote — can be compared by its uncompressed
+// bytes, which is the only comparison that is meaningful across zstd
+// implementations.
+func decompressBlob(blob []byte) ([]byte, error) {
+	if len(blob) < blobHeaderBytes {
+		return nil, fmt.Errorf("blob too small: %d bytes", len(blob))
+	}
+	header := make([]uint32, 6)
+	if err := binary.Read(bytes.NewReader(blob[:blobHeaderBytes]), binary.LittleEndian, header); err != nil {
+		return nil, fmt.Errorf("decode blob header: %w", err)
+	}
+	switch {
+	case header[0] != blobMagic:
+		return nil, fmt.Errorf("invalid blob magic: %#x", header[0])
+	case header[1] != blobVersion:
+		return nil, fmt.Errorf("unsupported blob version: %d", header[1])
+	case header[2] != algorithmZstd:
+		return nil, fmt.Errorf("unsupported compression algorithm: %d", header[2])
+	case header[4] != zstdHeaderVer:
+		return nil, fmt.Errorf("unsupported zstd header version: %d", header[4])
+	case header[5] != zstdDictionary:
+		return nil, fmt.Errorf("zstd dictionaries are not supported")
+	}
+	if header[3] == 0 {
+		return nil, nil
+	}
+	data, err := blobDecoder.DecodeAll(blob[blobHeaderBytes:], nil)
+	if err != nil {
+		return nil, fmt.Errorf("decompress blob: %w", err)
+	}
+	if uint32(len(data)) != header[3] {
+		return nil, fmt.Errorf("blob size mismatch: header says %d, got %d", header[3], len(data))
+	}
+	return data, nil
+}

internal/nwsync/emit.go

@@ -0,0 +1,278 @@
+package nwsync
+
+import (
+	"context"
+	"crypto/sha1"
+	"fmt"
+	"io"
+	"os"
+	"path"
+	"path/filepath"
+	"slices"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/buildinfo"
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/erf"
+)
+
+// fileSizeLimit matches upstream's --limit-file-size default of 15 MB. A
+// resource over it is a hard failure, not a skip: upstream quit(1)s and so do
+// we. Our largest resource today is 13.66 MiB, so the headroom is thin.
+const fileSizeLimit = 15 * 1024 * 1024
+
+// skippedTypes are never published, matching upstream's GobalResTypeSkipList.
+var skippedTypes = resTypes("nss", "ndb", "gic")
+
+// emitterVersion identifies the blob/manifest byte format this package
+// produces. assemble refuses to merge indexes that disagree on it, because two
+// producers of blobs mean a skewed emitter can otherwise write blobs the merged
+// manifest quietly disagrees with. Bump it only when emitted bytes change — it
+// is deliberately not the build revision, which would invalidate every
+// published index on every unrelated commit.
+const emitterVersion = "1"
+
+// serverTypes are loaded only server-side; a manifest holding nothing else
+// has no client contents. Mirrors upstream's GlobalResTypeServerList, whose
+// trailing 0 is RESTYPE_INVALID.
+var serverTypes = append(resTypes(
+	"are", "dlg", "fac", "gic", "git", "ifo", "itp", "jrl", "ncs", "ndb",
+	"nss", "ptm", "utc", "utd", "ute", "uti", "utm", "utp", "uts", "utt", "utw",
+), 0)
+
+func resTypes(extensions ...string) []uint16 {
+	types := make([]uint16, 0, len(extensions))
+	for _, extension := range extensions {
+		restype, ok := erf.ResourceTypeForExtension(extension)
+		if !ok {
+			panic("nwsync: unknown restype " + extension)
+		}
+		types = append(types, restype)
+	}
+	return types
+}
+
+// EmitResult reports what one emit run produced.
+type EmitResult struct {
+	Name         string // artifact name, without extension
+	ManifestPath string
+	Entries      int
+	BlobsWritten int
+}
+
+// EmitOptions describes one emit run.
+type EmitOptions struct {
+	ArtifactKey  string // depot key of the artifact; the NSYM key is derived from it
+	ArtifactPath string // the file on disk
+	As           string // name override, for a TLK whose filename is not its published name
+	OutDir       string // write locally instead of uploading — the conformance path
+	Sink         sink   // test seam; nil means OutDir or the zone
+}
+
+// Emit explodes one artifact — a .hak/.erf or a loose file such as the TLK —
+// into NWSync blobs plus a NSYM manifest describing only that artifact.
+//
+// Blobs go up as they are produced and the index lands last, so the presence of
+// an index is the publication marker: an artifact whose emit died halfway has
+// real blobs in the zone and no index, which is unambiguous. Blob names are
+// content hashes, so re-running skips whatever already landed.
+func Emit(options EmitOptions) (EmitResult, error) {
+	artifact, err := os.Open(options.ArtifactPath)
+	if err != nil {
+		return EmitResult{}, fmt.Errorf("read artifact: %w", err)
+	}
+	defer artifact.Close()
+	info, err := artifact.Stat()
+	if err != nil {
+		return EmitResult{}, fmt.Errorf("read artifact: %w", err)
+	}
+	// A section reader, not the file itself: hashing must not move the file
+	// offset out from under everything that reads the artifact afterwards.
+	if err := checkArtifactKey(options.ArtifactKey, io.NewSectionReader(artifact, 0, info.Size())); err != nil {
+		return EmitResult{}, err
+	}
+	name := options.As
+	if name == "" {
+		name = path.Base(options.ArtifactKey)
+	}
+	extension := path.Ext(name)
+	name = strings.TrimSuffix(name, extension)
+
+	key, err := resolveIndexKey(options.ArtifactKey, options.OutDir)
+	if err != nil {
+		return EmitResult{}, err
+	}
+
+	index, err := readArtifactIndex(options.ArtifactPath, artifact, info.Size(), name)
+	if err != nil {
+		return EmitResult{}, err
+	}
+
+	target, err := openSink(options.OutDir, options.Sink)
+	if err != nil {
+		return EmitResult{}, err
+	}
+
+	entries, blobs, onDiskBytes, err := emitResources(artifact, index, target)
+	if err != nil {
+		return EmitResult{}, err
+	}
+	if len(entries) == 0 {
+		return EmitResult{}, fmt.Errorf("%s: nothing to index (no publishable resources)", options.ArtifactPath)
+	}
+
+	data, err := writeManifest(entries)
+	if err != nil {
+		return EmitResult{}, err
+	}
+	if err := putManifestPair(target, key, data, entries, onDiskBytes, Sidecar{ModuleName: name}); err != nil {
+		return EmitResult{}, err
+	}
+	return EmitResult{Name: name, ManifestPath: target.describe(key), Entries: len(entries), BlobsWritten: blobs}, nil
+}
+
+// openSink returns the zone sink, or a local directory when outDir is set.
+func openSink(outDir string, injected sink) (sink, error) {
+	if injected != nil {
+		return injected, nil
+	}
+	if outDir != "" {
+		return dirSink{root: outDir}, nil
+	}
+	return newZoneSink(context.Background(), os.Getenv)
+}
+
+// readArtifactIndex locates the resources of an ERF/HAK/MOD, or the single
+// resource a loose file represents, without reading any payload. Upstream's
+// resman does the same dispatch on the file's first three bytes. name is the
+// artifact's published name, which for a loose file is also its resref.
+func readArtifactIndex(path string, artifact io.ReaderAt, size int64, name string) ([]erf.IndexEntry, error) {
+	magic := make([]byte, 3)
+	if size >= 3 {
+		if _, err := artifact.ReadAt(magic, 0); err != nil {
+			return nil, fmt.Errorf("%s: %w", path, err)
+		}
+	}
+	switch string(magic) {
+	case "ERF", "HAK":
+		index, err := erf.ReadIndex(artifact, size)
+		if err != nil {
+			return nil, fmt.Errorf("%s: %w", path, err)
+		}
+		return index.Entries, nil
+	case "MOD":
+		// A persistent world never publishes module contents, so the .mod
+		// contributes no bytes to a manifest — it only says which haks and
+		// which TLK the manifest covers.
+		return nil, fmt.Errorf("%s: a module is never emitted; a manifest is haks plus the TLK", path)
+	}
+	extension := filepath.Ext(filepath.Base(path))
+	restype, ok := erf.ResourceTypeForExtension(extension)
+	if !ok {
+		return nil, fmt.Errorf("%s: unknown resource type %q", path, extension)
+	}
+	return []erf.IndexEntry{{Name: name, Type: restype, Offset: 0, Size: size}}, nil
+}
+
+// emitResources hashes, compresses and stores one resource at a time, reading
+// each payload from the artifact only when its turn comes. Peak memory
+// therefore tracks the largest single resource, not the archive: a 2 GB hak
+// must emit inside a runner's few spare GB.
+func emitResources(artifact io.ReaderAt, index []erf.IndexEntry, target sink) ([]Entry, int, int64, error) {
+	// A resref appearing twice inside one artifact resolves to the last one,
+	// the way resman lets the last container added win.
+	order := make([]Identity, 0, len(index))
+	latest := make(map[Identity]erf.IndexEntry, len(index))
+	var tooBig []string
+	for _, entry := range index {
+		if _, ok := erf.ExtensionForResourceType(entry.Type); !ok {
+			return nil, 0, 0, fmt.Errorf("resref %s is not resolvable (unknown restype %d)", entry.Name, entry.Type)
+		}
+		if slices.Contains(skippedTypes, entry.Type) {
+			continue
+		}
+		if entry.Size > fileSizeLimit {
+			tooBig = append(tooBig, fmt.Sprintf("%s: %d bytes > %d", entry.Name, entry.Size, fileSizeLimit))
+			continue
+		}
+		identity := Identity{ResRef: strings.ToLower(entry.Name), ResType: entry.Type}
+		if _, seen := latest[identity]; !seen {
+			order = append(order, identity)
+		}
+		latest[identity] = entry
+	}
+	if len(tooBig) > 0 {
+		sort.Strings(tooBig)
+		return nil, 0, 0, fmt.Errorf("resources exceed the file size limit:\n  %s", strings.Join(tooBig, "\n  "))
+	}
+
+	entries := make([]Entry, 0, len(order))
+	var blobs int
+	var onDiskBytes int64
+	for _, identity := range order {
+		payload, err := erf.ReadPayload(artifact, latest[identity])
+		if err != nil {
+			return nil, 0, 0, err
+		}
+		sum := sha1.Sum(payload)
+		entries = append(entries, Entry{
+			SHA1:    sum,
+			Size:    uint32(len(payload)),
+			ResRef:  identity.ResRef,
+			ResType: identity.ResType,
+		})
+		written, err := target.putBlob(fmt.Sprintf("%x", sum), func() []byte { return compressBlob(payload) })
+		if err != nil {
+			return nil, 0, 0, err
+		}
+		if written > 0 {
+			blobs++
+			onDiskBytes += written
+		}
+	}
+	return entries, blobs, onDiskBytes, nil
+}
+
+// created is the sidecar timestamp. SOURCE_DATE_EPOCH pins it so a build can
+// be reproduced byte for byte; the manifest itself is deterministic already.
+func created() int64 {
+	if raw := os.Getenv("SOURCE_DATE_EPOCH"); raw != "" {
+		if seconds, err := strconv.ParseInt(raw, 10, 64); err == nil {
+			return seconds
+		}
+	}
+	return time.Now().Unix()
+}
+
+// putManifestPair stores a NSYM manifest and its .json sidecar at key. The
+// caller supplies the sidecar fields it knows; the rest are derived from the
+// entries. data must be the serialised form of entries.
+func putManifestPair(target sink, key string, data []byte, entries []Entry, onDiskBytes int64, sidecar Sidecar) error {
+	var totalBytes int64
+	clientContents := false
+	for _, entry := range entries {
+		totalBytes += int64(entry.Size)
+		if !slices.Contains(serverTypes, entry.ResType) {
+			clientContents = true
+		}
+	}
+	sidecar.Version = manifestVersion
+	sidecar.SHA1 = fmt.Sprintf("%x", sha1.Sum(data))
+	sidecar.HashTreeDepth = hashTreeDepth
+	sidecar.IncludesModuleContents = false
+	sidecar.IncludesClientContents = clientContents
+	sidecar.TotalFiles = len(entries)
+	sidecar.TotalBytes = totalBytes
+	sidecar.OnDiskBytes = onDiskBytes
+	sidecar.Created = created()
+	sidecar.CreatedWith = buildinfo.String()
+	sidecar.EmitterVersion = emitterVersion
+
+	body, err := marshalSidecar(sidecar)
+	if err != nil {
+		return err
+	}
+	return target.putIndex(key, data, body)
+}

internal/nwsync/manifest.go

@@ -0,0 +1,200 @@
+package nwsync
+
+import (
+	"bytes"
+	"encoding/binary"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"io"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// NSYM manifest, version 3, exactly as upstream neverwinter/nwsync.nim writes
+// it. Everything is little-endian:
+//
+//	"NSYM", uint32 version, uint32 entry count, uint32 mapping count,
+//	entries:  byte[20] raw sha1, uint32 size, char[16] resref, uint16 restype
+//	mappings: uint32 entry index,             char[16] resref, uint16 restype
+//
+// Entries are sorted by lowercase sha1 hex then resref, and a resource whose
+// sha1 was already written becomes a mapping instead of a second entry.
+const (
+	manifestVersion = 3
+	hashTreeDepth   = 2
+	resRefBytes     = 16
+)
+
+// Entry is one resource in a manifest.
+type Entry struct {
+	SHA1    [20]byte
+	Size    uint32
+	ResRef  string // lowercase, no extension, at most 16 characters
+	ResType uint16
+}
+
+func (e Entry) sha1Hex() string { return hex.EncodeToString(e.SHA1[:]) }
+
+// Identity is what a resref resolves by: name plus type. It is the merge key
+// inside one artifact and across artifacts alike.
+type Identity struct {
+	ResRef  string
+	ResType uint16
+}
+
+func (e Entry) identity() Identity { return Identity{ResRef: e.ResRef, ResType: e.ResType} }
+
+// writeManifest serialises entries into NSYM v3 bytes.
+func writeManifest(entries []Entry) ([]byte, error) {
+	sorted := make([]Entry, len(entries))
+	copy(sorted, entries)
+	sort.SliceStable(sorted, func(i, j int) bool {
+		left, right := sorted[i].sha1Hex(), sorted[j].sha1Hex()
+		if left != right {
+			return left < right
+		}
+		return sorted[i].ResRef < sorted[j].ResRef
+	})
+
+	var body, mappings bytes.Buffer
+	seen := make(map[string]uint32, len(sorted))
+	var entryCount, mappingCount uint32
+	for _, entry := range sorted {
+		padded, err := padResRef(entry.ResRef)
+		if err != nil {
+			return nil, err
+		}
+		if index, ok := seen[entry.sha1Hex()]; ok {
+			_ = binary.Write(&mappings, binary.LittleEndian, index)
+			mappings.Write(padded)
+			_ = binary.Write(&mappings, binary.LittleEndian, entry.ResType)
+			mappingCount++
+			continue
+		}
+		seen[entry.sha1Hex()] = entryCount
+		entryCount++
+		body.Write(entry.SHA1[:])
+		_ = binary.Write(&body, binary.LittleEndian, entry.Size)
+		body.Write(padded)
+		_ = binary.Write(&body, binary.LittleEndian, entry.ResType)
+	}
+
+	var out bytes.Buffer
+	out.WriteString("NSYM")
+	for _, field := range []uint32{manifestVersion, entryCount, mappingCount} {
+		_ = binary.Write(&out, binary.LittleEndian, field)
+	}
+	out.Write(body.Bytes())
+	out.Write(mappings.Bytes())
+	return out.Bytes(), nil
+}
+
+// readManifest parses NSYM v3 bytes. Mappings are expanded back into entries,
+// the way upstream's reader does, so a caller sees one entry per resref.
+func readManifest(data []byte) ([]Entry, error) {
+	reader := bytes.NewReader(data)
+	magic := make([]byte, 4)
+	if _, err := io.ReadFull(reader, magic); err != nil || string(magic) != "NSYM" {
+		return nil, fmt.Errorf("not a manifest (invalid magic bytes)")
+	}
+	var version, entryCount, mappingCount uint32
+	for _, field := range []*uint32{&version, &entryCount, &mappingCount} {
+		if err := binary.Read(reader, binary.LittleEndian, field); err != nil {
+			return nil, fmt.Errorf("truncated manifest header: %w", err)
+		}
+	}
+	if version != manifestVersion {
+		return nil, fmt.Errorf("unsupported manifest version %d", version)
+	}
+
+	entries := make([]Entry, 0, entryCount+mappingCount)
+	for i := uint32(0); i < entryCount; i++ {
+		var entry Entry
+		if _, err := io.ReadFull(reader, entry.SHA1[:]); err != nil {
+			return nil, fmt.Errorf("truncated entry %d: %w", i, err)
+		}
+		if err := binary.Read(reader, binary.LittleEndian, &entry.Size); err != nil {
+			return nil, fmt.Errorf("truncated entry %d: %w", i, err)
+		}
+		resref, restype, err := readResRef(reader)
+		if err != nil {
+			return nil, fmt.Errorf("truncated entry %d: %w", i, err)
+		}
+		entry.ResRef, entry.ResType = resref, restype
+		entries = append(entries, entry)
+	}
+	for i := uint32(0); i < mappingCount; i++ {
+		var index uint32
+		if err := binary.Read(reader, binary.LittleEndian, &index); err != nil {
+			return nil, fmt.Errorf("truncated mapping %d: %w", i, err)
+		}
+		if index >= entryCount {
+			return nil, fmt.Errorf("mapping %d references non-existent entry %d", i, index)
+		}
+		resref, restype, err := readResRef(reader)
+		if err != nil {
+			return nil, fmt.Errorf("truncated mapping %d: %w", i, err)
+		}
+		target := entries[index]
+		entries = append(entries, Entry{SHA1: target.SHA1, Size: target.Size, ResRef: resref, ResType: restype})
+	}
+	return entries, nil
+}
+
+func readResRef(reader *bytes.Reader) (string, uint16, error) {
+	raw := make([]byte, resRefBytes)
+	if _, err := io.ReadFull(reader, raw); err != nil {
+		return "", 0, err
+	}
+	var restype uint16
+	if err := binary.Read(reader, binary.LittleEndian, &restype); err != nil {
+		return "", 0, err
+	}
+	return strings.ToLower(string(bytes.TrimRight(raw, "\x00"))), restype, nil
+}
+
+func padResRef(resref string) ([]byte, error) {
+	if len(resref) > resRefBytes {
+		return nil, fmt.Errorf("resref %q exceeds %d characters", resref, resRefBytes)
+	}
+	padded := make([]byte, resRefBytes)
+	copy(padded, strings.ToLower(resref))
+	return padded, nil
+}
+
+// Sidecar is the .json file written next to every manifest. Clients fetch it
+// (nwn_nwsync_fetch.nim), so the field names and order match upstream.
+// Upstream omits an integer meta field whose value is 0, hence group_id's
+// omitempty: 0 means absent, not "group zero".
+type Sidecar struct {
+	Version                int    `json:"version"`
+	SHA1                   string `json:"sha1"`
+	HashTreeDepth          int    `json:"hash_tree_depth"`
+	ModuleName             string `json:"module_name"`
+	Description            string `json:"description"`
+	IncludesModuleContents bool   `json:"includes_module_contents"`
+	IncludesClientContents bool   `json:"includes_client_contents"`
+	TotalFiles             int    `json:"total_files"`
+	TotalBytes             int64  `json:"total_bytes"`
+	OnDiskBytes            int64  `json:"on_disk_bytes"`
+	Created                int64  `json:"created"`
+	CreatedWith            string `json:"created_with"`
+	EmitterVersion         string `json:"emitter_version,omitempty"`
+	GroupID                int    `json:"group_id,omitempty"`
+}
+
+func marshalSidecar(sidecar Sidecar) ([]byte, error) {
+	body, err := json.MarshalIndent(sidecar, "", "  ")
+	if err != nil {
+		return nil, err
+	}
+	// Upstream terminates the file with CRLF; match it.
+	return append(body, '\r', '\n'), nil
+}
+
+// blobPath is the data store path for a blob, hash tree depth 2.
+func blobPath(root, sha1Hex string) string {
+	return filepath.Join(root, "data", "sha1", sha1Hex[0:2], sha1Hex[2:4], sha1Hex)
+}

internal/nwsync/memory_test.go

@@ -0,0 +1,150 @@
+package nwsync
+
+import (
+	"bytes"
+	"fmt"
+	"math/rand"
+	"os"
+	"path/filepath"
+	"runtime"
+	"runtime/debug"
+	"testing"
+	"time"
+
+	"github.com/klauspost/compress/zstd"
+
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/erf"
+)
+
+// TestSingleThreadedEncoderMatchesDefault pins the claim the blob encoder's
+// concurrency setting rests on: it saves memory only, and a published blob is
+// the same bytes either way.
+func TestSingleThreadedEncoderMatchesDefault(t *testing.T) {
+	standard, err := zstd.NewWriter(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer standard.Close()
+
+	body := make([]byte, 4<<20)
+	random := rand.New(rand.NewSource(1))
+	random.Read(body[:len(body)/2])
+	for _, size := range []int{0, 1, 4 << 10, len(body)} {
+		if !bytes.Equal(blobEncoder.EncodeAll(body[:size], nil), standard.EncodeAll(body[:size], nil)) {
+			t.Fatalf("%d bytes compress differently at concurrency 1", size)
+		}
+	}
+}
+
+// resourceSize is one payload in the memory fixtures. Real haks hold a few MB
+// per resource, and peak memory is meant to track that, not the archive.
+const resourceSize = 1 << 20
+
+// writeStreamedHak builds a hak of count resources without ever holding the
+// archive in memory, so the fixture itself does not decide the measurement.
+// Payloads are distinct, so no blob is deduplicated away.
+func writeStreamedHak(t *testing.T, path string, count int) {
+	t.Helper()
+	payload := filepath.Join(t.TempDir(), "payload.bin")
+	body := make([]byte, resourceSize)
+	for index := range body {
+		body[index] = byte(index)
+	}
+
+	resources := make([]erf.Resource, 0, count)
+	for index := range count {
+		// A distinct first byte per resource is enough to give every payload
+		// its own sha1 while still streaming from one file per resource.
+		unique := filepath.Join(filepath.Dir(payload), fmt.Sprintf("p%d.bin", index))
+		body[0] = byte(index)
+		body[1] = byte(index >> 8)
+		if err := os.WriteFile(unique, body, 0o644); err != nil {
+			t.Fatal(err)
+		}
+		resources = append(resources, erf.Resource{
+			Name:       fmt.Sprintf("res%05d", index),
+			Type:       restype(t, "tga"),
+			SourcePath: unique,
+			Size:       resourceSize,
+		})
+	}
+
+	file, err := os.Create(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+	if err := erf.Write(file, erf.New("HAK", resources)); err != nil {
+		t.Fatalf("write hak: %v", err)
+	}
+}
+
+// peakHeapDuring runs work while sampling the heap, and returns the largest
+// live heap it saw.
+func peakHeapDuring(work func()) uint64 {
+	runtime.GC()
+	done := make(chan struct{})
+	peak := make(chan uint64, 1)
+	go func() {
+		var highest uint64
+		var stats runtime.MemStats
+		for {
+			select {
+			case <-done:
+				peak <- highest
+				return
+			default:
+			}
+			runtime.ReadMemStats(&stats)
+			if stats.HeapAlloc > highest {
+				highest = stats.HeapAlloc
+			}
+			time.Sleep(time.Millisecond)
+		}
+	}()
+	work()
+	close(done)
+	return <-peak
+}
+
+// TestEmitPeakMemoryDoesNotScaleWithArtifactSize is the regression check for
+// the OOM kills on large haks: emit used to hold the whole archive (twice), so
+// a 2 GB hak needed about 10 GB. Emitting an archive 8× bigger must not cost
+// meaningfully more memory.
+func TestEmitPeakMemoryDoesNotScaleWithArtifactSize(t *testing.T) {
+	if testing.Short() {
+		t.Skip("writes a 64 MB fixture")
+	}
+	// A lazy GC lets garbage pile up in proportion to the live heap, which
+	// hides the thing under test. Collecting eagerly makes the sampled heap
+	// track what emit actually holds.
+	defer debug.SetGCPercent(debug.SetGCPercent(10))
+
+	measure := func(count int) uint64 {
+		dir := t.TempDir()
+		hak := filepath.Join(dir, "big.hak")
+		writeStreamedHak(t, hak, count)
+		// The key is computed outside the measurement: the test helper reads
+		// the whole file to hash it, which emit itself no longer does.
+		options := EmitOptions{
+			ArtifactKey:  artifactKey(t, hak),
+			ArtifactPath: hak,
+			As:           filepath.Base(hak),
+			OutDir:       filepath.Join(dir, "out"),
+		}
+		return peakHeapDuring(func() {
+			if _, err := Emit(options); err != nil {
+				t.Fatalf("emit %d resources: %v", count, err)
+			}
+		})
+	}
+
+	small := measure(8)  // 8 MB
+	large := measure(64) // 64 MB
+	const slack = 24 << 20
+
+	t.Logf("peak heap: 8 MB hak %d bytes, 64 MB hak %d bytes", small, large)
+	if large > small+slack {
+		t.Fatalf("peak heap scaled with artifact size: 8 MB hak peaked at %d bytes, 64 MB hak at %d", small, large)
+	}
+}

internal/nwsync/nwsync_test.go

@@ -0,0 +1,476 @@
+package nwsync
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/hex"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/erf"
+)
+
+func restype(t *testing.T, extension string) uint16 {
+	t.Helper()
+	value, ok := erf.ResourceTypeForExtension(extension)
+	if !ok {
+		t.Fatalf("unknown restype %q", extension)
+	}
+	return value
+}
+
+// writeHak builds a HAK fixture from resref.ext => body pairs.
+func writeHak(t *testing.T, path string, contents map[string][]byte) {
+	t.Helper()
+	resources := make([]erf.Resource, 0, len(contents))
+	for name, body := range contents {
+		stem, extension, _ := strings.Cut(name, ".")
+		resources = append(resources, erf.Resource{
+			Name: stem,
+			Type: restype(t, extension),
+			Data: body,
+			Size: int64(len(body)),
+		})
+	}
+	var out bytes.Buffer
+	if err := erf.Write(&out, erf.New("HAK", resources)); err != nil {
+		t.Fatalf("write hak: %v", err)
+	}
+	if err := os.WriteFile(path, out.Bytes(), 0o644); err != nil {
+		t.Fatalf("write hak file: %v", err)
+	}
+}
+
+// artifactKey is the depot key a file would be published under: the sha256 of
+// its bytes, hash-tree depth 2, keeping the extension.
+func artifactKey(t *testing.T, path string) string {
+	t.Helper()
+	body, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	sum := sha256.Sum256(body)
+	digest := hex.EncodeToString(sum[:])
+	return "artifacts/haks/sha256/" + digest[0:2] + "/" + digest[2:4] + "/" + digest + filepath.Ext(path)
+}
+
+// emitLocal emits one artifact into a local tree, the conformance path.
+func emitLocal(t *testing.T, path, out string) (EmitResult, error) {
+	t.Helper()
+	return Emit(EmitOptions{
+		ArtifactKey:  artifactKey(t, path),
+		ArtifactPath: path,
+		As:           filepath.Base(path),
+		OutDir:       out,
+	})
+}
+
+func TestBlobFramingRoundTrips(t *testing.T) {
+	data := []byte("the quick brown fox jumps over the lazy dog, repeatedly and at length")
+	blob := compressBlob(data)
+
+	header := make([]uint32, 6)
+	if err := binary.Read(bytes.NewReader(blob[:blobHeaderBytes]), binary.LittleEndian, header); err != nil {
+		t.Fatalf("read header: %v", err)
+	}
+	want := []uint32{blobMagic, 3, 2, uint32(len(data)), 1, 0}
+	for i := range want {
+		if header[i] != want[i] {
+			t.Errorf("header field %d = %d, want %d", i, header[i], want[i])
+		}
+	}
+	if string(blob[:4]) != "NSYC" {
+		t.Errorf("magic bytes = %q, want NSYC", blob[:4])
+	}
+
+	got, err := decompressBlob(blob)
+	if err != nil {
+		t.Fatalf("decompress: %v", err)
+	}
+	if !bytes.Equal(got, data) {
+		t.Errorf("round trip mismatch: %q", got)
+	}
+}
+
+func TestManifestBytesMatchUpstreamLayout(t *testing.T) {
+	shared := sha1.Sum([]byte("shared"))
+	other := sha1.Sum([]byte("other"))
+	// Deliberately out of order, and with two resrefs sharing one sha1: the
+	// second one must become a mapping, not a second entry.
+	entries := []Entry{
+		{SHA1: other, Size: 5, ResRef: "zzz", ResType: 1},
+		{SHA1: shared, Size: 6, ResRef: "bbb", ResType: 2},
+		{SHA1: shared, Size: 6, ResRef: "aaa", ResType: 3},
+	}
+	data, err := writeManifest(entries)
+	if err != nil {
+		t.Fatalf("write manifest: %v", err)
+	}
+
+	if string(data[:4]) != "NSYM" {
+		t.Fatalf("magic = %q", data[:4])
+	}
+	var version, entryCount, mappingCount uint32
+	reader := bytes.NewReader(data[4:16])
+	for _, field := range []*uint32{&version, &entryCount, &mappingCount} {
+		_ = binary.Read(reader, binary.LittleEndian, field)
+	}
+	if version != 3 || entryCount != 2 || mappingCount != 1 {
+		t.Fatalf("header = version %d, %d entries, %d mappings; want 3/2/1", version, entryCount, mappingCount)
+	}
+	wantSize := 16 + int(entryCount)*(20+4+16+2) + int(mappingCount)*(4+16+2)
+	if len(data) != wantSize {
+		t.Fatalf("manifest is %d bytes, want %d", len(data), wantSize)
+	}
+
+	// Sorted by sha1 hex then resref, so the shared hash's "aaa" is the entry
+	// and "bbb" is demoted to a mapping.
+	round, err := readManifest(data)
+	if err != nil {
+		t.Fatalf("read manifest: %v", err)
+	}
+	if len(round) != 3 {
+		t.Fatalf("round trip returned %d entries, want 3", len(round))
+	}
+	byResRef := map[string]Entry{}
+	for _, entry := range round {
+		byResRef[entry.ResRef] = entry
+	}
+	for _, entry := range entries {
+		got, ok := byResRef[entry.ResRef]
+		if !ok {
+			t.Fatalf("resref %q lost in round trip", entry.ResRef)
+		}
+		if got != entry {
+			t.Errorf("resref %q = %+v, want %+v", entry.ResRef, got, entry)
+		}
+	}
+	if round[0].ResRef != "aaa" && round[1].ResRef != "aaa" {
+		t.Errorf("entries are not sorted by sha1 then resref: %+v", round)
+	}
+}
+
+func TestEmitWritesBlobsAndManifest(t *testing.T) {
+	dir := t.TempDir()
+	hak := filepath.Join(dir, "sow_test_01.hak")
+	body := []byte("texture bytes")
+	writeHak(t, hak, map[string][]byte{
+		"bloodstain1.tga": body,
+		"copy1.txi":       body, // same content, different resref: one blob
+		"script1.nss":     []byte("void main() {}"),
+		"debug1.ndb":      []byte("debug"),
+		"comment1.gic":    []byte("comment"),
+	})
+
+	out := filepath.Join(dir, "out")
+	result, err := emitLocal(t, hak, out)
+	if err != nil {
+		t.Fatalf("emit: %v", err)
+	}
+	if result.Entries != 2 {
+		t.Errorf("emitted %d entries, want 2 (nss/ndb/gic are always skipped)", result.Entries)
+	}
+	if result.BlobsWritten != 1 {
+		t.Errorf("wrote %d blobs, want 1 (identical content shares a blob)", result.BlobsWritten)
+	}
+
+	// The blob is named by the sha1 of the uncompressed bytes, under a depth-2
+	// hash tree, and decompresses back to exactly those bytes.
+	sum := sha1.Sum(body)
+	name := hex.EncodeToString(sum[:])
+	path := filepath.Join(out, "data", "sha1", name[0:2], name[2:4], name)
+	blob, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("blob missing at %s: %v", path, err)
+	}
+	got, err := decompressBlob(blob)
+	if err != nil {
+		t.Fatalf("decompress blob: %v", err)
+	}
+	if !bytes.Equal(got, body) {
+		t.Errorf("blob decompressed to %q, want %q", got, body)
+	}
+
+	entries := readEmitted(t, result.ManifestPath)
+	for _, entry := range entries {
+		if entry.ResType == restype(t, "nss") || entry.ResType == restype(t, "ndb") || entry.ResType == restype(t, "gic") {
+			t.Errorf("skipped restype leaked into the manifest: %+v", entry)
+		}
+	}
+
+	var sidecar Sidecar
+	body2, err := os.ReadFile(result.ManifestPath + ".json")
+	if err != nil {
+		t.Fatalf("sidecar missing: %v", err)
+	}
+	if err := json.Unmarshal(body2, &sidecar); err != nil {
+		t.Fatalf("sidecar json: %v", err)
+	}
+	if sidecar.TotalFiles != 2 || sidecar.HashTreeDepth != 2 || sidecar.Version != 3 {
+		t.Errorf("sidecar = %+v", sidecar)
+	}
+	if sidecar.IncludesModuleContents {
+		t.Error("sidecar claims module contents; a published manifest never has them")
+	}
+	if strings.Contains(string(body2), "group_id") {
+		t.Error("per-artifact sidecar should omit group_id (0 means absent)")
+	}
+	if _, err := os.Stat(filepath.Join(out, "latest")); err == nil {
+		t.Error("a latest file was written; there must never be one")
+	}
+}
+
+func readEmitted(t *testing.T, indexPath string) []Entry {
+	t.Helper()
+	data, err := os.ReadFile(indexPath)
+	if err != nil {
+		t.Fatalf("read emitted manifest: %v", err)
+	}
+	entries, err := readManifest(data)
+	if err != nil {
+		t.Fatalf("parse emitted manifest: %v", err)
+	}
+	return entries
+}
+
+func TestEmitFailsClosedOnOversizeResource(t *testing.T) {
+	dir := t.TempDir()
+	hak := filepath.Join(dir, "big.hak")
+	writeHak(t, hak, map[string][]byte{"huge1.tga": make([]byte, fileSizeLimit+1)})
+
+	if _, err := emitLocal(t, hak, filepath.Join(dir, "out")); err == nil {
+		t.Fatal("emit accepted a resource over the 15 MB limit")
+	}
+}
+
+func TestEmitLooseFile(t *testing.T) {
+	dir := t.TempDir()
+	tlk := filepath.Join(dir, "sow_tlk.tlk")
+	if err := os.WriteFile(tlk, []byte("TLK V3.0 payload"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	out := filepath.Join(dir, "out")
+	result, err := emitLocal(t, tlk, out)
+	if err != nil {
+		t.Fatalf("emit tlk: %v", err)
+	}
+	entries := readEmitted(t, result.ManifestPath)
+	if len(entries) != 1 || entries[0].ResRef != "sow_tlk" || entries[0].ResType != restype(t, "tlk") {
+		t.Fatalf("tlk emitted as %+v", entries)
+	}
+	if result.BlobsWritten != 1 {
+		t.Errorf("wrote %d blobs, want 1", result.BlobsWritten)
+	}
+}
+
+// emitFixture emits two haks that share a resref, so the merge rule is
+// observable: "top" holds the winning body, "assets" the shadowed one.
+func emitFixture(t *testing.T) (out string, keys map[string]string, topBody, assetBody []byte) {
+	t.Helper()
+	dir := t.TempDir()
+	topBody = []byte("2da from sow_top")
+	assetBody = []byte("2da from the asset hak")
+	writeHak(t, filepath.Join(dir, "sow_top.hak"), map[string][]byte{"appearance.2da": topBody})
+	writeHak(t, filepath.Join(dir, "sow_core_01.hak"), map[string][]byte{
+		"appearance.2da":  assetBody,
+		"bloodstain1.tga": []byte("blood"),
+	})
+	out = filepath.Join(dir, "out")
+	keys = map[string]string{}
+	for _, name := range []string{"sow_top", "sow_core_01"} {
+		path := filepath.Join(dir, name+".hak")
+		keys[name] = artifactKey(t, path)
+		if _, err := emitLocal(t, path, out); err != nil {
+			t.Fatalf("emit %s: %v", name, err)
+		}
+	}
+	return out, keys, topBody, assetBody
+}
+
+func TestAssembleShadowsByOrder(t *testing.T) {
+	entriesDir, keys, topBody, assetBody := emitFixture(t)
+
+	result, err := Assemble(AssembleOptions{
+		ArtifactKeys: []string{keys["sow_top"], keys["sow_core_01"]},
+		OutDir:       entriesDir,
+		GroupID:      2,
+	})
+	if err != nil {
+		t.Fatalf("assemble: %v", err)
+	}
+	if result.Entries != 2 {
+		t.Fatalf("merged %d entries, want 2 (appearance.2da is shadowed, not duplicated)", result.Entries)
+	}
+
+	data, err := os.ReadFile(result.ManifestPath)
+	if err != nil {
+		t.Fatalf("read merged manifest: %v", err)
+	}
+	merged := sha1.Sum(data)
+	if hex.EncodeToString(merged[:]) != result.SHA1 || filepath.Base(result.ManifestPath) != result.SHA1 {
+		t.Errorf("manifest is not named by its own sha1: %s", result.ManifestPath)
+	}
+	entries, err := readManifest(data)
+	if err != nil {
+		t.Fatalf("parse merged manifest: %v", err)
+	}
+	for _, entry := range entries {
+		if entry.ResRef != "appearance" {
+			continue
+		}
+		if entry.SHA1 != sha1.Sum(topBody) {
+			t.Errorf("appearance.2da resolved to the wrong hak; want the earliest in --order")
+		}
+		if entry.SHA1 == sha1.Sum(assetBody) {
+			t.Error("appearance.2da resolved to the shadowed hak")
+		}
+	}
+
+	sidecar := Sidecar{}
+	body, err := os.ReadFile(result.ManifestPath + ".json")
+	if err != nil {
+		t.Fatalf("merged sidecar missing: %v", err)
+	}
+	if err := json.Unmarshal(body, &sidecar); err != nil {
+		t.Fatalf("merged sidecar json: %v", err)
+	}
+	if sidecar.GroupID != 2 {
+		t.Errorf("group_id = %d, want 2 (testing)", sidecar.GroupID)
+	}
+	if sidecar.SHA1 != result.SHA1 {
+		t.Errorf("sidecar sha1 = %s, want %s", sidecar.SHA1, result.SHA1)
+	}
+	if sidecar.TotalFiles != 2 {
+		t.Errorf("total_files = %d, want 2", sidecar.TotalFiles)
+	}
+}
+
+func TestAssembleReversedOrderPicksTheOtherHak(t *testing.T) {
+	entriesDir, keys, topBody, assetBody := emitFixture(t)
+
+	result, err := Assemble(AssembleOptions{
+		ArtifactKeys: []string{keys["sow_core_01"], keys["sow_top"]},
+		OutDir:       entriesDir,
+	})
+	if err != nil {
+		t.Fatalf("assemble: %v", err)
+	}
+	data, _ := os.ReadFile(result.ManifestPath)
+	entries, err := readManifest(data)
+	if err != nil {
+		t.Fatalf("parse merged manifest: %v", err)
+	}
+	for _, entry := range entries {
+		if entry.ResRef == "appearance" && entry.SHA1 != sha1.Sum(assetBody) {
+			t.Errorf("appearance.2da did not follow --order; still resolves to %x", entry.SHA1)
+		}
+	}
+	_ = topBody
+}
+
+func TestAssembleRefusesMismatchedEmitterVersions(t *testing.T) {
+	entriesDir, keys, _, _ := emitFixture(t)
+
+	index, err := resolveIndexKey(keys["sow_core_01"], entriesDir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	path := filepath.Join(entriesDir, index+".json")
+	var sidecar Sidecar
+	body, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := json.Unmarshal(body, &sidecar); err != nil {
+		t.Fatal(err)
+	}
+	sidecar.EmitterVersion = "0"
+	patched, err := marshalSidecar(sidecar)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, patched, 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = Assemble(AssembleOptions{
+		ArtifactKeys: []string{keys["sow_top"], keys["sow_core_01"]},
+		OutDir:       entriesDir,
+	})
+	if err == nil || !strings.Contains(err.Error(), "emitter version mismatch") {
+		t.Fatalf("assemble merged across emitter versions: %v", err)
+	}
+}
+
+func TestEmitHonoursSourceDateEpoch(t *testing.T) {
+	t.Setenv("SOURCE_DATE_EPOCH", "1700000000")
+	dir := t.TempDir()
+	hak := filepath.Join(dir, "pinned.hak")
+	writeHak(t, hak, map[string][]byte{"one1.tga": []byte("body")})
+	result, err := emitLocal(t, hak, filepath.Join(dir, "out"))
+	if err != nil {
+		t.Fatalf("emit: %v", err)
+	}
+	body, err := os.ReadFile(result.ManifestPath + ".json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var sidecar Sidecar
+	if err := json.Unmarshal(body, &sidecar); err != nil {
+		t.Fatal(err)
+	}
+	if sidecar.Created != 1700000000 {
+		t.Errorf("created = %d, want the pinned SOURCE_DATE_EPOCH", sidecar.Created)
+	}
+}
+
+func TestEmitRejectsAModule(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "sow.mod")
+	var out bytes.Buffer
+	if err := erf.Write(&out, erf.New("MOD", []erf.Resource{
+		{Name: "module", Type: restype(t, "ifo"), Data: []byte("ifo"), Size: 3},
+	})); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, out.Bytes(), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := emitLocal(t, path, filepath.Join(dir, "out")); err == nil {
+		t.Fatal("emit accepted a .mod; a manifest never carries module contents")
+	}
+}
+
+func TestAssembleFailsClosedOnMissingIndex(t *testing.T) {
+	entriesDir, keys, _, _ := emitFixture(t)
+	missing := "artifacts/haks/sha256/00/11/" + strings.Repeat("0", 64) + ".hak"
+	_, err := Assemble(AssembleOptions{
+		ArtifactKeys: []string{keys["sow_top"], missing},
+		OutDir:       entriesDir,
+	})
+	if err == nil || !strings.Contains(err.Error(), missing) {
+		t.Fatalf("assemble did not fail closed and name the missing artifact: %v", err)
+	}
+}
+
+func TestRunUsageErrors(t *testing.T) {
+	cases := [][]string{
+		nil,
+		{"nope"},
+		{"emit"},
+		{"emit", "artifact-key.hak"},
+		{"emit", "a", "b", "c"},
+		{"assemble", "--out", "y"},
+	}
+	for _, args := range cases {
+		var out, errw bytes.Buffer
+		if code := Run(args, &out, &errw); code != exitUsage {
+			t.Errorf("Run(%v) exit=%d, want %d", args, code, exitUsage)
+		}
+	}
+}

internal/nwsync/run.go

@@ -0,0 +1,140 @@
+// Package nwsync publishes NWSync repository data: blobs and a per-artifact
+// NSYM manifest at each artifact's birth (emit), and one merged manifest at
+// module release (assemble).
+//
+// The split exists because upstream nwn_nwsync_write wants every hak, the TLK
+// and the module present in one run on one disk, which our build hosts cannot
+// hold. Upstream stays the conformance oracle: manifests compare byte for
+// byte, blobs compare after decompression.
+package nwsync
+
+import (
+	"flag"
+	"fmt"
+	"io"
+)
+
+const (
+	exitOK       = 0
+	exitUsage    = 64
+	exitInternal = 70
+)
+
+// Run executes an nwsync subcommand. args[0] is the subcommand (emit|assemble);
+// returns the process exit code.
+func Run(args []string, stdout, stderr io.Writer) int {
+	if len(args) == 0 {
+		printRunUsage(stderr)
+		return exitUsage
+	}
+	switch args[0] {
+	case "emit":
+		return runEmit(args[1:], stdout, stderr)
+	case "assemble":
+		return runAssemble(args[1:], stdout, stderr)
+	case "-h", "--help", "help":
+		printRunUsage(stdout)
+		return exitOK
+	default:
+		fmt.Fprintf(stderr, "nwsync: unknown subcommand %q\n\n", args[0])
+		printRunUsage(stderr)
+		return exitUsage
+	}
+}
+
+func printRunUsage(w io.Writer) {
+	fmt.Fprint(w, `usage:
+  nwsync emit     [--as NAME] [--out DIR] <artifact-key> <file>
+  nwsync assemble --group-id N [--tlk-key KEY] [--out DIR] <artifact-key>...
+
+emit explodes one .hak/.erf or one loose file (the TLK) into NWSync blobs plus
+a NSYM index covering only that artifact, and uploads both. assemble merges
+those indexes into one manifest, reading no bulk data. Artifact keys are depot
+keys; an index lives beside its artifact, with the extension replaced.
+
+--out DIR writes to a local repository tree instead of uploading, which is the
+conformance path against upstream nwn_nwsync_write. Without it, the zone comes
+from NWSYNC_STORAGE_ZONE, NWSYNC_STORAGE_PASSWORD and BUNNY_STORAGE_HOST.
+`)
+}
+
+// parseArgs parses flags that may appear before, after or between positionals.
+// Go's flag package stops at the first non-flag argument, which turns
+// `emit <key> <file> --out DIR` into a confusing arity error.
+func parseArgs(fs *flag.FlagSet, args []string) ([]string, error) {
+	var positional []string
+	for {
+		if err := fs.Parse(args); err != nil {
+			return nil, err
+		}
+		rest := fs.Args()
+		if len(rest) == 0 {
+			return positional, nil
+		}
+		positional = append(positional, rest[0])
+		args = rest[1:]
+	}
+}
+
+func runEmit(args []string, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("emit", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	as := fs.String("as", "", "published name of the artifact, when it differs from the key")
+	out := fs.String("out", "", "write to a local repository tree instead of uploading")
+	positional, err := parseArgs(fs, args)
+	if err != nil {
+		return exitUsage
+	}
+	if len(positional) != 2 {
+		fmt.Fprintf(stderr, "nwsync emit: <artifact-key> and <file> are both required\n")
+		return exitUsage
+	}
+
+	result, err := Emit(EmitOptions{
+		ArtifactKey:  positional[0],
+		ArtifactPath: positional[1],
+		As:           *as,
+		OutDir:       *out,
+	})
+	if err != nil {
+		fmt.Fprintf(stderr, "nwsync emit: %v\n", err)
+		return exitInternal
+	}
+	fmt.Fprintf(stdout, "emitted %s: %d resources, %d new blobs, index %s\n",
+		result.Name, result.Entries, result.BlobsWritten, result.ManifestPath)
+	return exitOK
+}
+
+func runAssemble(args []string, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("assemble", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	tlkKey := fs.String("tlk-key", "", "depot key of the TLK, which shadows nothing and merges last")
+	out := fs.String("out", "", "write to a local repository tree instead of uploading")
+	groupID := fs.Int("group-id", 0, "NWSync group id (1 = current, 2 = testing; 0 omits it)")
+	moduleName := fs.String("module-name", "", "module name recorded in the sidecar")
+	description := fs.String("description", "", "description recorded in the sidecar")
+	positional, err := parseArgs(fs, args)
+	if err != nil {
+		return exitUsage
+	}
+	if len(positional) == 0 {
+		fmt.Fprintf(stderr, "nwsync assemble: at least one artifact key is required\n")
+		return exitUsage
+	}
+
+	result, err := Assemble(AssembleOptions{
+		ArtifactKeys: positional,
+		TLKKey:       *tlkKey,
+		OutDir:       *out,
+		GroupID:      *groupID,
+		ModuleName:   *moduleName,
+		Description:  *description,
+	})
+	if err != nil {
+		fmt.Fprintf(stderr, "nwsync assemble: %v\n", err)
+		return exitInternal
+	}
+	fmt.Fprintf(stdout, "assembled manifest %s: %d resources, %s\n",
+		result.SHA1, result.Entries, result.ManifestPath)
+	return exitOK
+}

internal/nwsync/sink.go

@@ -0,0 +1,212 @@
+package nwsync
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"git.westgate.pw/ShadowsOverWestgate/sow-tools/internal/depot"
+)
+
+// sink is where an emit or assemble run puts what it produces. The zone is the
+// production sink; a local directory exists only as the conformance path, so
+// upstream's output and ours can be diffed on a developer machine.
+type sink interface {
+	// putBlob stores one NWCompressedBuffer blob under its sha1 name and
+	// returns the bytes stored, or 0 if the blob was already there. Blob names
+	// are content hashes, so an existing name is existing content — which is
+	// why body is a thunk: compression is the expensive part of emit and a
+	// blob that is already stored must not pay for it.
+	putBlob(sha1Hex string, body func() []byte) (int64, error)
+	// putIndex stores a NSYM manifest and its sidecar under key, which is
+	// either an artifact-derived object key or a local path.
+	putIndex(key string, manifest, sidecar []byte) error
+	// getIndex reads back a NSYM manifest and its sidecar.
+	getIndex(key string) (manifest, sidecar []byte, err error)
+	// describe names the sink for messages.
+	describe(key string) string
+}
+
+// dirSink writes a local NWSync repository tree.
+type dirSink struct{ root string }
+
+func (s dirSink) putBlob(sha1Hex string, body func() []byte) (int64, error) {
+	blob := blobPath(s.root, sha1Hex)
+	if _, err := os.Stat(blob); err == nil {
+		return 0, nil
+	}
+	if err := os.MkdirAll(filepath.Dir(blob), 0o755); err != nil {
+		return 0, fmt.Errorf("create blob directory: %w", err)
+	}
+	data := body()
+	if err := os.WriteFile(blob, data, 0o644); err != nil {
+		return 0, fmt.Errorf("write blob: %w", err)
+	}
+	return int64(len(data)), nil
+}
+
+func (s dirSink) putIndex(key string, manifest, sidecar []byte) error {
+	target := filepath.Join(s.root, filepath.FromSlash(key))
+	if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
+		return fmt.Errorf("create manifest directory: %w", err)
+	}
+	if err := os.WriteFile(target, manifest, 0o644); err != nil {
+		return fmt.Errorf("write manifest: %w", err)
+	}
+	if err := os.WriteFile(target+".json", sidecar, 0o644); err != nil {
+		return fmt.Errorf("write sidecar: %w", err)
+	}
+	return nil
+}
+
+func (s dirSink) getIndex(key string) ([]byte, []byte, error) {
+	target := filepath.Join(s.root, filepath.FromSlash(key))
+	manifest, err := os.ReadFile(target)
+	if err != nil {
+		return nil, nil, fmt.Errorf("read index: %w", err)
+	}
+	sidecar, err := os.ReadFile(target + ".json")
+	if err != nil {
+		return nil, nil, fmt.Errorf("read sidecar: %w", err)
+	}
+	return manifest, sidecar, nil
+}
+
+func (s dirSink) describe(key string) string {
+	return filepath.Join(s.root, filepath.FromSlash(key))
+}
+
+// zoneSink uploads straight to the NWSync storage zone. Nothing bulky is ever
+// written to the runner's disk: the working set is one resource at a time.
+type zoneSink struct {
+	store depot.KeyStore
+	ctx   context.Context
+	zone  string
+}
+
+func (s zoneSink) putBlob(sha1Hex string, body func() []byte) (int64, error) {
+	key := path.Join("data", "sha1", sha1Hex[0:2], sha1Hex[2:4], sha1Hex)
+	// A throttled probe must never be read as "missing, re-upload" or as
+	// "present, skip", so only a confirmed Present skips the upload.
+	state, _, err := s.store.ProbeKey(s.ctx, key)
+	if err != nil {
+		return 0, fmt.Errorf("probe blob %s: %w", sha1Hex, err)
+	}
+	if state == depot.Present {
+		return 0, nil
+	}
+	data := body()
+	if err := s.put(key, data); err != nil {
+		return 0, fmt.Errorf("upload blob %s: %w", sha1Hex, err)
+	}
+	return int64(len(data)), nil
+}
+
+func (s zoneSink) putIndex(key string, manifest, sidecar []byte) error {
+	// The manifest lands last: its presence is the publication marker, so it
+	// must never appear before the blobs it names.
+	if err := s.put(key+".json", sidecar); err != nil {
+		return fmt.Errorf("upload sidecar %s: %w", key, err)
+	}
+	if err := s.put(key, manifest); err != nil {
+		return fmt.Errorf("upload index %s: %w", key, err)
+	}
+	return nil
+}
+
+func (s zoneSink) getIndex(key string) ([]byte, []byte, error) {
+	manifest, err := s.store.GetKey(s.ctx, key)
+	if err != nil {
+		return nil, nil, fmt.Errorf("read index: %w", err)
+	}
+	sidecar, err := s.store.GetKey(s.ctx, key+".json")
+	if err != nil {
+		return nil, nil, fmt.Errorf("read sidecar: %w", err)
+	}
+	return manifest, sidecar, nil
+}
+
+func (s zoneSink) describe(key string) string { return s.zone + "/" + key }
+
+func (s zoneSink) put(key string, body []byte) error {
+	sum := sha256.Sum256(body)
+	return s.store.PutReader(s.ctx, key, bytes.NewReader(body), int64(len(body)), hex.EncodeToString(sum[:]))
+}
+
+// newZoneSink builds the upload sink from the environment. NWSync data lives
+// in its own zone, separate from the asset depot, so it has its own zone and
+// credential; only the host is shared, and Crucible has no default host.
+func newZoneSink(ctx context.Context, getenv func(string) string) (sink, error) {
+	cfg := depot.LoadConfig(getenv)
+	cfg.StorageZone = getenv("NWSYNC_STORAGE_ZONE")
+	cfg.WriteKey = getenv("NWSYNC_STORAGE_PASSWORD")
+	cfg.ReadKey = cfg.WriteKey
+	if cfg.StorageZone == "" {
+		return nil, fmt.Errorf("NWSYNC_STORAGE_ZONE is unset (or pass --out DIR to write locally)")
+	}
+	if cfg.WriteKey == "" {
+		return nil, fmt.Errorf("NWSYNC_STORAGE_PASSWORD is unset (or pass --out DIR to write locally)")
+	}
+	if cfg.StorageHost == "" {
+		return nil, fmt.Errorf("BUNNY_STORAGE_HOST is unset")
+	}
+	store, err := depot.NewKeyStore(cfg)
+	if err != nil {
+		return nil, err
+	}
+	return zoneSink{store: store, ctx: ctx, zone: cfg.StorageZone}, nil
+}
+
+// indexKey is where an artifact's NSYM lives: beside the artifact itself, with
+// the final extension replaced. emit and assemble must agree on this one rule,
+// so it lives here and nowhere else.
+//
+// artifacts/haks/sha256/30/46/3046….hak -> artifacts/haks/sha256/30/46/3046….nsym
+func indexKey(artifactKey string) (string, error) {
+	extension := path.Ext(artifactKey)
+	if extension == "" {
+		return "", fmt.Errorf("artifact key %q has no extension", artifactKey)
+	}
+	return strings.TrimSuffix(artifactKey, extension) + ".nsym", nil
+}
+
+// resolveIndexKey is where emit writes an artifact's index and where assemble
+// reads it from. On the zone that is beside the artifact; locally the indexes
+// sit flat beside the data tree, so upstream's output and ours diff directly.
+func resolveIndexKey(artifactKey, outDir string) (string, error) {
+	key, err := indexKey(artifactKey)
+	if err != nil {
+		return "", err
+	}
+	if outDir != "" {
+		return path.Base(key), nil
+	}
+	return key, nil
+}
+
+// checkArtifactKey fails closed when the key's embedded digest is not the
+// digest of the bytes being emitted. Publishing an index under the wrong key
+// silently pairs a manifest with the wrong artifact.
+// artifact is hashed by streaming, so a multi-gigabyte hak is never resident.
+func checkArtifactKey(artifactKey string, artifact io.Reader) error {
+	base := path.Base(artifactKey)
+	digest := strings.TrimSuffix(base, path.Ext(base))
+	if len(digest) != 64 {
+		return fmt.Errorf("artifact key %q does not name a sha256", artifactKey)
+	}
+	hash := sha256.New()
+	if _, err := io.Copy(hash, artifact); err != nil {
+		return fmt.Errorf("hash artifact: %w", err)
+	}
+	if got := hex.EncodeToString(hash.Sum(nil)); got != digest {
+		return fmt.Errorf("artifact key %q names digest %s but the file hashes to %s", artifactKey, digest, got)
+	}
+	return nil
+}

internal/nwsync/zone_test.go

@@ -0,0 +1,249 @@
+package nwsync
+
+import (
+	"crypto/sha1"
+	"crypto/sha256"
+	"encoding/hex"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+)
+
+// fakeZone is a Bunny-shaped object store: PUT stores, GET reads, and the
+// Checksum header is verified the way Bunny verifies it.
+type fakeZone struct {
+	mu      sync.Mutex
+	objects map[string][]byte
+	puts    []string
+	failOn  func(key string) bool // when true, the PUT fails
+}
+
+func newFakeZone(t *testing.T) (*fakeZone, func(string) string) {
+	t.Helper()
+	zone := &fakeZone{objects: map[string][]byte{}}
+	server := httptest.NewServer(zone)
+	t.Cleanup(server.Close)
+	getenv := func(name string) string {
+		switch name {
+		case "NWSYNC_STORAGE_ZONE":
+			return "sow-nwsync"
+		case "NWSYNC_STORAGE_PASSWORD":
+			return "write-key"
+		case "BUNNY_STORAGE_HOST":
+			return server.URL
+		}
+		return ""
+	}
+	return zone, getenv
+}
+
+func (z *fakeZone) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	key := strings.TrimPrefix(r.URL.Path, "/sow-nwsync/")
+	switch r.Method {
+	case http.MethodPut:
+		if z.failOn != nil && z.failOn(key) {
+			http.Error(w, "boom", http.StatusInternalServerError)
+			return
+		}
+		body, err := io.ReadAll(r.Body)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+		sum := sha256.Sum256(body)
+		if want := strings.ToUpper(hex.EncodeToString(sum[:])); r.Header.Get("Checksum") != want {
+			http.Error(w, "checksum mismatch", http.StatusBadRequest)
+			return
+		}
+		z.mu.Lock()
+		z.objects[key] = body
+		z.puts = append(z.puts, key)
+		z.mu.Unlock()
+		w.WriteHeader(http.StatusCreated)
+	case http.MethodGet:
+		z.mu.Lock()
+		body, ok := z.objects[key]
+		z.mu.Unlock()
+		if !ok {
+			http.Error(w, "not found", http.StatusNotFound)
+			return
+		}
+		_, _ = w.Write(body)
+	default:
+		http.Error(w, "unsupported", http.StatusMethodNotAllowed)
+	}
+}
+
+func (z *zoneSinkFixture) emit(t *testing.T, path string) EmitResult {
+	t.Helper()
+	result, err := Emit(EmitOptions{
+		ArtifactKey:  artifactKey(t, path),
+		ArtifactPath: path,
+		Sink:         z.sink,
+	})
+	if err != nil {
+		t.Fatalf("emit %s: %v", path, err)
+	}
+	return result
+}
+
+type zoneSinkFixture struct {
+	zone *fakeZone
+	sink sink
+}
+
+func newZoneFixture(t *testing.T) *zoneSinkFixture {
+	t.Helper()
+	zone, getenv := newFakeZone(t)
+	target, err := newZoneSink(t.Context(), getenv)
+	if err != nil {
+		t.Fatalf("zone sink: %v", err)
+	}
+	return &zoneSinkFixture{zone: zone, sink: target}
+}
+
+func sha1Of(body []byte) [20]byte { return sha1.Sum(body) }
+
+func TestEmitUploadsBlobsThenIndex(t *testing.T) {
+	fixture := newZoneFixture(t)
+	dir := t.TempDir()
+	hak := filepath.Join(dir, "sow_test_01.hak")
+	body := []byte("texture bytes")
+	writeHak(t, hak, map[string][]byte{"bloodstain1.tga": body, "copy1.txi": body})
+
+	key := artifactKey(t, hak)
+	result := fixture.emit(t, hak)
+
+	index, err := indexKey(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := fixture.zone.objects[index]; !ok {
+		t.Fatalf("no index at %s; zone holds %v", index, fixture.zone.puts)
+	}
+	if result.BlobsWritten != 1 {
+		t.Errorf("uploaded %d blobs, want 1 (identical content shares a blob)", result.BlobsWritten)
+	}
+
+	// The index is the publication marker, so it must land after every blob it
+	// names — including its own sidecar.
+	last := fixture.zone.puts[len(fixture.zone.puts)-1]
+	if last != index {
+		t.Errorf("index landed at position %d of %d; it must be last", len(fixture.zone.puts), len(fixture.zone.puts))
+	}
+	for _, key := range fixture.zone.puts[:len(fixture.zone.puts)-1] {
+		if strings.HasPrefix(key, "data/sha1/") || key == index+".json" {
+			continue
+		}
+		t.Errorf("unexpected object uploaded before the index: %s", key)
+	}
+}
+
+func TestEmitSkipsBlobsAlreadyInTheZone(t *testing.T) {
+	fixture := newZoneFixture(t)
+	dir := t.TempDir()
+	hak := filepath.Join(dir, "sow_test_01.hak")
+	writeHak(t, hak, map[string][]byte{"bloodstain1.tga": []byte("blood")})
+
+	first := fixture.emit(t, hak)
+	if first.BlobsWritten != 1 {
+		t.Fatalf("first emit uploaded %d blobs, want 1", first.BlobsWritten)
+	}
+	second := fixture.emit(t, hak)
+	if second.BlobsWritten != 0 {
+		t.Errorf("re-emit uploaded %d blobs, want 0 (a blob name is its content)", second.BlobsWritten)
+	}
+}
+
+func TestEmitLeavesNoIndexWhenAnUploadFails(t *testing.T) {
+	fixture := newZoneFixture(t)
+	fixture.zone.failOn = func(key string) bool { return strings.HasPrefix(key, "data/sha1/") }
+	dir := t.TempDir()
+	hak := filepath.Join(dir, "sow_test_01.hak")
+	writeHak(t, hak, map[string][]byte{"bloodstain1.tga": []byte("blood")})
+
+	_, err := Emit(EmitOptions{
+		ArtifactKey:  artifactKey(t, hak),
+		ArtifactPath: hak,
+		Sink:         fixture.sink,
+	})
+	if err == nil {
+		t.Fatal("emit reported success after an upload failed")
+	}
+	for key := range fixture.zone.objects {
+		if strings.HasSuffix(key, ".nsym") {
+			t.Errorf("a half-emitted artifact published an index: %s", key)
+		}
+	}
+}
+
+func TestEmitRejectsAKeyThatDoesNotMatchTheFile(t *testing.T) {
+	fixture := newZoneFixture(t)
+	dir := t.TempDir()
+	hak := filepath.Join(dir, "sow_test_01.hak")
+	writeHak(t, hak, map[string][]byte{"bloodstain1.tga": []byte("blood")})
+
+	wrong := "artifacts/haks/sha256/00/11/" + strings.Repeat("0", 64) + ".hak"
+	_, err := Emit(EmitOptions{ArtifactKey: wrong, ArtifactPath: hak, Sink: fixture.sink})
+	if err == nil || !strings.Contains(err.Error(), "hashes to") {
+		t.Fatalf("emit published under a key that names another artifact: %v", err)
+	}
+}
+
+func TestAssembleReadsIndexesFromTheZone(t *testing.T) {
+	fixture := newZoneFixture(t)
+	dir := t.TempDir()
+	topBody := []byte("2da from sow_top")
+	assetBody := []byte("2da from the asset hak")
+	top := filepath.Join(dir, "sow_top.hak")
+	core := filepath.Join(dir, "sow_core_01.hak")
+	writeHak(t, top, map[string][]byte{"appearance.2da": topBody})
+	writeHak(t, core, map[string][]byte{"appearance.2da": assetBody, "bloodstain1.tga": []byte("blood")})
+	tlkPath := filepath.Join(dir, "sow_tlk.tlk")
+	if err := os.WriteFile(tlkPath, []byte("TLK V3.0 payload"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	fixture.emit(t, top)
+	fixture.emit(t, core)
+	if _, err := Emit(EmitOptions{
+		ArtifactKey:  artifactKey(t, tlkPath),
+		ArtifactPath: tlkPath,
+		As:           "sow_tlk.tlk",
+		Sink:         fixture.sink,
+	}); err != nil {
+		t.Fatalf("emit tlk: %v", err)
+	}
+
+	result, err := Assemble(AssembleOptions{
+		ArtifactKeys: []string{artifactKey(t, top), artifactKey(t, core)},
+		TLKKey:       artifactKey(t, tlkPath),
+		GroupID:      2,
+		Sink:         fixture.sink,
+	})
+	if err != nil {
+		t.Fatalf("assemble: %v", err)
+	}
+	if result.Entries != 3 {
+		t.Fatalf("merged %d entries, want 3 (appearance.2da is shadowed, the TLK adds one)", result.Entries)
+	}
+
+	manifest, ok := fixture.zone.objects["manifests/"+result.SHA1]
+	if !ok {
+		t.Fatalf("no merged manifest in the zone; it holds %v", fixture.zone.puts)
+	}
+	entries, err := readManifest(manifest)
+	if err != nil {
+		t.Fatalf("parse merged manifest: %v", err)
+	}
+	for _, entry := range entries {
+		if entry.ResRef == "appearance" && entry.SHA1 != sha1Of(topBody) {
+			t.Errorf("appearance.2da resolved to the shadowed hak, not the first one given")
+		}
+	}
+}

scripts/crucible-smoke.sh

@@ -18,7 +18,7 @@ bin=bin
 
 # Keep in sync with internal/dispatch.Registry (Wired flag).
 unwired=()
-wired=(assets depot hak module topdata wiki)
+wired=(assets depot hak module nwsync topdata wiki)
 
 exit_of() { set +e; "$@" >/dev/null 2>&1; local c=$?; set -e; echo "${c}"; }