fix(nwsync): declare Frame_Content_Size on every blob, and verify what is published (#87)

Closes #86. Closes #85.

These land together on purpose. Fixing the encoder alone changes nothing for the blobs already in the zone, because `emit` skips whatever is already present.

## #86 — the framing fix

`klauspost/compress` omits the zstd `Frame_Content_Size` field for inputs under 256 bytes, which the format permits. Reference libzstd never does, so the NWN client — which sizes its output buffer from `ZSTD_getFrameContentSize` and has therefore never met a frame without one — rejected roughly 6% of our blobs outright. Any single one stops a sync dead, so no client could complete a sync of the live manifest.

No encoder option changes this, so `compressBlob` re-headers the affected frames into the shape libzstd itself emits: `Single_Segment_flag` set, `Window_Descriptor` dropped, and the freed byte spent on a one-byte `Frame_Content_Size`. Same length in, same length out, and the same descriptor byte (`0x24`) the issue recorded from libzstd.

`compressBlob` then asserts its own output. An encoder upgrade that finds another way to omit the field would otherwise reproduce #86 in silence, and a blob is skipped by every later emit once written.

`emitter_version` goes to `2`, so `assemble` refuses to merge an index written by the encoder that omitted the field.

**Proved against the reference decoder, not just a round trip.** A real emitted 175-byte blob:

```
Frames  Skips  Compressed  Uncompressed  Ratio  Check  Filename
     1      0      48   B       175   B  3.646  XXH64  frame.zst
c59d6620d4ffd4bf3fe73df43b19b7afcfe8fea4  -            <- zstd -dc | sha1sum
c59d6620d4ffd4bf3fe73df43b19b7afcfe8fea4               <- the blob's own name
```

Before the fix that `Uncompressed` column was blank.

## #85 — `nwsync verify`

`crucible nwsync verify <manifest-sha1>` reads a manifest and its blobs back through the **public pull zone**, with no credential, because what matters is the bytes a client is served, edge behaviour included. Every distinct blob is decompressed and hashed; failures are reported per blob as missing / malformed framing / size mismatch / hash mismatch, and the exit code is 1.

- `--sample N` makes a routine check cheap against a manifest that is ~69,000 blobs and 15 GB; the default is a full sweep.
- `--base URL` / `NWSYNC_PULL_BASE` overrides the public host.
- The manifest is checked against its own sha1 before a single blob is fetched.
- `emit --verify` applies the same check where `emit` would otherwise trust presence, and replaces a stored blob that is not what its name claims. This is what makes the #86 blobs repairable.

## Why the existing checks missed this

Both new checks assert the **frame property**, not just a round trip. The conformance suite (#59) compares decompressed bytes, so a frame that decodes correctly passes regardless of its header; and the earlier zone audit decompressed 68 blobs with the `zstd` CLI, a *more* capable decoder than the client's, which certified exactly the blobs the client rejects.

## Checks

`make check` and `make smoke` green. Second commit is the fixes from a two-axis review of the first.

## Not in this PR

Three follow-ups, filed separately: the backfill has not been run, replacing a blob does not purge the pull-zone edge cache, and #85's runbook line belongs to `sow-platform`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)Reviewed-on: #87

Co-authored-by: vickydotbat <vickydotbat@tutamail.com>

internal/nwsync/emit.go

@@ -33,7 +33,9 @@ var skippedTypes = resTypes("nss", "ndb", "gic")
 // 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"
+// Version 2 declares Frame_Content_Size on every blob (#86); version 1 omitted
+// it below 256 bytes and no client could sync past such a blob.
+const emitterVersion = "2"
 
 // serverTypes are loaded only server-side; a manifest holding nothing else
 // has no client contents. Mirrors upstream's GlobalResTypeServerList, whose
@@ -78,6 +80,7 @@ type EmitOptions struct {
 	As           string // name override, for a TLK whose filename is not its published name
 	OutDir       string // write locally instead of uploading — the conformance path
 	Jobs         int    // resources in flight at once; 0 means defaultEmitJobs
+	Verify       bool   // hash what would be skipped instead of trusting presence
 	Sink         sink   // test seam; nil means OutDir or the zone
 }
 
@@ -129,7 +132,7 @@ func Emit(options EmitOptions) (EmitResult, error) {
 	if jobs < 1 {
 		jobs = defaultEmitJobs
 	}
-	entries, blobs, onDiskBytes, err := emitResources(artifact, index, target, jobs)
+	entries, blobs, onDiskBytes, err := emitResources(artifact, index, target, jobs, options.Verify)
 	if err != nil {
 		return EmitResult{}, err
 	}
@@ -199,7 +202,7 @@ func readArtifactIndex(path string, artifact io.ReaderAt, size int64, name strin
 //
 // The returned entries are in artifact order whatever order the workers finish
 // in, because a manifest's bytes are promised deterministic by emitterVersion.
-func emitResources(artifact io.ReaderAt, index []erf.IndexEntry, target sink, jobs int) ([]Entry, int, int64, error) {
+func emitResources(artifact io.ReaderAt, index []erf.IndexEntry, target sink, jobs int, verify bool) ([]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))
@@ -271,7 +274,7 @@ func emitResources(artifact io.ReaderAt, index []erf.IndexEntry, target sink, jo
 		if duplicate {
 			return
 		}
-		written, err := target.putBlob(fmt.Sprintf("%x", sum), func() []byte { return compressBlob(payload) })
+		written, err := target.putBlob(fmt.Sprintf("%x", sum), verify, func() []byte { return compressBlob(payload) })
 		mu.Lock()
 		defer mu.Unlock()
 		if err != nil {