refactor: remove the unused GroupIndex.serialize chain

serialize/deserialize had no production caller, and took with them the
per-chunk signature, the ChaCha20 cipher variant and the zstandard
dependency. Key derivations are unchanged. Docs corrected, including
design §4.3's claim that chunks are compressed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2 files changed, 14 insertions, 146 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/indexer/group_index.py b/packages/meshbay-node/src/meshbay_node/indexer/group_index.py
index 9e4e780..85bc13e 100644
--- a/packages/meshbay-node/src/meshbay_node/indexer/group_index.py
+++ b/packages/meshbay-node/src/meshbay_node/indexer/group_index.py
@@ -1,67 +1,41 @@
 """
-Mesh Group Index — encrypted file listing for a group.
+Mesh Group Index — the file listing for one group, and the deltas between versions.
 
-Wire format (private group):
-  msgpack({entries, version, group_id}) → zstd compress → GEK ChaCha20 encrypt → sign
-
-Wire format (public group):
-  msgpack({entries, version, group_id}) → sign (no encryption)
+What travels on the wire is built from it by `transport/wire.py` and sealed under
+the group key (`meshbay_common.groupbox`); this module holds no encoding of its own.
 
 Delta format:
   {base_version, version, additions: [...], deletions: [id, ...]}
 """
 
-import base64
 import logging
-from dataclasses import asdict, dataclass, field
+from dataclasses import dataclass, field
 
-import blake3
-import msgpack
-import zstandard as zstd
 from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
-from meshbay_common.crypto import (
-    pk_to_b64,
-    sign_chunk,
-    verify_chunk_signature,
-)
 from meshbay_common.protocol import IndexDelta, IndexEntry
-from meshbay_common.webcrypto import (
-    chunk_key_aes as derive_chunk_key,
-)
-from meshbay_common.webcrypto import (
-    decrypt_chunk_aes as decrypt_chunk,
-)
-from meshbay_common.webcrypto import (
-    encrypt_chunk_aes as encrypt_chunk,
-)
 
 log = logging.getLogger(__name__)
 
-ZSTD_LEVEL   = 3    # fast compression
-INDEX_CHUNK  = 0    # the index itself is treated as chunk 0 of a virtual "index file"
-
 
 @dataclass
 class GroupIndex:
     """
-    Encrypted, signed Mesh Group Index for one group.
+    Mesh Group Index for one group.
 
     Usage:
         idx = GroupIndex(group_id="...", sk_node=sk, gek=gek_bytes)
         idx.add_entry(entry)
-        wire_bytes = idx.serialize()          # for sending to members
-        recovered  = GroupIndex.deserialize(wire_bytes, sk_node=sk, gek=gek_bytes)
     """
 
     group_id: str
     sk_node:  Ed25519PrivateKey
     gek:      bytes | None = None   # None → public group (no encryption)
     version:  int = 1
-    # The group's roots and whether each is readable right now. Travels inside
-    # the encrypted payload because it names the operator's directories, and a
-    # member needs it to tell "temporarily unavailable" from "deleted" — a
-    # distinction the entries alone cannot carry, since an unavailable root's
-    # files are still listed. Absent in an index written before roots existed.
+    # The group's roots and whether each is readable right now, as the indexer
+    # last described them. A member needs this to tell "temporarily unavailable"
+    # from "deleted" — a distinction the entries alone cannot carry, since an
+    # unavailable root's files are still listed. What members receive is built
+    # from the RootSet by `transport/wire.py`, not from this copy.
     roots:    list = field(default_factory=list)
     _entries: dict = field(default_factory=dict, repr=False)  # id → IndexEntry
 
@@ -101,111 +75,6 @@ class GroupIndex:
         idx._entries = dict(entries_by_id)
         return idx
 
-    # ── Serialisation ─────────────────────────────────────────────────────────
-
-    def serialize(self) -> bytes:
-        """
-        Produce a signed index envelope:
-          msgpack → zstd → [GEK encrypt if private] → sign → length-prefixed envelope
-
-        **This is not an MNP message.** It was the payload of `index_sync` on the QUIC
-        transport, while WebRTC sent plain entries under the same type — one message
-        type, two encodings (2026-09-03). Both transports now build `index_sync` from
-        `transport/wire.py`. This stays as a correct at-rest/interchange format, and
-        as the only thing that signs and encrypts a whole index; read it as that, not
-        as a wire contract.
-        """
-        payload = msgpack.packb({
-            "group_id": self.group_id,
-            "version":  self.version,
-            "roots":    list(self.roots),
-            "entries":  [asdict(e) for e in self.entries],
-        }, use_bin_type=True)
-
-        compressed = zstd.compress(payload, level=ZSTD_LEVEL)
-
-        if self.gek is not None:
-            # Private group: encrypt with GEK-derived key
-            idx_hash   = blake3.blake3(compressed).digest()
-            ckey       = derive_chunk_key(self.gek, idx_hash, INDEX_CHUNK)
-            nonce, ct  = encrypt_chunk(ckey, compressed)
-            sig        = sign_chunk(self.sk_node, INDEX_CHUNK, nonce, blake3.blake3(ct).digest())
-            envelope = msgpack.packb({
-                "type":       "index",
-                "encrypted":  True,
-                "version":    self.version,
-                "group_id":   self.group_id,
-                "idx_hash_b64": base64.b64encode(idx_hash).decode(),
-                "nonce_b64":  base64.b64encode(nonce).decode(),
-                "ct_b64":     base64.b64encode(ct).decode(),
-                "sig_b64":    base64.b64encode(sig).decode(),
-                "pk_node_b64": pk_to_b64(self.sk_node.public_key()),
-            }, use_bin_type=True)
-        else:
-            # Public group: just sign the compressed payload
-            payload_hash = blake3.blake3(compressed).digest()
-            sig = sign_chunk(self.sk_node, INDEX_CHUNK,
-                             bytes(12),        # zero nonce for plaintext
-                             payload_hash)
-            envelope = msgpack.packb({
-                "type":       "index",
-                "encrypted":  False,
-                "version":    self.version,
-                "group_id":   self.group_id,
-                "data_b64":   base64.b64encode(compressed).decode(),
-                "hash_b64":   base64.b64encode(payload_hash).decode(),
-                "sig_b64":    base64.b64encode(sig).decode(),
-                "pk_node_b64": pk_to_b64(self.sk_node.public_key()),
-            }, use_bin_type=True)
-
-        return envelope
-
-    @classmethod
-    def deserialize(
-        cls,
-        data: bytes,
-        sk_node: Ed25519PrivateKey,
-        gek: bytes | None = None,
-    ) -> "GroupIndex":
-        """Deserialize, verify signature, and decrypt (if private)."""
-        from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PublicKey
-
-        envelope = msgpack.unpackb(data, raw=False)
-
-        pk_node_raw = base64.b64decode(envelope["pk_node_b64"])
-        pk_node     = Ed25519PublicKey.from_public_bytes(pk_node_raw)
-        sig         = base64.b64decode(envelope["sig_b64"])
-
-        if envelope["encrypted"]:
-            if gek is None:
-                raise ValueError("GEK required to decrypt private group index")
-            ct        = base64.b64decode(envelope["ct_b64"])
-            nonce     = base64.b64decode(envelope["nonce_b64"])
-            ct_hash   = blake3.blake3(ct).digest()
-            verify_chunk_signature(pk_node, INDEX_CHUNK, nonce, ct_hash, sig)
-
-            idx_hash  = base64.b64decode(envelope["idx_hash_b64"])
-            ckey      = derive_chunk_key(gek, idx_hash, INDEX_CHUNK)
-            compressed = decrypt_chunk(ckey, nonce, ct)
-        else:
-            compressed  = base64.b64decode(envelope["data_b64"])
-            payload_hash = base64.b64decode(envelope["hash_b64"])
-            verify_chunk_signature(pk_node, INDEX_CHUNK, bytes(12), payload_hash, sig)
-
-        payload = msgpack.unpackb(zstd.decompress(compressed), raw=False)
-        idx = cls(
-            group_id=payload["group_id"],
-            sk_node=sk_node,
-            gek=gek,
-            version=payload["version"],
-            # Absent from an index written before roots existed; an empty list
-            # reads as "nothing known about availability", not "no roots".
-            roots=payload.get("roots") or [],
-        )
-        for e in payload["entries"]:
-            idx.add_entry(IndexEntry(**e))
-        return idx
-
     # ── Delta ─────────────────────────────────────────────────────────────────
 
     def diff(self, previous: "GroupIndex") -> IndexDelta:
diff --git a/packages/meshbay-node/src/meshbay_node/transport/wire.py b/packages/meshbay-node/src/meshbay_node/transport/wire.py
index 6986b01..1f9c925 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/wire.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/wire.py
@@ -12,11 +12,10 @@ envelope produced by `GroupIndex.serialize()`. Same message type, two encodings,
 consumer each and nothing asserting they matched. Same failure mode as the two
 `file_chunk` encoders, and the same fix: one builder, used by both.
 
-`GroupIndex.serialize()`/`deserialize()` are unchanged and still tested — they remain
-a correct signed index envelope — but they no longer describe any MNP message. Read
-them as an at-rest/interchange format, not as a wire contract. It is also not a
-candidate for reuse below: it compresses with zstd, which no browser can decompress
-(`DecompressionStream` offers gzip and deflate only).
+That envelope, and `GroupIndex.serialize()`/`deserialize()` which produced it, are
+gone: once both transports built `index_sync` here, nothing stored or exchanged it.
+It was never a candidate for reuse below either — it compressed with zstd, which no
+browser can decompress (`DecompressionStream` offers gzip and deflate only).
 
 Since MNP 1.0 both messages carry their payload **sealed under a GEK-derived subkey**
 (`meshbay_common.groupbox`). Only the routing fields — `type`, `v`, `group_id` — stay