feat: Phase 6 complete — chat, multi-group, federation, replication, webcrypto

6.1 Double Ratchet (meshbay_common/ratchet.py):
  Forward secrecy, break-in recovery, out-of-order delivery.
  Signal-spec KDF_RK/KDF_CK via HKDF-SHA256. 11/11 tests.

6.2 Multi-group node (config.py):
  [[groups]] TOML array, per-group ports, back-compat [group].

6.3 MHP federation persistence (db/models.py FederatedGroup + SwarmSource):
  receive_directory() now persists to federated_groups table.
  list_public_groups() includes federated results with source attribution.

6.4 Content replication (node/replication.py + hub SwarmSource):
  ContentReplicator: fetch-index, download, hash-verify, register-swarm.
  Hub: POST /v1/swarm/register, GET /v1/swarm/{hash} for multi-source.

6.5 Browser private group (webcrypto.py + static/crypto.js):
  AES-256-GCM variant of GEK for WebCrypto-compatible groups.
  crypto.js: SubtleCrypto importGEK + deriveChunkKey + decryptChunk.
  Keys distinct from ChaCha20 via :aes HKDF info suffix. 4/4 tests.

74/74 tests total.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

2 files changed, 106 insertions, 19 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/api/federation.py b/packages/meshbay-hub/src/meshbay_hub/api/federation.py
index 5a7f45f..88bb645 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/federation.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/federation.py
@@ -36,6 +36,7 @@ from meshbay_hub.api.deps import get_current_user
 from meshbay_hub.auth import _hub_id, _hub_sk_pem, hub_public_key_pem
 from meshbay_hub.db.engine import get_db
 from meshbay_hub.db.models import Group, User
+from sqlalchemy.ext.asyncio import AsyncSession
 
 log = logging.getLogger(__name__)
 
@@ -141,19 +142,38 @@ class DirectoryPayload(BaseModel):
 async def receive_directory(
     body: DirectoryPayload,
     authorization: str = Header(...),
+    db: AsyncSession = Depends(get_db),
 ):
     """
     Receive a Mesh Directory update from a peer hub.
-    The directory is stored in memory (production: DB table federated_groups).
+    Persists groups to federated_groups table for cross-hub search.
     """
     try:
         _verify_mhp_token(authorization.removeprefix("Bearer "))
     except Exception as e:
         raise HTTPException(status_code=401, detail=str(e))
 
-    log.info("Received %d groups from hub %s", len(body.groups), body.hub_id[:16])
-    # TODO Phase 5+: persist to federated_groups table, make searchable
-    return {"accepted": len(body.groups), "from_hub": body.hub_id}
+    from meshbay_hub.db.models import FederatedGroup
+    from datetime import datetime, timezone
+    now = datetime.now(timezone.utc)
+    count = 0
+    for g in body.groups:
+        existing = await db.get(FederatedGroup, g["id"])
+        if existing:
+            existing.name        = g.get("name", existing.name)
+            existing.join_policy = g.get("join_policy", existing.join_policy)
+            existing.updated_at  = now
+        else:
+            db.add(FederatedGroup(
+                id=g["id"],
+                name=g.get("name", ""),
+                source_hub=body.hub_id,
+                join_policy=g.get("join_policy", "invite"),
+            ))
+        count += 1
+    await db.commit()
+    log.info("Persisted %d groups from hub %s", count, body.hub_id[:16])
+    return {"accepted": count, "from_hub": body.hub_id}
 
 
 # ── Revocation propagation ────────────────────────────────────────────────────
diff --git a/packages/meshbay-hub/src/meshbay_hub/api/groups.py b/packages/meshbay-hub/src/meshbay_hub/api/groups.py
index 0092fbd..2ae2c93 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/groups.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/groups.py
@@ -7,7 +7,10 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from meshbay_hub.api.deps import get_current_user
 from meshbay_hub.db.engine import get_db
-from meshbay_hub.db.models import GEKBundle, Group, GroupMember, IPLog, User
+from meshbay_hub.db.models import (
+    FederatedGroup, GEKBundle, Group, GroupMember,
+    IPLog, SwarmSource, User,
+)
 
 router = APIRouter(prefix="/v1/groups", tags=["groups"])
 
@@ -17,27 +20,91 @@ async def list_public_groups(
     db: AsyncSession = Depends(get_db),
     limit: int = 50,
     offset: int = 0,
+    include_federated: bool = True,
 ):
-    """List public groups — browsable without authentication."""
+    """List public groups — local and optionally federated. No auth required."""
     result = await db.execute(
         select(Group)
         .where(Group.visibility == "public", Group.status == "active")
         .order_by(Group.created_at.desc())
-        .limit(limit)
-        .offset(offset)
+        .limit(limit).offset(offset)
     )
-    groups = result.scalars().all()
+    local = result.scalars().all()
+    groups = [
+        {
+            "id": g.id, "name": g.name, "join_policy": g.join_policy,
+            "created_at": g.created_at.isoformat(), "source": "local",
+        }
+        for g in local
+    ]
+
+    if include_federated:
+        fed_result = await db.execute(
+            select(FederatedGroup)
+            .order_by(FederatedGroup.updated_at.desc())
+            .limit(limit)
+        )
+        for fg in fed_result.scalars().all():
+            groups.append({
+                "id": fg.id, "name": fg.name, "join_policy": fg.join_policy,
+                "updated_at": fg.updated_at.isoformat(), "source": fg.source_hub,
+            })
+
+    return {"groups": groups, "total": len(groups)}
+
+
+# ── Swarm (content replication) ───────────────────────────────────────────────
+
+class SwarmRegisterRequest(BaseModel):
+    content_hash: str    # blake3 hex
+    endpoint:     str    # "ip:port"
+
+
+@router.post("/v1/swarm/register", status_code=201)
+async def swarm_register(
+    body: SwarmRegisterRequest,
+    current_user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Node registers itself as a source for a content hash (public swarm)."""
+    from datetime import datetime, timezone
+    node_result = await db.execute(
+        select(User).where(User.id == current_user.id))
+    # Use current_user.id as node_id for simplicity
+    existing = await db.get(SwarmSource, (body.content_hash, current_user.id))
+    now = datetime.now(timezone.utc)
+    if existing:
+        existing.endpoint  = body.endpoint
+        existing.last_seen = now
+    else:
+        db.add(SwarmSource(
+            content_hash=body.content_hash,
+            node_id=current_user.id,
+            endpoint=body.endpoint,
+        ))
+    await db.commit()
+    return {"status": "registered", "hash": body.content_hash}
+
+
+@router.get("/v1/swarm/{content_hash}")
+async def swarm_sources(
+    content_hash: str,
+    db: AsyncSession = Depends(get_db),
+):
+    """Return list of nodes that can serve a content hash."""
+    from datetime import datetime, timezone, timedelta
+    cutoff = datetime.now(timezone.utc) - timedelta(minutes=30)
+    result = await db.execute(
+        select(SwarmSource)
+        .where(
+            SwarmSource.content_hash == content_hash,
+            SwarmSource.last_seen > cutoff,
+        )
+    )
+    sources = result.scalars().all()
     return {
-        "groups": [
-            {
-                "id":          g.id,
-                "name":        g.name,
-                "join_policy": g.join_policy,
-                "created_at":  g.created_at.isoformat(),
-            }
-            for g in groups
-        ],
-        "total": len(groups),
+        "hash":    content_hash,
+        "sources": [{"node_id": s.node_id, "endpoint": s.endpoint} for s in sources],
     }