merge: Phase 11.5 security remediation, invite redesign, per-node identity

Brings in the security remediation branch. Three bodies of work, and what they
changed about what this project may claim.

Phase 11.5 closed the gap between the documents and the code: the unauthenticated
node HTTP API and the TCP transport deleted, one handshake shared by the
remaining two transports, mutual authentication, structured admin transcripts,
upload confinement, group isolation, revocation that reaches nodes. Six critical
and seven high findings closed, bounded, or deferred by decision.

The invite redesign closed H3 and M3 — the last open High. The hub was the key
directory: an inviter fetched the invitee's key from it and wrapped the group key
for whatever came back, so a hub answering with its own key was handed the group
key by an honest member following the protocol exactly. That lookup is gone. The
node holds the group key and wraps it itself, for a key its recipient proves
possession of, bound to an account by a one-time code the hub never sees. M3 fell
out of the same work: node authority comes from a local roster, never from the
hub.

Per-node identity cut what remains of C4 down to one operator. A single keypair
used to be copied to every node its owner joined; each node now gets its own, so
cracking the bundle on one machine yields a key that is a stranger everywhere
else — and on that machine, one that unlocks nothing its holder did not already
serve. The bundle KDF moved to Argon2id 128 MB, and the hub stopped storing or
publishing user keys at all.

What this project may now say: the hub cannot read your content unless it ships
you malicious client code. T3 remains, accepted (D1), and is what the native
client removes. C4 is reduced, not closed, until 13.3. Chat is still plaintext at
rest until Phase 15. Draft-v5 §2 states each claim against the adversary it holds
against, which is the convention this branch exists to keep.

Four defects were found by deploying it and using a browser, none by the test
suite: a node going deaf on its hub socket, a token that predated group
membership, a client reading values before they were assigned, and identity keys
a browser held but never re-read. The lessons are recorded in CLAUDE.md.

Tests: 343 across the three packages, plus QE/deploy/e2e.py — register, pair,
invite, join, download, stream, second browser, revoke — run against the live
deployment on a wiped hub and node.

1 files changed, 32 insertions, 8 deletions

diff --git a/packages/meshbay-common/src/meshbay_common/crypto.py b/packages/meshbay-common/src/meshbay_common/crypto.py
index 682e1c0..b2ff3c0 100644
--- a/packages/meshbay-common/src/meshbay_common/crypto.py
+++ b/packages/meshbay-common/src/meshbay_common/crypto.py
@@ -168,21 +168,45 @@ def unwrap_gek_aes(bundle: dict, sk_recipient: bytes, pk_recipient: bytes) -> by
 
 # ── Keystore (local key storage) ──────────────────────────────────────────────
 
-# Argon2id parameters — calibrate to ~500ms on target hardware before production.
-# POC measured 78ms with these; increase memory_cost to 262144 (256MB) for prod.
+# Argon2id parameters for the node keystore.
+#
+# Finding M2: these sat at 64 MB long after the hub's password verifier was raised
+# to 256 MB, and the docs recorded the bump as done — true for the hub, false here.
+# The keystore protects the node's Ed25519 and X25519 private keys, so it is the
+# more valuable target of the two.
+#
+# Parameters are recorded in each keystore envelope, so raising them does not
+# invalidate existing files: LEGACY_* is used when an envelope predates the field.
 ARGON2_ITERATIONS   = 3
-ARGON2_MEMORY_COST  = 65536   # 64 MB — increase to 262144 for production
+ARGON2_MEMORY_COST  = 262144   # 256 MB
 ARGON2_LANES        = 4
 ARGON2_KEY_LENGTH   = 32
 
-def derive_keystore_key(password: str, salt: bytes) -> bytes:
-    """Derive AES-256 key from password using Argon2id."""
+LEGACY_ARGON2_ITERATIONS  = 3
+LEGACY_ARGON2_MEMORY_COST = 65536    # 64 MB — keystores written before M2
+LEGACY_ARGON2_LANES       = 4
+
+
+def derive_keystore_key(
+    password: str,
+    salt: bytes,
+    *,
+    iterations: int | None = None,
+    memory_cost: int | None = None,
+    lanes: int | None = None,
+) -> bytes:
+    """
+    Derive an AES-256 key from a password using Argon2id.
+
+    Parameters default to the current production values; callers pass the values
+    recorded in an existing envelope when opening an older keystore.
+    """
     return Argon2id(
         salt=salt,
         length=ARGON2_KEY_LENGTH,
-        iterations=ARGON2_ITERATIONS,
-        lanes=ARGON2_LANES,
-        memory_cost=ARGON2_MEMORY_COST,
+        iterations=ARGON2_ITERATIONS if iterations is None else iterations,
+        lanes=ARGON2_LANES if lanes is None else lanes,
+        memory_cost=ARGON2_MEMORY_COST if memory_cost is None else memory_cost,
     ).derive(password.encode())
 
 def encrypt_keystore(plaintext: bytes, key: bytes) -> tuple[bytes, bytes, bytes]: