Cordn group chats: MLS groups delivered through a coordinator (Amethyst 1.17 interop)

src/contextvm.js speaks ContextVM (kind 25910 inside ephemeral gift wraps)
to a coordinator; src/cordn.js is the protocol (KeyPackages with hex-text
identities, the 0xC04D metadata extension, exporter-keyed ChaCha20 sealing,
unsigned nostr-shaped envelopes with the sender as MLS AAD, cordn1 group
refs, a record engine like marmot.js); src/cordn-client.js mirrors
marmot-client.js with the same interface, so the Messages group screens
drive both — New group gains a White Noise / Cordn toggle.

Verified against @cordn/cli (ts-mls) on the public coordinator both ways,
from the engine (tools/cordn-interop-test.js) and from the real app
(tools/cordn-ui-test.js). mls.js: the OpenMLS required_capabilities rule for
GroupContextExtensions now applies only to groups that carry one.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YRC6aKhwAud231ot9FPmhi

1 files changed, 7 insertions, 3 deletions

diff --git a/src/mls.js b/src/mls.js
index 449036b..5a273b6 100644
--- a/src/mls.js
+++ b/src/mls.js
@@ -1578,9 +1578,13 @@ const applyProposals = (s, list, committer, { appData, psks, now, own } = {}) =>
   let extensions = gce.length ? gce[0].proposal.extensions : s.extensions;
   if (gce.length) {
     uniqueTypes(extensions, "group context");
-    // an OpenMLS rule, not an RFC one: whatever the context carries must be required of every member
-    let required = requiredCapabilities(extensions)?.extensions || [];
-    if (!extensions.every((e) => supportsExtension({ extensions: required }, e.type)))
+    // An OpenMLS rule, not an RFC one: whatever the context carries must be
+    // required of every member. Applied where the group plays by it (a
+    // required_capabilities extension in the context, as White Noise groups
+    // have); a ts-mls group (Cordn) carries none and changes its metadata
+    // extension freely, as the RFC allows.
+    let required = requiredCapabilities(extensions)?.extensions;
+    if (required && !extensions.every((e) => supportsExtension({ extensions: required }, e.type)))
       fail("group context extension type missing from required_capabilities");
     // with app_data_update required, the dictionary only changes through app_data_update
     if (requiresAppDataUpdate(s.extensions) || requiresAppDataUpdate(extensions)) {