Merge branch 'fix/third-review-h1-h2-m1-m6'

Third security review (docs/third-review.md) plus its remediation.

Fixed and verified:
- H1  moderator could grant admin / hard-revoke  → handler split by field
- H2  unauthenticated 2-report global blocklist  → auth + distinct reporters
      + rate limit + refused when public groups are off
- M1  registration reCAPTCHA was inert           → gate unconditional; the
      desktop client's CSP allows the widget
- M2  QUIC chat/stream handlers lagged WebRTC    → brought to parity; the QUIC
      listener is now off by default ([node] quic_enabled)
- M3  link-preview SSRF gaps                      → rate limit + port allowlist
      + connect-address re-check + decompression-bomb guard
- M4  federated peer over-trust                   → source bound to the signer,
      push capped, revocation prunes the peer's own entries, replay rejected
- M5  no CSP / security headers on the SPA        → middleware; verified against
      the live app with no violations

Withdrawn:
- M6  add_group_member accepting node tokens is deliberate (commit 0443cf8,
      the CLI invite flow). The "fix" broke that flow on the deployed hub and
      was reverted.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011pG75yGK3NthNfyjH74omG

2 files changed, 13 insertions, 2 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/auth-page.js b/packages/meshbay-hub/src/meshbay_hub/static/auth-page.js
index df08bc4..4c00137 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/auth-page.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/auth-page.js
@@ -237,8 +237,11 @@ export function RegisterPage() {
         const rk = window.MeshBayKeys.generateRecoveryKey();
         // `name` (trimmed), not the raw field: the hub stores the trimmed
         // username and every key derivation must fold in the same string.
+        // `captcha.token` rides along — the submit button is already disabled
+        // until it is set when a captcha is configured (see the form below).
         await window.MeshBayKeys.registerUser(
-          name, email, password, emailRecovery ? rk.mnemonic : null);
+          name, email, password, emailRecovery ? rk.mnemonic : null,
+          captcha.token);
         setRecoveryMnemonic(rk.mnemonic);
         session.recoveryKey =
           await window.MeshBayKeys.deriveRecoveryKey(rk.mnemonic, name);
@@ -257,6 +260,10 @@ export function RegisterPage() {
       }
     } catch (err) {
       setError(err.message);
+      // A reCAPTCHA token is single-use: after a failed attempt (name taken,
+      // e-mail in use…) it is spent, so clear it and make the user solve a
+      // fresh one before the next try. No-op when no captcha is configured.
+      captcha.reset();
     } finally {
       setLoading(false);
     }
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/keyderive.js b/packages/meshbay-hub/src/meshbay_hub/static/keyderive.js
index 0aaa6a5..a540a94 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/keyderive.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/keyderive.js
@@ -276,7 +276,7 @@ async function decryptBundle(bundleB64, password, username) {
  *
  * Returns the raw private keys for immediate use after registration.
  */
-async function registerUser(username, email, password, recoveryMnemonic) {
+async function registerUser(username, email, password, recoveryMnemonic, captchaToken) {
   // No keypair here any more. Identity keys are per node: one is generated the
   // first time this account joins a given node, encrypted under the passphrase,
   // and left with that node. So an operator who cracks what sits on their own
@@ -291,6 +291,10 @@ async function registerUser(username, email, password, recoveryMnemonic) {
   // appends it to the verification e-mail and stores it nowhere
   // (docs/auth-confirm.md §4.4). Omitted when they chose to save it themselves.
   if (recoveryMnemonic) payload.recovery_key = recoveryMnemonic;
+  // reCAPTCHA response, when the hub has a captcha configured. The widget lives
+  // in RegisterPage (auth-page.js); this function just forwards its token. A
+  // hub with no captcha configured sends nothing and the server does not check.
+  if (captchaToken) payload.captcha_token = captchaToken;
 
   const resp = await hubCall('/v1/users/register', {
     method: 'POST',