let members use chat

The owner authorized this explicitly. Two refusals removed together, because
they were always one guard in two places: the wholesale isSuperAdmin middleware
in api/chat/chat.ts, and the chat socket's 403 in server.tsx.

They were right for the day they stood. A turn spawned claude as the OWNER and
every transcript path resolved through the owner's home, so a granted member
would have read the owner's sessions and run an agent as them.

What replaced them, rather than what deleted them:

  the turn runs as the member    spawnClaudeAsMember through sudo setpriv,
                                 proven against a real account by reading file
                                 ownership rather than trusting the process
  the credential is theirs       --reset-env plus an allowlist, so the owner's
                                 proxy variables cannot cross
  the transcripts are theirs     ChatIdentity carries a home from resolveHomeDir
                                 and claude-sessions cannot invent one
  the sessions are theirs        every session records its owner and all six
                                 sidecar commands refuse a mismatch

Also adds the precondition host asked for in 10: a member whose claude is not
signed in gets the instruction rather than a turn that dies on an auth error and
reads as a broken agent. Not installed and not signed in are separate messages
because they need different actions.

registry.ts and registry.test.ts now describe chat as confined in fact rather
than ahead of its implementation. The comments at both former guards say what
had to exist first, and that a revert should go back to a refusal rather than to
a narrower one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/capabilities/registry.ts

@@ -272,11 +272,10 @@ export const CAPABILITIES: Capability[] = [
     ws: ['terminal'],
     routes: ['/terminal'],
   },
-  // Confined so the owner can grant it and the route resolves — but the agent underneath still runs as the
-  // OWNER, so `api/chat/chat.ts` refuses a non-owner outright and the chat socket is refused in server.tsx.
-  // A deliberate, temporary gap: the permission exists, the functionality follows when a turn can be spawned
-  // under `runAs` with the member's own HOME. Until then this grant buys a route and a refusal, and the
-  // comments at both guards say so.
+  // Confined, and true since 2026-08-12: a member's turn spawns their own `claude` as their own Linux account
+  // through `sudo setpriv`, with their own `~/.claude` credential, their own transcripts and sessions that
+  // record whose they are. The two owner-only refusals that held this open — `api/chat/chat.ts` and the socket
+  // in `server.tsx` — were removed together once each of those was in place.
   {
     key: 'chat',
     label: 'Chat',