Add a new SubjectTypeChatd RBAC subject with minimal permissions:
- Chat: CRUD
- Workspace: Read
- DeploymentConfig: Read
Replace all 10 AsSystemRestricted calls in coderd/chatd/chatd.go:
- Line 890: Use AsChatd instead of AsSystemRestricted for the background
processor context.
- Subscribe() path (5 calls): Remove system escalation entirely; these
run under the authenticated user's context from the HTTP handler.
- processChat path (4 calls): Remove redundant per-call wraps; the
context already carries AsChatd from the processor start.
Add TestAsChatd verifying allowed and denied actions.
Created using Mux (Opus 4.6)