wip(rescue): OCP Phase 6c stream-json port + opus 4.8 (uncommitted /tmp work)

Rescue commit — preserves the subagent-produced Phase 6c port (claude -p →
stream-json + --system-prompt + NDJSON parser) and opus 4.8 model addition
done 2026-05-30 in a /tmp clone (volatile). NOT reviewed-for-merge; this is
preservation only on a WIP branch so a /tmp reboot does not lose the work.

Strategy context: OCP is being made the first-mover for TUI-mode (users are
on OCP). Phase 6c here is the DEFAULT-path foundation (stream-json = sdk-cli =
the "Max-user stable mode" fallback). TUI-mode (cc_entrypoint=cli subscription
bridge) lands on top as an opt-in. Re-review before merging to main.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

models.json

@@ -2,6 +2,14 @@
   "$schema": "./models.schema.json",
   "version": 1,
   "models": [
+    {
+      "id": "claude-opus-4-8",
+      "displayName": "Claude Opus 4.8",
+      "openclawName": "Claude Opus 4.8 (via CLI)",
+      "reasoning": true,
+      "contextWindow": 200000,
+      "maxTokens": 16384
+    },
     {
       "id": "claude-opus-4-7",
       "displayName": "Claude Opus 4.7",
@@ -36,7 +44,7 @@
     }
   ],
   "aliases": {
-    "opus": "claude-opus-4-7",
+    "opus": "claude-opus-4-8",
     "sonnet": "claude-sonnet-4-6",
     "haiku": "claude-haiku-4-5-20251001"
   },