fix(companion): emit draft from user-turn tool_result + stamp space_id on created entities

- driver: tool_results arrive as type:'user' content blocks (not bare); parse them
- route: tool_result content is a JSON string; parse it for pending_change_id → draft event
- propose_change: inject ctx.space_id into create payloads (model can't know the uuid; tables require it)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/ai/agent/tools/propose_change.js

@@ -23,13 +23,22 @@ export const proposeChangeTool = {
     if (tier === 'deny') {
       return { error: `not permitted to ${action} ${entity_type}` };
     }
+    // Stamp the current Space onto newly-created space-scoped entities — the
+    // model doesn't know the Space uuid, and these tables require space_id NOT NULL.
+    const SPACE_SCOPED = ['task', 'page', 'project', 'resource'];
+    const finalPayload = { ...(payload ?? {}) };
+    if (action === 'create' && ctx.space_id && SPACE_SCOPED.includes(entity_type)
+        && finalPayload.space_id == null) {
+      finalPayload.space_id = ctx.space_id;
+    }
+
     // v1: drafting always routes through approval, even for allow-tier agents.
     const change = await pendingChanges.create({
       agent_id: ctx.agent.id,
       entity_type,
       entity_id: entity_id ?? null,
       action,
-      payload: payload ?? {},
+      payload: finalPayload,
       reason: reason ?? null
     });
     return {