feat(mcp): stdio MCP server exposing the four companion tools

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

lib/mcp/context.js

@@ -0,0 +1,18 @@
+/**
+ * Builds the tool ctx object from environment variables.
+ * Used by companion-stdio.js when a tool call arrives, so each call reads
+ * fresh env values (useful if the process restarts or env is injected at launch).
+ *
+ * Environment variables:
+ *   VOID_AGENT_JSON  – JSON-serialised agent actor object (required for most tools)
+ *   VOID_SPACE_ID    – UUID of the active space
+ *   VOID_VIEW_JSON   – JSON-serialised view object (optional)
+ */
+export function buildCtxFromEnv(env = process.env) {
+  return {
+    agent: env.VOID_AGENT_JSON ? JSON.parse(env.VOID_AGENT_JSON) : null,
+    space_id: env.VOID_SPACE_ID || null,
+    view: env.VOID_VIEW_JSON ? JSON.parse(env.VOID_VIEW_JSON) : null,
+    actor: { kind: 'user', id: null }
+  };
+}