fix(grillme): vendor gcp-vertex.env for BYOA overlay gap

.fullsend/custom/env/gcp-vertex.env

@@ -0,0 +1,13 @@
+# Vertex AI env for the grillme sandbox.
+# Vendored from fullsend-ai/agents env/gcp-vertex.env.
+#
+# v0.36 overlay copies internal/scaffold/fullsend-repo (no env/) into
+# .fullsend/, not the agents package. Built-in agents get this file because
+# they resolve remotely; BYOA local harnesses must ship it themselves.
+# expand: true in the harness substitutes runner values before copy.
+
+export CLAUDE_CODE_USE_VERTEX=1
+export ANTHROPIC_VERTEX_PROJECT_ID=${ANTHROPIC_VERTEX_PROJECT_ID}
+export CLOUD_ML_REGION=${CLOUD_ML_REGION}
+export GOOGLE_APPLICATION_CREDENTIALS=/tmp/.gcp-credentials.json
+export GOOGLE_CLOUD_PROJECT=${GOOGLE_CLOUD_PROJECT}

.fullsend/custom/harness/grillme.yaml

@@ -25,7 +25,8 @@ skills:
   - custom/skills/grilling
 
 host_files:
-  - src: env/gcp-vertex.env
+  # Vendored: v0.36 overlay does not copy fullsend-ai/agents env/.
+  - src: custom/env/gcp-vertex.env
     dest: /sandbox/workspace/.env.d/gcp-vertex.env
     expand: true
   - src: custom/env/grillme.env