docs(blender): desktop Blender + MCP registration per working session, not per task (Prime 2026-09-28)

stacks/blender/README.md

@@ -79,13 +79,24 @@ not a sandbox.
 
 ### For an agent
 
+**Per working SESSION** (Prime, 2026-09-28, relayed by draupnir; supersedes the 2026-09-27
+per-task rule): a session that does design work brings the desktop up once at its start and
+takes it down at its end. It is still not always-on, and the registration is still never user-
+or project-wide.
+
 ```bash
-scripts/blender-mcp up          # GPU 3 is borrowed: start only when needed
+# session start
+scripts/blender-mcp up          # GPU 3 is borrowed: only for a session that needs it
 scripts/blender-mcp status      # wait for "mcp add-on: answering" (~10-40 s)
-claude mcp add blender -- /home/lkraven/development/eshpfi-management/scripts/blender-mcp   # PER TASK (Prime 2026-09-27): never user/project-wide
-scripts/blender-mcp down        # when finished: the card goes back to 0
+claude mcp add blender -- /home/lkraven/development/eshpfi-management/scripts/blender-mcp
+# session end
+claude mcp remove blender       # `mcp add` defaults to local scope, which PERSISTS for this directory
+scripts/blender-mcp down        # the card goes back to 0
 ```
 
+- **One GUI, one scene: MCP work serializes fleet-wide.** Two sessions driving it at once
+  trample each other's scene. Parallel parts belong on `blender-run` (`--cpu` if nothing renders).
+
 - **Always pass `user_prompt`.** The tools require it; it is a short statement of the user's
   request.
 - **Render on the GPU:** set `scene.cycles.device = 'GPU'` on any scene you create. Safe mode