feat(good-fences): a Think agent mows with a codemode mower connector

Neighbor is a Project Think agent on gpt-oss-120b. Its execute tool
runs model-written code in a dynamic worker; MowerConnector puts the
mower there as the `mower.*` namespace (start/push/turn/stop, each
taking an args object). makeMower is the Logo-turtle mower on a
wrapping yard; for now it lives inside the agent's DO.

Getting to green, one symptom at a time:
- chatted instead of acting: say it acts by running code
- reply cut mid-sentence: maxOutputTokens 4096 via beforeTurn
- execute failed creating codemode's runtime facet ("Incorrect type
  for the 'class' field"): declare CodemodeRuntime as a DO class
- looked for the mower in the workspace filesystem: activeTools
  ["execute"], and name the namespace in the prompt
- found the mower, then asked for lawn dimensions: "don't ask me
  questions: put it to use"

Green: 36 mower calls, a 30-cell rectangle.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

good-fences/wrangler.model-tests.jsonc

@@ -11,6 +11,8 @@
 		"bindings": [{ "name": "Neighbor", "class_name": "Neighbor" }]
 	},
 	"exports": {
-		"Neighbor": { "type": "durable-object", "storage": "sqlite" }
+		"Neighbor": { "type": "durable-object", "storage": "sqlite" },
+		// codemode's runtime, a facet of the agent's DO
+		"CodemodeRuntime": { "type": "durable-object", "storage": "sqlite" }
 	}
 }