release v2.6.0

The cutover's first real lesson ships: tool_choice "required" was a
workaround for a backend that ignored it, and became an unbreakable
tool loop on a backend that obeys it every request (~80 s arithmetic
turns, observed). The health check now learns which server answers
behind OLLAMA_HOST (/props is llama-server's own surface) and only
Ollama gets the advisory nudge. Probed unforced on llama-server: 3/3
tool calls via the --jinja template.

Also carries BACKEND_SLOT_PINNING (default off) for the P3 pilot.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/contracts/test_service_contracts.py

@@ -114,16 +114,18 @@ class TestLocalBackendContract:
         )
 
     async def test_openai_compat_tool_calling(self):
-        # Mirrors the request PydanticAI's OpenAIChatModel sends for the
-        # orchestration phase, including the extra_body tool_choice.
+        # Mirrors the orchestration-phase request on llama-server: tools
+        # attached, NO tool_choice. The backend must call the tool unforced
+        # — "required" is deliberately absent because llama-server enforces
+        # it on every request in a run, which turns the tool loop
+        # unbreakable (observed at cutover: ~80 s turns).
         response = await _post_or_skip(
             f"{OLLAMA}/v1/chat/completions",
-            "ollama",
+            "local-backend",
             {
                 "model": config.OLLAMA_DEFAULT_MODEL,
                 "messages": [{"role": "user", "content": "What is 6 * 7? Use the calculator."}],
                 "tools": [CALCULATOR_TOOL],
-                "tool_choice": "required",
                 "stream": False,
             },
             timeout=config.OLLAMA_TIMEOUT,