[CREDO23]

Summary

• A new thread is the agent's only when the selected model is tested (or the developer switch is on) and is known to call tools: llama-server reports supports_tool_calls for a local model's template, or the remote catalog records tool_call: true under the connection's catalog provider. Unknown or unreadable counts as no, and the thread opens as a chat.
• agent_answers is renamed selected_model_can_run_agent, after what it decides.
• A turn sent to an agent thread after the selected model changes to one that fails the check is refused with 409 before any prompt is sent. A thread left with no model still gets the existing "no chat model selected" answer.
• llama.cpp capabilities now read supports_tool_calls beside supports_tools: a template can render tools while llama-server parses none of its calls.
• Tests: test_engine_choice.py covers each case against the real catalog and a stand-in llama-server; the agent-thread fixture now selects gpt-4o-mini (catalog provider openai), and a new test checks the send-time refusal.
• Docs: agent.md, chat.md, 01-which-engine.md and the proposal README. The old Known gap is gone; a new one records that the composer shows the refusal as an error rather than offering a new thread.

Follows #2135

High-level PR Summary

This PR modifies the agent engine selection logic to ensure only models that can actually call tools are assigned to agent threads. It adds checks for both local models (via llama-server's supports_tool_calls capability) and remote models (via catalog's tool_call field), preventing the agent from being assigned to models that would fail to execute tool calls. The change includes runtime validation that refuses turns sent to agent threads when the selected model changes to one without tool-calling support.

⏱️ Estimated Review Time: 15-30 minutes

💡 Review Order Suggestion

Order	File Path
1	surfsense_local/backend/modules/llm/providers/llamacpp/capabilities.py
2	surfsense_local/backend/modules/agent/engine_choice.py
3	surfsense_local/backend/modules/agent/agent_threads/turn.py
4	surfsense_local/backend/modules/chat/router.py
5	surfsense_local/backend/tests/integration/agent/conftest.py
6	surfsense_local/backend/tests/integration/agent/test_agent_threads.py
7	surfsense_local/backend/tests/integration/agent/test_engine_choice.py
8	surfsense_local/backend/tests/unit/llm/test_system_role.py
9	docs/proposals/agent/01-which-engine.md
10	docs/architecture/agent.md
11	docs/architecture/chat.md
12	docs/proposals/agent/README.md

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Project	Deployment	Actions	Updated
surf-sense-frontend	Error		Oct 2, 2026 3:36pm UTC

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Reviewing files that changed from the base of the PR and between 4dc375e and 59949ad.

📒 Files selected for processing (12)

• docs/architecture/agent.md
• docs/architecture/chat.md
• docs/proposals/agent/01-which-engine.md
• docs/proposals/agent/README.md
• surfsense_local/backend/modules/agent/agent_threads/turn.py
• surfsense_local/backend/modules/agent/engine_choice.py
• surfsense_local/backend/modules/chat/router.py
• surfsense_local/backend/modules/llm/providers/llamacpp/capabilities.py
• surfsense_local/backend/tests/integration/agent/conftest.py
• surfsense_local/backend/tests/integration/agent/test_agent_threads.py
• surfsense_local/backend/tests/integration/agent/test_engine_choice.py
• surfsense_local/backend/tests/unit/llm/test_system_role.py

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