Fix a live answer that was correct and invisible

[adamjohnwright]

#216 shipped a live destination that answers correctly and shows the user nothing.

The Chainlit UI displays only what the callback handlers stream — bin/chat-chainlit.py reads chainlit_cb.final_stream and has no path that posts result["answer"]. Callbacks travel in the RunnableConfig, and the live path took no config at all.

Measured through the graph, the way the app calls it:

Q: What species are included in the Reactome database?
   answer present  : True  'Reactome covers a total of 96 species...'
   streamed tokens : 0        <-- what the user sees

After: 103 tokens, streamed text matching the answer exactly.

Three things, one cause

• config is now threaded from the graph node through the tool loop into every model call — including the forced final answer after the round cap, which is the call that produces the text.
• A streaming copy of the llm, the same model_copy(update={"streaming": True}) every RAG chain uses. The live path was using the shared non-streaming instance.
• The unreachable-MCP fallback passed a freshly constructed RunnableConfig() instead of the real one, so even the fallback would have been invisible.

Also fixed

chat_history was a parameter of answer_from_live_services that nothing ever passed, so every live answer was asked cold. A follow-up like "can you tell me?" — a real question from a real session — had no context. Typed Sequence rather than list so a caller holding list[HumanMessage] can pass it without a cast.

Tests

Three regression tests. Two fail against the shipped code:

FAILED test_the_config_reaches_every_model_call
FAILED test_the_config_reaches_the_forced_final_answer_too

How this got merged is worth more than the fix

I tested answer_from_live_services directly, it returned the right text, and I reported it working. The constitution's first principle:

A component test passing is not evidence the feature works... Before claiming something works, run it the way a user or the server would.

I wrote that principle into this repository this week and then didn't follow it. The test that would have caught it is the one that drives the compiled graph with a callback handler and counts tokens — which is what I ran only when reviewing my own merged work.

Not affected

Beta is unaffected: it has no REACTOME_MCP_SERVER set, so the live destination is not offered there at all. Verified both retrievers still work in the running container (user guide 6 hits, reactome 40).

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