When tools change mid-conversation, LLMs can produce a few different
flavors of tool-call-related hallucination: calling tools that have
been removed, avoiding tools that have been re-added, or hallucinating
output (made-up answers or tool-call-shaped non-tool-calls) when tools
are unavailable.
This change introduces an opt-in ``add_tool_change_messages`` flag on
the LLM aggregators (preferred entry point: ``LLMContextAggregatorPair(
..., add_tool_change_messages=True)``) that appends a developer-role
message to the context whenever ``LLMSetToolsFrame`` changes the set
of advertised standard tools. Helps the LLM stay coherent across tool
changes by spelling out exactly what just became available or
unavailable. Both aggregators participate; whichever handles the
frame first wins, and the other (if any) sees an empty diff against
the shared context and stays silent — order-independent regardless of
whether the frame flows downstream or upstream.
Also tightens the existing missing-handler path (introduced in #4301):
- Reworded the terminal tool result to a neutral "The function
``X`` is not currently available." (overridable via
``LLMService.MISSING_FUNCTION_CALL_MESSAGE_TEMPLATE``). Previously
read "Error: function 'X' is not registered."
- Logs at the call site now distinguish developer error (tool
advertised but no handler registered → ``logger.error``) from
hallucination (tool not advertised → ``logger.warning``).
Includes a manual validation harness
(``examples/features/features-add-tool-change-messages.py``) that
exercises the new ``add_tool_change_messages`` mitigation by flipping
tool availability on a turn counter so its effect can be observed
end-to-end with the flag on vs. off.
Two follow-ups now that LLMService is generic over its adapter:
- Add an explicit backward-compat test verifying that an LLMService
subclass with no generic parameter (the third-party-provider
pattern) instantiates and returns a usable adapter. The existing
MockLLMService (declared without brackets) already exercised this
implicitly, but it's worth a named assertion.
- Drop the now-redundant `params: SomeLLMInvocationParams = ...`
variable annotations on `adapter.get_llm_invocation_params()`
results. Since `get_llm_adapter()` now returns the precise adapter
type, and `BaseLLMAdapter` is generic in its invocation-params
type, the call already infers the right TypedDict.
Bound methods are created fresh on each attribute access, so
'self._missing_function_call_handler is self._missing_function_call_handler'
is always False. Using 'is' meant the placeholder branch never fired and
both warnings logged when a function was missing at queue time.
Switch to == so equality compares the underlying function and instance.
Strengthen the missing-at-queue-time test to assert the second warning
does not fire.
Address review feedback: a function may be unregistered between when
run_function_calls queues it and when _run_function_call executes it.
Restore the live lookup, falling back to the missing-function handler
when the entry is gone, so the call still terminates with a normal
tool result. Factor the missing-handler item construction into a
helper since it's now built in two places.
