fix: prevent tool name duplication in streaming accumulator (MiniMax/NVIDIA NIM)

Based on #11984 by @maxchernin.  Fixes #8259.

Some providers (MiniMax M2.7 via NVIDIA NIM) resend the full function
name in every streaming chunk instead of only the first.  The old
accumulator used += which concatenated them into 'read_fileread_file'.

Changed to simple assignment (=), matching the OpenAI Node SDK, LiteLLM,
and Vercel AI SDK patterns.  Function names are atomic identifiers
delivered complete — no provider splits them across chunks, so
concatenation was never correct semantics.

run_agent.py

@@ -5868,7 +5868,15 @@ class AIAgent:
                             entry["id"] = tc_delta.id
                         if tc_delta.function:
                             if tc_delta.function.name:
-                                entry["function"]["name"] += tc_delta.function.name
+                                # Use assignment, not +=.  Function names are
+                                # atomic identifiers delivered complete in the
+                                # first chunk (OpenAI spec).  Some providers
+                                # (MiniMax M2.7 via NVIDIA NIM) resend the full
+                                # name in every chunk; concatenation would
+                                # produce "read_fileread_file".  Assignment
+                                # (matching the OpenAI Node SDK / LiteLLM /
+                                # Vercel AI patterns) is immune to this.
+                                entry["function"]["name"] = tc_delta.function.name
                             if tc_delta.function.arguments:
                                 entry["function"]["arguments"] += tc_delta.function.arguments
                         extra = getattr(tc_delta, "extra_content", None)