fix: Fixes agent graph tool calls in fanned out graphs

[jsonbailey]

Note

Medium Risk
Refactors LangGraph graph construction, tool binding, and routing logic; mistakes could cause incorrect agent traversal or tool execution/metrics attribution in production agent graphs.

Overview
Fixes LangGraph execution for multi-child (previously fan-out) agent graphs by introducing explicit handoff tools (transfer_to_*) that route via Command(goto=...), disabling parallel tool calls during handoff, and adding conditional tool-node loopback logic when a node has both functional tools and handoff tools.

Adds build_structured_tools() to wrap LD tool definitions as LangChain StructuredTool (sync/async supported) and skips unsupported/built-in tool types. Introduces LDMetricsCallbackHandler to collect per-node tokens/durations/tool calls via LangChain callbacks and flush them to LaunchDarkly trackers after the run; tests are updated/added to cover the new routing behavior and callback-based tracking.

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Unconditional break prevents backward scan in router

Medium Severity

The break on line 218 is at the for-loop level (same indentation as if), not inside the if block. This means if the very last message doesn't have a truthy .name, the loop exits immediately without checking any earlier messages. The for msg in reversed(...) pattern implies a backward scan, but the unconditional break makes the loop always terminate after one iteration, rendering reversed() useless. If the last message in state ever lacks a truthy name, the router silently defaults to looping back to the parent instead of finding the most recent named message.

 

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