docs(core): add message-type-specific documentation for message name fields

[mdrxy]

Updates the name field documentation in v1 messages to provide message-type-specific guidance instead of generic descriptions. The current documentation incorrectly presents the field as purely "human-readable" when it serves critical functional purposes that vary by message type.

• ToolMessage.name is effectively required by most providers despite being typed as Optional[str]
• AIMessage.name is critical for multi-agent systems but optional for single-agent scenarios

Examples

langchain-openai

• AIMessage.name
  • Message conversion to OpenAI API format includes name when present on a message
• ToolMessage.name

langgraph-supervisor-py

• AIMessage.name
  • Multi-agent handoff coordination preserving agent identity
  • Agent message lookup for forwarding searches
  • Agent attribution in handoff back messages
  • Inline agent formatting / identity embedding

langchain-google

• Uses message.name when creating FunctionResponse objects

langchain-community

• Multiple chat model providers require message.name for tool/function calling

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[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #32469 will not alter performance

_{Comparing mdrxy/messages-name-docs (56379fb) with wip-v0.4 (2f0c642)¹}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched benchmarks

Footnotes

1. No successful run was found on wip-v0.4 (7f989d3) during the generation of this report, so 132ed67 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #32469 will not alter performance

_{Comparing mdrxy/messages-name-docs (56379fb) with wip-v0.4 (2f0c642)¹}

Summary

✅ 14 untouched benchmarks

Footnotes

1. No successful run was found on wip-v0.4 (7f989d3) during the generation of this report, so 132ed67 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩