fix(instrumentation-js): repair LangChain, LlamaIndex, and Mastra OTel 2.x spans

[Nightingalelyy]

Summary

• preserve current LangChain callback typing, workflow grouping, agent boundaries, and Langflow component hierarchy
• export LlamaIndex failures and pending callbacks with sanitized diagnostics and stable id-less callback correlation
• buffer Mastra children until their parent is exported and propagate late agent failures to model spans
• add patch release intent for all three instrumentation packages

Validation

• package builds passed for LangChain, LlamaIndex, and Mastra

• focused tests passed: 13 + 6 + 4 (23 total)

• npm pack --dry-run passed for all three packages

• release inventory and release-intent validation passed

• complete locally linked example suites passed with marker otel2-fix-js-group-02-20260815T075000Z

• Respan MCP audit passed for 42 traces and 124 full span records, including tree integrity, content, model/token data, tool execution, expected errors, grouping, and duplicate checks

• Contribution re-audit against every current document under contribution/ passed after f37d4a8: LangChain text LLMs use canonical chat request type, automatic span-kind and direct model/input/output/token/tool aliases are absent, and tool definitions/current-turn calls use canonical JSON attributes.

• Fresh correction validation: all three package builds and 23/23 focused tests passed; release inventory/intents and diff checks passed; marker otel2-pr367-contract-correction-20260818T133700Z produced 3/3 representative LangChain traces and all 3 full records were inspected for chat/text/tool semantics, content, usage, aliases, and duplicates.

External follow-ups

• None documented.

Companion examples

• fix(examples-js): validate LangChain, LlamaIndex, and Mastra OTel 2.x spans respan-example-projects#54

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