feat(langchain): Record run_name in on_chat_model_start

[alexander-alderman-webb]

Description

Issues

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

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Semver Impact of This PR

🟡 Minor (new features)

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New Features ✨

• (ci) Cancel in-progress PR workflows on new commit push by joshuarli in #5994

• (langchain) Record run_name in on_chat_model_start by alexander-alderman-webb in #5924

Bug Fixes 🐛

• (langchain) Set agent name as gen_ai.agent.name for chat and tool spans by alexander-alderman-webb in #5877

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Codecov Results 📊

✅ 79 passed | Total: 79 | Pass Rate: 100% | Execution Time: 889ms

All tests are passing successfully.

❌ Patch coverage is 40.00%. Project has 15366 uncovered lines.

Files with missing lines (2)

File	Patch %	Lines
langchain.py	18.31%	⚠️ 482 Missing
consts.py	99.43%	⚠️ 2 Missing

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

There are 2 total unresolved issues (including 1 from previous review).

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