[https://nvbugs/6463831][fix] Replace isinstance(self.mpi_session, MpiPoolSession) with `not…

[trtllm-agent]

Summary

• Root cause: isinstance(self.mpi_session, MpiPoolSession) raises TypeError when tests/test_common/session_reuse.py monkey-patches the module-level MpiPoolSession symbol with a factory function.
• Fix: Replace isinstance(self.mpi_session, MpiPoolSession) with not self.mpi_session.is_comm_session(), the polymorphic predicate already defined on MpiSession base class — immune to module-level symbol rebinding, matches the same session set.
• Automated fix generated by repair-bot

Test plan

• Verify fix on the same GPU type as the original failure
• Check for regressions in related tests

Links

• Bug: https://nvbugs/6463831

Summary by CodeRabbit

• Bug Fixes
  • Improved worker-process initialization across MPI session types.
  • Prevented test and runtime session substitutions from causing incorrect session detection.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

Plan: Enterprise

Run ID: 235cd13f-1e7f-4d8a-8250-686aa0b206e7

📥 Commits

Reviewing files that changed from the base of the PR and between 274043a and 7655db6.

📒 Files selected for processing (1)

• tensorrt_llm/executor/proxy.py

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📝 Walkthrough

Walkthrough

The executor worker startup path now uses is_comm_session() instead of an isinstance check when handling three-element worker status, avoiding failures when MpiPoolSession is rebound by test infrastructure.

Changes

Executor session detection

Layer / File(s)	Summary
Worker identity registration predicate tensorrt_llm/executor/proxy.py	The len(status) == 3 branch uses the polymorphic MPI session predicate and documents the test-time rebinding hazard.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• NVIDIA/TensorRT-LLM#16489: Updates the same worker identity registration condition.
• NVIDIA/TensorRT-LLM#16490: Changes the same MPI session detection logic.
• NVIDIA/TensorRT-LLM#16421: Replaces the concrete session type check in the same startup path.

Suggested reviewers: schetlur-nv, tburt-nv

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is specific and directly matches the main fix, including the bug link and fix type.
Description check	✅ Passed	It includes the root cause, fix, test plan, and bug link, so the key template content is covered.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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