[https://nvbugs/6104831][test] Add cascade-prune reproducer tests

[chienchunhung]

Summary by CodeRabbit

• Bug Fixes

  • Fixed a critical assertion error in batch manager operations that could cause crashes during memory block removal and reallocation sequences.

• Tests

  • Added comprehensive unit tests covering batch manager edge cases to prevent assertion failure regression.

Summary

Add four RadixBlockTreeTest regression tests that lock in the fixed behavior for the KV-cache-block trie cascade-prune assertion reported in NVBugs 6104831 (templatedTrie.h:249 cascade prune: parent did not find this node as a child).

Note on the fix

The original templatedTrie.h fix from this PR is already in main — it landed earlier as part of #13578 ("[None][fix] Add TestServePrefixAwareScheduling base on LMBenchmark/synthetic-multi-round-qa"), where the same itr->second->setPrevNode(NodePtr{}) line was bundled together with a prefix-aware scheduling test. PR #13578 was opened on 2026-04-20, ~8 days before this PR, and merged into main ~47 minutes before this PR was opened.

After rebasing onto current main, this PR no longer carries any change to cpp/include/tensorrt_llm/batch_manager/templatedTrie.h; only the four reproducer tests remain. They were not part of #13578, so they're still useful as a focused regression net for the trie invariant.

Test Coverage

Four new RadixBlockTreeTest cases isolate the cascade-prune regression at three layers, all using EXPECT_NO_THROW against the fixed behavior:

• Regression_NVBugs6104831_DetachOrphanedBlockDoesNotFireAssertion — minimal direct repro (one block, no descendants).
• Regression_NVBugs6104831_FreeBlockAndAllDescendantsOnOrphanedSubtreeDoesNotFireAssertion — same root cause through freeBlockAndAllDescendants, matching the bug report's stack trace literally.
• Regression_NVBugs6104831_StoreBlocksRekeyDoesNotTriggerAssertion — production storeBlocks-style re-keying via removeNextBlock + addNextBlock.
• Regression_NVBugs6104831_StressPrefixOverlappingInsertEvictReuseLoop — stress loop on prefix-overlapping sequences mirroring the disagg insert/evict workload.

The full radixBlockTreeTest suite remains green.

PR Checklist

Please review the following before submitting your PR:

• PR description clearly explains what and why.
• PR follows TRT-LLM CODING GUIDELINES to the best of your knowledge.
• Test cases are provided for new code paths.
• No new dependencies introduced.
• No CODEOWNERS changes.
• No documentation changes needed.
• No tava architecture changes.
• The reviewers assigned automatically/manually are appropriate for the PR.
• Please check this after reviewing the above items as appropriate for this PR.

PR Checklist

Please review the following before submitting your PR:

• PR description clearly explains what and why. If using CodeRabbit's summary, please make sure it makes sense.

• PR Follows TRT-LLM CODING GUIDELINES to the best of your knowledge.

• Test cases are provided for new code paths (see test instructions)

• Any new dependencies have been scanned for license and vulnerabilities

• CODEOWNERS updated if ownership changes

• Documentation updated as needed

• Update tava architecture diagram if there is a significant design change in PR.

• The reviewers assigned automatically/manually are appropriate for the PR.

• Please check this after reviewing the above items as appropriate for this PR.

GitHub Bot Help

To see a list of available CI bot commands, please comment /bot help.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds a bidirectional edge cleanup in the Node::clearNode method to properly detach child nodes from their parent by resetting back-pointers, and introduces four comprehensive unit tests to validate the fix prevents cascade-prune assertion failures during block reattachment operations.

Changes

Cohort / File(s)	Summary
Bidirectional edge cleanup and regression tests cpp/include/tensorrt_llm/batch_manager/templatedTrie.h, cpp/tests/unit_tests/batch_manager/radixBlockTreeTest.cpp	Added bidirectional edge update in Node::clearNode to reset child node back-pointers before removal, and introduced four new unit tests covering orphaned block detachment, cascade-prune scenarios, block re-keying sequences, and stress testing for overlapping prefix operations.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 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
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.
Title check	✅ Passed	The title accurately summarizes the main change: adding reproducer tests for the cascade-prune assertion regression (NVBugs 6104831), matching the file changes in the PR.
Description check	✅ Passed	The PR description comprehensively explains the issue, fix, test coverage, and includes a properly formatted title with NVBugs ID and [fix] type.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Tip

💬 Introducing Slack Agent: The best way for teams to turn conversations into code.

Slack Agent is built on CodeRabbit's deep understanding of your code, so your team can collaborate across the entire SDLC without losing context.

• Generate code and open pull requests
• Plan features and break down work
• Investigate incidents and troubleshoot customer tickets together
• Automate recurring tasks and respond to alerts with triggers
• Summarize progress and report instantly

Built for teams:

• Shared memory across your entire org—no repeating context
• Per-thread sandboxes to safely plan and execute work
• Governance built-in—scoped access, auditability, and budget controls

One agent for your entire SDLC. Right inside Slack.

👉 Get started

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[chienchunhung]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #46515 [ run ] triggered by Bot. Commit: d301166 Link to invocation

[tensorrt-cicd]

PR_Github #46515 [ run ] completed with state SUCCESS. Commit: d301166
/LLM/main/L0_MergeRequest_PR pipeline #36574 completed with status: 'FAILURE'

CI Report

⚠️ Action Required:

• Please check the failed tests and fix your PR
• If you cannot view the failures, ask the CI triggerer to share details
• Once fixed, request an NVIDIA team member to trigger CI again

Link to invocation

[SimengLiu-nv]

LGTM.

[chienchunhung]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #46675 [ run ] triggered by Bot. Commit: d8395a5 Link to invocation

[tensorrt-cicd]

PR_Github #46675 [ run ] completed with state SUCCESS. Commit: d8395a5
/LLM/main/L0_MergeRequest_PR pipeline #36716 completed with status: 'SUCCESS'

CI Report

Link to invocation