[KV Offload] Deduplicate lockstep MLA pending job cleanup

[procr1337]

This fixes another bug with native KV offload (now superseded by LMCache, for completeness)

Lockstep MLA groups share physical block IDs, so a transfer job may contain the same block ID once per logical group. Iterate the deduplicated set of block IDs in _remove_pending_job() so each (block, job) pair is only removed once from the set-backed pending-job index, instead of crashing with KeyError on the second occurrence.

Fixes a KeyError in _remove_pending_job() observed when KV cache offloading (--kv-offloading-size) is enabled while serving GLM-5.2 (MLA + decode context parallelism), reproduced by
offload-fix-glm52/probe_gpu_cache.py.

Purpose

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Summary by CodeRabbit

• Bug Fixes
  • Improved transfer-job cleanup when duplicate block identifiers are present.
  • Prevented repeated removals and incorrect pending-job tracking during offloading operations.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 0010d5b4-63c1-456f-bdc7-04070df2cdcf

📥 Commits

Reviewing files that changed from the base of the PR and between 4247d67 and 74309be.

📒 Files selected for processing (1)

• vllm/distributed/kv_transfer/kv_connector/v1/offloading/scheduler.py

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📝 Walkthrough

Walkthrough

The offloading scheduler now de-duplicates block IDs during pending-job cleanup, preventing repeated bookkeeping updates when lockstep MLA groups reference the same physical block.

Changes

Pending Job Cleanup

Layer / File(s)	Summary
Deduplicate pending block cleanup vllm/distributed/kv_transfer/kv_connector/v1/offloading/scheduler.py	_remove_pending_job processes unique block IDs before removing the job from pending-job mappings and deleting empty entries.

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

Suggested reviewers: ronensc, alex-ai-future, change72

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the fix: deduplicating pending-job cleanup for lockstep MLA KV offload.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

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