feat(lmcache): add cuMem CUDA IPC transfer lifecycle

[devinkuhn]

Summary

Adds the cuMem/CUDA-IPC lifecycle and sparse hybrid transfer normalization required by exact Mamba boundary-state caching.

Behavior

• refcounted CUDA cuMem allocation import/export
• cross-process FD broker transport for all four ranks
• context-preserving unregister; no cudaDeviceReset
• rollback for partial imports and wrapper creation
• engine-driven store/retrieve cleanup
• production-safe legacy D2H routing for compressed logical geometry
• effective per-window block-count validation for store and retrieve
• accepts both raw full-chunk block tables and already-windowed exact-state tables
• normalizes before null-chunk masking so unavailable historical Mamba checkpoints are skipped, not copied
• native H2D and uncompressed native D2H remain available

Exact Mamba handoff and connector semantics are in #525. Separated object groups are enabled by #527.

Why this update

The original D16 qualification was invalidated by delayed recurrent-state corruption. D22 demonstrated that transfer validation must use the same effective sliding-window geometry consumed by the kernels; requiring raw full-chunk Mamba counts rejects the correct one-checkpoint representation.

Verification

• focused transfer normalization/lifecycle tests: reported in the latest branch commit
• git diff --check: clean
• D22 runtime: 60 L1 objects / 993,329,152 bytes after 131,041-token store; two concurrent requests reloaded 129,024 tokens each (258,048 total); coherent outputs and post-reload probe; no fatal runtime errors

Supersedes the transfer portion of closed umbrella PR #522.

Duplicate-work note

This updates the existing focused transfer PR; it does not duplicate the scheduler-local prefix work in #403 or #482.

AI assistance disclosure

AI assistance was used in preparing this contribution.

Final D22 production receipt (2026-08-30)

The reviewed transfer stack is live with the rebuilt SM120 CUDA extension ff81d0cc81720a0016d085c6cd88f704685162695814fe2e4454279bbc270db4. Its pybind ABI exposes block_stride_elems, and the source includes the xword-alignment guard. Forced external reload transferred 119,808 tokens on each of four ranks with no transfer fault or corruption.

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📥 Commits

Reviewing files that changed from the base of the PR and between 0b67266 and edd5644.

📒 Files selected for processing (8)

• docker/glm53-flash/lmcache-d16-overlay/cumem_shareable_interposer.c
• docker/glm53-flash/lmcache-d16-overlay/overlay/lmcache/v1/multiprocess/modules/lmcache_driven_transfer.py
• docker/glm53-flash/lmcache-d16-overlay/overlay/lmcache/v1/multiprocess/transfer_context/worker_transfer.py
• docker/glm53-flash/lmcache-d16-overlay/overlay/lmcache/v1/platform/cuda/cache_context.py
• docker/glm53-flash/lmcache-d16-overlay/overlay/lmcache/v1/platform/cuda/cumem_ipc.py
• docker/glm53-flash/lmcache-d16-overlay/overlay/lmcache/v1/platform/cuda/ipc_wrapper.py
• docker/glm53-flash/lmcache-d16-overlay/overlay/lmcache/v1/platform/kv_wrap.py
• tests/v1/kv_connector/unit/test_lmcache_d16_transfer.py

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[devinkuhn]

Important qualification update: the stores-enabled D16 control reproduced a GPU2 illegal-memory-access/Xid 31 during startup warmup, while the otherwise identical store-disabled control started and passed the bounded 32k/128k/256k C1-C4 sentinel matrix. This PR is not ready for adoption; D2H store ownership/ordering remains under investigation.

[devinkuhn]

D22 qualification update: sparse exact-state transfer normalization is included in edd5644. Store/retrieve validation now uses effective sliding-window counts, accepts pre-windowed exact-state tables, and performs null-chunk masking after normalization. The corrected production run stored 60 objects / 993,329,152 bytes and externally reloaded 258,048 tokens coherently. This supersedes the earlier warning comment; full evidence is in #528.