[CAICAIIs]

Overview

Step S1 of #62243: move the Mooncake P2P connector metadata and wire structs into mooncake/metadata.py and mooncake/protocol.py, plus a test that pins the encoded wire bytes.

Claims

• Definition-site move: ReqId, TransferId, PullReqMeta, SendBlockMeta, MooncakeConnectorMetadata move to mooncake/metadata.py; MooncakeXferMetadata, MooncakeXferResponseStatus, MooncakeXferResponse move to mooncake/protocol.py.
• Wire formats unchanged: field order, wire names, types, defaults, the omit_defaults flag and the status values (FINISH=0, CONTINUE=1, ERROR=2, LAYOUT_MISS=3) all match main, and test_mooncake_wire_format.py now states that contract as a table.
• Behavior unchanged: no logic edits; mooncake_connector.py still re-exports every moved name, so existing from ...mooncake_connector import MooncakeXferMetadata imports keep working.
• One rename inside the moved code: MooncakeConnectorMetadata.reqs_not_processed becomes transfers_not_processed, with the scheduler field it is assigned from.

Validation

Tests (before = main at 34ac4f96a, after = this branch, same command, macOS, VLLM_TARGET_DEVICE=cpu):

VLLM_TARGET_DEVICE=cpu PYTHONPATH=<worktree>:<vllm>/scratch \
  .venv/bin/python -m pytest \
  tests/v1/kv_connector/unit/test_mooncake_connector.py \
  tests/v1/kv_connector/unit/test_mooncake_connector_hma.py \
  tests/v1/kv_connector/unit/test_mooncake_connector_hybrid_mamba.py \
  tests/v1/kv_connector/unit/test_mooncake_stats.py \
  tests/v1/kv_connector/unit/test_mooncake_store_connector.py \
  tests/v1/kv_connector/unit/test_mooncake_store_worker.py \
  tests/v1/kv_connector/unit/test_mooncake_wire_format.py -q

• Before: 424 passed in 84.72s.
• After: 429 passed in 90.79s. The extra five are the new wire-format cases.

-p no_mps_cleanup_plugin is only a local workaround for a macOS-only teardown segfault in torch.accelerator.empty_host_cache(); it is applied to both runs and touches no repository file.

Lint and types:

.venv/bin/pre-commit run --files \
  vllm/distributed/kv_transfer/kv_connector/v1/mooncake/metadata.py \
  vllm/distributed/kv_transfer/kv_connector/v1/mooncake/protocol.py \
  vllm/distributed/kv_transfer/kv_connector/v1/mooncake/mooncake_connector.py \
  tests/v1/kv_connector/unit/test_mooncake_connector.py \
  tests/v1/kv_connector/unit/test_mooncake_wire_format.py

All hooks pass: ruff check, ruff format, typos, mypy (oldest supported Python), check-spdx-header, check-forbidden-imports, check-root-lazy-imports, check-test-tethering, plus the remaining hooks that apply to Python files.

Name-level checks:

• Moved code is byte-identical to main: the metadata.py body matches mooncake_connector.py lines 99-100 and 658-714 of main apart from the one rename below, and the protocol.py body matches lines 608-657 exactly (diff of the extracted regions is empty).
• The worker and scheduler bodies are unchanged: diffing class MooncakeConnector through group_concurrent_contiguous against main yields only the six renamed lines.
• Public namespace of mooncake_connector is unchanged apart from IntEnum, which was an incidental re-export of from enum import IntEnum and is now unused there (ruff flagged it). Every name the module defined before is still importable from it:

python -c "from vllm.distributed.kv_transfer.kv_connector.v1.mooncake.mooncake_connector import MooncakeXferMetadata, PullReqMeta, SendBlockMeta, MooncakeConnectorMetadata, MooncakeXferResponse; print('ok')"

Details

Names moved, and their new homes:

Definition	New module
ReqId, TransferId	mooncake/metadata.py
PullReqMeta, SendBlockMeta	mooncake/metadata.py
MooncakeConnectorMetadata	mooncake/metadata.py
MooncakeXferMetadata, MooncakeXferResponseStatus, MooncakeXferResponse	mooncake/protocol.py

Dependency direction is one-way and acyclic: protocol.py imports ReqId/TransferId from metadata.py; metadata.py imports KVConnectorMetadata from ..base and EngineId from kv_connector/utils.py, and does not import protocol.py. mooncake_connector.py imports both and keeps them in its namespace, so tests and any external imports of those names are unaffected.

The rename: MooncakeConnectorMetadata.reqs_not_processed holds set[TransferId], not request ids, while the identically named field in nixl/metadata.py does hold set[ReqId]. Since the definition moves here, it is renamed to transfers_not_processed together with the scheduler field assigned into it (_transfers_not_processed). Seven lines in the package and one attribute name in an existing assertion in test_mooncake_connector.py; no assertion semantics change, no wire impact.

The wire test: tests/v1/kv_connector/unit/test_mooncake_wire_format.py states the push wire contract once, as data — nothing else. For each message it asserts the ordered (field, type, required-or-default) list read from msgspec.structs.fields(), the struct configuration that shapes the encoding (omit_defaults, tag, tag_field, array_like, forbid_unknown_fields), and the status values. A reordered field, a renamed wire key, a changed type or default, a dropped omit_defaults, a switched forbid_unknown_fields or a changed status value fails there, and the failing row is the diff. Golden byte strings would catch the same, but nobody can review them, and every deliberate format change turns into pasting new bytes, after which the guard is worth nothing. This table is the review-time half of the contract; the runtime half is the compatibility hash that #61974 adds and that #62243 folds into metadata.py, which refuses a P/D pair whose wire differs. The pull structs get the same tables in that PR's rebase and the bootstrap payload in S2, since neither exists on main yet.

Rebase note: the branch is on main at 34ac4f96a. The conflict with #62282 was in the moved block itself, where that PR rewrote the PullReqMeta.failed comment; the new wording is in metadata.py, and its _complete_pull_task accounting is carried over unchanged.

Names inside the moved code that were left alone, and why:

• msgspec field names in protocol.py are wire keys; renaming any of them changes the encoded format.
• reqs_to_recv / reqs_to_send / need_send / sent / sending / PullReqMeta / SendBlockMeta / d_req_id / p_req_id keep their names: reqs_to_recv and reqs_to_send are shared with nixl/metadata.py, and [Feature][KV Connector][Mooncake] Add MooncakePullConnector for decode-side reads #61974 constructs SendBlockMeta(p_req_id=...) and inserts aborted next to sending, so renaming those here would only move conflict into that PR.
• The mooncake_ prefix in mooncake_connector.py / mooncake_utils.py and the MooncakeXfer* class names belong to the later steps: [RFC]: Module layout for the Mooncake P2P KV connector #62243 keeps mooncake_connector.py as the compatibility shim until connector.py exists in S5.

Follow-ups

• The rest of the split is S2-S5 of [RFC]: Module layout for the Mooncake P2P KV connector #62243: bootstrap.py and scheduler.py, the push-side geometry moving into the existing transfer_plan.py, the worker becoming base_worker.py + push_worker.py + pull_worker.py, and the facades moving to connector.py. Each step waits for an in-flight PR to merge first: [KVConnector] Classify transfer groups from the framework's spec kinds #57309 for the spec classification, [Feature][KV Connector][Mooncake] Add MooncakePullConnector for decode-side reads #61974 for the pull connector, [KVConnector][Mooncake] Add a failure ledger for the failure spine #57529 for the failure ledger, [KV Connector][Mooncake] Expose transfer stats via Prometheus #56939 for metrics.
• The runtime half of the wire contract is the compatibility hash from [Feature][KV Connector][Mooncake] Add MooncakePullConnector for decode-side reads #61974, which this plan moves into metadata.py. The two wire protocols stay separate; unifying them would change the format.
• Two str aliases are the only reason protocol.py depends on metadata.py, and metadata.py pulls in v1.base and kv_connector/utils.py. Whether those aliases belong in a leaf module is a layout decision for [RFC]: Module layout for the Mooncake P2P KV connector #62243 or [RFC]: Share KV transfer planning primitives across KV connectors #57373, not something to change inside a move.
• mooncake_connector.py keeps its mooncake_ prefix and the MooncakeXfer* class names until S5, when connector.py exists and the old path becomes an __all__ shim.
• Two PRs land after this one and both touch the same package. [Mooncake][PD] Support DCP transfer for MLA/GQA models #53205 changes the wire: each req_blocks entry gains a third element and remote_dcp_size / remote_block_size are appended, so the schema tables here and the compatibility hash are edited in whichever PR merges second. [Feature][KV Connector][Mooncake] Add layerwise and chunk-wise KV transfer #62504 adds a second execution shape of the WRITE path, so S3 and S4 keep transfer_plan.py, push_worker.py and scheduler.py subclassable rather than closed.

Why this is not a duplicate

• No other open PR moves these definitions; no open PR references [RFC]: Module layout for the Mooncake P2P KV connector #62243 in its body.
• [KVConnector] Classify transfer groups from the framework's spec kinds #57309 touches the same file only to swap the spec-classification helpers to framework spec kinds; it moves no metadata or wire struct, and none of its hunks overlap the renamed lines.
• [Feature][KV Connector][Mooncake] Add MooncakePullConnector for decode-side reads #61974 adds mooncake_pull_connector.py, transfer_plan.py and compat.py; its pull wire structs, planning module and compatibility hash stay with that PR and are not absorbed here.

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Pull Request Checklist

• I used vLLM's /pr-checklist skill. (Mandatory for agents, optional for humans).

• AI assistance was used during the creation of this PR.

• Design Fit: Minimizes impact on core components, reuses existing functionality, and justifies added complexity.

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• Code Quality and Style: Keeps code and comments clear and concise, and updates relevant documentation and examples.

• Pull Request Contents: Includes a brief summary and relevant links, supports claims with evidence, explains root causes and implementation trade-offs, and follows the contributing guide.

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