docs: define module ownership contracts

Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com>

docs/design/module/input_output_modality_contracts.md

@@ -2,46 +2,132 @@
 title: Input, Output, and Modality Contracts
 kind: module
 status: draft
+architecture_state: current
 owners:
+  - "@Sy0307"
+  - "@amy-why-3459"
+document_stewards:
+  - "@hsliuustc0106"
+  - "@Gaohan123"
+  - "@david6666666"
+required_reviewers:
   - "@tzhouam"
-  - "@gcanlin"
+  - "@linyueqian"
+  - "@david6666666"
+  - "@yenuo26"
+  - "@NickCao"
 primary_code_paths:
   - vllm_omni/inputs/**
   - vllm_omni/outputs/**
+  - vllm_omni/request.py
+  - vllm_omni/data_entry_keys.py
+  - vllm_omni/engine/messages.py
+  - vllm_omni/engine/serialization.py
+  - vllm_omni/engine/mm_outputs.py
+  - vllm_omni/engine/output_modality.py
+  - vllm_omni/engine/output_processor.py
 related_code_paths:
-  - vllm_omni/tokenizers/**
-depends_on: []
+  - vllm_omni/model_executor/stage_input_processors/**
+  - vllm_omni/core/sched/**
+  - vllm_omni/distributed/omni_connectors/**
+  - vllm_omni/diffusion/request.py
+  - vllm_omni/diffusion/worker/request_batch.py
+  - vllm_omni/errors.py
+depends_on:
+  - error_contracts.md
 validation_paths:
   - tests/inputs/**
+  - tests/engine/test_data_entry_keys.py
+  - tests/engine/test_omni_request.py
+  - tests/engine/test_omni_request_output.py
+  - tests/engine/test_multimodal_accumulation.py
+  - tests/engine/test_output_modality.py
+  - tests/engine/test_output_processor.py
+  - tests/engine/test_wire_multimodal_output.py
+  - tests/utils/test_mm_outputs.py
+  - tests/utils/test_mm_outputs_partition.py
+  - tests/diffusion/test_diffusion_output_metadata.py
 upstream_refs:
-  - vllm.inputs
-  - vllm.outputs
-last_reviewed: 2026-07-16
+  - vllm.inputs/**
+  - vllm.outputs/**
+  - vllm.v1.request.Request
+  - vllm.v1.engine.EngineCoreRequest
+  - vllm.v1.engine.EngineCoreOutput
+  - vllm.v1.engine.output_processor.OutputProcessor
+invariant_namespace: IO-INV
+last_reviewed: 2026-08-07
+last_verified_commit: 3d7fc3b9ba3cac88d579d4dc35b78b0b641675fc
 ---
 
 # Input, output, and modality contracts
 
 These contracts define the data that may cross entrypoint, orchestration,
-stage, and model boundaries.
+stage, connector, and model boundaries.
+
+## Contract status
+
+This document is a draft description of the current request, message,
+serialization, modality, accumulation, and output types. It does not assign
+semantic error ownership to the wire schema.
+
+## Ownership boundary
+
+This document owns request identity, prompt/input types, modality keys and
+metadata, queue and wire message schemas, serialization, output types,
+accumulation, completion semantics, and compatibility shims.
+
+It does not own route-specific validation or rendering, model-specific
+interpretation, connector transport mechanics, scheduling policy, or semantic
+error classification. The `ErrorMessage` schema belongs here; the meaning and
+public rendering of its error fields belong to `error_contracts.md`.
 
 ## Candidate invariants
 
+These identifiers are proposals while the document is `draft`.
+
 ### IO-INV-001: Boundary data has an explicit modality
 
 **Rule:** Data crossing a module or stage boundary MUST identify its modality
 and use the corresponding validated contract.
 
-### IO-INV-002: Request identity is stable
+### IO-INV-100: Request identity is stable
 
 **Rule:** Request identity MUST be preserved across conversions, stages,
 streaming updates, cancellation, and errors.
 
-### IO-INV-003: Internal objects do not leak into public protocols
+### IO-INV-101: Completion is explicit
+
+**Rule:** Producers MUST distinguish partial updates from the terminal update
+for every output modality.
+
+### IO-INV-300: Internal objects do not leak into public protocols
 
 **Rule:** Entrypoints MUST explicitly translate internal output objects into
 public response types.
 
+## Invariant namespace
+
+`IO-INV` reserves `001-099` for schema ownership and dependency direction,
+`100-199` for identity, modality, accumulation, ordering, and completion,
+`200-299` for serialization failure and payload cleanup, and `300-399` for
+upstream extension, deprecation, and compatibility. Numbers become
+append-only after normative promotion.
+
 ## Safe-change guide
 
-Test construction, validation, serialization, streaming, optional fields, and
-compatibility at every affected producer-consumer boundary.
+Test construction, validation, serialization, round trips, streaming,
+accumulation, completion, optional fields, unknown fields, and compatibility
+at every affected producer-consumer boundary.
+
+## Promotion gate
+
+- Add explicit CODEOWNERS for the primary I/O paths or confirm that fallback
+  ownership is intentional.
+- Document the compatibility window for deprecated `vllm_omni.engine`
+  I/O-related imports.
+- Verify wire round trips and rejection of unknown or incompatible schema
+  fields.
+- Define payload-versus-metadata rules and completion semantics for streaming
+  and batched outputs.
+- Obtain approval from a technical owner and independent AR, diffusion,
+  connector, entrypoint, and validation reviewers as applicable.