docs: define module ownership contracts

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

docs/.nav.yml

@@ -138,12 +138,28 @@ nav:
       - Prometheus Metrics: design/metrics.md
       - Speech Generation Performance Optimizations: design/qwen3_omni_tts_performance_optimization.md
     - Module Design:
-      - Runtime Modules:
+      - Entrypoints: design/module/entrypoints.md
-        - AR Module: design/module/ar_module.md
+      - vLLM-Omni Configuration: design/module/vllm_omni_config.md
-        - DIT Module: design/module/dit_module.md
+      - Input, Output, and Modality Contracts: design/module/input_output_modality_contracts.md
-      - Orchestration:
+      - Error Contracts: design/module/error_contracts.md
-        - Entrypoint Module: design/module/entrypoint_module.md
+      - Engine Orchestration: design/module/engine_orchestration.md
-        - AsyncOmni Architecture: design/module/async_omni_architecture.md
+      - Stage Runtime: design/module/stage_runtime.md
+      - OmniConnector: design/module/omni_connector.md
+      - Model Integration: design/module/model_integration.md
+      - Autoregressive Runtime: design/module/ar_runtime.md
+      - Diffusion:
+        - Overview: design/module/diffusion/index.md
+        - Runtime: design/module/diffusion/diffusion_runtime.md
+        - Model Integration: design/module/diffusion/diffusion_model_integration.md
+        - Continuous Batching: design/module/diffusion/continuous_batching.md
+        - Parallelism: design/module/diffusion/parallelism.md
+        - Offloader: design/module/diffusion/offloader.md
+      - Execution Platforms: design/module/execution_platforms.md
+      - Cache Management: design/module/cache_management.md
+      - Quantization: design/module/quantization.md
+      - Observability: design/module/observability.md
+      - Profiling: design/module/profiling.md
+      - Benchmarking: design/module/benchmarking.md
   - Docs Guide: contributing/DOCS_GUIDE.md
 - API Reference:
   - api/README.md

docs/design/index.md

@@ -1,8 +1,9 @@
 # Design Documents
 
 This section contains design documents and architecture specifications for
-vLLM-Omni. The sidebar groups documents by the system concern they describe,
+vLLM-Omni. The sidebar groups documents by the system concern they describe;
-while the source paths remain stable so existing links continue to work.
+retired module pages are preserved in the legacy archive instead of remaining
+in the active navigation.
 
 ## Architecture Documents
 
@@ -61,12 +62,29 @@ while the source paths remain stable so existing links continue to work.
 
 ## Module Design Documents
 
-### Runtime Modules
+- [Entrypoints and Serving Boundaries](module/entrypoints.md)
+- [vLLM-Omni Configuration](module/vllm_omni_config.md)
+- [Input, Output, and Modality Contracts](module/input_output_modality_contracts.md)
+- [Error Classification, Propagation, and Rendering](module/error_contracts.md)
+- [Engine Orchestration](module/engine_orchestration.md)
+- [Stage Runtime and Replica Lifecycle](module/stage_runtime.md)
+- [OmniConnector](module/omni_connector.md)
+- [Model Integration](module/model_integration.md)
+- [Autoregressive Runtime](module/ar_runtime.md)
+- Diffusion
+  - [Overview](module/diffusion/index.md)
+  - [Runtime](module/diffusion/diffusion_runtime.md)
+  - [Model Integration](module/diffusion/diffusion_model_integration.md)
+  - [Continuous Batching](module/diffusion/continuous_batching.md)
+  - [Parallelism](module/diffusion/parallelism.md)
+  - [Offloader](module/diffusion/offloader.md)
+- [Execution Platforms](module/execution_platforms.md)
+- [Cache Management](module/cache_management.md)
+- [Quantization](module/quantization.md)
+- [Observability](module/observability.md)
+- [Profiling](module/profiling.md)
+- [Benchmarking](module/benchmarking.md)
 
-- [AR Module](module/ar_module.md)
+The pre-#5137 pages are preserved in the
-- [DIT Module](module/dit_module.md)
+[legacy module archive](module/archive/README.md) for historical reference and
-
+are not active design contracts.
-### Orchestration
-
-- [Entrypoint Module](module/entrypoint_module.md)
-- [AsyncOmni Architecture (Qwen3-Omni Example)](module/async_omni_architecture.md)

docs/design/module/ar_runtime.md

@@ -0,0 +1,52 @@
+---
+title: Autoregressive Runtime
+kind: module
+status: draft
+owners:
+  - "@tzhouam"
+  - "@yinpeiqi"
+  - "@fake0fan"
+  - "@Sy0307"
+primary_code_paths:
+  - vllm_omni/core/**
+  - vllm_omni/worker/**
+related_code_paths:
+  - vllm_omni/model_executor/**
+depends_on:
+  - engine_orchestration.md
+  - model_integration.md
+  - input_output_modality_contracts.md
+validation_paths:
+  - tests/core/**
+  - tests/worker/**
+upstream_refs:
+  - vllm.v1.core
+  - vllm.v1.worker
+last_reviewed: 2026-07-16
+---
+
+# Autoregressive runtime
+
+The AR runtime extends vLLM scheduling and worker execution for omni-stage
+inputs and outputs while preserving vLLM scheduling and cache semantics.
+
+## Candidate invariants
+
+### AR-INV-001: vLLM owns base scheduling semantics
+
+**Rule:** Omni schedulers MUST preserve upstream request-state and cache
+transitions unless an Omni-specific difference is documented and tested.
+
+### AR-INV-002: Omni data crosses explicit adapters
+
+**Rule:** Modality-specific stage data MUST be converted at an input or output
+adapter, not injected through unrelated scheduler state.
+
+### AR-INV-003: Workers execute assigned work
+
+**Rule:** Workers and model runners MUST NOT implement cross-stage routing.
+
+## Safe-change guide
+
+Test request lifecycle, abort, cache state, and every affected worker execution
+mode against the supported upstream vLLM contract.

docs/design/module/archive/README.md

@@ -0,0 +1,18 @@
+# Archived module design pages
+
+This directory preserves module-design pages that predate the structure
+proposed in [issue #5137](https://github.com/vllm-project/vllm-omni/issues/5137).
+They are historical snapshots, not active architectural contracts, and are
+intentionally excluded from the documentation navigation.
+
+| Archived page | Active destination |
+| --- | --- |
+| [AR Module](ar_module.md) | [Autoregressive Runtime](../ar_runtime.md) |
+| [AsyncOmni Architecture](async_omni_architecture.md) | [Engine Orchestration](../engine_orchestration.md) and [Stage Runtime](../stage_runtime.md) |
+| [DiT Module](dit_module.md) | [Diffusion module overview](../diffusion/index.md) |
+| [Entrypoint Module](entrypoint_module.md) | [Entrypoints and Serving Boundaries](../entrypoints.md) |
+
+Do not update these pages with current design guidance. Move still-useful
+material into the active destination and review it against current code and
+tests instead. No compatibility redirect pages are provided at the former
+paths.

docs/design/module/archive/ar_module.md

@@ -12,7 +12,7 @@ The AR module of vLLM-Omni extends vLLM's core components to support:
 - **Hidden state exposure**: Exposing per-request hidden representations for downstream stages
 - **Basic generator support**: Support some basic heterogeneous architecture such as Convolution, LSTM, etc.
 
-As shown in the [end2end example](../../user_guide/examples/offline_inference/qwen3_omni.md), AR module can be widely applied across multiple stages, generating text tokens in thinker(AR), audio latent tokens in talker(AR) and audio wave in code2wav(Convolution).
+As shown in the [end2end example](../../../user_guide/examples/offline_inference/qwen3_omni.md), AR module can be widely applied across multiple stages, generating text tokens in thinker(AR), audio latent tokens in talker(AR) and audio wave in code2wav(Convolution).
 
 ## 2. Relationship with vLLM
 

docs/design/module/archive/dit_module.md

@@ -252,7 +252,7 @@ while True:
   batch of compatible independent requests for one full pipeline forward when
   the pipeline supports request-level batching; the step-wise path can also
   admit or remove compatible requests between denoise steps. See
-  [Diffusion Continuous Batching](../feature/diffusion_continuous_batching.md).
+  [Diffusion Continuous Batching](../../feature/diffusion_continuous_batching.md).
 
 ---
 
@@ -541,7 +541,7 @@ def get_attn_backend_for_role(role, head_size, attention_config=None, role_categ
 
 A backend that needs configuration exposes it as a typed field on `AttentionSpec`; `AttentionSpec.backend_kwargs()` serializes it into the `backend_kwargs` the impl consumes. Today those fields are `skip_softmax` (TRTLLM_ATTN) and `block_sparse` (any block-sparse backend, currently RAINFUSION_ATTN), so e.g. `target_sparsity` or `sparsity` can be set without changing model code.
 
-For the user-facing CLI surface, see [Diffusion Attention Backends](../../user_guide/diffusion/attention_backends.md). For the role declaration contract on the model side, see [Adding a Diffusion Model](../../contributing/model/adding_diffusion_model.md).
+For the user-facing CLI surface, see [Diffusion Attention Backends](../../../user_guide/diffusion/attention_backends.md). For the role declaration contract on the model side, see [Adding a Diffusion Model](../../../contributing/model/adding_diffusion_model.md).
 
 **Backend Availability**:
 

docs/design/module/benchmarking.md

@@ -0,0 +1,47 @@
+---
+title: Benchmarking
+kind: module
+status: draft
+owners:
+  - "@alex-jw-brooks"
+primary_code_paths:
+  - vllm_omni/benchmarks/**
+  - vllm_omni/entrypoints/cli/benchmark/**
+related_code_paths:
+  - benchmarks/**
+depends_on:
+  - entrypoints.md
+  - profiling.md
+validation_paths:
+  - tests/benchmarks/**
+  - tests/dfx/perf/**
+upstream_refs:
+  - vllm.benchmarks
+last_reviewed: 2026-07-16
+---
+
+# Benchmarking
+
+Benchmarking defines reproducible workloads, metrics, warm-up, measurement,
+and result metadata for comparing vLLM-Omni performance.
+
+## Candidate invariants
+
+### BENCH-INV-001: Results are reproducible
+
+**Rule:** Results MUST identify the model, revision, commit, hardware,
+configuration, workload, concurrency, warm-up, and measurement window.
+
+### BENCH-INV-002: Correctness precedes performance
+
+**Rule:** A benchmark MUST validate successful and semantically acceptable
+outputs before using timings as performance evidence.
+
+### BENCH-INV-003: Metric definitions are explicit
+
+**Rule:** Metrics MUST state their unit, population, and aggregation.
+
+## Safe-change guide
+
+Test workload parsing and metric calculations with deterministic fixtures. Do
+not compare materially different workloads or runtime settings.

docs/design/module/cache_management.md

@@ -0,0 +1,47 @@
+---
+title: Cache Management
+kind: module
+status: draft
+owners:
+  - "@Isotr0py"
+  - "@princepride"
+primary_code_paths:
+  - vllm_omni/diffusion/cache/**
+related_code_paths:
+  - vllm_omni/experimental/ar_diffusion/kv_cache/**
+  - vllm_omni/core/**
+depends_on:
+  - ar_runtime.md
+  - diffusion/diffusion_runtime.md
+validation_paths:
+  - tests/diffusion/cache/**
+upstream_refs:
+  - vllm.v1.core.kv_cache_manager
+last_reviewed: 2026-07-16
+---
+
+# Cache management
+
+Cache management defines reusable state, cache identity, validity, lifecycle,
+and eviction across AR and diffusion execution.
+
+## Candidate invariants
+
+### CACHE-INV-001: Cache identity is complete
+
+**Rule:** A cache key MUST include every input and execution property that can
+change the reused value.
+
+### CACHE-INV-002: Reuse preserves correctness
+
+**Rule:** A cache optimization MUST provide a disabled path and MUST NOT reuse
+state after its validity conditions change.
+
+### CACHE-INV-003: Ownership has an end
+
+**Rule:** Request-scoped and model-scoped cache entries MUST have explicit
+reset, eviction, or teardown behavior.
+
+## Safe-change guide
+
+Test hit, miss, invalidation, disabled, concurrent-request, and teardown paths.

docs/design/module/diffusion/continuous_batching.md

@@ -0,0 +1,51 @@
+---
+title: Diffusion Continuous Batching
+kind: module
+status: draft
+owners:
+  - "@Isotr0py"
+  - "@princepride"
+primary_code_paths:
+  - vllm_omni/diffusion/sched/**
+related_code_paths:
+  - vllm_omni/diffusion/executor/**
+depends_on:
+  - diffusion_runtime.md
+validation_paths:
+  - tests/diffusion/batching/**
+upstream_refs: []
+last_reviewed: 2026-07-16
+---
+
+# Diffusion continuous batching
+
+Continuous batching defines when diffusion requests are compatible, how they
+share an execution step, and how each request advances independently.
+
+## Candidate invariants
+
+### BATCH-INV-001: Compatibility is explicit
+
+**Rule:** Requests MAY share a batch only when all properties required by the
+selected pipeline, scheduler step, shape, precision, and execution features are
+compatible.
+
+### BATCH-INV-002: Per-request state remains isolated
+
+**Rule:** Batch assembly MUST preserve each request's random generator, progress,
+conditioning, outputs, cancellation, and errors.
+
+### BATCH-INV-003: Admission is bounded
+
+**Rule:** Admission MUST respect configured capacity and MUST NOT rely on an
+unbounded waiting or active-request collection.
+
+### BATCH-INV-004: Batch order is not completion order
+
+**Rule:** Output association MUST use stable request identity rather than batch
+position across execution steps.
+
+## Safe-change guide
+
+Test heterogeneous requests, partial completion, cancellation, deterministic
+seeds, capacity limits, and batch sizes of one and many.

docs/design/module/diffusion/diffusion_model_integration.md

@@ -0,0 +1,58 @@
+---
+title: Diffusion Model Integration
+kind: module
+status: draft
+owners:
+  - "@Isotr0py"
+  - "@wtomin"
+  - "@ZJY0516"
+primary_code_paths:
+  - vllm_omni/diffusion/models/**
+  - vllm_omni/diffusion/model_loader/**
+related_code_paths:
+  - vllm_omni/diffusion/layers/**
+  - vllm_omni/diffusion/lora/**
+  - vllm_omni/diffusion/utils/**
+depends_on:
+  - diffusion_runtime.md
+  - ../input_output_modality_contracts.md
+validation_paths:
+  - tests/diffusion/models/**
+  - tests/diffusion/model_loader/**
+  - tests/diffusion/layers/**
+  - tests/diffusion/lora/**
+upstream_refs:
+  - diffusers.DiffusionPipeline
+last_reviewed: 2026-07-16
+---
+
+# Diffusion model integration
+
+Diffusion model integration owns pipeline contracts, registration, checkpoint
+loading, adapters, shared layers, and model-specific processing.
+
+## Candidate invariants
+
+### DIFF-MODEL-INV-001: Pipelines implement one runtime contract
+
+**Rule:** A pipeline MUST declare its supported modalities, configuration,
+inputs, outputs, loading path, and runtime capabilities.
+
+### DIFF-MODEL-INV-002: Registration is the selection boundary
+
+**Rule:** Runtime code MUST select model implementations through the registry or
+loader contract rather than scattered model-name conditionals.
+
+### DIFF-MODEL-INV-003: Model code does not schedule requests
+
+**Rule:** Pipeline code MUST NOT own admission, batching, cancellation, or
+cross-stage routing.
+
+### DIFF-MODEL-INV-004: Shared behavior stays shared
+
+**Rule:** Model directories SHOULD contain only genuine model differences.
+
+## Safe-change guide
+
+Test registry selection, checkpoint loading, minimal inference, input and output
+contracts, and every declared optional capability.

docs/design/module/diffusion/diffusion_runtime.md

@@ -0,0 +1,58 @@
+---
+title: Diffusion Runtime
+kind: module
+status: draft
+owners:
+  - "@Isotr0py"
+  - "@princepride"
+  - "@SamitHuang"
+primary_code_paths:
+  - vllm_omni/diffusion/sched/**
+  - vllm_omni/diffusion/executor/**
+  - vllm_omni/diffusion/worker/**
+related_code_paths:
+  - vllm_omni/diffusion/hooks/**
+  - vllm_omni/diffusion/postprocess/**
+depends_on:
+  - ../engine_orchestration.md
+  - ../input_output_modality_contracts.md
+  - diffusion_model_integration.md
+validation_paths:
+  - tests/diffusion/diffusion_backend/**
+  - tests/diffusion/hooks/**
+upstream_refs:
+  - diffusers.DiffusionPipeline
+last_reviewed: 2026-07-16
+---
+
+# Diffusion runtime
+
+The diffusion runtime owns request admission, scheduling, execution, progress,
+output, cancellation, and cleanup inside a diffusion stage.
+
+## Candidate invariants
+
+### DIFF-RUNTIME-INV-001: One lifecycle owner
+
+**Rule:** Every admitted request MUST have exactly one scheduler-owned lifecycle
+until completion, cancellation, or failure.
+
+### DIFF-RUNTIME-INV-002: Execution follows scheduler output
+
+**Rule:** Executors and workers MUST execute scheduler decisions without
+admitting, reordering, or forwarding requests independently.
+
+### DIFF-RUNTIME-INV-003: Terminal cleanup is complete
+
+**Rule:** Every terminal path MUST release request state, temporary tensors,
+hooks, and runtime-owned resources.
+
+### DIFF-RUNTIME-INV-004: Optional features use runtime hooks
+
+**Rule:** Cache, profiling, offload, and parallel features SHOULD integrate at
+defined hooks instead of creating another request lifecycle.
+
+## Safe-change guide
+
+Test success, cancellation, failure, shutdown, multiple requests, and resource
+cleanup.

docs/design/module/diffusion/index.md

@@ -0,0 +1,42 @@
+---
+title: Diffusion Modules
+kind: module-index
+status: draft
+owners:
+  - "@Isotr0py"
+  - "@princepride"
+  - "@SamitHuang"
+  - "@wtomin"
+  - "@ZJY0516"
+  - "@RuixiangMa"
+  - "@david6666666"
+  - "@xuechendi"
+primary_code_paths:
+  - vllm_omni/diffusion/**
+related_code_paths:
+  - vllm_omni/platforms/**
+depends_on:
+  - ../engine_orchestration.md
+  - ../input_output_modality_contracts.md
+validation_paths:
+  - tests/diffusion/**
+upstream_refs:
+  - diffusers
+last_reviewed: 2026-07-16
+---
+
+# Diffusion modules
+
+Diffusion is a module family containing runtime, model integration, batching,
+distributed execution, and memory-management subsystems.
+
+## Module documents
+
+- [Diffusion runtime](diffusion_runtime.md)
+- [Diffusion model integration](diffusion_model_integration.md)
+- [Continuous batching](continuous_batching.md)
+- [Parallelism](parallelism.md)
+- [Offloader](offloader.md)
+
+Cache, quantization, profiling, and benchmarking follow their top-level module
+documents.

docs/design/module/diffusion/offloader.md

@@ -0,0 +1,53 @@
+---
+title: Diffusion Offloader
+kind: module
+status: draft
+owners:
+  - "@yuanheng-zhao"
+  - "@Isotr0py"
+primary_code_paths:
+  - vllm_omni/diffusion/offloader/**
+related_code_paths:
+  - vllm_omni/diffusion/models/**
+  - vllm_omni/diffusion/worker/**
+depends_on:
+  - diffusion_runtime.md
+  - ../execution_platforms.md
+validation_paths:
+  - tests/diffusion/offloader/**
+upstream_refs:
+  - torch.nn.Module.to
+last_reviewed: 2026-07-16
+---
+
+# Diffusion offloader
+
+The offloader owns component residency, transfer scheduling, memory accounting,
+prefetch, and teardown for diffusion execution.
+
+## Candidate invariants
+
+### OFFLOAD-INV-001: Residency is explicit
+
+**Rule:** Each managed component MUST have one known residency state and one
+owner responsible for transitions.
+
+### OFFLOAD-INV-002: Use follows readiness
+
+**Rule:** Runtime execution MUST NOT consume a component until its transfer to
+the required device is complete.
+
+### OFFLOAD-INV-003: Transfers preserve model state
+
+**Rule:** Offloading MUST preserve parameter and buffer identity, dtype, device,
+and correctness required by the selected execution mode.
+
+### OFFLOAD-INV-004: Memory is bounded and released
+
+**Rule:** Retained host and device copies MUST respect configured limits and
+provide deterministic teardown.
+
+## Safe-change guide
+
+Test enabled and disabled paths, repeated execution, asynchronous transfer,
+memory limits, failure, teardown, and numerical equivalence.

docs/design/module/diffusion/parallelism.md

@@ -0,0 +1,56 @@
+---
+title: Diffusion Parallelism
+kind: module
+status: draft
+owners:
+  - "@princepride"
+  - "@yuanheng-zhao"
+  - "@xuechendi"
+primary_code_paths:
+  - vllm_omni/diffusion/distributed/**
+  - vllm_omni/diffusion/attention/parallel/**
+related_code_paths:
+  - vllm_omni/distributed/**
+  - vllm_omni/config/composable_parallel/**
+depends_on:
+  - diffusion_runtime.md
+  - ../vllm_omni_config.md
+validation_paths:
+  - tests/diffusion/distributed/**
+  - tests/diffusion/attention/**
+upstream_refs:
+  - torch.distributed
+last_reviewed: 2026-07-16
+---
+
+# Diffusion parallelism
+
+Parallelism owns diffusion rank topology, process groups, tensor and sequence
+sharding, collectives, and distributed execution.
+
+## Candidate invariants
+
+### PARALLEL-INV-001: Topology has one source of truth
+
+**Rule:** Rank coordinates, group membership, and parallel dimensions MUST be
+derived from validated configuration.
+
+### PARALLEL-INV-002: Sharding contracts are explicit
+
+**Rule:** Every distributed boundary MUST define tensor shape, sharded
+dimension, placement, dtype, producer, and consumer.
+
+### PARALLEL-INV-003: Collectives are symmetric
+
+**Rule:** Process-group members MUST invoke compatible collectives in the same
+logical order.
+
+### PARALLEL-INV-004: Single-rank behavior remains valid
+
+**Rule:** Distributed implementations SHOULD preserve a supported single-rank
+path without distributed initialization.
+
+## Safe-change guide
+
+Test topology validation, single-rank execution, affected parallel modes,
+combined modes, invalid shapes, and orderly teardown.

docs/design/module/engine_orchestration.md

@@ -0,0 +1,122 @@
+---
+title: Engine Orchestration
+kind: module
+status: draft
+architecture_state: current-plus-in-flight
+owners:
+  - "@tzhouam"
+  - "@fake0fan"
+document_stewards:
+  - "@hsliuustc0106"
+  - "@Gaohan123"
+  - "@david6666666"
+required_reviewers:
+  - "@yinpeiqi"
+  - "@Sy0307"
+  - "@yenuo26"
+  - "@NickCao"
+primary_code_paths:
+  - vllm_omni/engine/async_omni_engine.py
+  - vllm_omni/engine/async_engine_utils.py
+  - vllm_omni/engine/orchestrator.py
+  - vllm_omni/engine/cfg_companion_tracker.py
+  - vllm_omni/engine/rpc_result_router.py
+related_code_paths:
+  - vllm_omni/engine/messages.py
+  - vllm_omni/engine/orchestrator_monitor.py
+  - vllm_omni/engine/stage_client.py
+  - vllm_omni/engine/stage_pool.py
+  - vllm_omni/outputs/output_processor.py
+  - vllm_omni/distributed/omni_coordinator/**
+depends_on:
+  - input_output_modality_contracts.md
+  - error_contracts.md
+  - stage_runtime.md
+  - omni_connector.md
+validation_paths:
+  - tests/engine/test_async_omni_engine_input.py
+  - tests/engine/test_async_omni_engine_outputs.py
+  - tests/engine/test_async_omni_engine_abort.py
+  - tests/engine/test_async_omni_engine_stage_init.py
+  - tests/engine/test_orchestrator.py
+  - tests/engine/test_orchestrator_error_handling.py
+  - tests/engine/test_orchestrator_stage_input_bridge.py
+  - tests/engine/test_cfg_companion_lifecycle.py
+  - tests/engine/test_rpc_result_router.py
+  - tests/e2e/features/fullduplex/engine/**
+upstream_refs:
+  - vllm.v1.engine.EngineCoreRequest
+  - vllm.v1.engine.EngineCoreOutputs
+  - vllm.v1.engine.exceptions.EngineDeadError
+  - vllm.outputs.RequestOutput
+invariant_namespace: ORCH-INV
+last_reviewed: 2026-08-07
+last_verified_commit: 3d7fc3b9ba3cac88d579d4dc35b78b0b641675fc
+---
+
+# Engine orchestration
+
+Engine orchestration coordinates configured AR and diffusion stages while
+keeping public clients independent from stage processes and transports.
+
+## Contract status
+
+This document is a draft description of current behavior. It also identifies
+the boundary affected by the in-flight stage client/process refactor in
+[#5441](https://github.com/vllm-project/vllm-omni/pull/5441). Names and
+responsibilities proposed only by that PR are not current contracts.
+
+## Ownership boundary
+
+This document owns `AsyncOmniEngine`, `Orchestrator`, request-state creation,
+cross-stage routing, output ordering, companion tracking, control/RPC
+correlation, cancellation propagation, and terminal-state convergence.
+
+It does not own stage placement, replica selection, stage-process startup,
+payload schemas, public protocol rendering, connector transport, or semantic
+error classification. Those responsibilities belong to the stage runtime,
+I/O, entrypoint, connector, and error contracts.
+
+## Candidate invariants
+
+These identifiers are proposals while the document is `draft`.
+
+### ORCH-INV-001: The orchestrator owns cross-stage routing
+
+**Rule:** Entrypoints and stage clients MUST NOT independently forward a
+request to a downstream logical stage.
+
+### ORCH-INV-002: Stage clients do not own routing policy
+
+**Rule:** Stage clients MUST implement communication and lifecycle operations
+without selecting the next logical stage.
+
+### ORCH-INV-100: Terminal state is monotonic
+
+**Rule:** Once a request reaches a terminal state, orchestration MUST NOT
+forward new work for that request.
+
+## Invariant namespace
+
+`ORCH-INV` reserves `001-099` for dependency direction, `100-199` for
+request state and ordering, `200-299` for failure/cancellation/cleanup, and
+`300-399` for extension points, shutdown ordering, and upstream alignment.
+Numbers become append-only after normative promotion.
+
+## Safe-change guide
+
+Test routing, output ordering, queue correlation, cancellation, failure
+propagation, shutdown ordering, and representative multi-stage execution.
+Changes that cross into stage runtime or public error behavior require review
+from that contract's owners.
+
+## Promotion gate
+
+- Reconcile current names and boundaries after #5441 merges, closes, or is
+  replaced.
+- Demonstrate one terminal outcome per request across success, abort,
+  request-scoped failure, and fatal engine failure.
+- Verify queue correlation and orchestrator-before-runtime shutdown ordering
+  in the cited validation paths.
+- Obtain approval from a technical owner and an independent validation
+  reviewer.

docs/design/module/entrypoints.md

@@ -0,0 +1,134 @@
+---
+title: Entrypoints and Serving Boundaries
+kind: module
+status: draft
+architecture_state: current-plus-in-flight
+owners:
+  - "@alex-jw-brooks"
+  - "@linyueqian"
+document_stewards:
+  - "@hsliuustc0106"
+  - "@Gaohan123"
+  - "@david6666666"
+required_reviewers:
+  - "@tzhouam"
+  - "@herotai214"
+  - "@yenuo26"
+  - "@NickCao"
+primary_code_paths:
+  - vllm_omni/entrypoints/omni.py
+  - vllm_omni/entrypoints/async_omni.py
+  - vllm_omni/entrypoints/omni_base.py
+  - vllm_omni/entrypoints/cli/**
+  - vllm_omni/entrypoints/openai/**
+  - vllm_omni/entrypoints/openpi/**
+  - vllm_omni/entrypoints/client_request_state.py
+  - vllm_omni/entrypoints/stage_utils.py
+  - vllm_omni/entrypoints/utils.py
+primary_path_exceptions:
+  - path: vllm_omni/entrypoints/openai/errors.py
+    owner: error_contracts.md
+related_code_paths:
+  - vllm_omni/errors.py
+  - vllm_omni/inputs/**
+  - vllm_omni/outputs/**
+  - vllm_omni/engine/async_omni_engine.py
+  - vllm_omni/config/**
+  - vllm_omni/deploy/**
+depends_on:
+  - input_output_modality_contracts.md
+  - error_contracts.md
+  - engine_orchestration.md
+validation_paths:
+  - tests/entrypoints/test_omni_entrypoints.py
+  - tests/entrypoints/test_async_omni.py
+  - tests/entrypoints/test_async_omni_duplex.py
+  - tests/entrypoints/test_serve.py
+  - tests/entrypoints/test_stream_finish_reason.py
+  - tests/entrypoints/openai/**
+  - tests/entrypoints/openai_api/**
+  - tests/e2e/online_serving/**
+upstream_refs:
+  - vllm.engine.protocol.EngineClient
+  - vllm.entrypoints.openai/**
+  - vllm.entrypoints.serve/**
+  - vllm.renderers/**
+  - vllm.v1.engine.exceptions/**
+invariant_namespace: ENTRY-INV
+last_reviewed: 2026-08-07
+last_verified_commit: 3d7fc3b9ba3cac88d579d4dc35b78b0b641675fc
+---
+
+# Entrypoints and serving boundaries
+
+Entrypoints translate offline, CLI, and serving requests into stable engine
+operations and translate engine outputs into public responses.
+
+## Contract status
+
+This document describes current entrypoint responsibilities plus the boundary
+under review in the open roadmap
+[#5227](https://github.com/vllm-project/vllm-omni/issues/5227) and helper-move
+PR [#5453](https://github.com/vllm-project/vllm-omni/pull/5453). In-flight
+helper locations are not treated as current paths.
+
+## Ownership boundary
+
+This document owns offline API semantics, CLI and serve composition,
+supported OpenAI-compatible routes, request validation and normalization,
+response conversion, streaming/session behavior, and engine handoff.
+
+It does not own configuration precedence, cross-stage routing, stage
+placement, payload implementation, or semantic error classification.
+`entrypoints/openai/errors.py` is an explicit primary-path exception owned by
+`error_contracts.md`.
+
+## Candidate invariants
+
+These identifiers are proposals while the document is `draft`.
+
+### ENTRY-INV-001: Entrypoints adapt but do not orchestrate
+
+**Rule:** Entrypoints MUST NOT implement cross-stage routing or stage lifecycle
+policy.
+
+### ENTRY-INV-100: Public requests are normalized once
+
+**Rule:** Public protocol values MUST be validated and converted to internal
+request contracts before engine submission.
+
+### ENTRY-INV-101: Streaming preserves request identity
+
+**Rule:** Every streamed response MUST remain associated with the request and
+output modality that produced it.
+
+The reviewer-proposed rule that model-specific behavior should stay behind a
+common adapter or processor abstraction remains an unnumbered candidate until
+the entrypoint refactor makes that boundary enforceable.
+
+## Invariant namespace
+
+`ENTRY-INV` reserves `001-099` for boundary and dependency direction,
+`100-199` for normalization, sessions, and streaming, `200-299` for
+disconnect, cancellation, rendering, and cleanup, and `300-399` for upstream
+route and renderer compatibility. Numbers become append-only after normative
+promotion.
+
+## Safe-change guide
+
+Test request validation, protocol conversion, model-adapter routing,
+streaming, session identity, disconnect/cancellation, and error mapping for
+each affected offline or serving entrypoint.
+
+## Promotion gate
+
+- Reconcile the page after #5227's P0 ownership work and #5453's final
+  disposition.
+- Publish a supported route/transport matrix rather than claiming blanket
+  OpenAI parity.
+- Verify one normalization and handoff path per route family and one terminal
+  outcome per streaming transport.
+- Promote the `api_server.py` composition-root rule only after helper moves and
+  import boundaries enforce it.
+- Obtain approval from a technical owner and an independent validation
+  reviewer.

docs/design/module/error_contracts.md

@@ -0,0 +1,109 @@
+---
+title: Error Classification, Propagation, and Rendering
+kind: module
+status: draft
+architecture_state: current-plus-rfc
+owners:
+  - "@alex-jw-brooks"
+  - "@NickCao"
+document_stewards:
+  - "@hsliuustc0106"
+  - "@Gaohan123"
+  - "@david6666666"
+required_reviewers:
+  - "@yinpeiqi"
+  - "@tzhouam"
+  - "@yenuo26"
+primary_code_paths:
+  - vllm_omni/errors.py
+  - vllm_omni/entrypoints/openai/errors.py
+related_code_paths:
+  - vllm_omni/engine/messages.py
+  - vllm_omni/engine/orchestrator.py
+  - vllm_omni/entrypoints/omni_base.py
+  - vllm_omni/entrypoints/async_omni.py
+  - vllm_omni/entrypoints/openai/api_server.py
+  - vllm_omni/entrypoints/openai/serving_chat.py
+  - vllm_omni/entrypoints/openai/serving_speech.py
+  - vllm_omni/entrypoints/openai/serving_audio_generate.py
+  - vllm_omni/entrypoints/openai/protocol/images.py
+  - vllm_omni/entrypoints/openai/protocol/videos.py
+depends_on: []
+validation_paths:
+  - tests/engine/test_orchestrator_error_handling.py
+  - tests/engine/test_async_omni_engine_outputs.py
+  - tests/entrypoints/test_omni_entrypoints.py
+  - tests/entrypoints/test_stream_finish_reason.py
+  - tests/entrypoints/openai_api/test_image_server.py
+  - tests/entrypoints/openai_api/test_video_server.py
+  - tests/entrypoints/openai_api/test_serving_audio_generate.py
+  - tests/entrypoints/openai_api/test_serving_speech.py
+  - tests/metrics/test_prometheus.py
+upstream_refs:
+  - vllm.v1.engine.exceptions.EngineDeadError
+  - vllm.v1.engine.exceptions.EngineGenerateError
+  - vllm.entrypoints.serve.utils.error_response
+  - vLLM RFC #48227
+  - vLLM PR #49665
+invariant_namespace: ERR-INV
+last_reviewed: 2026-08-07
+last_verified_commit: 3d7fc3b9ba3cac88d579d4dc35b78b0b641675fc
+---
+
+# Error classification, propagation, and rendering
+
+This contract separates the meaning of a failure from the transport used to
+carry it and the public protocol used to render it.
+
+## Contract status
+
+Current behavior is distributed across engine, message, and entrypoint code.
+The semantic hierarchy proposed by
+[#5570](https://github.com/vllm-project/vllm-omni/issues/5570) remains an open
+RFC. Proposed types and wire records from that RFC are not current contracts.
+
+## Ownership boundary
+
+This document owns semantic classification, fatal versus request-scoped
+failure, cross-process error context, compatibility policy, sanitization, and
+offline, HTTP, SSE, WebSocket, and asynchronous-job rendering rules.
+
+`engine/messages.py` remains primarily owned by the I/O contract; this page
+owns the semantics of its error fields. Route and serving files remain
+primarily owned by `entrypoints.md`; this page owns their rendering
+constraints.
+
+## Candidate invariants
+
+The following topics require owner review before receiving stable IDs:
+
+- A request-scoped failure terminates only the affected request unless the
+  underlying engine is no longer usable.
+- Every public rendering path preserves a stable classification while
+  removing sensitive internal context.
+- Cancellation remains distinguishable from internal failure across process
+  and protocol boundaries.
+
+## Invariant namespace
+
+`ERR-INV` reserves `001-099` for classification ownership, `100-199` for wire
+context and compatibility, `200-299` for fatality, termination, sanitization,
+and rendering, and `300-399` for upstream alignment and transport extension
+points. Numbers become append-only after normative promotion.
+
+## Safe-change guide
+
+Exercise exception classification, stage wire round trips, fatal and
+request-scoped propagation, cancellation, sanitization, offline exceptions,
+HTTP status/body consistency, streaming terminal events, asynchronous-job
+persistence, and metrics classification.
+
+## Promotion gate
+
+- Resolve #5570's hierarchy, wire record, sanitization, and mixed-version
+  questions.
+- Add table-driven exception/status/type tests and stage wire round trips.
+- Verify all public transports terminate once and do not leak sensitive
+  payload data.
+- Obtain approval from both technical owners and an independent validation
+  reviewer.

docs/design/module/execution_platforms.md

@@ -0,0 +1,48 @@
+---
+title: Execution Platforms
+kind: module
+status: draft
+owners:
+  - "@gcanlin"
+  - "@tjtanaa"
+  - "@xuechendi"
+primary_code_paths:
+  - vllm_omni/platforms/**
+related_code_paths:
+  - vllm_omni/attention/**
+depends_on:
+  - ar_runtime.md
+  - diffusion/index.md
+validation_paths:
+  - tests/platforms/**
+upstream_refs:
+  - vllm.platforms
+last_reviewed: 2026-07-16
+---
+
+# Execution platforms
+
+Execution platforms isolate hardware-specific capability detection, worker
+selection, patches, kernels, and configuration adjustments.
+
+## Candidate invariants
+
+### PLATFORM-INV-001: Capabilities are explicit
+
+**Rule:** Hardware-dependent behavior MUST be guarded by platform selection or
+capability detection and MUST fail clearly when unsupported.
+
+### PLATFORM-INV-002: Portable code remains portable
+
+**Rule:** Platform-neutral modules MUST NOT import a vendor implementation
+directly when a common selection interface exists.
+
+### PLATFORM-INV-003: Overrides are minimal
+
+**Rule:** A platform implementation SHOULD override only behavior that differs
+from the common or upstream implementation.
+
+## Safe-change guide
+
+Validate common import paths without the target accelerator and run focused
+tests in a fresh `uv` environment on every affected device platform.

docs/design/module/input_output_modality_contracts.md

@@ -0,0 +1,133 @@
+---
+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"
+  - "@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/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/**
+  - 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, 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-100: Request identity is stable
+
+**Rule:** Request identity MUST be preserved across conversions, stages,
+streaming updates, cancellation, and errors.
+
+### 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, 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.

docs/design/module/model_integration.md

@@ -0,0 +1,51 @@
+---
+title: Model Integration
+kind: module
+status: draft
+owners:
+  - "@tzhouam"
+  - "@gcanlin"
+primary_code_paths:
+  - vllm_omni/model_executor/**
+  - vllm_omni/model_extras/**
+  - vllm_omni/plugins/**
+related_code_paths:
+  - vllm_omni/transformers_utils/**
+  - vllm_omni/tokenizers/**
+depends_on:
+  - input_output_modality_contracts.md
+  - ar_runtime.md
+validation_paths:
+  - tests/model_executor/**
+  - tests/model_extras/**
+  - tests/plugin/**
+upstream_refs:
+  - vllm.model_executor
+last_reviewed: 2026-07-16
+---
+
+# Model integration
+
+Model integration adapts model-specific configuration, preprocessing, loading,
+and execution behavior to stable runtime contracts.
+
+## Candidate invariants
+
+### MODEL-INV-001: Registration is explicit
+
+**Rule:** A model integration MUST declare how its model class, loader, input
+processor, and stage configuration are selected.
+
+### MODEL-INV-002: Model code does not route stages
+
+**Rule:** Model-specific code MUST NOT select or invoke a downstream omni stage.
+
+### MODEL-INV-003: Upstream behavior is reused deliberately
+
+**Rule:** An upstream vLLM implementation SHOULD be reused when its contract is
+sufficient; an override MUST document the behavioral difference.
+
+## Safe-change guide
+
+Test registration, checkpoint loading, input conversion, and representative
+model execution. Test shared utilities against more than one integration.

docs/design/module/observability.md

@@ -0,0 +1,46 @@
+---
+title: Observability
+kind: module
+status: draft
+owners:
+  - "@lishunyang12"
+primary_code_paths:
+  - vllm_omni/metrics/**
+related_code_paths:
+  - vllm_omni/engine/**
+  - vllm_omni/entrypoints/**
+depends_on:
+  - engine_orchestration.md
+validation_paths:
+  - tests/metrics/**
+upstream_refs:
+  - vllm.v1.metrics
+last_reviewed: 2026-07-16
+---
+
+# Observability
+
+Observability defines stable metrics, logs, and correlation fields for tracing a
+request across entrypoints, orchestration, stages, and workers.
+
+## Candidate invariants
+
+### OBS-INV-001: Request correlation survives stage boundaries
+
+**Rule:** Logs and metrics for the same request SHOULD carry a stable request
+identifier and stage identity.
+
+### OBS-INV-002: Metric meaning is stable
+
+**Rule:** A metric's unit, labels, aggregation, and lifecycle MUST be documented;
+changing any of them is a contract change.
+
+### OBS-INV-003: Labels are bounded
+
+**Rule:** Metrics MUST NOT use request IDs, prompts, outputs, or other unbounded
+values as labels.
+
+## Safe-change guide
+
+Test registration, label sets, units, lifecycle resets, and representative
+multi-stage emission.

docs/design/module/omni_connector.md

@@ -0,0 +1,50 @@
+---
+title: OmniConnector
+kind: module
+status: draft
+owners:
+  - "@princepride"
+  - "@yuanheng-zhao"
+  - "@xuechendi"
+  - "@natureofnature"
+  - "@fake0fan"
+primary_code_paths:
+  - vllm_omni/distributed/omni_connectors/**
+related_code_paths:
+  - vllm_omni/platforms/*/omni_connectors/**
+depends_on:
+  - input_output_modality_contracts.md
+  - vllm_omni_config.md
+validation_paths:
+  - tests/distributed/omni_connectors/**
+upstream_refs:
+  - vllm.distributed
+last_reviewed: 2026-07-16
+---
+
+# OmniConnector
+
+OmniConnector defines model-agnostic transport and synchronization contracts
+for data exchanged across stages, processes, devices, and nodes.
+
+## Candidate invariants
+
+### CONNECTOR-INV-001: Connectors transport but do not route
+
+**Rule:** A connector MUST NOT select the next stage or implement model-specific
+execution policy.
+
+### CONNECTOR-INV-002: Producer and consumer contracts agree
+
+**Rule:** Both ends MUST agree on data identity, shape, dtype, placement,
+ownership, and completion semantics.
+
+### CONNECTOR-INV-003: Resources have deterministic cleanup
+
+**Rule:** Connections, buffers, handles, and background work MUST be released on
+normal completion, cancellation, failure, and shutdown.
+
+## Safe-change guide
+
+Test setup, transfer, synchronization, timeout, cancellation, failure, and
+cleanup across every affected backend.

docs/design/module/profiling.md

@@ -0,0 +1,46 @@
+---
+title: Profiling
+kind: module
+status: draft
+owners:
+  - "@gcanlin"
+primary_code_paths:
+  - vllm_omni/profiler/**
+  - vllm_omni/diffusion/profiler/**
+related_code_paths:
+  - vllm_omni/entrypoints/**
+depends_on:
+  - observability.md
+validation_paths:
+  - tests/profile/**
+upstream_refs:
+  - vllm.profiler
+last_reviewed: 2026-07-16
+---
+
+# Profiling
+
+Profiling owns opt-in instrumentation and trace collection used to locate
+runtime bottlenecks without changing model results or execution policy.
+
+## Candidate invariants
+
+### PROFILE-INV-001: Profiling is opt-in
+
+**Rule:** Expensive trace collection MUST be disabled by default and bounded by
+an explicit start and stop lifecycle.
+
+### PROFILE-INV-002: Instrumentation preserves semantics
+
+**Rule:** Profiling MUST NOT change scheduling decisions, generated outputs, or
+resource ownership beyond documented synchronization overhead.
+
+### PROFILE-INV-003: Trace context is sufficient
+
+**Rule:** Trace events SHOULD identify stage, rank, worker, operation, and
+request where available without embedding user payloads.
+
+## Safe-change guide
+
+Test disabled overhead, repeated start and stop, cleanup, multi-rank trace
+naming, and each supported profiler backend.

docs/design/module/quantization.md

@@ -0,0 +1,50 @@
+---
+title: Quantization
+kind: module
+status: draft
+owners:
+  - "@david6666666"
+  - "@Isotr0py"
+  - "@lishunyang12"
+primary_code_paths:
+  - vllm_omni/quantization/**
+  - vllm_omni/diffusion/quantization/**
+related_code_paths:
+  - vllm_omni/platforms/*/quant/**
+depends_on:
+  - model_integration.md
+  - diffusion/diffusion_model_integration.md
+validation_paths:
+  - tests/quantization/**
+  - tests/diffusion/quantization/**
+upstream_refs:
+  - vllm.model_executor.layers.quantization
+last_reviewed: 2026-07-16
+---
+
+# Quantization
+
+Quantization owns method registration, checkpoint interpretation, layer
+replacement, and runtime constraints for reduced-precision execution.
+
+## Candidate invariants
+
+### QUANT-INV-001: Checkpoint and runtime methods agree
+
+**Rule:** The selected method MUST validate checkpoint metadata, supported
+layers, device capabilities, and required dependencies before use.
+
+### QUANT-INV-002: Unsupported combinations fail clearly
+
+**Rule:** Quantization MUST NOT silently fall back to a different precision or
+method when a requested combination is unsupported.
+
+### QUANT-INV-003: Numerical validation is required
+
+**Rule:** A new method or layer mapping MUST include correctness comparison
+against a defined reference result.
+
+## Safe-change guide
+
+Test loading, representative layers, metadata, platform guards, and numerical
+tolerances separately from performance.

docs/design/module/stage_runtime.md

@@ -0,0 +1,126 @@
+---
+title: Stage Runtime and Replica Lifecycle
+kind: module
+status: draft
+architecture_state: current-plus-in-flight
+owners:
+  - "@tzhouam"
+  - "@fake0fan"
+document_stewards:
+  - "@hsliuustc0106"
+  - "@Gaohan123"
+  - "@david6666666"
+required_reviewers:
+  - "@Sy0307"
+  - "@princepride"
+  - "@chickeyton"
+  - "@yenuo26"
+  - "@NickCao"
+primary_code_paths:
+  - vllm_omni/engine/stage_runtime.py
+  - vllm_omni/engine/stage_pool.py
+  - vllm_omni/engine/stage_client.py
+  - vllm_omni/engine/membership_controller.py
+  - vllm_omni/engine/stage_engine_startup.py
+  - vllm_omni/engine/stage_engine_core_client.py
+  - vllm_omni/engine/stage_engine_core_proc.py
+  - vllm_omni/engine/stage_engine_core_proc_manager.py
+  - vllm_omni/engine/stage_init_utils.py
+related_code_paths:
+  - vllm_omni/distributed/omni_coordinator/**
+  - vllm_omni/distributed/ray_utils/**
+  - vllm_omni/diffusion/inline_stage_diffusion_client.py
+  - vllm_omni/diffusion/stage_diffusion_client.py
+  - vllm_omni/diffusion/stage_diffusion_proc.py
+  - vllm_omni/config/**
+depends_on:
+  - input_output_modality_contracts.md
+  - error_contracts.md
+  - omni_connector.md
+validation_paths:
+  - tests/engine/test_async_omni_engine_stage_init.py
+  - tests/engine/test_membership_controller.py
+  - tests/engine/test_single_stage_mode.py
+  - tests/engine/test_stage_engine_core_client.py
+  - tests/engine/test_stage_engine_core_proc.py
+  - tests/diffusion/test_inline_stage_diffusion_client.py
+  - tests/diffusion/test_stage_diffusion_proc.py
+  - tests/distributed/omni_coordinator/**
+upstream_refs:
+  - vllm.v1.engine.core_client.AsyncMPClient
+  - vllm.v1.engine.core_client.DPLBAsyncMPClient
+  - vllm.v1.engine.core.EngineCoreProc
+  - vllm.v1.engine.utils.CoreEngineProcManager
+  - vllm.v1.engine.coordinator.DPCoordinator
+invariant_namespace: STAGE-INV
+last_reviewed: 2026-08-07
+last_verified_commit: 3d7fc3b9ba3cac88d579d4dc35b78b0b641675fc
+---
+
+# Stage runtime and replica lifecycle
+
+The stage runtime turns a logical stage definition into ready local or
+distributed replicas and provides the lifecycle boundary used by the
+orchestrator.
+
+## Contract status
+
+This document describes the current `StageRuntime`, `StagePool`, stage-client,
+and stage-process layout. The unified LLM/diffusion direction in
+[#5441](https://github.com/vllm-project/vllm-omni/pull/5441) remains in flight
+and is not presented as current behavior.
+
+## Ownership boundary
+
+This document owns local and distributed stage placement, startup and
+readiness, one pool per logical stage, replica identity and membership,
+selection and affinity, stage-client/process lifecycle, liveness, draining,
+and shutdown.
+
+It does not own cross-stage request policy, model scheduler policy, connector
+transfer semantics, configuration precedence, or public error rendering.
+
+## Candidate invariants
+
+These identifiers are proposals while the document is `draft`.
+
+### STAGE-INV-001: The runtime owns replica lifecycle
+
+**Rule:** Orchestration MUST acquire stage capacity through the stage runtime
+and MUST NOT construct or retire backend replicas directly.
+
+### STAGE-INV-100: Affinity uses stable replica identity
+
+**Rule:** Follow-up operations for a request with replica affinity MUST resolve
+the same logical replica until the request terminates or the replica is
+declared lost.
+
+### STAGE-INV-200: Shutdown is idempotent
+
+**Rule:** Repeated shutdown or cleanup signals MUST NOT leak stage clients,
+process managers, or membership registrations.
+
+## Invariant namespace
+
+`STAGE-INV` reserves `001-099` for placement and ownership, `100-199` for
+replica identity/readiness/affinity, `200-299` for liveness loss, draining and
+cleanup, and `300-399` for local/distributed and upstream compatibility.
+Numbers become append-only after normative promotion.
+
+## Safe-change guide
+
+Exercise local and distributed startup, readiness, replica selection,
+affinity, membership changes, abort routing, process failure, draining, and
+repeated shutdown. Cross-stage policy changes belong in
+`engine_orchestration.md`.
+
+## Promotion gate
+
+- Reconcile terminology and ownership after #5441 reaches a final state.
+- Add or identify a dedicated StageRuntime/StagePool lifecycle suite; current
+  evidence is distributed across the cited tests.
+- Demonstrate affinity preservation for update, interaction, and abort paths.
+- Demonstrate membership loss and repeated shutdown without leaked clients or
+  processes.
+- Obtain approval from a technical owner and an independent validation
+  reviewer.

docs/design/module/vllm_omni_config.md

@@ -0,0 +1,56 @@
+---
+title: vLLM-Omni Configuration
+kind: module
+status: draft
+architecture_state: deferred-pending-refactor
+ownership_status: provisional
+owners:
+  - "@lishunyang12"
+  - "@alex-jw-brooks"
+primary_code_paths:
+  - vllm_omni/config/**
+  - vllm_omni/deploy/**
+  - vllm_omni/model_executor/stage_configs/**
+related_code_paths:
+  - vllm_omni/platforms/*/stage_configs/**
+depends_on: []
+validation_paths:
+  - tests/config/**
+upstream_refs:
+  - vllm.config
+last_reviewed: 2026-08-07
+last_verified_commit: 3d7fc3b9ba3cac88d579d4dc35b78b0b641675fc
+---
+
+# vLLM-Omni configuration
+
+This page intentionally records discovery paths only. Substantive
+configuration ownership and contract work is deferred until the active
+configuration refactoring has settled.
+
+## Deferred contract scope
+
+The current code and tests remain authoritative for parsing, defaults,
+overrides, deployment topology, stage construction, and runtime projection.
+This draft does not define a stable precedence model, environment-variable
+capture rule, canonical configuration object, or invariant namespace.
+
+The PR review proposal to capture environment-derived values in configuration
+objects at initialization is an open design question, not a current
+invariant.
+
+## Safe-change guide while deferred
+
+Changes should trace every affected producer to its runtime consumer and test
+the structured, legacy, CLI, and deployment paths that are actually supported.
+Do not infer a stable contract from this placeholder page.
+
+## Promotion gate
+
+- Finish or stabilize the configuration refactor and identify the canonical
+  runtime configuration representation.
+- Confirm technical owners, primary path exceptions, and validation owners.
+- Document parsing and override precedence, including when environment values
+  are captured.
+- Allocate an invariant namespace only after those behaviors are enforced and
+  owner-approved.