docs: reorganize module design documents

Signed-off-by: hsliuustc0106 <liuhongsheng4@huawei.com>

docs/design/module/entrypoints.md

@@ -0,0 +1,51 @@
+---
+title: Entrypoints
+kind: module
+status: draft
+owners:
+  - "@tzhouam"
+  - "@yinpeiqi"
+  - "@fake0fan"
+  - "@alex-jw-brooks"
+primary_code_paths:
+  - vllm_omni/entrypoints/**
+related_code_paths:
+  - vllm_omni/reasoning/**
+depends_on:
+  - vllm_omni_config.md
+  - input_output_modality_contracts.md
+  - engine_orchestration.md
+validation_paths:
+  - tests/entrypoints/**
+  - tests/reasoning/**
+upstream_refs:
+  - vllm.entrypoints
+last_reviewed: 2026-07-16
+---
+
+# Entrypoints
+
+Entrypoints translate offline, CLI, and serving requests into stable engine
+operations and translate engine outputs into public responses.
+
+## Candidate invariants
+
+### ENTRY-INV-001: Entrypoints adapt but do not orchestrate
+
+**Rule:** Entrypoints MUST NOT implement cross-stage routing or stage lifecycle
+policy.
+
+### ENTRY-INV-002: Public requests are normalized once
+
+**Rule:** Public protocol values MUST be validated and converted to internal
+request contracts before engine submission.
+
+### ENTRY-INV-003: Streaming preserves request identity
+
+**Rule:** Every streamed response MUST remain associated with the request and
+output modality that produced it.
+
+## Safe-change guide
+
+Test request validation, protocol conversion, streaming, cancellation, and
+error mapping for each affected entrypoint.