调整嵌套类位置 + 制订阶段 5 task

openspec/changes/optimize-high-frequency-sync/specs/shared-network-foundation/spec.md

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+## MODIFIED Requirements
+
+### Requirement: Shared core preserves current transport and message contracts
+The shared client/server foundation SHALL preserve the envelope-based business-message contract across client and server hosts while allowing delivery-policy selection behind the shared message-routing layer. Reliable control traffic MUST continue to use the existing `ITransport` contract, and high-frequency sync traffic MUST be composable through a host-agnostic sync strategy without introducing Unity-specific runtime types into the shared networking core.
+
+#### Scenario: Shared hosts exchange the same envelope format across delivery lanes
+- **WHEN** a client host sends a business message through either the reliable control path or the high-frequency sync path
+- **THEN** the payload is encoded with the same shared envelope and message-type contract
+- **THEN** the server host decodes and routes it through shared networking logic without a host-specific protocol fork
+
+#### Scenario: Hosts compose delivery-policy selection without Unity dependencies
+- **WHEN** a non-Unity server host constructs the runtime networking stack with reliable control traffic and a high-frequency sync lane
+- **THEN** it uses shared delivery-policy abstractions without depending on Unity frame-loop types
+- **THEN** the Unity client can use the same abstractions while still supplying its own host-specific dispatch behavior