docs(openspec): add harden-opencode-runtime-integration spec.md

Author: loong10k

openspec/changes/harden-opencode-runtime-integration/specs/configuration-model/spec.md

@@ -0,0 +1,23 @@
+# Delta for Configuration Model
+
+## MODIFIED Requirements
+
+### Requirement: Server configuration is represented explicitly
+
+The configuration DTO MUST expose OpenCode server configuration using a typed or typed-plus-extensible model appropriate to the upstream schema.
+
+#### Scenario: Read server config
+
+- GIVEN the server returns a configuration object containing `server`
+- WHEN the SDK deserializes it
+- THEN callers MUST be able to access that server configuration without manually traversing a raw root map
+
+### Requirement: Unknown configuration fields survive round trip
+
+The SDK MUST preserve unknown configuration properties during read-modify-write workflows.
+
+#### Scenario: Upstream introduces a new root property
+
+- GIVEN the OpenCode server returns a root configuration property unknown to this SDK version
+- WHEN the SDK deserializes and later serializes the configuration object
+- THEN the unknown property MUST remain present unless the caller explicitly removes it