Add OpenCode provider integration and strict model selection

packages/adapters/opencode-local/src/index.ts

@@ -0,0 +1,28 @@
+export const type = "opencode_local";
+export const label = "OpenCode (local)";
+
+export const models: Array<{ id: string; label: string }> = [];
+
+export const agentConfigurationDoc = `# opencode_local agent configuration
+
+Adapter: opencode_local
+
+Core fields:
+- cwd (string, optional): default absolute working directory fallback for the agent process (created if missing when possible)
+- instructionsFilePath (string, optional): absolute path to a markdown instructions file prepended to the run prompt
+- model (string, required): OpenCode model id in provider/model format (for example anthropic/claude-sonnet-4-5)
+- variant (string, optional): provider-specific model variant (for example minimal|low|medium|high|max)
+- promptTemplate (string, optional): run prompt template
+- command (string, optional): defaults to "opencode"
+- extraArgs (string[], optional): additional CLI args
+- env (object, optional): KEY=VALUE environment variables
+
+Operational fields:
+- timeoutSec (number, optional): run timeout in seconds
+- graceSec (number, optional): SIGTERM grace period in seconds
+
+Notes:
+- OpenCode supports multiple providers and models. Use \
+  \`opencode models\` to list available options in provider/model format.
+- Paperclip requires an explicit \`model\` value for \`opencode_local\` agents.
+`;