core: Add User-Agent header to identify client version in HTTP requests

packages/opencode/src/session/llm.ts

@@ -373,6 +373,7 @@ const live: Layer.Layer<
                 "x-opencode-session": input.sessionID,
                 "x-opencode-request": input.user.id,
                 "x-opencode-client": Flag.OPENCODE_CLIENT,
+                "User-Agent": `opencode/${InstallationVersion}`,
               }
             : {
                 "x-session-affinity": input.sessionID,