diff --git a/packages/opencode/test/server/httpapi-exercise/environment.ts b/packages/opencode/test/server/httpapi-exercise/environment.ts
index 9d3eaa0e5329..17fd967fb65a 100644
--- a/packages/opencode/test/server/httpapi-exercise/environment.ts
+++ b/packages/opencode/test/server/httpapi-exercise/environment.ts
@@ -11,6 +11,29 @@ process.env.XDG_CONFIG_HOME = path.join(exerciseGlobalRoot, "config")
 process.env.XDG_STATE_HOME = path.join(exerciseGlobalRoot, "state")
 process.env.XDG_CACHE_HOME = path.join(exerciseGlobalRoot, "cache")
 process.env.OPENCODE_DISABLE_SHARE = "true"
+
+/**
+ * Make this harness's own 500s readable.
+ *
+ * The httpapi error middleware already logs the real Cause of every defect-500
+ * (`Effect.logError("failed", { ref, error, cause })`), but core's observability layer
+ * installs ONLY a file logger unless OPENCODE_PRINT_LOGS is set -- it builds with
+ * `Logger.layer(..., { mergeWithExisting: false })`, which replaces the console logger
+ * rather than adding to it. So the cause was never lost, only written somewhere nobody
+ * reading exercise output would look, and a failing scenario showed
+ * `{"name":"UnknownError","ref":"err_xxxxxxxx"}` and nothing else. That cost a full
+ * diagnosis assignment on TKT-323, where the answer was one line
+ * (`Unbound layer node: @opencode/InstanceBootstrap`).
+ *
+ * Error level only, so the added output is one line per defect and nothing else. A green
+ * effect-mode run currently prints exactly four, from the integration scenarios that
+ * deliberately assert 500 (`Key method not found`, `OAuth method not found`, and two
+ * `OAuth attempt not found`) -- those routes raise plain Errors rather than returning a
+ * typed 404, which this makes visible rather than causes. Both variables are overridable
+ * for a noisier local run.
+ */
+process.env.OPENCODE_PRINT_LOGS ??= "1"
+process.env.OPENCODE_LOG_LEVEL ??= "ERROR"
 export const exerciseConfigDirectory = path.join(exerciseGlobalRoot, "config", "opencode")
 export const exerciseDataDirectory = path.join(exerciseGlobalRoot, "data", "opencode")