docs: document eval concurrency defaults

docs/eval/index.md

@@ -82,7 +82,9 @@ When you run `runme eval` without extra path configuration, Runme uses these def
 - Dataset path: `./evals/tasks`
 - Jobs directory: `.runme/evals/jobs`
 - Agent: `oracle`, Harbor's built-in oracle solution runner
-- Environment: Runme's Harbor environment
+- Environment: Runme's Harbor environment, with one concurrent trial by default
+
+When you select another Harbor environment, such as `--env docker`, Runme uses Harbor's concurrency default instead. Override either behavior with passthrough Harbor flags, for example `-- --n-concurrent 4`.
 
 ## Commands
 

docs/eval/quickstart.md

@@ -80,6 +80,8 @@ To run the same rubric with the deterministic oracle solution runner, replace `c
 
 Use `--env` to select one of the Harbor environments provided by the task dataset. When `--env` is omitted, Runme uses its default environment. For Docker environment configuration and task authoring details, see Harbor's [task environment docs](https://www.harborframework.com/docs/tasks#environment).
 
+Runme's default environment runs one concurrent trial because it shares the host workspace. Other Harbor environments, including Docker, use Harbor's configured or default concurrency. Pass Harbor flags after `--` to override concurrency, such as `-- --n-concurrent 4`.
+
 The RewardKit example also provides a Docker environment. Pass `OPENAI_API_KEY` explicitly because Docker runs hermetically and does not reuse your local agent OAuth session:
 
 ```sh

docs/eval/reference.md

@@ -40,6 +40,8 @@ Important flags:
 - `--runme-harbor-bin`: `runme-harbor` executable.
 - `--debug`: print delegated commands.
 
+Runme's environment defaults to one concurrent trial. Other Harbor environments, such as `--env docker`, use Harbor's configured or default concurrency. Pass Harbor flags after `--`, for example `-- --n-concurrent 4`, to override concurrency for any environment.
+
 Supported agents:
 
 - `oracle`: Harbor's built-in oracle solution runner. It runs the task's provided solution and is not an external agent CLI.