feat(coding-agent-eval): added runEvalAgent bridge for agent plan checks

- Added `agent()` in JS/Python preludes to call host bridge and parse returned text when schema is set.
- Added JS `parallel()` and `pipeline()` with bounded `__pool()` pools and concurrency normalization.
- Added `runEvalAgent` bridge logic with argument parsing plus plan-mode, allowlist, depth, and artifacts checks.
- Added tool routing and tests documenting new `agent/parallel/pipeline` behavior, defaults, and validation failures.

docs/python-repl.md

@@ -10,6 +10,7 @@ It covers tool behavior, runner lifecycle, environment handling, execution seman
 - Subprocess kernel client: `src/eval/py/kernel.ts`
 - Python wrapper / NDJSON server: `src/eval/py/runner.py`
 - Prelude helpers loaded into every kernel: `src/eval/py/prelude.py`
+- Host-side subagent helper bridge: `src/eval/agent-bridge.ts`
 - MIME bundle renderer (text + structured outputs): `src/eval/py/display.ts`
 - Interactive-mode renderer for user-triggered Python runs: `src/modes/components/eval-execution.ts`
 - Runtime/env filtering and Python resolution: `src/eval/py/runtime.ts`
@@ -159,6 +160,8 @@ The runner additionally receives `PYTHONUNBUFFERED=1` and `PYTHONIOENCODING=utf-
 
 If Python preflight fails and `eval.js` is enabled, `eval` remains available for `js` cells; `py` cells fail with a Python-backend availability error.
 
+Python prelude helpers include `agent(prompt, *, agent_type="task", model=None, context=None, label=None, schema=None)`. It synchronously calls the host bridge, runs one subagent through the task executor, and returns the final text. When `schema` is supplied, the helper parses the subagent's JSON output and returns the object.
+
 ## Execution flow and cancellation/timeout
 
 ### Cell timeout