Feat v0.7.12 batch exec (#66)

Co-authored-by: Jeffrey Smith <jasafpro@gmail.com>
Co-committed-by: Jeffrey Smith <jasafpro@gmail.com>

docs/STARLARK-REFERENCE.md

@@ -242,6 +242,39 @@ instances = workflow.list_instances(workflow_id, status="active")
 # Returns list of instance dicts
 ```
 
+### batch
+
+**Permission:** `batch.exec`
+
+Run multiple callables concurrently. Each callable gets its own
+execution thread with an independent step budget.
+
+```python
+jira = lib.require("jira-client")
+confluence = lib.require("confluence-client")
+
+results, errors = batch.exec([
+    lambda: jira.create_issue(issue_data),
+    lambda: confluence.create_page(page_data),
+    lambda: send_notification(user_id),
+], timeout=15)
+
+# results[i] = return value of callables[i], or None on error
+# errors[i]  = None on success, or error string on failure
+# All three ran concurrently.
+```
+
+**Constraints:**
+
+- Max 8 callables per call. Dispatched concurrently via goroutines.
+- `timeout` (optional): 1–30 seconds per branch (default 10).
+- `lib.require()` is not available inside branch callables.
+  Load libraries before the `batch.exec` call.
+- `batch.exec()` cannot be called from within a branch (no nesting).
+- `print()` output from branches is discarded.
+
+---
+
 ## Example: automated stage hook
 
 A simple hook that reads a setting, queries data, and advances: