Asyncio TaskGroup Structured-Concurrency Python Script Prompt

You are a senior Python engineer who writes correct async automation. I have a concurrent job that fans out I/O-bound work (HTTP calls, DB queries, subprocess launches) and I keep hitting the classic `asyncio.gather` traps: a failing task leaves siblings running, exceptions get swallowed, and Ctrl-C leaves "Task was destroyed but it is pending" warnings. I want to rewrite it with `asyncio.TaskGroup` (Python 3.11+) so concurrency is structured and failures are deterministic.

I will provide:
- The unit of work (a coroutine) and the collection of inputs to run it over
- The concurrency ceiling (max in-flight), timeouts, and whether partial success is acceptable
- Python version and whether a 3.10 fallback is needed

Your job:

1. **Model the fan-out with `async with asyncio.TaskGroup() as tg`** — create tasks via `tg.create_task(...)`, and explain the core guarantee: when the block exits, every task has completed or the group has cancelled the rest and re-raised.
2. **Bound concurrency** — pair the TaskGroup with an `asyncio.Semaphore` so only N coroutines run at once; show the `async with sem:` wrapper inside the worker, not around task creation.
3. **Aggregate errors correctly** — a TaskGroup raises an `ExceptionGroup`; show how to catch it with `except* SomeError:` (3.11 syntax) and how to separate "cancel everything on first failure" from "collect all results and report failures at the end" (return exceptions as values when partial success is fine).
4. **Add per-task timeouts** — use `asyncio.timeout()` inside each worker so one slow task can't stall the group, and make the timeout error carry which input it came from.
5. **Handle cancellation cleanly** — ensure Ctrl-C / SIGINT cancels the group, awaits teardown, and exits without pending-task warnings; note the re-raise of `CancelledError`.
6. **Provide the 3.10 fallback** — show the equivalent `asyncio.gather(..., return_exceptions=True)` pattern and call out exactly what safety you lose versus TaskGroup.

Output: the complete typed script with a runnable `asyncio.run(main())` entrypoint, a table comparing `gather` vs `TaskGroup` semantics, and two tests — one where a mid-flight task raises (proving siblings cancel) and one all-success run.