[ndonkoHenri]

Fixes #6515.

page.run_task() returned the concurrent.futures.Future from asyncio.run_coroutine_threadsafe(), which a coroutine can't await, so async code couldn't start a task through Flet and wait for its result (await page.run_task(fetch) raised TypeError). The workarounds are worse: .result() blocks the very loop running the task, and page.loop.create_task() skips what run_task() sets up, such as the current page context.

Changes

• TaskFuture: a concurrent.futures.Future subclass whose __await__ delegates to asyncio.wrap_future(). await page.run_task(handler) returns the handler's value or raises its exception, from the page's loop or any other. run_task() switches the class of the future asyncio already created, so its link to the task is kept. isinstance(f, Future), result(), cancel() and add_done_callback() behave as before. As with an asyncio.Task, cancelling the awaiting coroutine cancels the task, and asyncio.shield() keeps it running.
• Awaiters no longer hang on a BaseException (found by a Codex review). run_task()'s done callback re-raised the task's exception so concurrent.futures logs it, but that logger only catches Exception. A BaseException, for example the asyncio.CancelledError asyncio makes from a handler's concurrent.futures.CancelledError, skipped the remaining callbacks, including the one that wakes the awaiter. The callback now re-raises only Exceptions. The outcome reaches awaiters through their own callback either way, so logging of normal errors is unchanged.
• Docs: the TaskFuture and run_task() docstrings (with an example) explain that awaiting returns the value or raises, and that the future keeps its outcome. The async-apps cookbook shows awaiting two tasks, and notes that an un-awaited task's exception is logged.

Testing

Checked against the same run_coroutine_threadsafe() + class switch as run_task(), on Python 3.10, 3.13 and 3.14 (the BaseException cases on 3.10 to 3.14):

Scenario	Result
await returns the value	✅
exception raised to the awaiter	✅
asyncio.gather() of several tasks	✅
cancelling the awaiter cancels the task	✅
asyncio.shield() keeps it running	✅
.result() from another thread	✅
still an instance of concurrent.futures.Future	✅
handler raising concurrent.futures.CancelledError / a custom BaseException	raised to the awaiter (hung before the second commit)

Also checked end to end in a web app, and the flet test suite passes.

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