fix(run): cancel sibling guardrail tasks when one raises

[adityasingh2400]

Summary

run_input_guardrails and run_output_guardrails in src/agents/run_internal/guardrails.py iterate guardrail tasks via asyncio.as_completed and only cancel siblings on the tripwire branch. If one guardrail raises a non-tripwire exception, the loop exits but unfinished sibling tasks are left scheduled and continue running past the function's return — wasting work, possibly producing observable side effects (e.g. an LLM-based guardrail finishing a network request after the caller already saw a different exception), and triggering Task was destroyed but it is pending! warnings at event-loop shutdown.

The fix wraps the as_completed loop in try / except BaseException and, on any exit that is not a normal return, cancels still-running siblings and gathers them (return_exceptions=True) before re-raising. This is distinct from #3187, which targets the tripwire branch of run_output_guardrails; this PR targets the raise branch in both functions.

Repro

async def raising(ctx, agent, input): raise RuntimeError("boom")
async def slow(ctx, agent, input):
    await asyncio.sleep(0.5)        # leaks past run_input_guardrails return
    print("oops, ran after caller raised")
    return GuardrailFunctionOutput(None, False)

await run_input_guardrails(agent, [InputGuardrail(slow), InputGuardrail(raising)], "x", ctx)
# raises RuntimeError, but `slow` keeps running.

Test plan

• New test_input_guardrail_raise_cancels_siblings — asserts the slow sibling is cancelled (not completed) by the time the raise propagates.
• New test_output_guardrail_raise_cancels_siblings — same for output guardrails.
• Existing 37 guardrail tests still pass (tests/test_guardrails.py).
• tests/test_runner_guardrail_resume.py, tests/test_stream_input_guardrail_timing.py, tests/test_tool_guardrails.py still pass.
• ruff check passes for changed files.

🤖 Generated with Claude Code

[seratch]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep it up!

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[seratch]

can you resolve the conflicts?

[adityasingh2400]

Rebased onto current main; conflicts resolved (combined with #3187's tripwire-branch await). Tests + lint clean.