[core] decouple main loop cadence from scheduler wake timing (#15792)

tests/integration/test_loop_interval_decoupling.py

@@ -0,0 +1,75 @@
+"""Test that loop_interval_ no longer clamps scheduler cadence.
+
+Regression test for the decoupling of Application::loop() component-phase
+cadence from scheduler wake timing.
+
+Setup:
+- App.set_loop_interval(500) — raised for power-savings style cadence
+- Scheduler interval at 50ms — should fire at 50ms regardless of loop_interval_
+- Component loop (LoopTestComponent) — should run at 500ms cadence
+
+Before the decoupling fix the old `std::max(next_schedule, delay_time / 2)`
+floor clamped the sleep to ~250ms, so the 50ms scheduler only fired ~8 times
+per 2s (vs the ~40 expected). After the fix the scheduler fires close to its
+requested cadence while the component phase stays gated at loop_interval_.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import re
+
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_loop_interval_decoupling(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Raised loop_interval_ must not clamp scheduler item cadence."""
+    loop = asyncio.get_running_loop()
+    measurement_done: asyncio.Future[tuple[int, int]] = loop.create_future()
+
+    def on_log_line(line: str) -> None:
+        match = re.search(r"MEASUREMENT_DONE loop_delta=(\d+) sched_delta=(\d+)", line)
+        if match and not measurement_done.done():
+            measurement_done.set_result((int(match.group(1)), int(match.group(2))))
+
+    async with (
+        run_compiled(yaml_config, line_callback=on_log_line),
+        api_client_connected() as client,
+    ):
+        device_info = await client.device_info()
+        assert device_info is not None
+        assert device_info.name == "loop-interval-decouple"
+
+        try:
+            loop_delta, sched_delta = await asyncio.wait_for(
+                measurement_done, timeout=10.0
+            )
+        except TimeoutError:
+            pytest.fail("MEASUREMENT_DONE marker never appeared")
+
+        # Observation window = 2s, loop_interval_ = 500ms.
+        # Component phase should fire ~4 times in 2s. The upper bound must be
+        # less than 8: the pre-decoupling behavior clamped to ~250ms cadence
+        # giving ~8 loops/2s, so allowing 8 would let the old behavior pass.
+        # Lower bound 3 (not 2) keeps the test honest: a >30% slowdown from
+        # the ~4 nominal is not normal CI jitter and should fail.
+        assert 3 <= loop_delta <= 6, (
+            f"Component loop should fire ~4 times in 2s at loop_interval=500ms, "
+            f"got {loop_delta}"
+        )
+
+        # Scheduler interval = 50ms → ~40 fires in 2s. Before the decoupling
+        # fix this clamped to ~8 fires. Assert >= 20 to catch the old clamped
+        # behavior with comfortable jitter headroom for slow CI hosts.
+        assert sched_delta >= 20, (
+            f"50ms scheduler interval should fire ~40 times in 2s but only "
+            f"fired {sched_delta}. This indicates loop_interval_ is still "
+            f"clamping scheduler cadence."
+        )