checks.py still hand-rolls five numeric guards that _field_guards now covers

[kstonekuan]

#487 landed the guard set in _field_guards (#494) and converted batching.py and the configuration half of build_ai_vlm_checks.py. checks.py is the largest file still hand-rolling it.

Measured on current main

38 hand-rolled isinstance(x, bool) sites remain across 16 files. Two groups are deliberately not targets:

• catalog.py (6): coerces NumPy scalars, which _field_guards deliberately does not. See its module docstring. Leave it.
• build_ai_vlm_checks.py (4): three parse external model responses and one is a genuine bool field. All four are correct as they are, and Centralize numeric range validation #494's review covers why.

That leaves checks.py as the biggest convertible one, with 5:

line	parameter	current shape
:991	shake_threshold_dps	bool + np.isfinite + < 0
:998	unstable_min_duration_s	bool + np.isfinite + < 0
:1005	horizontal_field_of_view_degrees	bool + np.isfinite + not 0 < x <= 360
:1659	max_plausible_fps	bool, then np.isfinite + <= 0
:1664	downsample_tolerance_fps	bool, then np.isfinite + < 0

Four of the five map straight onto the new helpers:

require_non_negative_float(shake_threshold_dps, "shake_threshold_dps")
require_non_negative_float(unstable_min_duration_s, "unstable_min_duration_s")
require_positive_float(max_plausible_fps, "max_plausible_fps")
require_non_negative_float(downsample_tolerance_fps, "downsample_tolerance_fps")

horizontal_field_of_view_degrees is the odd one: it wants a half-open range, 0 < x <= 360. There is no helper for that. Add one only if a second caller wants the same shape; otherwise compose require_finite_float with the bound left in place, and say which you chose.

What this costs, which is the part to decide

Every message changes to _field_guards's spelling. "shake_threshold_dps must be finite and non-negative" becomes "shake_threshold_dps must be >= 0, got -1". The second names the offending value, which is better, but it is a user-visible string change across five parameters and it will move test assertions.

That was accepted for #487 and it is accepted here. Two things not to lose:

• The guards must stay above selected_cameras, which is what camera_stability accepts an invalid field of view on an episode with no cameras, because that guard lives inside the per-camera loop #445 and camera_frame_stats and camera_signal_quality skip their threshold guards on a camera-less episode, and name internal fields when they do fire #447 were about. A guard inside the per-camera loop does not fire on a camera-less episode.
• The messages must name the parameter as the signature spells it, never the internal settings field. That was the other half of camera_frame_stats and camera_signal_quality skip their threshold guards on a camera-less episode, and name internal fields when they do fire #447.

Definition of done

1. rg -c "isinstance\([a-z_.]+, bool\)" src/hflow/checks.py reports at most 1 (the field-of-view case, if you leave it composed).
2. Every refusal the file made before, it still makes: bool, non-finite, and out-of-range for all five parameters, each on a camera-less episode.
3. Tests use match= with anchored patterns. On an episode with cameras a camera-processing failure also raises ValueError, so an unanchored pytest.raises(ValueError) passes whether or not the guard is there. fix: validate camera FPS thresholds #492 has the shape to copy.
4. Mutation: neuter each guard in turn and confirm a test goes red.

Sequencing

Wait for #459 to merge. It is open against the guards in camera_frame_stats and camera_signal_quality in this same file and will add more of them. Converting underneath it would conflict.

Validation

uv sync --locked --all-extras
uv run ruff check
uv run ruff format --check
uv run ty check
uv run pytest -q

[Kaileshwar16]

@kstonekuan can I take this issue

[amansingh-121]

i want to take it