added ruff test

ruff.toml

@@ -0,0 +1,56 @@
+# Ruff configuration — pinned deliberately.
+#
+# Before this file existed the repo had no Ruff config, so `ruff check .` ran whatever the
+# installed Ruff version enables by default (Ruff 0.16 turns on a very broad set: UP/RUF/PLR/
+# S/TRY/PERF/FURB/YTT/ASYNC...). The same tree therefore produced different findings on
+# different machines and between a developer and a runner. Never rely on tool defaults.
+#
+# Policy, decided from the measured findings rather than from taste:
+#
+#   * `select` is explicit. High-signal correctness rules first, then only the mechanical
+#     modernisation rules we are willing to apply without human review.
+#   * BLE001 is selected so the existing `# noqa: BLE001 - <reason>` suppressions stay *used*
+#     and RUF100 can never delete their rationale — a broad `except Exception` is a legitimate
+#     choice in hardware, GL and teardown paths. It is deliberately NOT part of the gate.
+#   * S110 / S112 / E722 ARE part of the gate: a silent handler hides a failure. Silence is
+#     acceptable only with a reasoned suppression, or with a handler that reports/re-raises.
+#   * RUF100 reports unused suppressions but is `unfixable`: a machine must not remove a
+#     suppression whose comment records why it exists. Triage those by hand.
+#   * The mechanical sweep never uses `--unsafe-fixes`.
+#
+# The gate (pre-merge / runner) selects the narrow set explicitly, so BLE001 cannot fail a
+# build, and only ever touches changed files:
+#
+#   tools/lint_gate.py                       # the gate: changed files, machine-readable
+#   ruff format --check <changed files>      # never a whole-tree rewrite mid-diff
+
+target-version = "py310"
+line-length = 88
+
+[lint]
+select = [
+  "E9", "E722",        # syntax/IO errors, and bare `except:`
+  "E402",              # module import not at top of file — SELECTED for visibility, NOT gated.
+                       # `import` after `os.environ[...]` is deliberate in this codebase (the
+                       # environment must be set before Qt/cv2 load), so gating it would be noise;
+                       # but it is the only rule that would catch an accidental import moved above
+                       # that setup, so it stays reported. An intentional site belongs in a
+                       # `# noqa: E402 - <reason>` when it is touched.
+  "F",                 # pyflakes: F401 unused import, F811 redefinition, F821/F822 undefined name
+  "S110", "S112",      # try-except-pass / try-except-continue — an invisible failure
+  "B023",              # function definition does not bind loop variable
+  "PLW1510",           # subprocess.run without an explicit check
+  "RUF100",            # unused noqa — reported for triage, never auto-removed
+  "UP",                # pyupgrade (Optional[X] -> X | None, deprecated imports)
+  "I",                 # import sorting
+  "RUF022", "RUF023",  # __all__ / __slots__ ordering
+  "PIE",               # flake8-pie
+  "RET501", "PLR1711", # useless return / return None
+  "SIM114",            # if-with-same-arms
+  "BLE001",            # selected for suppression hygiene only — excluded from the gate
+]
+unfixable = ["RUF100"]
+
+[format]
+quote-style = "double"
+indent-style = "space"