Add cross-size/cross-screen plugin safety harness (#361)

* feat(testing): add cross-size/cross-screen plugin safety harness

Render every plugin across all supported matrix sizes (64x32, 128x32,
128x64, 256x32) and every declared screen, failing on crashes, content
drawn past the panel edge, or visual drift vs committed golden images.

- BoundsCheckingDisplayManager: oversized-canvas overflow detection
- harness.py: multi-size/multi-screen render engine + golden compare
- scripts/check_plugin.py: CLI (functional+bounds, --out-dir, --update-golden,
  --freeze-time); render_plugin.py refactored onto shared loading helpers
- test/plugins/test_harness.py + test_plugin_matrix.py (parametrized,
  honors per-plugin test/harness.json; skips when no plugins present)
- MockCacheManager.cache_dir so cache-dir-using plugins load headlessly
- .github/workflows/test.yml + docs/plugin-safety-harness.md

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(testing): address PR review feedback on plugin safety harness

- check_plugin: friendly error for non-numeric --sizes; reject non-object
  --config / --mock-data JSON; sanitize plugin mode before using as a
  filename; stop --update-golden from masking crash/overflow failures
- bounds_display_manager: pad the canvas out to the largest supported panel
  (not a fixed 16px) so far-overshoot coordinates are caught, not clipped
- harness: merge config_schema defaults inside render_plugin_matrix; surface
  update() failures as a non-fatal warning + result field instead of a debug
  log; sanitize mode in golden_path
- loading: fail fast when harness.json references a missing mock_data fixture
- mocks: clean up the per-instance temp cache dir via weakref.finalize
- test_plugin_matrix: add a discovery guard that fails when
  LEDMATRIX_REQUIRE_PLUGINS=1 but none found (still skips locally); type hints
- bound test deps with upper version pins for deterministic CI

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* feat(testing): render plugins across arbitrary panel sizes, not a fixed list

Addresses maintainer feedback that there is no canonical set of supported
panel sizes — a build can be any size/configuration (square, 2x2, 4x4, 8x2,
long strips, tall stacks).

- sizes.py: SUPPORTED_SIZES -> DEFAULT_TEST_SIZES (back-compat alias kept),
  reframed as a representative SAMPLE of real panel-grid arrangements rather
  than an authoritative list; add parse_size_token / coerce_sizes /
  resolve_test_sizes helpers
- sizes are now fully overridable: LEDMATRIX_TEST_SIZES env (global, e.g. test
  on your exact hardware) > per-plugin harness.json "sizes" > default sample;
  CLI --sizes unchanged
- bounds_display_manager: pad the canvas to the largest panel IN THE CURRENT
  RUN (via overflow_extent) instead of a hardcoded max, so cross-size overflow
  detection scales to whatever sizes a run uses
- harness: compute per-run extent and thread it into the bounds manager
- tests: arbitrary-shape + size-parsing/precedence coverage
- docs: rewrite "Supported sizes" -> "Sizes: a sample, not a fixed list"

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(testing): fail the harness on non-connectivity update() errors

Addresses the remaining review thread: recording every update() exception as a
non-fatal warning still let a real update() regression pass green as long as
display() survived. Now update() failures are classified — a tolerated set of
connectivity errors (ConnectionError/TimeoutError/socket/ssl/urllib/http/
requests) is recorded non-fatally (expected with no network in CI), while any
other exception is treated as a genuine bug and fails that render.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* ci(security): pin actions to SHAs and disable checkout credential persistence

Addresses the CodeRabbit/zizmor workflow-hardening finding: pin
actions/checkout and actions/setup-python to full commit SHAs and set
persist-credentials: false on checkout to reduce supply-chain and
token-exposure risk.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(testing): validate positive sizes; narrow requests import except

Two review findings:
- sizes.py: parse_size_token / coerce_sizes now reject non-positive
  dimensions (0x32, -64x32) with a clear message instead of passing invalid
  sizes downstream (CodeRabbit).
- harness.py: the optional `requests` import now catches ImportError
  specifically and logs instead of `except Exception: pass`, clearing the
  Codacy medium "Try, Except, Pass" (harness.py L52) and Ruff S110/BLE001.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

test/plugins/test_harness.py

@@ -0,0 +1,182 @@
+"""
+Unit tests for the plugin safety harness primitives:
+bounds detection, image comparison, and mode enumeration.
+
+These don't load real plugins, so they run anywhere (including core CI where
+plugin-repos is empty).
+"""
+
+import pytest
+from PIL import Image
+
+from src.plugin_system.testing.bounds_display_manager import BoundsCheckingDisplayManager
+from src.plugin_system.testing.harness import (
+    _TOLERATED_UPDATE_ERRORS, compare_images, list_modes,
+)
+from src.plugin_system.testing.sizes import (
+    DEFAULT_TEST_SIZES, coerce_sizes, parse_size_token, resolve_test_sizes,
+)
+
+
+class TestBoundsDetection:
+    def test_reports_declared_size_not_canvas_size(self):
+        dm = BoundsCheckingDisplayManager(width=64, height=32)
+        assert dm.width == 64 and dm.height == 32
+        assert dm.matrix.width == 64 and dm.matrix.height == 32
+        # Backing canvas is padded out past the declared panel so far-overshoot
+        # coordinates land on-canvas and get flagged instead of clipped.
+        canvas_w, canvas_h = dm.image.size
+        assert canvas_w > 64 and canvas_h > 32
+
+    def test_far_overshoot_on_small_panel_is_detected(self):
+        # A coordinate meant for a wide build (x past 64) must still be caught
+        # when the declared panel is only 64 wide.
+        dm = BoundsCheckingDisplayManager(width=64, height=32)
+        dm.draw.rectangle([200, 5, 210, 10], fill=(255, 0, 0))
+        bbox = dm.check_overflow()
+        assert bbox is not None
+        assert bbox[0] >= 64
+
+    def test_in_bounds_drawing_has_no_overflow(self):
+        dm = BoundsCheckingDisplayManager(width=64, height=32)
+        dm.draw.rectangle([0, 0, 63, 31], fill=(255, 255, 255))
+        assert dm.check_overflow() is None
+
+    def test_right_overflow_is_detected(self):
+        dm = BoundsCheckingDisplayManager(width=64, height=32)
+        # Draw a few pixels past the right edge.
+        dm.draw.rectangle([60, 5, 70, 10], fill=(255, 0, 0))
+        bbox = dm.check_overflow()
+        assert bbox is not None
+        assert bbox[0] >= 64  # overflow starts at or past the declared width
+
+    def test_bottom_overflow_is_detected(self):
+        dm = BoundsCheckingDisplayManager(width=64, height=32)
+        dm.draw.rectangle([5, 30, 10, 40], fill=(0, 255, 0))
+        bbox = dm.check_overflow()
+        assert bbox is not None
+        assert bbox[3] > 32  # overflow extends past the declared height
+
+    def test_declared_image_is_cropped_to_panel(self):
+        dm = BoundsCheckingDisplayManager(width=64, height=32)
+        assert dm.get_image().size == (64, 32)
+
+    def test_snapshot_saves_cropped_panel(self, tmp_path):
+        dm = BoundsCheckingDisplayManager(width=128, height=32)
+        out = tmp_path / "snap.png"
+        dm.save_snapshot(str(out))
+        with Image.open(out) as img:
+            assert img.size == (128, 32)
+
+
+class TestArbitraryPanelSizes:
+    """The harness must handle any panel shape, not a fixed supported list."""
+
+    def test_overflow_extent_pads_to_largest_in_run(self):
+        # A wide run (extent 256) means content at x=200 on a 64-wide panel is
+        # caught; the same draw with a small extent would be clipped (false pass).
+        wide = BoundsCheckingDisplayManager(width=64, height=32, overflow_extent=(256, 32))
+        wide.draw.rectangle([200, 5, 210, 10], fill=(255, 0, 0))
+        assert wide.check_overflow() is not None
+
+        tight = BoundsCheckingDisplayManager(width=64, height=32, overflow_extent=(64, 32))
+        tight.draw.rectangle([200, 5, 210, 10], fill=(255, 0, 0))
+        assert tight.check_overflow() is None  # clipped beyond the small canvas
+
+    def test_unusual_shapes_report_their_declared_size(self):
+        for w, h in [(8, 2), (6, 6), (200, 8), (64, 96)]:
+            dm = BoundsCheckingDisplayManager(width=w, height=h)
+            assert dm.width == w and dm.height == h
+            assert dm.matrix.width == w and dm.matrix.height == h
+
+
+class TestUpdateErrorClassification:
+    """update() may fail for lack of network (tolerated) but a logic bug must
+    not pass green just because display() survives."""
+
+    def test_connectivity_errors_are_tolerated(self):
+        import socket
+        import urllib.error
+        for exc in (ConnectionError("x"), TimeoutError("x"), socket.gaierror("x"),
+                    urllib.error.URLError("x")):
+            assert isinstance(exc, _TOLERATED_UPDATE_ERRORS)
+
+    def test_logic_errors_are_not_tolerated(self):
+        for exc in (ValueError("x"), KeyError("x"), AttributeError("x"), TypeError("x")):
+            assert not isinstance(exc, _TOLERATED_UPDATE_ERRORS)
+
+
+class TestSizeParsing:
+    def test_parse_size_token_ok(self):
+        assert parse_size_token(" 128X32 ") == (128, 32)
+
+    def test_parse_size_token_rejects_garbage(self):
+        with pytest.raises(ValueError):
+            parse_size_token("128xabc")
+        with pytest.raises(ValueError):
+            parse_size_token("128-32")
+
+    def test_rejects_non_positive_dimensions(self):
+        for bad in ("0x32", "-64x32", "64x0", "64x-1"):
+            with pytest.raises(ValueError):
+                parse_size_token(bad)
+        with pytest.raises(ValueError):
+            coerce_sizes([[0, 32]])
+        with pytest.raises(ValueError):
+            coerce_sizes("64x-1")
+
+    def test_coerce_sizes_from_string_and_pairs(self):
+        assert coerce_sizes("8x16,64x64") == [(8, 16), (64, 64)]
+        assert coerce_sizes([[8, 16], (64, 64)]) == [(8, 16), (64, 64)]
+        assert coerce_sizes(None) is None
+        assert coerce_sizes("") is None
+
+    def test_resolve_precedence_env_then_spec_then_default(self, monkeypatch):
+        monkeypatch.delenv("LEDMATRIX_TEST_SIZES", raising=False)
+        assert resolve_test_sizes(None) == list(DEFAULT_TEST_SIZES)
+        assert resolve_test_sizes([[8, 16]]) == [(8, 16)]
+        monkeypatch.setenv("LEDMATRIX_TEST_SIZES", "5x5")
+        # env wins over a per-plugin spec
+        assert resolve_test_sizes([[8, 16]]) == [(5, 5)]
+
+
+class TestCompareImages:
+    def test_identical_images_match(self):
+        a = Image.new("RGB", (16, 16), (10, 20, 30))
+        b = a.copy()
+        ok, diff_pixels, max_delta = compare_images(a, b)
+        assert ok and diff_pixels == 0 and max_delta == 0
+
+    def test_different_images_fail_at_zero_tolerance(self):
+        a = Image.new("RGB", (16, 16), (0, 0, 0))
+        b = a.copy()
+        b.putpixel((1, 1), (255, 255, 255))
+        ok, diff_pixels, max_delta = compare_images(a, b)
+        assert not ok and diff_pixels == 1 and max_delta == 255
+
+    def test_tolerance_absorbs_small_noise(self):
+        a = Image.new("RGB", (16, 16), (100, 100, 100))
+        b = a.copy()
+        b.putpixel((2, 2), (103, 100, 100))  # delta 3
+        ok, _, max_delta = compare_images(a, b, max_delta=5, max_diff_pixels=0)
+        assert ok and max_delta == 3
+
+    def test_size_mismatch_fails(self):
+        a = Image.new("RGB", (16, 16))
+        b = Image.new("RGB", (32, 16))
+        ok, _, _ = compare_images(a, b)
+        assert not ok
+
+
+class TestListModes:
+    def test_instance_modes_take_precedence(self):
+        inst = type("P", (), {"modes": ["a", "b"]})()
+        assert list_modes(inst, {"display_modes": ["x"]}, "pid") == ["a", "b"]
+
+    def test_falls_back_to_manifest_display_modes(self):
+        inst = type("P", (), {})()
+        assert list_modes(inst, {"display_modes": ["x", "y"]}, "pid") == ["x", "y"]
+
+    def test_falls_back_to_plugin_id(self):
+        inst = type("P", (), {})()
+        assert list_modes(inst, {}, "pid") == ["pid"]