feat(layout): adaptive layout & font scaling system for plugins

Add src/adaptive_layout.py — opt-in core helpers so plugins render
legibly on any panel size without hand-tuned per-display layouts:

- Region: integer rect algebra (bands/columns/weighted splits/centering)
  that partitions space so text bands can't overlap by construction
- Font ladders: ordered (family, size) steps known to render crisply
  (LADDER_GRID: X11 BDFs at native sizes; LADDER_ARCADE: PressStart2P at
  8px multiples) — fitting walks the ladder instead of scaling pixel
  fonts fractionally
- LayoutContext: breakpoint tiers, geometry scale vs. a declared design
  size, and cached fit_text/fit_lines/font_for_rows queries

Generalizes the three patterns proven in the field: f1-scoreboard's
scale factor, masters-tournament's tiers, baseball-scoreboard's font
fallback ladder.

Wiring: BasePlugin gains a lazy .layout property and draw_fit();
FontManager gains get_native_bdf_size() and a cache_generation counter;
manifest schema gains display.design_size and requires.display_size
max_width/max_height; 96x48 joins DEFAULT_TEST_SIZES; the bounds-check
harness records negative-coordinate draws; TextHelper's broken
measurement helpers are fixed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/test_adaptive_layout.py

@@ -0,0 +1,255 @@
+"""Tests for the adaptive layout system (src/adaptive_layout.py)."""
+
+import pytest
+
+from src.adaptive_layout import (
+    DEFAULT_DESIGN_SIZE,
+    LADDER_ARCADE,
+    LADDER_GRID,
+    LayoutContext,
+    Region,
+    draw_fitted_text,
+    measure_ink,
+)
+from src.font_manager import FontManager
+
+
+@pytest.fixture(scope="module")
+def font_manager():
+    """Real FontManager over assets/fonts — the ladders depend on it."""
+    return FontManager({})
+
+
+@pytest.fixture
+def ctx(font_manager):
+    return LayoutContext(128, 32, font_manager)
+
+
+class TestRegion:
+    """Pure integer rect algebra."""
+
+    def test_bands_partition_without_overlap(self):
+        r = Region(0, 0, 128, 32)
+        top = r.top_band(7)
+        bottom = r.bottom_band(7)
+        middle = r.middle(7, 7)
+        assert top.bottom == middle.y
+        assert middle.bottom == bottom.y
+        assert top.h + middle.h + bottom.h == r.h
+
+    def test_bands_clamp_on_short_panel(self):
+        # The classic failure: y=1 top band and y=height-7 bottom band
+        # overlapping on a short panel. Bands can't exceed the region.
+        r = Region(0, 0, 32, 8)
+        assert r.top_band(16).h == 8
+        assert r.bottom_band(16).h == 8
+        assert r.middle(8, 8).h == 0  # degenerate, never negative
+
+    def test_split_v_weights_sum_to_height(self):
+        r = Region(0, 0, 64, 33)
+        rows = r.split_v(3, 1, 1, gap=1)
+        assert len(rows) == 3
+        assert sum(row.h for row in rows) == 33 - 2  # two 1px gaps
+        assert rows[0].h > rows[1].h
+        assert rows[-1].bottom == r.bottom
+
+    def test_split_h_columns_advance(self):
+        r = Region(0, 0, 100, 32)
+        cols = r.split_h(1, 1, gap=2)
+        assert cols[0].right + 2 == cols[1].x
+        assert cols[1].right == r.right
+
+    def test_degenerate_sizes_never_negative(self):
+        for w, h in [(8, 8), (32, 16), (1, 1)]:
+            r = Region(0, 0, w, h).inset(4)
+            assert r.w >= 0 and r.h >= 0
+            for sub in r.split_v(1, 1) + r.split_h(1, 1, gap=3):
+                assert sub.w >= 0 and sub.h >= 0
+
+    def test_align_xy(self):
+        r = Region(10, 10, 100, 20)
+        assert r.align_xy(20, 10, "left", "top") == (10, 10)
+        assert r.align_xy(20, 10, "right", "bottom") == (90, 20)
+        assert r.align_xy(20, 10) == (50, 15)
+
+    def test_left_right_cols(self):
+        r = Region(0, 0, 128, 32)
+        assert r.left_col(32) == Region(0, 0, 32, 32)
+        assert r.right_col(32) == Region(96, 0, 32, 32)
+
+
+class TestLayoutContext:
+    def test_tiers(self, font_manager):
+        assert LayoutContext(128, 32, font_manager).tier == "sm"
+        assert LayoutContext(96, 48, font_manager).tier == "md"
+        assert LayoutContext(128, 64, font_manager).tier == "lg"
+        assert LayoutContext(64, 16, font_manager).tier == "xs"
+        assert LayoutContext(256, 128, font_manager).tier == "xl"
+
+    def test_wide_short_flag(self, font_manager):
+        assert LayoutContext(128, 32, font_manager).is_wide_short
+        assert not LayoutContext(128, 64, font_manager).is_wide_short
+
+    def test_scale_against_design_size(self, font_manager):
+        assert LayoutContext(128, 32, font_manager).scale == 1.0
+        assert LayoutContext(256, 64, font_manager).scale == 2.0
+        # min() of the two axes: don't overscale the constrained one
+        assert LayoutContext(256, 32, font_manager).scale == 1.0
+        assert DEFAULT_DESIGN_SIZE == (128, 32)
+
+    def test_px_scales_and_clamps(self, font_manager):
+        big = LayoutContext(256, 64, font_manager)
+        assert big.px(4) == 8
+        assert big.px(4, maximum=6) == 6
+        tiny = LayoutContext(32, 16, font_manager)
+        assert tiny.px(4, minimum=2) == 2
+
+    def test_by_tier_nearest_at_or_below(self, font_manager):
+        mapping = {"sm": 10, "lg": 18}
+        assert LayoutContext(128, 32, font_manager).by_tier(mapping) == 10
+        assert LayoutContext(96, 48, font_manager).by_tier(mapping) == 10  # md -> sm
+        assert LayoutContext(128, 64, font_manager).by_tier(mapping) == 18
+        assert LayoutContext(256, 128, font_manager).by_tier(mapping) == 18  # xl -> lg
+        # nothing at-or-below: fall forward to smallest defined above
+        assert LayoutContext(64, 16, font_manager).by_tier(mapping) == 10
+
+
+class TestFontFitting:
+    def test_ladder_monotonic(self, font_manager):
+        """Each ladder rung must render no taller than the one before it."""
+        for ladder in (LADDER_GRID, LADDER_ARCADE):
+            heights = []
+            for step in ladder:
+                font = font_manager.get_font(step.family, step.size_px)
+                heights.append(measure_ink("Ay0", font)[1])
+            assert heights == sorted(heights, reverse=True), (
+                f"ladder not monotonically shrinking: {heights}")
+
+    def test_fit_text_grows_on_taller_panel(self, font_manager):
+        small = LayoutContext(64, 32, font_manager)
+        large = LayoutContext(128, 64, font_manager)
+        text = "12:34"
+        fit_small = small.fit_text(text, small.bounds, ladder=LADDER_ARCADE)
+        fit_large = large.fit_text(text, large.bounds, ladder=LADDER_ARCADE)
+        assert fit_small.fits and fit_large.fits
+        assert fit_large.size_px > fit_small.size_px
+
+    def test_fit_text_fits_the_box(self, ctx):
+        box = ctx.bounds.inset(1)
+        fit = ctx.fit_text("HELLO WORLD", box)
+        assert fit.fits
+        assert fit.width <= box.w and fit.height <= box.h
+
+    def test_fit_text_ellipsizes_overlong_text(self, font_manager):
+        tiny = LayoutContext(32, 16, font_manager)
+        fit = tiny.fit_text("SUPERCALIFRAGILISTIC", tiny.bounds)
+        assert fit.text != "SUPERCALIFRAGILISTIC"
+        assert fit.text.endswith("…")
+        assert fit.width <= tiny.bounds.w
+
+    def test_fit_text_cached(self, ctx):
+        first = ctx.fit_text("CACHED", ctx.bounds)
+        second = ctx.fit_text("CACHED", ctx.bounds)
+        assert first is second
+        ctx.clear_cache()
+        assert ctx.fit_text("CACHED", ctx.bounds) is not first
+
+    def test_fit_lines_stacks_within_height(self, ctx):
+        box = ctx.bounds
+        lines = ["LINE ONE", "LINE TWO", "LINE THREE"]
+        fit = ctx.fit_lines(lines, box, spacing=1)
+        assert fit.fits
+        assert 3 * fit.line_height + 2 <= box.h
+
+    def test_font_for_rows(self, ctx):
+        fit = ctx.font_for_rows(4, 32)
+        assert fit.fits
+        assert 4 * fit.line_height <= 32
+
+    def test_ellipsize_returns_original_when_it_fits(self, ctx):
+        font = ctx.font_manager.get_font("4x6", 6)
+        assert ctx.ellipsize("HI", font, 1000) == "HI"
+
+
+class TestDrawFittedText:
+    def test_draws_within_region(self, ctx):
+        calls = []
+
+        class _DM:
+            def draw_text(self, text, x=None, y=None, color=None, font=None):
+                calls.append((text, x, y))
+
+        box = Region(10, 4, 100, 24)
+        fit = ctx.fit_text("SCORE", box)
+        draw_fitted_text(_DM(), fit, box)
+        text, x, y = calls[0]
+        assert text == "SCORE"
+        assert box.x <= x <= box.right - fit.width
+        # the ink (y + y_offset .. + height) must land inside the box
+        assert box.y <= y + fit.y_offset
+        assert y + fit.y_offset + fit.height <= box.bottom
+
+
+class TestBasePluginIntegration:
+    def test_layout_property_and_draw_fit(self):
+        from src.plugin_system.base_plugin import BasePlugin
+        from src.plugin_system.testing.mocks import (
+            MockCacheManager, MockDisplayManager, MockPluginManager,
+        )
+
+        class _Plugin(BasePlugin):
+            def update(self):
+                pass
+
+            def display(self, force_clear=False):
+                pass
+
+        plugin = _Plugin("test-plugin", {}, MockDisplayManager(96, 48),
+                         MockCacheManager(), MockPluginManager())
+        assert (plugin.layout.width, plugin.layout.height) == (96, 48)
+        assert plugin.layout is plugin.layout  # cached
+        fit = plugin.draw_fit("HELLO", plugin.layout.bounds.inset(1))
+        assert fit.fits
+        assert plugin.display_manager.draw_calls  # actually drew
+
+    def test_layout_rebuilds_on_size_change(self):
+        from src.plugin_system.base_plugin import BasePlugin
+        from src.plugin_system.testing.mocks import (
+            MockCacheManager, MockDisplayManager, MockPluginManager,
+        )
+
+        class _Plugin(BasePlugin):
+            def update(self):
+                pass
+
+            def display(self, force_clear=False):
+                pass
+
+        dm = MockDisplayManager(128, 32)
+        plugin = _Plugin("test-plugin", {}, dm,
+                         MockCacheManager(), MockPluginManager())
+        assert plugin.layout.tier == "sm"
+        dm.width, dm.height = 128, 64
+        assert plugin.layout.tier == "lg"
+
+    def test_design_size_from_manifest(self):
+        from src.plugin_system.base_plugin import BasePlugin
+        from src.plugin_system.testing.mocks import (
+            MockCacheManager, MockDisplayManager, MockPluginManager,
+        )
+
+        class _Plugin(BasePlugin):
+            def update(self):
+                pass
+
+            def display(self, force_clear=False):
+                pass
+
+        pm = MockPluginManager()
+        pm.plugin_manifests["test-plugin"] = {
+            "display": {"design_size": {"width": 64, "height": 32}}
+        }
+        plugin = _Plugin("test-plugin", {}, MockDisplayManager(128, 64),
+                         MockCacheManager(), pm)
+        assert plugin.layout.design_size == (64, 32)
+        assert plugin.layout.scale == 2.0