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>

docs/ADAPTIVE_LAYOUT.md

@@ -0,0 +1,135 @@
+# Adaptive Layout & Font Scaling
+
+`src/adaptive_layout.py` lets a plugin render legibly on **any** panel size
+(64x32, 128x32, 96x48, 128x64, 256x64, ...) without hand-tuned per-display
+layouts. It is **opt-in**: nothing changes for plugins that don't use it.
+
+It generalizes three patterns proven in the plugin ecosystem:
+
+| Pattern | Origin | Core API |
+|---|---|---|
+| Geometry scale factor vs. a design size | f1-scoreboard | `ctx.px(base)` / `ctx.scale` |
+| Breakpoint tiers | masters-tournament | `ctx.tier` / `ctx.by_tier({...})` |
+| "Largest crisp font that fits" ladder | baseball-scoreboard | `ctx.fit_text(...)` and friends |
+
+## Quick start
+
+Every `BasePlugin` has a lazy `self.layout` (a `LayoutContext` for the
+current logical display size, rebuilt automatically if the size changes)
+and a one-liner `self.draw_fit(...)`:
+
+```python
+def display(self, force_clear=False):
+    from src.adaptive_layout import LADDER_ARCADE
+
+    b = self.layout.bounds.inset(1)          # Region(0,0,W,H) minus 1px margin
+    rows = b.split_v(3, 1, 1, gap=1)          # 3/5 for time, 1/5 each for the rest
+
+    self.draw_fit(self.time_str, rows[0], ladder=LADDER_ARCADE)
+    self.draw_fit(self.weekday, rows[1])      # default LADDER_GRID
+    self.draw_fit(self.date_str, rows[2])
+    self.display_manager.update_display()
+```
+
+On 128x64 the time renders at press_start 24px; on 64x32 it steps down to
+8px. The rows partition the height, so bands can never overlap — no more
+`y = height - 7` magic numbers.
+
+## Region — rect algebra
+
+`Region(x, y, w, h)` is a frozen dataclass. All carving clamps to
+non-negative dimensions, so degenerate panels behave.
+
+- Carving: `inset(dx, dy)`, `top_band(h)`, `bottom_band(h)`,
+  `middle(top_h, bottom_h)`, `left_col(w)`, `right_col(w)`,
+  `split_h(*weights, gap=0)`, `split_v(*weights, gap=0)`
+- Placement: `align_xy(w, h, align, valign)`, `center_xy(w, h)`,
+  `contains(w, h)`, `.center`, `.right`, `.bottom`
+
+Scoreboard-style layout:
+
+```python
+b = self.layout.bounds
+status = b.top_band(self.layout.px(7))
+detail = b.bottom_band(self.layout.px(7))
+score_area = b.middle(status.h, detail.h)
+away_slot, home_slot = b.left_col(b.h), b.right_col(b.h)
+```
+
+## Font ladders — discrete, never fractional
+
+Pixel fonts (BDF, PressStart2P) only look right at native/integer sizes, so
+fonts are never scaled continuously. A `FontLadder` is an ordered tuple of
+`FontStep(family, size_px)` rungs, largest first; fitting walks down until
+the measured text fits.
+
+- `LADDER_GRID` (default): X11 BDFs at native sizes — 10x20 → 9x18 → 9x15 →
+  8x13 → 7x13 → 6x13 → 6x12 → 6x10 → 6x9 → 5x8 → 5x7 → 4x6 → tom-thumb.
+  Body text, labels, multi-row content.
+- `LADDER_ARCADE`: PressStart2P at 32/24/16/8 (integer multiples of its 8px
+  grid). Headline text: clocks, scores.
+
+Custom ladders are just tuples — e.g. to add your plugin's registered font
+on top: `(FontStep("myplugin::digits", 16),) + LADDER_GRID`.
+
+## LayoutContext
+
+Built per (width, height); exposes facts and fit queries:
+
+- `bounds`, `width`, `height`, `aspect`
+- `tier` by height (`xs`≤16, `sm`≤32, `md`≤48, `lg`≤64, `xl`) and
+  `width_tier` (`narrow`≤64, `normal`≤128, `wide`≤256, `ultrawide`)
+- `is_wide_short` — aspect ≥ 2.5 and height ≤ 32 (the classic 128x32 shape)
+- `scale` — `min(w/design_w, h/design_h)` vs. your manifest's
+  `display.design_size` (default 128x32). **Geometry only** — gaps, icon
+  and logo sizes via `px(base, minimum, maximum)`; fonts use ladders.
+- `by_tier({"sm": 10, "lg": 18})` — value for the nearest defined tier
+  at-or-below the panel's tier.
+- `fit_text(text, box, ladder, ellipsis=True)` → `FitResult` — largest rung
+  that fits; ellipsizes as a last resort. Cached per (text, box, ladder).
+- `fit_lines(lines, box, ladder, spacing)` — every line fits the width and
+  the stack fits the height (measures the actual strings).
+- `font_for_rows(rows, box_h, ladder)` — largest rung whose line height
+  fits `rows` rows.
+
+`FitResult` carries the ready-to-use `font` (drops straight into
+`display_manager.draw_text(font=...)`), the possibly-ellipsized `text`,
+ink `width`/`height`, `baseline`, `y_offset`, `line_height`, and `fits`.
+
+## Manifest declaration
+
+Declare the size your layout was authored against so `ctx.scale` means
+something:
+
+```json
+"display": { "design_size": { "width": 128, "height": 32 } }
+```
+
+Also available under `requires.display_size`: `min_width`, `min_height`,
+`max_width`, `max_height`.
+
+## Performance notes (Pi)
+
+Fit queries are cached, so cost is O(unique strings). For per-second text
+(clocks, live scores), fit on a **shape placeholder** and reuse the font:
+
+```python
+fit = self.layout.fit_text("00:00", box, ladder=LADDER_ARCADE)  # cached once
+self.display_manager.draw_text(current_time, font=fit.font, ...)
+```
+
+## Testing across sizes
+
+The harness already renders every plugin at a spread of sizes (now
+including 96x48):
+
+```bash
+python scripts/check_plugin.py <plugin-dir> --sizes 64x32,128x32,96x48,128x64,256x64
+python scripts/render_plugin.py <plugin-dir> --width 96 --height 48
+```
+
+`BoundsCheckingDisplayManager` flags right/bottom overflow and now records
+mediated draw calls with negative coordinates in
+`negative_coordinate_calls` (raw-PIL draws remain uncovered).
+
+Reference migration: the **text-display** plugin's `font_mode: "auto"`.

schema/manifest_schema.json

@@ -90,11 +90,40 @@
             "min_height": {
               "type": "integer",
               "minimum": 1
+            },
+            "max_width": {
+              "type": "integer",
+              "minimum": 1
+            },
+            "max_height": {
+              "type": "integer",
+              "minimum": 1
             }
           }
         }
       }
     },
+    "display": {
+      "type": "object",
+      "properties": {
+        "design_size": {
+          "type": "object",
+          "properties": {
+            "width": {
+              "type": "integer",
+              "minimum": 8
+            },
+            "height": {
+              "type": "integer",
+              "minimum": 8
+            }
+          },
+          "required": ["width", "height"],
+          "description": "Panel size the plugin's layout was authored against; core derives the adaptive-layout scale factor from it. Defaults to 128x32 when omitted."
+        }
+      },
+      "description": "Display/layout hints for the adaptive layout system"
+    },
     "config_schema": {
       "type": "string",
       "description": "Path to configuration schema file"

src/adaptive_layout.py

@@ -0,0 +1,464 @@
+"""
+Adaptive layout and font scaling helpers for plugins.
+
+Generalizes the three size-adaptation patterns proven in the plugin
+ecosystem into small composable core helpers, so plugins render legibly on
+any panel size (64x32, 128x32, 96x48, 128x64, 256x64, ...) without
+hand-tuned per-display layouts:
+
+- Region: integer rect algebra (bands, columns, weighted splits, centering).
+  Regions partition space, so text bands can't overlap by construction —
+  replacing the magic ``y = 1`` / ``y = height - 7`` offsets tuned for 128x32.
+- Font ladders: ordered (family, size) steps known to render crisply.
+  Pixel fonts (BDF, PressStart2P) only look right at native/integer sizes,
+  so fonts are never scaled continuously — fitting walks a ladder from the
+  largest rung down until the measured text fits the target box. This is
+  baseball-scoreboard's fallback-ladder pattern promoted to core.
+- LayoutContext: per-(width, height) facts — breakpoint tiers
+  (masters-tournament's pattern), a geometry scale factor vs. a declared
+  design size (f1-scoreboard's pattern), and cached fit-text queries.
+
+Everything is opt-in: plugins get a context via ``self.layout`` on
+BasePlugin (or construct one directly) and existing plugins are unaffected.
+
+Fonts are resolved through FontManager's catalog (family names are
+lowercased file stems from assets/fonts, e.g. "9x15", "tom-thumb", plus
+aliases like "press_start"). FitResult.font is a plain PIL font or
+freetype.Face, so it drops straight into DisplayManager.draw_text().
+"""
+
+import logging
+from dataclasses import dataclass, field
+from typing import Any, Dict, List, Optional, Sequence, Tuple, Union
+
+import freetype
+
+logger = logging.getLogger(__name__)
+
+# Height-based breakpoint tiers, smallest to largest. A 32px-tall panel is
+# the ecosystem baseline ("sm"); 96x48 lands in "md"; 128x64 in "lg".
+_HEIGHT_TIERS: Tuple[Tuple[str, int], ...] = (
+    ("xs", 16), ("sm", 32), ("md", 48), ("lg", 64), ("xl", 10 ** 9),
+)
+TIER_ORDER: Tuple[str, ...] = tuple(name for name, _ in _HEIGHT_TIERS)
+
+_WIDTH_TIERS: Tuple[Tuple[str, int], ...] = (
+    ("narrow", 64), ("normal", 128), ("wide", 256), ("ultrawide", 10 ** 9),
+)
+WIDTH_TIER_ORDER: Tuple[str, ...] = tuple(name for name, _ in _WIDTH_TIERS)
+
+# The panel size most existing plugins were authored against.
+DEFAULT_DESIGN_SIZE: Tuple[int, int] = (128, 32)
+
+
+@dataclass(frozen=True)
+class Region:
+    """An integer rectangle. Carving methods return sub-Regions clamped to
+    non-negative dimensions, so degenerate panels never produce negative
+    boxes — a band request larger than the region simply consumes it all."""
+
+    x: int
+    y: int
+    w: int
+    h: int
+
+    def __post_init__(self):
+        object.__setattr__(self, "w", max(0, int(self.w)))
+        object.__setattr__(self, "h", max(0, int(self.h)))
+        object.__setattr__(self, "x", int(self.x))
+        object.__setattr__(self, "y", int(self.y))
+
+    @property
+    def right(self) -> int:
+        return self.x + self.w
+
+    @property
+    def bottom(self) -> int:
+        return self.y + self.h
+
+    @property
+    def center(self) -> Tuple[int, int]:
+        return (self.x + self.w // 2, self.y + self.h // 2)
+
+    # ---- carving -----------------------------------------------------
+
+    def inset(self, dx: int, dy: Optional[int] = None) -> "Region":
+        """Shrink by dx horizontally and dy (default dx) vertically, each side."""
+        if dy is None:
+            dy = dx
+        return Region(self.x + dx, self.y + dy, self.w - 2 * dx, self.h - 2 * dy)
+
+    def top_band(self, h: int) -> "Region":
+        return Region(self.x, self.y, self.w, min(h, self.h))
+
+    def bottom_band(self, h: int) -> "Region":
+        h = min(h, self.h)
+        return Region(self.x, self.bottom - h, self.w, h)
+
+    def middle(self, top_h: int = 0, bottom_h: int = 0) -> "Region":
+        """What remains between a top band and a bottom band."""
+        return Region(self.x, self.y + top_h, self.w, self.h - top_h - bottom_h)
+
+    def left_col(self, w: int) -> "Region":
+        return Region(self.x, self.y, min(w, self.w), self.h)
+
+    def right_col(self, w: int) -> "Region":
+        w = min(w, self.w)
+        return Region(self.right - w, self.y, w, self.h)
+
+    def split_h(self, *weights: float, gap: int = 0) -> List["Region"]:
+        """Side-by-side columns sized by weight; gaps between them."""
+        sizes = _weighted_sizes(self.w, weights, gap)
+        cols, cursor = [], self.x
+        for size in sizes:
+            cols.append(Region(cursor, self.y, size, self.h))
+            cursor += size + gap
+        return cols
+
+    def split_v(self, *weights: float, gap: int = 0) -> List["Region"]:
+        """Stacked rows sized by weight; gaps between them."""
+        sizes = _weighted_sizes(self.h, weights, gap)
+        rows, cursor = [], self.y
+        for size in sizes:
+            rows.append(Region(self.x, cursor, self.w, size))
+            cursor += size + gap
+        return rows
+
+    # ---- placement ---------------------------------------------------
+
+    def align_xy(self, w: int, h: int, align: str = "center",
+                 valign: str = "center") -> Tuple[int, int]:
+        """Top-left position for a w x h box aligned within this region.
+        align: left|center|right; valign: top|center|bottom."""
+        if align == "left":
+            x = self.x
+        elif align == "right":
+            x = self.right - w
+        else:
+            x = self.x + (self.w - w) // 2
+        if valign == "top":
+            y = self.y
+        elif valign == "bottom":
+            y = self.bottom - h
+        else:
+            y = self.y + (self.h - h) // 2
+        return (x, y)
+
+    def center_xy(self, w: int, h: int) -> Tuple[int, int]:
+        return self.align_xy(w, h)
+
+    def contains(self, w: int, h: int) -> bool:
+        return w <= self.w and h <= self.h
+
+
+def _weighted_sizes(total: int, weights: Sequence[float], gap: int) -> List[int]:
+    """Integer sizes proportional to weights, remainder spread left-to-right."""
+    if not weights:
+        return []
+    usable = max(0, total - gap * (len(weights) - 1))
+    weight_sum = sum(weights) or 1
+    sizes = [int(usable * w / weight_sum) for w in weights]
+    remainder = usable - sum(sizes)
+    for i in range(remainder):
+        sizes[i % len(sizes)] += 1
+    return sizes
+
+
+# ---------------------------------------------------------------------------
+# Font ladders
+# ---------------------------------------------------------------------------
+
+@dataclass(frozen=True)
+class FontStep:
+    """One rung: a FontManager catalog family at a size it renders crisply."""
+    family: str
+    size_px: int
+
+
+FontLadder = Tuple[FontStep, ...]
+
+# X11 BDF bitmap fonts at their native pixel sizes, largest to smallest —
+# baseball-scoreboard's fallback ladder extended upward. Same-height rungs
+# are ordered widest first so width-constrained text steps to a narrower
+# face before dropping a size.
+LADDER_GRID: FontLadder = (
+    FontStep("10x20", 20),
+    FontStep("9x18", 18),
+    FontStep("9x15", 15),
+    FontStep("8x13", 13),
+    FontStep("7x13", 13),
+    FontStep("6x13", 13),
+    FontStep("6x12", 12),
+    FontStep("6x10", 10),
+    FontStep("6x9", 9),
+    FontStep("5x8", 8),
+    FontStep("5x7", 7),
+    FontStep("4x6", 6),
+    FontStep("tom-thumb", 6),
+)
+
+# PressStart2P at integer multiples of its 8px pixel grid only — fractional
+# sizes blur a pixel font. For headline text (clocks, scores).
+LADDER_ARCADE: FontLadder = (
+    FontStep("press_start", 32),
+    FontStep("press_start", 24),
+    FontStep("press_start", 16),
+    FontStep("press_start", 8),
+)
+
+LADDER_DEFAULT: FontLadder = LADDER_GRID
+
+ELLIPSIS = "…"
+
+
+@dataclass(frozen=True)
+class FitResult:
+    """A fitted font plus the ink metrics of the (possibly ellipsized) text.
+
+    ``y_offset`` is the gap between the y passed to draw_text() and where
+    ink actually starts; subtract it from the desired ink-top position when
+    drawing (draw_fitted_text does this for you).
+    """
+    font: Any
+    family: str
+    size_px: int
+    text: str
+    width: int
+    height: int
+    baseline: int
+    y_offset: int
+    fits: bool
+    line_height: int = 0
+
+
+def measure_ink(text: str, font: Any) -> Tuple[int, int, int, int]:
+    """Measure the ink box of text: (width, height, baseline, y_offset).
+
+    y_offset is the distance from the y coordinate DisplayManager.draw_text()
+    is given to the top of the actual ink — PIL draws TTF from the em-box
+    top and _draw_bdf_text derives the baseline from y + ascender, so both
+    leave a font-dependent gap that matters when centering in short bands.
+    """
+    if isinstance(font, freetype.Face):
+        width = 0
+        ascender = font.size.ascender >> 6
+        ink_top, ink_bottom = None, None
+        for char in text:
+            font.load_char(char)
+            width += font.glyph.advance.x >> 6
+            rows = font.glyph.bitmap.rows
+            if rows:
+                top = ascender - font.glyph.bitmap_top
+                ink_top = top if ink_top is None else min(ink_top, top)
+                ink_bottom = top + rows if ink_bottom is None else max(ink_bottom, top + rows)
+        if ink_top is None:
+            ink_top, ink_bottom = 0, 0
+        return (width, ink_bottom - ink_top, ascender, ink_top)
+    bbox = font.getbbox(text)
+    return (bbox[2] - bbox[0], bbox[3] - bbox[1], -bbox[1], bbox[1])
+
+
+def font_line_height(font: Any) -> int:
+    """Recommended line spacing for a font (matches DisplayManager.get_font_height)."""
+    if isinstance(font, freetype.Face):
+        return font.size.height >> 6
+    ascent, descent = font.getmetrics()
+    return ascent + descent
+
+
+class LayoutContext:
+    """Per-render-size layout facts and fit-text queries for one panel size.
+
+    Construct once per (width, height); BasePlugin.layout does this and
+    rebuilds automatically when the logical display size changes.
+    """
+
+    def __init__(self, width: int, height: int, font_manager: Any,
+                 design_size: Tuple[int, int] = DEFAULT_DESIGN_SIZE):
+        self.width = int(width)
+        self.height = int(height)
+        self.font_manager = font_manager
+        self.design_size = design_size
+        self.bounds = Region(0, 0, self.width, self.height)
+        self.aspect = self.width / max(1, self.height)
+        self.tier = _pick_tier(_HEIGHT_TIERS, self.height)
+        self.width_tier = _pick_tier(_WIDTH_TIERS, self.width)
+        self.is_wide_short = self.aspect >= 2.5 and self.height <= 32
+        design_w, design_h = design_size
+        # Geometry scale only (gaps, icon/logo sizes) — never applied to
+        # fonts, which step between crisp ladder rungs instead.
+        self.scale = min(self.width / max(1, design_w),
+                         self.height / max(1, design_h))
+        self._fit_cache: Dict[Any, FitResult] = {}
+
+    # ---- the three adaptation patterns --------------------------------
+
+    def px(self, base: int, minimum: int = 1, maximum: Optional[int] = None) -> int:
+        """Scale a design-size pixel measurement (f1's pattern): gaps,
+        icon sizes, logo slots. Clamped to [minimum, maximum]."""
+        value = max(minimum, round(base * self.scale))
+        if maximum is not None:
+            value = min(value, maximum)
+        return value
+
+    def by_tier(self, mapping: Dict[str, Any], default: Any = None) -> Any:
+        """Pick the value for the nearest defined tier at-or-below the
+        panel's height tier (masters' pattern). Falls forward to the
+        smallest defined tier above, then to default.
+
+        by_tier({"sm": 10, "lg": 18}) -> 10 on 128x32, 18 on 128x64.
+        Keys may also use width tiers ("narrow", "wide", ...)."""
+        order = TIER_ORDER if any(k in TIER_ORDER for k in mapping) else WIDTH_TIER_ORDER
+        current = self.tier if order is TIER_ORDER else self.width_tier
+        idx = order.index(current)
+        for name in reversed(order[: idx + 1]):
+            if name in mapping:
+                return mapping[name]
+        for name in order[idx + 1:]:
+            if name in mapping:
+                return mapping[name]
+        return default
+
+    def fit_text(self, text: str, box: Union[Region, Tuple[int, int]],
+                 ladder: FontLadder = LADDER_DEFAULT,
+                 ellipsis: bool = True) -> FitResult:
+        """Largest ladder rung whose rendered text fits the box (baseball's
+        pattern). If even the smallest rung is too wide, the text is
+        ellipsized to fit (unless ellipsis=False); fits=False only when no
+        acceptable rendering exists."""
+        box_w, box_h = _box_dims(box)
+        key = ("text", text, box_w, box_h, ladder, ellipsis)
+        cached = self._fit_cache.get(key)
+        if cached is not None:
+            return cached
+
+        result = None
+        for step in ladder:
+            font = self.font_manager.get_font(step.family, step.size_px)
+            width, height, baseline, y_offset = measure_ink(text, font)
+            result = FitResult(font, step.family, step.size_px, text,
+                               width, height, baseline, y_offset,
+                               fits=(width <= box_w and height <= box_h),
+                               line_height=font_line_height(font))
+            if result.fits:
+                break
+
+        if result is not None and not result.fits and ellipsis:
+            short = self.ellipsize(text, result.font, box_w)
+            width, height, baseline, y_offset = measure_ink(short, result.font)
+            result = FitResult(result.font, result.family, result.size_px,
+                               short, width, height, baseline, y_offset,
+                               fits=(width <= box_w and height <= box_h),
+                               line_height=result.line_height)
+
+        self._fit_cache[key] = result
+        return result
+
+    def fit_lines(self, lines: Sequence[str], box: Union[Region, Tuple[int, int]],
+                  ladder: FontLadder = LADDER_DEFAULT,
+                  spacing: int = 1) -> FitResult:
+        """Largest rung where every line fits the box width and the stacked
+        lines (line_height + spacing apart) fit the box height. Measures the
+        actual strings, so a long line pushes the ladder down a rung a short
+        one wouldn't (baseball's multiline pattern). Text is the widest line."""
+        box_w, box_h = _box_dims(box)
+        key = ("lines", tuple(lines), box_w, box_h, ladder, spacing)
+        cached = self._fit_cache.get(key)
+        if cached is not None:
+            return cached
+
+        rows = max(1, len(lines))
+        result = None
+        for step in ladder:
+            font = self.font_manager.get_font(step.family, step.size_px)
+            line_h = font_line_height(font)
+            widest, metrics = "", (0, 0, 0, 0)
+            for line in lines:
+                m = measure_ink(line, font)
+                if m[0] >= metrics[0]:
+                    widest, metrics = line, m
+            total_h = rows * line_h + (rows - 1) * spacing
+            result = FitResult(font, step.family, step.size_px, widest,
+                               metrics[0], metrics[1], metrics[2], metrics[3],
+                               fits=(metrics[0] <= box_w and total_h <= box_h),
+                               line_height=line_h)
+            if result.fits:
+                break
+
+        self._fit_cache[key] = result
+        return result
+
+    def font_for_rows(self, rows: int, box_h: int,
+                      ladder: FontLadder = LADDER_GRID) -> FitResult:
+        """Largest rung whose line height lets `rows` rows fit in box_h
+        (baseball's traditional-scoreboard pattern). Measures a digit/cap
+        sample rather than specific strings."""
+        key = ("rows", rows, box_h, ladder)
+        cached = self._fit_cache.get(key)
+        if cached is not None:
+            return cached
+
+        sample = "0Ay"
+        result = None
+        for step in ladder:
+            font = self.font_manager.get_font(step.family, step.size_px)
+            line_h = font_line_height(font)
+            width, height, baseline, y_offset = measure_ink(sample, font)
+            result = FitResult(font, step.family, step.size_px, sample,
+                               width, height, baseline, y_offset,
+                               fits=(max(1, rows) * line_h <= box_h),
+                               line_height=line_h)
+            if result.fits:
+                break
+
+        self._fit_cache[key] = result
+        return result
+
+    # ---- text utilities ------------------------------------------------
+
+    def ellipsize(self, text: str, font: Any, max_w: int) -> str:
+        """Trim text to fit max_w, appending an ellipsis. Returns '' when
+        not even the ellipsis fits."""
+        if measure_ink(text, font)[0] <= max_w:
+            return text
+        for end in range(len(text) - 1, 0, -1):
+            candidate = text[:end].rstrip() + ELLIPSIS
+            if measure_ink(candidate, font)[0] <= max_w:
+                return candidate
+        return ELLIPSIS if measure_ink(ELLIPSIS, font)[0] <= max_w else ""
+
+    def measure(self, text: str, font: Any) -> Tuple[int, int, int]:
+        """Ink (width, height, baseline) of text — see measure_ink."""
+        width, height, baseline, _ = measure_ink(text, font)
+        return (width, height, baseline)
+
+    def clear_cache(self) -> None:
+        """Drop cached fit results (call after fonts are reloaded)."""
+        self._fit_cache.clear()
+
+
+def _pick_tier(tiers: Tuple[Tuple[str, int], ...], value: int) -> str:
+    for name, limit in tiers:
+        if value <= limit:
+            return name
+    return tiers[-1][0]
+
+
+def _box_dims(box: Union[Region, Tuple[int, int]]) -> Tuple[int, int]:
+    if isinstance(box, Region):
+        return (box.w, box.h)
+    w, h = box
+    return (int(w), int(h))
+
+
+def draw_fitted_text(display_manager: Any, fit: FitResult,
+                     box: Union[Region, Tuple[int, int]],
+                     color: Tuple[int, int, int] = (255, 255, 255),
+                     align: str = "center", valign: str = "center") -> None:
+    """Draw a FitResult's text aligned within a Region via
+    DisplayManager.draw_text(), compensating for the font's ink offset so
+    the ink (not the em box) is what gets aligned."""
+    region = box if isinstance(box, Region) else Region(0, 0, box[0], box[1])
+    x, y = region.align_xy(fit.width, fit.height, align, valign)
+    display_manager.draw_text(fit.text, x=x, y=y - fit.y_offset,
+                              color=color, font=fit.font)

src/common/text_helper.py

@@ -11,6 +11,9 @@ from typing import Dict, List, Optional, Tuple, Union
 
 from PIL import Image, ImageDraw, ImageFont
 
+# Shared throwaway draw surface for measuring text without a target canvas.
+_measure_draw = ImageDraw.Draw(Image.new("RGB", (1, 1)))
+
 
 class TextHelper:
     """
@@ -112,10 +115,10 @@ class TextHelper:
             Width in pixels
         """
         try:
-            return draw.textlength(text, font=font)
+            return int(_measure_draw.textlength(text, font=font))
         except AttributeError:
             # Fallback for older PIL versions
-            bbox = draw.textbbox((0, 0), text, font=font)
+            bbox = _measure_draw.textbbox((0, 0), text, font=font)
             return bbox[2] - bbox[0]
     
     def get_text_height(self, text: str, font: ImageFont.ImageFont) -> int:
@@ -129,13 +132,8 @@ class TextHelper:
         Returns:
             Height in pixels
         """
-        try:
+        bbox = _measure_draw.textbbox((0, 0), text, font=font)
-            bbox = draw.textbbox((0, 0), text, font=font)
+        return bbox[3] - bbox[1]
-            return bbox[3] - bbox[1]
-        except AttributeError:
-            # Fallback for older PIL versions
-            bbox = draw.textbbox((0, 0), text, font=font)
-            return bbox[3] - bbox[1]
     
     def get_text_dimensions(self, text: str, font: ImageFont.ImageFont) -> Tuple[int, int]:
         """

src/font_manager.py

@@ -103,6 +103,10 @@ class FontManager:
         # Font overrides storage (for manual overrides)
         self.font_overrides_file = "config/font_overrides.json"
         self.font_overrides: Dict[str, Dict[str, Any]] = {}
+
+        # Bumped whenever cached font objects are invalidated, so holders of
+        # derived caches (e.g. adaptive-layout fit results) know to rebuild.
+        self.cache_generation = 0
         
         self._initialize_fonts()
     
@@ -112,6 +116,7 @@ class FontManager:
         self.fonts_config = new_config.get("fonts", {})
         self.font_cache.clear()  # Clear cache to force reload
         self.metrics_cache.clear()  # Clear metrics cache
+        self.cache_generation += 1
         self._initialize_fonts()
         logger.info("FontManager configuration reloaded successfully")
 
@@ -482,6 +487,14 @@ class FontManager:
     def _load_bdf_font(self, font_path: str, size_px: int) -> freetype.Face:
         """Load a BDF font using FreeType."""
         try:
+            native_size = self._read_bdf_native_size(font_path)
+            if native_size is not None and native_size != size_px:
+                # BDF is a fixed-strike bitmap format: FreeType renders the
+                # native size no matter what set_char_size asks for.
+                logger.debug(
+                    "BDF font %s requested at %spx but renders at its native "
+                    "%spx", font_path, size_px, native_size
+                )
             face = freetype.Face(font_path)
             # Set character size (width, height) in 1/64th of points
             face.set_char_size(size_px * 64, size_px * 64, 72, 72)
@@ -490,6 +503,41 @@ class FontManager:
             logger.error(f"Error loading BDF font {font_path}: {e}")
             raise
 
+    def get_native_bdf_size(self, family: str) -> Optional[int]:
+        """The one true pixel size of a BDF family in the catalog, or None
+        for scalable (TTF) families / unknown families."""
+        font_path = self.font_catalog.get(family)
+        if not font_path or not font_path.endswith('.bdf'):
+            return None
+        return self._read_bdf_native_size(font_path)
+
+    @staticmethod
+    def _read_bdf_native_size(bdf_path: str) -> Optional[int]:
+        """Read a BDF file's own header to find its one true pixel size.
+        Prefers the PIXEL_SIZE property, which states the real pixel height
+        directly; falls back to the SIZE line's point-size only if PIXEL_SIZE
+        is absent, since point-size only equals pixel height at exactly
+        100dpi — several bundled fonts (e.g. 6x13.bdf, 5x8.bdf) are defined
+        at 75dpi, where the two values genuinely differ."""
+        size_line_value = None
+        try:
+            with open(bdf_path, "r", encoding="ascii", errors="ignore") as f:
+                for line in f:
+                    if line.startswith("PIXEL_SIZE"):
+                        parts = line.split()
+                        if len(parts) >= 2:
+                            return int(float(parts[1]))
+                    elif line.startswith("SIZE") and size_line_value is None:
+                        # Format: "SIZE <point_size> <xres> <yres>"
+                        parts = line.split()
+                        if len(parts) >= 2:
+                            size_line_value = int(float(parts[1]))
+                    elif line.startswith("STARTCHAR"):
+                        break
+        except (OSError, ValueError):
+            return None
+        return size_line_value
+
     def _get_fallback_font(self) -> ImageFont.ImageFont:
         """Get a fallback font when loading fails."""
         return ImageFont.load_default()

src/plugin_system/base_plugin.py

@@ -15,6 +15,19 @@ import logging
 from src.logging_config import get_logger
 
 
+_shared_fallback_font_manager: Optional[Any] = None
+
+
+def _fallback_font_manager() -> Any:
+    """Shared FontManager for environments (unit tests, mocks) where the
+    plugin manager doesn't carry one. Scans assets/fonts like the real one."""
+    global _shared_fallback_font_manager
+    if _shared_fallback_font_manager is None:
+        from src.font_manager import FontManager
+        _shared_fallback_font_manager = FontManager({})
+    return _shared_fallback_font_manager
+
+
 class VegasDisplayMode(Enum):
     """
     Display mode for Vegas scroll integration.
@@ -130,6 +143,97 @@ class BasePlugin(ABC):
         """
         raise NotImplementedError("Plugins must implement display()")
 
+    # -------------------------------------------------------------------------
+    # Adaptive layout support (opt-in)
+    # -------------------------------------------------------------------------
+    @property
+    def layout(self) -> Any:
+        """
+        LayoutContext for the current logical display size.
+
+        Lazily built and rebuilt automatically when the display size changes
+        (e.g. Vegas segment widths, double-sided logical screens). Provides
+        Region carving (self.layout.bounds), breakpoint tiers, a geometry
+        scale factor vs. the manifest's display.design_size, and fit-text
+        queries against font ladders. See src/adaptive_layout.py.
+
+        Example:
+            rows = self.layout.bounds.inset(1).split_v(3, 1, gap=1)
+            self.draw_fit(big_text, rows[0], ladder=LADDER_ARCADE)
+            self.draw_fit(small_text, rows[1])
+        """
+        from src.adaptive_layout import LayoutContext
+
+        width = getattr(self.display_manager, "width", None)
+        height = getattr(self.display_manager, "height", None)
+        if not width or not height:
+            matrix = getattr(self.display_manager, "matrix", None)
+            width = getattr(matrix, "width", 128)
+            height = getattr(matrix, "height", 32)
+
+        font_manager = self._get_font_manager()
+        generation = getattr(font_manager, "cache_generation", 0)
+        cached = getattr(self, "_layout_context", None)
+        if (cached is not None
+                and (cached.width, cached.height) == (width, height)
+                and getattr(self, "_layout_font_generation", None) == generation):
+            return cached
+
+        context = LayoutContext(
+            width, height, font_manager,
+            design_size=self._get_design_size(),
+        )
+        self._layout_context = context
+        self._layout_font_generation = generation
+        return context
+
+    def draw_fit(self, text: str, box: Any,
+                 color: tuple = (255, 255, 255),
+                 ladder: Optional[Any] = None,
+                 align: str = "center", valign: str = "center") -> Any:
+        """
+        Fit text to a Region with the largest crisp font that fits, then draw
+        it aligned within that region via the display manager.
+
+        Args:
+            text: Text to display (ellipsized if even the smallest rung is too wide)
+            box: Region (or (w, h) tuple anchored at 0,0) to fit and align within
+            color: RGB color tuple
+            ladder: FontLadder to walk (default LADDER_GRID; use LADDER_ARCADE
+                    for headline text like clocks and scores)
+            align/valign: alignment of the text ink within the box
+
+        Returns:
+            FitResult (font, family, size_px, text, ink metrics, fits flag)
+        """
+        from src.adaptive_layout import LADDER_DEFAULT, draw_fitted_text
+
+        fit = self.layout.fit_text(text, box, ladder=ladder or LADDER_DEFAULT)
+        draw_fitted_text(self.display_manager, fit, box,
+                         color=color, align=align, valign=valign)
+        return fit
+
+    def _get_font_manager(self) -> Any:
+        """The shared FontManager, or a module-level fallback when running
+        under mocks/harnesses that don't provide one."""
+        font_manager = getattr(self.plugin_manager, "font_manager", None)
+        if font_manager is not None and hasattr(font_manager, "get_font"):
+            return font_manager
+        return _fallback_font_manager()
+
+    def _get_design_size(self) -> tuple:
+        """Panel size this plugin's layout was authored against, from the
+        manifest's optional display.design_size (defaults to 128x32)."""
+        from src.adaptive_layout import DEFAULT_DESIGN_SIZE
+
+        if self.plugin_manager and hasattr(self.plugin_manager, "plugin_manifests"):
+            manifest = self.plugin_manager.plugin_manifests.get(self.plugin_id, {})
+            declared = manifest.get("display", {}).get("design_size", {})
+            width, height = declared.get("width"), declared.get("height")
+            if width and height:
+                return (int(width), int(height))
+        return DEFAULT_DESIGN_SIZE
+
     def get_display_duration(self) -> float:
         """
         Get the display duration for this plugin instance.

src/plugin_system/testing/bounds_display_manager.py

@@ -10,8 +10,11 @@ that don't scale down to a smaller panel.
 
 Limitations (documented on purpose):
 - Overflow past the LEFT or TOP edge (negative coordinates) is still clipped by
-  PIL and not detected here. The dominant real-world breakage is content that is
+  PIL and not detected pixel-wise here. The dominant real-world breakage is
-  too wide/tall for a smaller panel, which this catches.
+  content that is too wide/tall for a smaller panel, which this catches.
+  As a partial net, draw_text/draw_image calls made with negative coordinates
+  through this manager are recorded in `negative_coordinate_calls` — but draws
+  made directly on the raw PIL canvas remain uncovered.
 - BDF text is clipped to the declared bounds by the parent's bitmap drawer, so
   BDF overflow is not flagged. Golden-image regression covers those plugins.
 - If a plugin replaces the canvas with its own image (display_manager.image = ...),
@@ -56,6 +59,21 @@ class BoundsCheckingDisplayManager(VisualTestDisplayManager):
         super().__init__(self._canvas_width, self._canvas_height)
         # Plugins must see the DECLARED size, not the padded canvas size.
         self.matrix = _MatrixProxy(self._declared_width, self._declared_height)
+        # (text-or-'image', x, y) for every mediated draw call given a
+        # negative coordinate — PIL clips these silently, so record them.
+        self.negative_coordinate_calls: list = []
+
+    # -- negative-coordinate (left/top overflow) recording --
+
+    def draw_text(self, text, x=None, y=None, *args, **kwargs):
+        if (x is not None and x < 0) or (y is not None and y < 0):
+            self.negative_coordinate_calls.append((text, x, y))
+        return super().draw_text(text, x, y, *args, **kwargs)
+
+    def draw_image(self, image, x, y, *args, **kwargs):
+        if x < 0 or y < 0:
+            self.negative_coordinate_calls.append(('image', x, y))
+        return super().draw_image(image, x, y, *args, **kwargs)
 
     # -- declared dimensions (override parent's image-derived properties) --
 

src/plugin_system/testing/mocks.py

@@ -161,6 +161,13 @@ class MockPluginManager:
         self.plugin_manifests: Dict[str, Dict] = {}
         self.get_plugin_calls = []
         self.get_all_plugins_calls = []
+        # Real FontManager so BasePlugin.layout / draw_fit behave identically
+        # under the harness (it only needs assets/fonts on disk).
+        try:
+            from src.font_manager import FontManager
+            self.font_manager: Optional[Any] = FontManager({})
+        except Exception:
+            self.font_manager = None
     
     def get_plugin(self, plugin_id: str) -> Optional[Any]:
         """Get a plugin instance."""

src/plugin_system/testing/sizes.py

@@ -28,6 +28,7 @@ DEFAULT_TEST_SIZES: List[Tuple[int, int]] = [
     (64, 32),    # 1x1 — single panel, the tightest common rectangle
     (128, 32),   # 2x1 — the baseline most plugins are tuned for
     (64, 64),    # 1x2 — stacked, exercises tall-narrow centering
+    (96, 48),    # non-64x32-module panel (e.g. Waveshare), off-grid dims
     (128, 64),   # 2x2 — block, icon scaling / vertical centering
     (256, 32),   # 4x1 — long strip, wide horizontal layout
     (128, 96),   # 2x3 — tall, exercises vertical overflow

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