feat(pipeline): add Canvas and FontStage for rendering

- Add Canvas class for 2D surface management
- Add CanvasStage for pipeline integration
- Add FontStage as Transform for font rendering
- Update Camera with x, y, w, h, zoom and guardrails
- Add get_dimensions() to Display protocol

engine/camera.py

@@ -6,6 +6,8 @@ Provides abstraction for camera motion in different modes:
 - Horizontal: left/right movement
 - Omni: combination of both
 - Floating: sinusoidal/bobbing motion
+
+The camera defines a visible viewport into a larger Canvas.
 """
 
 import math
@@ -21,15 +23,32 @@ class CameraMode(Enum):
     FLOATING = auto()
 
 
+@dataclass
+class CameraViewport:
+    """Represents the visible viewport."""
+
+    x: int
+    y: int
+    width: int
+    height: int
+
+
 @dataclass
 class Camera:
     """Camera for viewport scrolling.
 
+    The camera defines a visible viewport into a Canvas.
+    It can be smaller than the canvas to allow scrolling,
+    and supports zoom to scale the view.
+
     Attributes:
         x: Current horizontal offset (positive = scroll left)
         y: Current vertical offset (positive = scroll up)
         mode: Current camera mode
         speed: Base scroll speed
+        zoom: Zoom factor (1.0 = 100%, 2.0 = 200% zoom out)
+        canvas_width: Width of the canvas being viewed
+        canvas_height: Height of the canvas being viewed
         custom_update: Optional custom update function
     """
 
@@ -37,9 +56,65 @@ class Camera:
     y: int = 0
     mode: CameraMode = CameraMode.VERTICAL
     speed: float = 1.0
+    zoom: float = 1.0
+    canvas_width: int = 200  # Larger than viewport for scrolling
+    canvas_height: int = 200
     custom_update: Callable[["Camera", float], None] | None = None
     _time: float = field(default=0.0, repr=False)
 
+    @property
+    def w(self) -> int:
+        """Shorthand for viewport_width."""
+        return self.viewport_width
+
+    @property
+    def h(self) -> int:
+        """Shorthand for viewport_height."""
+        return self.viewport_height
+
+    @property
+    def viewport_width(self) -> int:
+        """Get the visible viewport width.
+
+        This is the canvas width divided by zoom.
+        """
+        return max(1, int(self.canvas_width / self.zoom))
+
+    @property
+    def viewport_height(self) -> int:
+        """Get the visible viewport height.
+
+        This is the canvas height divided by zoom.
+        """
+        return max(1, int(self.canvas_height / self.zoom))
+
+    def get_viewport(self) -> CameraViewport:
+        """Get the current viewport bounds.
+
+        Returns:
+            CameraViewport with position and size (clamped to canvas bounds)
+        """
+        vw = self.viewport_width
+        vh = self.viewport_height
+
+        clamped_x = max(0, min(self.x, self.canvas_width - vw))
+        clamped_y = max(0, min(self.y, self.canvas_height - vh))
+
+        return CameraViewport(
+            x=clamped_x,
+            y=clamped_y,
+            width=vw,
+            height=vh,
+        )
+
+    def set_zoom(self, zoom: float) -> None:
+        """Set the zoom factor.
+
+        Args:
+            zoom: Zoom factor (1.0 = 100%, 2.0 = zoomed out 2x, 0.5 = zoomed in 2x)
+        """
+        self.zoom = max(0.1, min(10.0, zoom))
+
     def update(self, dt: float) -> None:
         """Update camera position based on mode.
 
@@ -61,6 +136,24 @@ class Camera:
         elif self.mode == CameraMode.FLOATING:
             self._update_floating(dt)
 
+        self._clamp_to_bounds()
+
+    def _clamp_to_bounds(self) -> None:
+        """Clamp camera position to stay within canvas bounds.
+
+        Only clamps if the viewport is smaller than the canvas.
+        If viewport equals canvas (no scrolling needed), allows any position
+        for backwards compatibility with original behavior.
+        """
+        vw = self.viewport_width
+        vh = self.viewport_height
+
+        # Only clamp if there's room to scroll
+        if vw < self.canvas_width:
+            self.x = max(0, min(self.x, self.canvas_width - vw))
+        if vh < self.canvas_height:
+            self.y = max(0, min(self.y, self.canvas_height - vh))
+
     def _update_vertical(self, dt: float) -> None:
         self.y += int(self.speed * dt * 60)
 
@@ -82,26 +175,42 @@ class Camera:
         self.x = 0
         self.y = 0
         self._time = 0.0
+        self.zoom = 1.0
+
+    def set_canvas_size(self, width: int, height: int) -> None:
+        """Set the canvas size and clamp position if needed.
+
+        Args:
+            width: New canvas width
+            height: New canvas height
+        """
+        self.canvas_width = width
+        self.canvas_height = height
+        self._clamp_to_bounds()
 
     @classmethod
     def vertical(cls, speed: float = 1.0) -> "Camera":
         """Create a vertical scrolling camera."""
-        return cls(mode=CameraMode.VERTICAL, speed=speed)
+        return cls(mode=CameraMode.VERTICAL, speed=speed, canvas_height=200)
 
     @classmethod
     def horizontal(cls, speed: float = 1.0) -> "Camera":
         """Create a horizontal scrolling camera."""
-        return cls(mode=CameraMode.HORIZONTAL, speed=speed)
+        return cls(mode=CameraMode.HORIZONTAL, speed=speed, canvas_width=200)
 
     @classmethod
     def omni(cls, speed: float = 1.0) -> "Camera":
         """Create an omnidirectional scrolling camera."""
-        return cls(mode=CameraMode.OMNI, speed=speed)
+        return cls(
+            mode=CameraMode.OMNI, speed=speed, canvas_width=200, canvas_height=200
+        )
 
     @classmethod
     def floating(cls, speed: float = 1.0) -> "Camera":
         """Create a floating/bobbing camera."""
-        return cls(mode=CameraMode.FLOATING, speed=speed)
+        return cls(
+            mode=CameraMode.FLOATING, speed=speed, canvas_width=200, canvas_height=200
+        )
 
     @classmethod
     def custom(cls, update_fn: Callable[["Camera", float], None]) -> "Camera":

engine/canvas.py

@@ -0,0 +1,146 @@
+"""
+Canvas - 2D surface for rendering.
+
+The Canvas represents a full rendered surface that can be larger than the display.
+The Camera then defines the visible viewport into this canvas.
+"""
+
+from dataclasses import dataclass
+
+
+@dataclass
+class CanvasRegion:
+    """A rectangular region on the canvas."""
+
+    x: int
+    y: int
+    width: int
+    height: int
+
+    def is_valid(self) -> bool:
+        """Check if region has positive dimensions."""
+        return self.width > 0 and self.height > 0
+
+
+class Canvas:
+    """2D canvas for rendering content.
+
+    The canvas is a 2D grid of cells that can hold text content.
+    It can be larger than the visible viewport (display).
+
+    Attributes:
+        width: Total width in characters
+        height: Total height in characters
+    """
+
+    def __init__(self, width: int = 80, height: int = 24):
+        self.width = width
+        self.height = height
+        self._grid: list[list[str]] = [
+            [" " for _ in range(width)] for _ in range(height)
+        ]
+
+    def clear(self) -> None:
+        """Clear the entire canvas."""
+        self._grid = [[" " for _ in range(self.width)] for _ in range(self.height)]
+
+    def get_region(self, x: int, y: int, width: int, height: int) -> list[list[str]]:
+        """Get a rectangular region from the canvas.
+
+        Args:
+            x: Left position
+            y: Top position
+            width: Region width
+            height: Region height
+
+        Returns:
+            2D list of characters (height rows, width columns)
+        """
+        region: list[list[str]] = []
+        for py in range(y, y + height):
+            row: list[str] = []
+            for px in range(x, x + width):
+                if 0 <= py < self.height and 0 <= px < self.width:
+                    row.append(self._grid[py][px])
+                else:
+                    row.append(" ")
+            region.append(row)
+        return region
+
+    def get_region_flat(self, x: int, y: int, width: int, height: int) -> list[str]:
+        """Get a rectangular region as flat list of lines.
+
+        Args:
+            x: Left position
+            y: Top position
+            width: Region width
+            height: Region height
+
+        Returns:
+            List of strings (one per row)
+        """
+        region = self.get_region(x, y, width, height)
+        return ["".join(row) for row in region]
+
+    def put_region(self, x: int, y: int, content: list[list[str]]) -> None:
+        """Put content into a rectangular region on the canvas.
+
+        Args:
+            x: Left position
+            y: Top position
+            content: 2D list of characters to place
+        """
+        for py, row in enumerate(content):
+            for px, char in enumerate(row):
+                canvas_x = x + px
+                canvas_y = y + py
+                if 0 <= canvas_y < self.height and 0 <= canvas_x < self.width:
+                    self._grid[canvas_y][canvas_x] = char
+
+    def put_text(self, x: int, y: int, text: str) -> None:
+        """Put a single line of text at position.
+
+        Args:
+            x: Left position
+            y: Row position
+            text: Text to place
+        """
+        for i, char in enumerate(text):
+            canvas_x = x + i
+            if 0 <= canvas_x < self.width and 0 <= y < self.height:
+                self._grid[y][canvas_x] = char
+
+    def fill(self, x: int, y: int, width: int, height: int, char: str = " ") -> None:
+        """Fill a rectangular region with a character.
+
+        Args:
+            x: Left position
+            y: Top position
+            width: Region width
+            height: Region height
+            char: Character to fill with
+        """
+        for py in range(y, y + height):
+            for px in range(x, x + width):
+                if 0 <= py < self.height and 0 <= px < self.width:
+                    self._grid[py][px] = char
+
+    def resize(self, width: int, height: int) -> None:
+        """Resize the canvas.
+
+        Args:
+            width: New width
+            height: New height
+        """
+        if width == self.width and height == self.height:
+            return
+
+        new_grid: list[list[str]] = [[" " for _ in range(width)] for _ in range(height)]
+
+        for py in range(min(self.height, height)):
+            for px in range(min(self.width, width)):
+                new_grid[py][px] = self._grid[py][px]
+
+        self.width = width
+        self.height = height
+        self._grid = new_grid

engine/display/__init__.py

@@ -67,6 +67,18 @@ class Display(Protocol):
         """Shutdown display."""
         ...
 
+    def get_dimensions(self) -> tuple[int, int]:
+        """Get current terminal dimensions.
+
+        Returns:
+            (width, height) in character cells
+
+        This method is called after show() to check if the display
+        was resized. The main loop should compare this to the current
+        viewport dimensions and update accordingly.
+        """
+        ...
+
 
 class DisplayRegistry:
     """Registry for display backends with auto-discovery."""