docs(01): capture phase context

.planning/phases/01-foundation/01-CONTEXT.md

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+# Phase 1: Foundation - Context
+
+**Gathered:** 2026-03-10
+**Status:** Ready for planning
+
+<domain>
+## Phase Boundary
+
+Build the technical foundation: game loop, HiDPI-aware canvas rendering, Player 1 keyboard input (W/S), ball physics (continuous movement, wall bouncing, zone-based angle deflection, per-hit speed increase). No scoring, no AI, no UI screens yet.
+
+</domain>
+
+<decisions>
+## Implementation Decisions
+
+### File Structure
+- Single HTML file — everything embedded (JS + CSS in one `.html` file)
+- JavaScript organized into a module pattern: `GameLoop`, `Physics`, `Renderer`, `Input` objects within a single `<script>` tag
+- No build tooling; runs directly from the filesystem
+
+### Canvas Sizing
+- Full-window canvas — fills the entire browser window
+- Resizes immediately on window resize
+- Maintains aspect ratio during resize; minimum 4:3 aspect ratio enforced
+- No maximum size cap — grows unbounded to fill any screen
+- Must be HiDPI/Retina aware (devicePixelRatio scaling)
+
+### Ball Physics Feel
+- Zone-based deflection: paddle divided into 5 zones
+  - Top edge → ~60° angle upward
+  - Upper zone → ~30° angle
+  - Center → ~5° angle (nearly flat)
+  - Lower zone → ~30° angle
+  - Bottom edge → ~60° angle downward
+- Speed increases per paddle hit (small increment each rally)
+- Speed resets on each point scored
+- No maximum speed cap — ball accelerates indefinitely through long rallies
+
+### Claude's Discretion
+- Exact speed increment value per hit (tune for feel)
+- Precise zone boundary definitions and angle values (within the ~5°–60° range)
+- Game loop timing implementation (requestAnimationFrame + delta time)
+- Serve direction and initial ball velocity for dev testing
+- Input handling internals (keydown/keyup state tracking)
+
+</decisions>
+
+<specifics>
+## Specific Ideas
+
+- No specific requirements — open to standard approaches
+
+</specifics>
+
+<code_context>
+## Existing Code Insights
+
+### Reusable Assets
+- None — fresh project, no existing code
+
+### Established Patterns
+- None yet — Phase 1 establishes the patterns all subsequent phases follow
+
+### Integration Points
+- Phase 2 will add scoring, Player 2 input, and AI — the game loop and physics module must be structured to accommodate adding a second paddle and score tracking without refactoring
+
+</code_context>
+
+<deferred>
+## Deferred Ideas
+
+- None — discussion stayed within phase scope
+
+</deferred>
+
+---
+
+*Phase: 01-foundation*
+*Context gathered: 2026-03-10*