[mkh-user]

Overview

This PR redesigns Pite's Python scripting API and engine runtime integration based on our architectural proposal and expert review:

1. Vec2 PyClass & Direct Struct-Backed Transform Handles:

   • Vec2 supports vector arithmetic (+, -, *, /), in-place mutation (+=, -=, *=, /=), indexing [0], [1], unpacking x, y = self.position, tuple assignment self.position = (x, y), and .length() / .normalized().
   • Node transform getters and setters directly target ScriptHost (self.position.x += 10.0 writes straight to engine tree state).
   • Removed the redundant end-of-frame getattr / mutex lock / string allocation sync pass in GameSession::update.

2. Attribute-Based Input API with Deprecation Cut:

   • pite.held.<key>, pite.pressed.<key>, and pite.released.<key> (e.g. pite.held.right, pite.pressed.space).
   • Hard cut throws TypeError when invoking with strings (e.g., pite.held("Space")).

3. Declarative Descriptors:

   • pite.child("Name") (PyChildDescriptor) and pite.node("../Path") (PyNodeDescriptor).
   • Caches resolved NodeProxy instances in _descriptor_cache on first access to avoid repeated lookups.

4. NodeProxy Caching & Hybrid Signals:

   • ScriptHost::proxy_cache caches resolved NodeProxy objects by (caller, path).
   • BoundSignal supports arbitrary Python callables (lambdas, functions, bound methods), while built-in engine signals (Button.pressed, Timer.timeout, Area2D entry/exit) remain engine-dispatched.

5. Enhanced Error Handling & Pause-On-Error:

   • GameSession::pause_on_error captures formatted stack traces and script locations.
   • Editor automatically pauses gameplay (self.playing = false), logs formatted tracebacks, and opens the offending script.

Verification

• cargo fmt --all -- --check passed.
• cargo build --workspace --locked passed.
• cargo test --workspace --locked passed (all crates including pite-runtime, pite-script, pite-core, pite-editor).
• cargo run --locked -p pite-cli -- check passed.