fix(coding-agent): align ToolDefinition.execute signature with AgentTool

BREAKING CHANGE: ToolDefinition.execute parameter order changed from
(id, params, onUpdate, ctx, signal) to (id, params, signal, onUpdate, ctx).

This aligns with AgentTool.execute so wrapping built-in tools no longer
requires parameter reordering. Update extensions by swapping signal and
onUpdate parameters.

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,17 @@
 
 ## [Unreleased]
 
+### Breaking Changes
+
+- **Extension tool signature change**: `ToolDefinition.execute` now uses `(toolCallId, params, signal, onUpdate, ctx)` parameter order to match `AgentTool.execute`. Previously it was `(toolCallId, params, onUpdate, ctx, signal)`. This makes wrapping built-in tools trivial since the first four parameters now align. Update your extensions by swapping the `signal` and `onUpdate` parameters:
+  ```ts
+  // Before
+  async execute(toolCallId, params, onUpdate, ctx, signal) { ... }
+
+  // After
+  async execute(toolCallId, params, signal, onUpdate, ctx) { ... }
+  ```
+
 ### New Features
 
 - **Android/Termux support**: Pi now runs on Android via Termux. Install with: