feat(agent,coding-agent): per-tool executionMode override for sequential tool execution (#3345)

* feat(agent,coding-agent): add per-tool executionMode field to AgentTool and ToolDefinition

Add optional executionMode?: ToolExecutionMode to AgentTool and
ToolDefinition interfaces. Propagate through wrapToolDefinition and
createToolDefinitionFromAgentTool. No behavioral change yet — agent
loop will read this field in a follow-up.

* feat(agent): support per-tool executionMode override for sequential execution

When a tool defines executionMode='sequential', the agent loop
forces sequential execution of all tool calls in that batch,
even if the global config is parallel.

* feat(coding-agent): re-export ToolExecutionMode from @mariozechner/pi-agent-core

Makes the type available to extensions that want to set
executionMode on tool definitions.

* feat(coding-agent): add tic-tac-toe extension example with executionMode: sequential

Demonstrates per-tool executionMode: the agent plays via move/play
tool calls that share a cursor. Without sequential execution, play
can resolve before earlier moves finish, landing on the wrong cell.

packages/coding-agent/src/core/tools/tool-definition-wrapper.ts

@@ -12,6 +12,7 @@ export function wrapToolDefinition<TDetails = unknown>(
 		description: definition.description,
 		parameters: definition.parameters,
 		prepareArguments: definition.prepareArguments,
+		executionMode: definition.executionMode,
 		execute: (toolCallId, params, signal, onUpdate) =>
 			definition.execute(toolCallId, params, signal, onUpdate, ctxFactory?.() as ExtensionContext),
 	};
@@ -38,6 +39,7 @@ export function createToolDefinitionFromAgentTool(tool: AgentTool<any>): ToolDef
 		description: tool.description,
 		parameters: tool.parameters as any,
 		prepareArguments: tool.prepareArguments,
+		executionMode: tool.executionMode,
 		execute: async (toolCallId, params, signal, onUpdate) => tool.execute(toolCallId, params, signal, onUpdate),
 	};
 }