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/extensions/index.ts

@@ -134,6 +134,8 @@ export type {
 	ToolDefinition,
 	// Events - Tool Execution
 	ToolExecutionEndEvent,
+	// Tool execution mode
+	ToolExecutionMode,
 	ToolExecutionStartEvent,
 	ToolExecutionUpdateEvent,
 	ToolInfo,

packages/coding-agent/src/core/extensions/types.ts

@@ -13,6 +13,7 @@ import type {
 	AgentToolResult,
 	AgentToolUpdateCallback,
 	ThinkingLevel,
+	ToolExecutionMode,
 } from "@mariozechner/pi-agent-core";
 import type {
 	Api,
@@ -74,7 +75,7 @@ import type {
 } from "../tools/index.js";
 
 export type { ExecOptions, ExecResult } from "../exec.js";
-export type { AgentToolResult, AgentToolUpdateCallback };
+export type { AgentToolResult, AgentToolUpdateCallback, ToolExecutionMode };
 export type { AppKeybinding, KeybindingsManager } from "../keybindings.js";
 
 // ============================================================================
@@ -385,6 +386,15 @@ export interface ToolDefinition<TParams extends TSchema = TSchema, TDetails = un
 	/** Optional compatibility shim to prepare raw tool call arguments before schema validation. Must return an object conforming to TParams. */
 	prepareArguments?: (args: unknown) => Static<TParams>;
 
+	/**
+	 * Per-tool execution mode override.
+	 * - "sequential": this tool must execute one at a time with other tool calls.
+	 * - "parallel": this tool can execute concurrently with other tool calls.
+	 *
+	 * If omitted, the default execution mode applies.
+	 */
+	executionMode?: ToolExecutionMode;
+
 	/** Execute the tool. */
 	execute(
 		toolCallId: string,