Split HookContext and HookCommandContext to prevent deadlocks

HookContext (all events):
- isIdle() - read-only state check
- hasQueuedMessages() - read-only state check
- abort() - fire-and-forget, does not wait

HookCommandContext (slash commands only):
- waitForIdle() - waits for agent to finish
- newSession(options?) - create new session
- branch(entryId) - branch from entry
- navigateTree(targetId, options?) - navigate session tree

Session control methods moved from HookAPI (pi.*) to HookCommandContext (ctx.*)
because they can deadlock when called from event handlers that run inside
the agent loop (tool_call, tool_result, context events).

packages/coding-agent/src/core/sdk.ts

@@ -140,7 +140,7 @@ export interface CreateAgentSessionResult {
 // Re-exports
 
 export type { CustomTool } from "./custom-tools/types.js";
-export type { HookAPI, HookContext, HookFactory } from "./hooks/types.js";
+export type { HookAPI, HookCommandContext, HookContext, HookFactory } from "./hooks/types.js";
 export type { Settings, SkillsSettings } from "./settings-manager.js";
 export type { Skill } from "./skills.js";
 export type { FileSlashCommand } from "./slash-commands.js";