feat(coding-agent): add hook API for CLI flags, shortcuts, and tool control

Hook API additions:
- pi.getTools() / pi.setTools(toolNames) - dynamically enable/disable tools
- pi.registerFlag(name, options) / pi.getFlag(name) - register custom CLI flags
- pi.registerShortcut(shortcut, options) - register keyboard shortcuts

Plan mode hook (examples/hooks/plan-mode.ts):
- /plan command or Shift+P shortcut to toggle
- --plan CLI flag to start in plan mode
- Read-only tools: read, bash, grep, find, ls
- Bash restricted to non-destructive commands (blocks rm, mv, git commit, etc.)
- Interactive prompt after each response: execute, stay, or refine
- Shows plan indicator in footer when active
- State persists across sessions

packages/coding-agent/test/compaction-hooks.test.ts

@@ -78,10 +78,14 @@ describe.skipIf(!API_KEY)("Compaction hooks", () => {
 			handlers,
 			messageRenderers: new Map(),
 			commands: new Map(),
+			flags: new Map(),
+			flagValues: new Map(),
+			shortcuts: new Map(),
 			setSendMessageHandler: () => {},
 			setAppendEntryHandler: () => {},
 			setGetToolsHandler: () => {},
 			setSetToolsHandler: () => {},
+			setFlagValue: () => {},
 		};
 	}
 
@@ -269,10 +273,14 @@ describe.skipIf(!API_KEY)("Compaction hooks", () => {
 			]),
 			messageRenderers: new Map(),
 			commands: new Map(),
+			flags: new Map(),
+			flagValues: new Map(),
+			shortcuts: new Map(),
 			setSendMessageHandler: () => {},
 			setAppendEntryHandler: () => {},
 			setGetToolsHandler: () => {},
 			setSetToolsHandler: () => {},
+			setFlagValue: () => {},
 		};
 
 		createSession([throwingHook]);
@@ -318,10 +326,14 @@ describe.skipIf(!API_KEY)("Compaction hooks", () => {
 			]),
 			messageRenderers: new Map(),
 			commands: new Map(),
+			flags: new Map(),
+			flagValues: new Map(),
+			shortcuts: new Map(),
 			setSendMessageHandler: () => {},
 			setAppendEntryHandler: () => {},
 			setGetToolsHandler: () => {},
 			setSetToolsHandler: () => {},
+			setFlagValue: () => {},
 		};
 
 		const hook2: LoadedHook = {
@@ -349,10 +361,14 @@ describe.skipIf(!API_KEY)("Compaction hooks", () => {
 			]),
 			messageRenderers: new Map(),
 			commands: new Map(),
+			flags: new Map(),
+			flagValues: new Map(),
+			shortcuts: new Map(),
 			setSendMessageHandler: () => {},
 			setAppendEntryHandler: () => {},
 			setGetToolsHandler: () => {},
 			setSetToolsHandler: () => {},
+			setFlagValue: () => {},
 		};
 
 		createSession([hook1, hook2]);