feat(coding-agent): add extension compaction helpers

packages/coding-agent/examples/extensions/README.md

@@ -77,6 +77,7 @@ cp permission-gate.ts ~/.pi/agent/extensions/
 | `pirate.ts` | Demonstrates `systemPromptAppend` to dynamically modify system prompt |
 | `claude-rules.ts` | Scans `.claude/rules/` folder and lists rules in system prompt |
 | `custom-compaction.ts` | Custom compaction that summarizes entire conversation |
+| `trigger-compact.ts` | Triggers compaction when context usage exceeds 100k tokens and adds `/trigger-compact` command |
 
 ### System Integration
 

packages/coding-agent/examples/extensions/trigger-compact.ts

@@ -0,0 +1,32 @@
+import type { ExtensionAPI, ExtensionContext } from "@mariozechner/pi-coding-agent";
+
+const COMPACT_THRESHOLD_TOKENS = 100_000;
+
+export default function (pi: ExtensionAPI) {
+	const triggerCompaction = (ctx: ExtensionContext, customInstructions?: string) => {
+		ctx.compact({
+			customInstructions,
+			onError: (error) => {
+				if (ctx.hasUI) {
+					ctx.ui.notify(`Compaction failed: ${error.message}`, "error");
+				}
+			},
+		});
+	};
+
+	pi.on("turn_end", (_event, ctx) => {
+		const usage = ctx.getContextUsage();
+		if (!usage || usage.tokens <= COMPACT_THRESHOLD_TOKENS) {
+			return;
+		}
+		triggerCompaction(ctx);
+	});
+
+	pi.registerCommand("trigger-compact", {
+		description: "Trigger compaction immediately",
+		handler: async (args, ctx) => {
+			const instructions = args.trim() || undefined;
+			triggerCompaction(ctx, instructions);
+		},
+	});
+}