Add full-compaction hook example

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

@@ -25,6 +25,9 @@ Prevents session changes when there are uncommitted git changes. Blocks clear/sw
 ### auto-commit-on-exit.ts
 Automatically commits changes when the agent exits (shutdown event). Uses the last assistant message to generate a commit message.
 
+### full-compaction.ts
+Custom context compaction that summarizes the entire conversation instead of keeping recent turns. Uses the `before_compact` hook event to intercept compaction and generate a comprehensive summary using `complete()` from the AI package. Useful when you want maximum context window space at the cost of losing exact conversation history.
+
 ## Usage
 
 ```bash

packages/coding-agent/examples/hooks/full-compaction.ts

@@ -0,0 +1,89 @@
+/**
+ * Full Context Compaction Hook
+ *
+ * Replaces the default compaction behavior with a full summary of the entire context.
+ * Instead of keeping the last 20k tokens of conversation turns, this hook:
+ * 1. Summarizes ALL messages being compacted into a single comprehensive summary
+ * 2. Discards all old turns completely
+ *
+ * This is useful when you want maximum context window space for new work
+ * at the cost of losing exact conversation history.
+ *
+ * Usage:
+ *   pi --hook examples/hooks/full-compaction.ts
+ */
+
+import { complete } from "@mariozechner/pi-ai";
+import { messageTransformer } from "@mariozechner/pi-coding-agent";
+import type { HookAPI } from "@mariozechner/pi-coding-agent/hooks";
+
+export default function (pi: HookAPI) {
+	pi.on("session", async (event, ctx) => {
+		if (event.reason !== "before_compact") return;
+
+		const { messagesToSummarize, tokensBefore, model, apiKey, cutPoint } = event;
+
+		ctx.ui.notify(`Compacting ${tokensBefore.toLocaleString()} tokens with full summary...`, "info");
+
+		// Transform app messages to LLM-compatible format
+		const transformedMessages = messageTransformer(messagesToSummarize);
+
+		// Build messages that ask for a comprehensive summary
+		const summaryMessages = [
+			...transformedMessages,
+			{
+				role: "user" as const,
+				content: [
+					{
+						type: "text" as const,
+						text: `You are a conversation summarizer. Create a comprehensive summary of this conversation that captures:
+
+1. The main goals and objectives discussed
+2. Key decisions made and their rationale
+3. Important code changes, file modifications, or technical details
+4. Current state of any ongoing work
+5. Any blockers, issues, or open questions
+6. Next steps that were planned or suggested
+
+Be thorough but concise. The summary will replace the entire conversation history, so include all information needed to continue the work effectively.
+
+Format the summary as structured markdown with clear sections.`,
+					},
+				],
+				timestamp: Date.now(),
+			},
+		];
+
+		try {
+			// Use the same model and API key that would be used for compaction
+			const response = await complete(model, { messages: summaryMessages }, { apiKey, maxTokens: 8192 });
+
+			const summary = response.content
+				.filter((c): c is { type: "text"; text: string } => c.type === "text")
+				.map((c) => c.text)
+				.join("\n");
+
+			if (!summary.trim()) {
+				ctx.ui.notify("Compaction summary was empty, using default compaction", "warning");
+				return; // Fall back to default compaction
+			}
+
+			// Return a compaction entry that discards ALL old messages
+			// firstKeptEntryIndex points to after all summarized content
+			return {
+				compactionEntry: {
+					type: "compaction" as const,
+					timestamp: new Date().toISOString(),
+					summary,
+					firstKeptEntryIndex: cutPoint.firstKeptEntryIndex,
+					tokensBefore,
+				},
+			};
+		} catch (error) {
+			const message = error instanceof Error ? error.message : String(error);
+			ctx.ui.notify(`Compaction failed: ${message}`, "error");
+			// Fall back to default compaction on error
+			return;
+		}
+	});
+}