diff --git a/.pi/extensions/goal-driven-loop/index.ts b/.pi/extensions/goal-driven-loop/index.ts
new file mode 100644
index 0000000..f91eadb
--- /dev/null
+++ b/.pi/extensions/goal-driven-loop/index.ts
@@ -0,0 +1,137 @@
+/**
+ * goal-driven-loop extension for Pi.
+ *
+ * Wires together trigger detection, state injection, and timed
+ * auto-defaults to eliminate unnecessary user interaction.
+ */
+
+import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
+import { join } from "node:path";
+import { existsSync, unlinkSync } from "node:fs";
+import { detectTrigger, isCoarseGrained } from "./trigger-detector.js";
+import {
+  readGoalState,
+  buildInjectionText,
+  buildContinuationPrompt,
+} from "./state-injector.js";
+import {
+  promptStaleState,
+  notifyCoarseGrainedDelegation,
+  notifyStagnation,
+  shouldNotifyStagnation,
+  type UIContext,
+} from "./ui-prompts.js";
+
+const CONTEXT_TENSION_THRESHOLD = 0.8;
+const ABANDON_KEYWORDS = ["abandon", "cancel", "不要了", "放弃", "停"];
+
+export default function (pi: ExtensionAPI) {
+  // ---- Trigger detection on user input ----
+  pi.on("input", async (event, ctx) => {
+    if (event.source === "extension") {
+      return { action: "continue" };
+    }
+
+    // Check for explicit abandon first
+    const lowerText = event.text.toLowerCase();
+    const isAbandon = ABANDON_KEYWORDS.some((kw) =>
+      lowerText.includes(kw.toLowerCase())
+    );
+    if (isAbandon) {
+      const state = readGoalState(ctx.cwd);
+      if (state) {
+        handleAbandon(ctx);
+        return { action: "continue" };
+      }
+    }
+
+    // Try to detect a goal-setting trigger
+    const match = detectTrigger(event.text);
+    if (!match) {
+      return { action: "continue" };
+    }
+
+    // Trigger detected — check stale state
+    const existingState = readGoalState(ctx.cwd);
+    if (existingState && existingState.status === "in-progress") {
+      const ui = buildUIContext(ctx);
+      const choice = await promptStaleState(ui);
+      if (choice === "abandon") {
+        handleAbandon(ctx);
+        return { action: "continue" };
+      }
+      if (choice === "replace") {
+        // Let the skill handle replacement on the next turn
+        return { action: "continue" };
+      }
+      // "continue" or undefined → let the skill resume
+    }
+
+    // Granularity check
+    if (isCoarseGrained(match.goalText)) {
+      const ui = buildUIContext(ctx);
+      notifyCoarseGrainedDelegation(ui, match.goalText);
+      pi.sendUserMessage(`/skill:comet-open ${match.goalText}`, {
+        deliverAs: "followUp",
+      });
+      return { action: "continue" };
+    }
+
+    // Fine-grained — let the skill handle it
+    return { action: "continue" };
+  });
+
+  // ---- State injection on every agent start ----
+  pi.on("before_agent_start", async (event, ctx) => {
+    const state = readGoalState(ctx.cwd);
+    if (!state) {
+      return;
+    }
+
+    // Context tension check
+    const usage = ctx.getContextUsage();
+    if (
+      usage &&
+      usage.contextWindow > 0 &&
+      usage.tokens / usage.contextWindow > CONTEXT_TENSION_THRESHOLD
+    ) {
+      const continuationMsg = buildContinuationPrompt(state);
+      return {
+        systemPrompt:
+          event.systemPrompt +
+          "\n\n" +
+          continuationMsg +
+          "\n\nContext is tight. Finalize .agents/goal/GOAL.md updates before completing this turn.",
+      };
+    }
+
+    // Inject goal state
+    const injection = buildInjectionText(state);
+    return {
+      systemPrompt: event.systemPrompt + "\n\n" + injection,
+    };
+  });
+}
+
+function buildUIContext(ctx: any): UIContext {
+  return {
+    hasUI: ctx.hasUI,
+    select: ctx.ui.select.bind(ctx.ui),
+    notify: ctx.ui.notify.bind(ctx.ui),
+    confirm: ctx.ui.confirm.bind(ctx.ui),
+  };
+}
+
+function handleAbandon(ctx: any): void {
+  const goalPath = join(ctx.cwd, ".agents", "goal", "GOAL.md");
+  try {
+    if (existsSync(goalPath)) {
+      unlinkSync(goalPath);
+    }
+  } catch {
+    // best effort
+  }
+  if (ctx.hasUI) {
+    ctx.ui.notify("目标已放弃", "info");
+  }
+}