diff --git a/src/index.ts b/src/index.ts
index 0d61010..e1661d5 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -16,8 +16,8 @@ import {
 } from "./compaction.js";
 import { detectSlashSkill, matchReadPathToSkillWhenEnabled, parseSkillBlocksFromText, userMessageText } from "./detect.js";
 import {
+	applyPendingReinjectAfterCompact,
 	clearPendingReinjectOnUserPrompt,
-	enqueueDeferredReinjectFromCompact,
 	planReinject,
 	sendImmediateReinjectAllFollowUp,
 	sendImmediateReinjectIdle,
@@ -91,34 +91,36 @@ export default function skillReinject(pi: ExtensionAPI): void {
 
 	function handleSessionCompact(event: SessionCompactEvent, ctx: ExtensionContext): void {
 		const settings = readSettings(ctx);
+		const skills = resolveRegisteredSkills(ctx.cwd, registeredSkills);
+		const planned = planReinject(state, settings, ctx, event, skills);
 		const shouldReinject = consumeCompactionOnSessionCompact(
 			compactionRuntime,
 			state,
 			state.sessionOverride,
 			settings,
 		);
+		const deliveryMode = resolveDeliveryMode(settings, runtime, state.sessionIntegrationOverride);
+
+		if (deliveryMode === "defer") {
+			applyPendingReinjectAfterCompact(state, compactionRuntime, shouldReinject, planned);
+			persistState();
+			return;
+		}
+
+		applyPendingReinjectAfterCompact(state, compactionRuntime, shouldReinject, planned);
 		if (!shouldReinject) {
 			persistState();
 			return;
 		}
 
-		const skills = resolveRegisteredSkills(ctx.cwd, registeredSkills);
-		const deliveryMode = resolveDeliveryMode(settings, runtime, state.sessionIntegrationOverride);
-		if (deliveryMode === "defer") {
-			enqueueDeferredReinjectFromCompact(state, settings, ctx, event, skills);
-			persistState();
-			return;
-		}
-
-		const skillNames = planReinject(state, settings, ctx, event, skills);
-		if (skillNames.length === 0) {
+		if (planned.length === 0) {
 			persistState();
 			return;
 		}
 		if (ctx.isIdle()) {
-			sendImmediateReinjectIdle(pi, skillNames, state, settings, skills, ctx);
+			sendImmediateReinjectIdle(pi, planned, state, settings, skills, ctx);
 		} else {
-			sendImmediateReinjectAllFollowUp(pi, skillNames, state, settings, skills, ctx);
+			sendImmediateReinjectAllFollowUp(pi, planned, state, settings, skills, ctx);
 		}
 		persistState();
 	}
diff --git a/src/reinject.ts b/src/reinject.ts
index 60252b4..8799ff4 100644
--- a/src/reinject.ts
+++ b/src/reinject.ts
@@ -96,6 +96,25 @@ export function enqueueDeferredReinjectFromCompact(
 	);
 }
 
+/**
+ * Update pending queue after session_compact; each compact recalculates or clears (SPEC §16.6).
+ * Manual compaction with default settings keeps stale pending until the next user prompt.
+ */
+export function applyPendingReinjectAfterCompact(
+	state: ExtensionState,
+	compactionRuntime: CompactionRuntime,
+	shouldReinject: boolean,
+	planned: readonly string[],
+): void {
+	if (shouldReinject) {
+		state.pendingReinject = [...planned];
+		return;
+	}
+	if (!compactionRuntime.clearPendingReinjectOnNextUserInput) {
+		state.pendingReinject = [];
+	}
+}
+
 /** Warn when re-injecting many skills; unlimited by default with soft warn above 3 (SPEC §15). */
 export function maybeWarnManySkills(
 	skillCount: number,
diff --git a/test/reinject-double-compact.test.ts b/test/reinject-double-compact.test.ts
new file mode 100644
index 0000000..36920c8
--- /dev/null
+++ b/test/reinject-double-compact.test.ts
@@ -0,0 +1,37 @@
+import { describe, expect, it } from "vitest";
+import { createCompactionRuntime } from "../src/compaction";
+import { applyPendingReinjectAfterCompact } from "../src/reinject";
+import { createInitialState } from "../src/state";
+
+describe("applyPendingReinjectAfterCompact", () => {
+	it("replaces pending with a new plan on each compact", () => {
+		const runtime = createCompactionRuntime();
+		const state = createInitialState();
+		state.pendingReinject = ["alpha"];
+
+		applyPendingReinjectAfterCompact(state, runtime, true, ["beta", "gamma"]);
+
+		expect(state.pendingReinject).toEqual(["beta", "gamma"]);
+	});
+
+	it("clears pending when reinject is skipped", () => {
+		const runtime = createCompactionRuntime();
+		const state = createInitialState();
+		state.pendingReinject = ["alpha"];
+
+		applyPendingReinjectAfterCompact(state, runtime, false, ["beta"]);
+
+		expect(state.pendingReinject).toEqual([]);
+	});
+
+	it("keeps stale pending when manual compaction scheduled a user-prompt clear", () => {
+		const runtime = createCompactionRuntime();
+		runtime.clearPendingReinjectOnNextUserInput = true;
+		const state = createInitialState();
+		state.pendingReinject = ["alpha"];
+
+		applyPendingReinjectAfterCompact(state, runtime, false, ["beta"]);
+
+		expect(state.pendingReinject).toEqual(["alpha"]);
+	});
+});