Phase 15: add mid-turn defer reinject via sendMessage steer

Deliver pending skills on session_compact when agent is not idle, and
skip before_agent_start consume when steer already ran for compaction.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/compaction.ts

@@ -8,6 +8,10 @@ export interface CompactionRuntime {
 	clearPendingReinjectOnNextUserInput: boolean;
 	/** Last compact firstKeptEntryId for debug kept-window snapshots (Phase 14). */
 	lastCompactionFirstKeptEntryId: string | null;
+	/** Last compaction entry id on session_compact (Phase 15 / B-003 dedup). */
+	lastCompactionEntryId: string | null;
+	/** Compaction id when mid-turn steer already delivered reinject (Phase 15 / §6.5.1). */
+	deferredDeliveredForCompactionId: string | null;
 }
 
 export function createCompactionRuntime(): CompactionRuntime {
@@ -15,6 +19,8 @@ export function createCompactionRuntime(): CompactionRuntime {
 		pendingCompactionSource: null,
 		clearPendingReinjectOnNextUserInput: false,
 		lastCompactionFirstKeptEntryId: null,
+		lastCompactionEntryId: null,
+		deferredDeliveredForCompactionId: null,
 	};
 }
 

src/reinject.ts

@@ -352,6 +352,46 @@ export function filterPendingReinjectForConsume(
 	return resolved;
 }
 
+/**
+ * Mid-turn defer delivery via sendMessage/steer (SPEC §6.5.1, Phase 15 / B-003).
+ * Clears pendingReinject and records compaction id so before_agent_start does not duplicate.
+ */
+export function deliverDeferredReinjectSteer(
+	pi: ExtensionAPI,
+	state: ExtensionState,
+	settings: SkillReinjectSettings,
+	registeredSkills: readonly Pick<Skill, "name" | "filePath" | "baseDir">[],
+	compactionRuntime: CompactionRuntime,
+	compactionEntryId: string,
+	ctx?: ExtensionContext,
+): boolean {
+	if (state.pendingReinject.length === 0) {
+		return false;
+	}
+	const pendingNames = filterPendingReinjectForConsume(
+		state.pendingReinject,
+		state,
+		settings,
+		registeredSkills,
+		ctx,
+	);
+	const content = buildDeferredReinjectContent(pendingNames, state, settings, registeredSkills, ctx);
+	state.pendingReinject = [];
+	if (!content) {
+		return false;
+	}
+	pi.sendMessage(
+		{
+			customType: DEFERRED_REINJECT_CUSTOM_TYPE,
+			content,
+			display: true,
+		},
+		{ deliverAs: "steer" },
+	);
+	compactionRuntime.deferredDeliveredForCompactionId = compactionEntryId;
+	return true;
+}
+
 /**
  * Defer path on before_agent_start: inject one combined message, then clear queue (SPEC §6.5.1).
  * Returns undefined when pendingReinject is empty or manual compaction scheduled a clear (SPEC §16.5).
@@ -366,6 +406,12 @@ export function tryConsumeDeferredReinject(
 	if (compactionRuntime?.clearPendingReinjectOnNextUserInput) {
 		return undefined;
 	}
+	if (
+		compactionRuntime?.deferredDeliveredForCompactionId &&
+		compactionRuntime.deferredDeliveredForCompactionId === compactionRuntime.lastCompactionEntryId
+	) {
+		return undefined;
+	}
 	if (state.pendingReinject.length === 0) {
 		return undefined;
 	}