diff --git a/src/diag.ts b/src/diag.ts
index 70c02d3..03f844b 100644
--- a/src/diag.ts
+++ b/src/diag.ts
@@ -1,16 +1,28 @@
 import type { ExtensionContext, Skill } from "@earendil-works/pi-coding-agent";
 import type { SkillReinjectSettings } from "./settings.js";
-import type { ExtensionState } from "./state.js";
+import type { CompactionSource, ExtensionState } from "./state.js";
 
-export type ReinjectDiagPhase = "session_compact" | "before_agent_start";
+export type ReinjectDiagPhase = "session_compact" | "before_agent_start" | "mid_turn_deliver";
 
-/** Filter snapshot for debug logging (Phase 14 / B-002). */
+/** Optional compaction/delivery context for debug snapshots (Phase 15 / B-003). */
+export interface ReinjectDiagContext {
+	compactionSource?: CompactionSource | null;
+	sourceInferred?: boolean;
+	deliveryBranch?: "before_agent_start" | "steer" | "none";
+	isIdle?: boolean;
+}
+
+/** Filter snapshot for debug logging (Phase 14 / B-002, Phase 15 / B-003). */
 export interface ReinjectDiagSnapshot {
 	tracked: string[];
 	kept: string[];
 	registered: string[];
 	planned: string[];
 	pending: string[];
+	compactionSource?: CompactionSource | null;
+	sourceInferred?: boolean;
+	deliveryBranch?: "before_agent_start" | "steer" | "none";
+	isIdle?: boolean;
 }
 
 export function buildReinjectDiagSnapshot(
@@ -18,6 +30,7 @@ export function buildReinjectDiagSnapshot(
 	registeredSkills: readonly Pick<Skill, "name">[],
 	keptPresent: ReadonlySet<string>,
 	planned: readonly string[],
+	context?: ReinjectDiagContext,
 ): ReinjectDiagSnapshot {
 	return {
 		tracked: state.skills.map((skill) => skill.name),
@@ -25,6 +38,7 @@ export function buildReinjectDiagSnapshot(
 		registered: registeredSkills.map((skill) => skill.name),
 		planned: [...planned],
 		pending: [...state.pendingReinject],
+		...context,
 	};
 }
 
diff --git a/src/index.ts b/src/index.ts
index bde8cea..1a58901 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -107,7 +107,9 @@ export default function skillReinject(pi: ExtensionAPI): void {
 		const trackedNames = state.skills.map((skill) => skill.name);
 		const keptEntries = getKeptEntries(branch, event.compactionEntry.firstKeptEntryId);
 		const keptPresent = skillsPresentInKeptWindow(keptEntries, trackedNames);
+		const sourceBeforeMark = compactionRuntime.pendingCompactionSource;
 		ensureCompactionSourceMarked(compactionRuntime);
+		const sourceInferred = sourceBeforeMark === null;
 		const shouldReinject = consumeCompactionOnSessionCompact(
 			compactionRuntime,
 			state,
@@ -121,16 +123,30 @@ export default function skillReinject(pi: ExtensionAPI): void {
 				: planReinject(state, settings, ctx, event, skills);
 
 		applyPendingReinjectAfterCompact(state, compactionRuntime, shouldReinject, planned);
+		const isIdle = ctx.isIdle();
+		const deliveryBranch: "before_agent_start" | "steer" | "none" =
+			!shouldReinject || planned.length === 0
+				? "none"
+				: deliveryMode === "defer" && !isIdle
+					? "steer"
+					: deliveryMode === "defer"
+						? "before_agent_start"
+						: "none";
 		notifyReinjectDiag(
 			ctx,
 			settings,
 			"session_compact",
-			buildReinjectDiagSnapshot(state, skills, keptPresent, planned),
+			buildReinjectDiagSnapshot(state, skills, keptPresent, planned, {
+				compactionSource: state.lastCompactionSource,
+				sourceInferred,
+				deliveryBranch,
+				isIdle,
+			}),
 		);
 
 		if (deliveryMode === "defer") {
-			if (shouldReinject && planned.length > 0 && !ctx.isIdle()) {
-				deliverDeferredReinjectSteer(
+			if (shouldReinject && planned.length > 0 && !isIdle) {
+				const steered = deliverDeferredReinjectSteer(
 					pi,
 					state,
 					settings,
@@ -139,6 +155,19 @@ export default function skillReinject(pi: ExtensionAPI): void {
 					event.compactionEntry.id,
 					ctx,
 				);
+				if (steered) {
+					notifyReinjectDiag(
+						ctx,
+						settings,
+						"mid_turn_deliver",
+						buildReinjectDiagSnapshot(state, skills, keptPresent, planned, {
+							compactionSource: state.lastCompactionSource,
+							sourceInferred,
+							deliveryBranch: "steer",
+							isIdle,
+						}),
+					);
+				}
 			}
 			persistState();
 			return;
@@ -201,7 +230,11 @@ export default function skillReinject(pi: ExtensionAPI): void {
 			ctx,
 			settings,
 			"before_agent_start",
-			buildReinjectDiagSnapshot(state, skills, keptPresent, []),
+			buildReinjectDiagSnapshot(state, skills, keptPresent, [], {
+				deliveryBranch:
+					state.pendingReinject.length > 0 ? "before_agent_start" : "none",
+				isIdle: ctx.isIdle(),
+			}),
 		);
 		const pendingBefore = state.pendingReinject.length;
 		const deferred = tryConsumeDeferredReinject(
diff --git a/test/diag.test.ts b/test/diag.test.ts
index bab1914..09717d4 100644
--- a/test/diag.test.ts
+++ b/test/diag.test.ts
@@ -22,6 +22,12 @@ describe("buildReinjectDiagSnapshot", () => {
 				[{ name: "beta" }],
 				new Set(["gamma"]),
 				["alpha"],
+				{
+					compactionSource: "auto",
+					sourceInferred: true,
+					deliveryBranch: "steer",
+					isIdle: false,
+				},
 			),
 		).toEqual({
 			tracked: ["alpha"],
@@ -29,6 +35,10 @@ describe("buildReinjectDiagSnapshot", () => {
 			registered: ["beta"],
 			planned: ["alpha"],
 			pending: ["alpha"],
+			compactionSource: "auto",
+			sourceInferred: true,
+			deliveryBranch: "steer",
+			isIdle: false,
 		});
 	});
 });