diff --git a/src/resources/extensions/sf/auto/phases-unit.js b/src/resources/extensions/sf/auto/phases-unit.js
index e7818a0c1..6227605c4 100644
--- a/src/resources/extensions/sf/auto/phases-unit.js
+++ b/src/resources/extensions/sf/auto/phases-unit.js
@@ -522,11 +522,11 @@ export async function runUnitPhase(ic, iterData, loopState, sidecarItem) {
 	}
 	// Cache-optimize prompt section ordering; split at the semi-static→dynamic
 	// boundary so providers can mark the stable prefix with cache_control:ephemeral.
-	let promptParts = null;
+	let promptCacheSplit = null;
 	try {
-		promptParts = deps.reorderAndSplitForCaching?.(finalPrompt) ?? null;
-		if (promptParts) {
-			finalPrompt = promptParts.before + "\n" + promptParts.after;
+		promptCacheSplit = deps.reorderAndSplitForCaching?.(finalPrompt) ?? null;
+		if (promptCacheSplit) {
+			finalPrompt = promptCacheSplit.before + "\n" + promptCacheSplit.after;
 		} else {
 			finalPrompt = deps.reorderForCaching(finalPrompt);
 		}
@@ -729,7 +729,7 @@ export async function runUnitPhase(ic, iterData, loopState, sidecarItem) {
 		unitId,
 	});
 	const unitResult = await runUnit(ctx, pi, s, unitType, unitId, finalPrompt, {
-		promptParts: promptParts ?? undefined,
+		promptCacheSplit: promptCacheSplit ?? undefined,
 	});
 	s.lastUnitAgentEndMessages = unitResult.event?.messages ?? null;
 	let currentUnitResult = unitResult;
diff --git a/src/resources/extensions/sf/auto/run-unit.js b/src/resources/extensions/sf/auto/run-unit.js
index 6aca7f81c..3e4e54781 100644
--- a/src/resources/extensions/sf/auto/run-unit.js
+++ b/src/resources/extensions/sf/auto/run-unit.js
@@ -40,15 +40,15 @@ let sessionSwitchGeneration = 0;
  *
  * Consumer: runUnit before pi.sendMessage dispatches the autonomous unit turn.
  */
-export function buildUnitPromptMessageContent(prompt, promptParts) {
-	if (!promptParts) return prompt;
+export function buildUnitPromptMessageContent(prompt, promptCacheSplit) {
+	if (!promptCacheSplit) return prompt;
 	return [
 		{
 			type: "text",
-			text: `${promptParts.before}\n`,
+			text: `${promptCacheSplit.before}\n`,
 			cache_control: { type: "ephemeral" },
 		},
-		{ type: "text", text: promptParts.after },
+		{ type: "text", text: promptCacheSplit.after },
 	];
 }
 
@@ -98,10 +98,10 @@ export function scopeActiveToolsForRunUnit(
  */
 export async function runUnit(ctx, pi, s, unitType, unitId, prompt, options) {
 	const keepSession = options?.keepSession === true;
-	// promptParts: {before, after} — stable prefix (to cache) + dynamic suffix.
+	// promptCacheSplit: {before, after} — stable prefix (to cache) + dynamic suffix.
 	// When present, passes the content as a two-block array so providers can mark
 	// the stable prefix with cache_control:ephemeral.
-	const promptParts = options?.promptParts ?? null;
+	const promptCacheSplit = options?.promptCacheSplit ?? null;
 	debugLog("runUnit", { phase: "start", unitType, unitId, keepSession });
 	// GAP-10: Ensure cwd matches basePath BEFORE newSession() captures it. The
 	// new session reads process.cwd() during construction to anchor its tool
@@ -313,10 +313,13 @@ export async function runUnit(ctx, pi, s, unitType, unitId, prompt, options) {
 		}
 	}
 	try {
-		// When promptParts is available, send structured content so the provider can
-		// apply cache_control:ephemeral to the stable prefix (before) while leaving
-		// the dynamic suffix (after) uncached.
-		const messageContent = buildUnitPromptMessageContent(prompt, promptParts);
+		// When a cache split is available, send structured content so the provider
+		// can apply cache_control:ephemeral to the stable prefix while leaving the
+		// dynamic suffix uncached.
+		const messageContent = buildUnitPromptMessageContent(
+			prompt,
+			promptCacheSplit,
+		);
 		await pi.sendMessage(
 			{ customType: "sf-auto", content: messageContent, display: s.verbose },
 			{ triggerTurn: true },
diff --git a/src/resources/extensions/sf/tests/run-unit.test.mjs b/src/resources/extensions/sf/tests/run-unit.test.mjs
index 92675b13b..adeb45e01 100644
--- a/src/resources/extensions/sf/tests/run-unit.test.mjs
+++ b/src/resources/extensions/sf/tests/run-unit.test.mjs
@@ -6,7 +6,7 @@ import {
 	scopeActiveToolsForRunUnit,
 } from "../auto/run-unit.js";
 
-test("buildUnitPromptMessageContent_when_prompt_parts_present_preserves_join_boundary", () => {
+test("buildUnitPromptMessageContent_when_cache_split_present_preserves_join_boundary", () => {
 	const content = buildUnitPromptMessageContent("flat", {
 		before: "## Working Directory\n/repo",
 		after: "## Inlined Task Plan\nDo it.",
@@ -28,7 +28,7 @@ test("buildUnitPromptMessageContent_when_prompt_parts_present_preserves_join_bou
 	);
 });
 
-test("buildUnitPromptMessageContent_when_no_prompt_parts_returns_flat_prompt", () => {
+test("buildUnitPromptMessageContent_when_no_cache_split_returns_flat_prompt", () => {
 	assert.equal(buildUnitPromptMessageContent("flat", null), "flat");
 });