diff --git a/app/L0/_all/mod/_core/spaces/storage.js b/app/L0/_all/mod/_core/spaces/storage.js
index 853f8b45..661ef25d 100644
--- a/app/L0/_all/mod/_core/spaces/storage.js
+++ b/app/L0/_all/mod/_core/spaces/storage.js
@@ -596,11 +596,23 @@ function buildWidgetMetadataLines(widgetRecord) {
 
 function getWidgetRendererReadLines(widgetRecord) {
   const normalizedWidget = normalizeWidgetRecord(widgetRecord, widgetRecord);
-  return dedentMultilineText(normalizedWidget.rendererSource)
+  return getRendererSourceReadLines(normalizedWidget.rendererSource);
+}
+
+function getRendererSourceReadLines(rendererSource) {
+  return dedentMultilineText(typeof rendererSource === "string" ? rendererSource : "")
     .replace(/\r\n?/gu, "\n")
     .split("\n");
 }
 
+function countRendererSourceReadLines(rendererSource) {
+  if (typeof rendererSource !== "string" || !rendererSource.length) {
+    return 0;
+  }
+
+  return getRendererSourceReadLines(rendererSource).length;
+}
+
 function formatWidgetRecordForRead(widgetRecord) {
   const rendererLines = getWidgetRendererReadLines(widgetRecord);
   return [
@@ -956,15 +968,29 @@ function applyPatchedWidgetAttributes(widgetRecord, options = {}) {
   );
 }
 
-function buildWidgetWriteResult(spaceRecord, widgetId) {
+function buildWidgetWriteResult(spaceRecord, widgetId, priorRendererSource = null) {
   const widgetRecord = spaceRecord?.widgets?.[widgetId];
-
-  return {
+  const result = {
     space: spaceRecord,
     widgetId,
     widgetPath: buildSpaceWidgetFilePath(spaceRecord.id, widgetId),
     widgetText: widgetRecord ? formatWidgetRecordForRead(widgetRecord) : ""
   };
+
+  // Expose line counts (not full source strings) so consumers can report
+  // change magnitude in tool result status without parsing renderer text.
+  // Both counts use the same dedent + LF-normalize + split path that
+  // formatWidgetRecordForRead emits, so the numbers always match what the
+  // agent counts in the numbered renderer readback.
+  if (typeof priorRendererSource === "string") {
+    result.priorRendererLineCount = countRendererSourceReadLines(priorRendererSource);
+  }
+
+  if (typeof widgetRecord?.rendererSource === "string") {
+    result.nextRendererLineCount = countRendererSourceReadLines(widgetRecord.rendererSource);
+  }
+
+  return result;
 }
 
 function buildWidgetWriteResults(spaceRecord, widgetIds = []) {
@@ -2056,6 +2082,7 @@ export async function upsertWidget(options = {}) {
   const currentSpace = cloneSpaceRecord(await readSpace(spaceId));
   const widgetFallbackId = normalizeWidgetId(options.widgetId || options.id || options.name || options.title || "widget");
   const existingWidget = currentSpace.widgets[widgetFallbackId] || null;
+  const priorRendererSource = typeof existingWidget?.rendererSource === "string" ? existingWidget.rendererSource : null;
   const widgetRecord = validateWidgetRendererSourceForWrite(
     previewWidgetRecord(options, {
       ...existingWidget,
@@ -2103,7 +2130,7 @@ export async function upsertWidget(options = {}) {
   await runtime.api.fileWrite({ files });
   clearRecentListedSpaceRecords();
 
-  return buildWidgetWriteResult(nextSpace, widgetId);
+  return buildWidgetWriteResult(nextSpace, widgetId, priorRendererSource);
 }
 
 export async function upsertWidgets(options = {}) {
@@ -2219,6 +2246,7 @@ export async function patchWidget(options = {}) {
     throw new Error(`Cannot patch widget "${widgetId}": widget not found in space "${spaceId}".`);
   }
 
+  const priorRendererSource = typeof currentWidget.rendererSource === "string" ? currentWidget.rendererSource : null;
   const patchedRendererSource = applyWidgetPatchEdits(currentWidget, options.edits ?? options.lineEdits);
   const nextWidget = validateWidgetRendererSourceForWrite(
     applyPatchedWidgetAttributes(
@@ -2251,7 +2279,7 @@ export async function patchWidget(options = {}) {
   await runtime.api.fileWrite({ files });
   clearRecentListedSpaceRecords();
 
-  return buildWidgetWriteResult(nextSpace, widgetId);
+  return buildWidgetWriteResult(nextSpace, widgetId, priorRendererSource);
 }
 
 export async function removeWidget(options = {}) {
diff --git a/app/L0/_all/mod/_core/spaces/store.js b/app/L0/_all/mod/_core/spaces/store.js
index 84d61cfe..a4954193 100644
--- a/app/L0/_all/mod/_core/spaces/store.js
+++ b/app/L0/_all/mod/_core/spaces/store.js
@@ -1017,21 +1017,57 @@ function getWidgetOperationStatusVerb(operationLabel) {
   }
 }
 
+// Render the change magnitude for a widget write. The line counts come from
+// `buildWidgetWriteResult` in spaces/storage.js, which uses the same
+// dedent + LF-normalize + split path that emits the numbered renderer
+// readback the agent sees in `widgetText`. So the count printed here always
+// matches the highest line index the agent counts in the readback.
+function formatWidgetOperationChangeMagnitude({ priorLineCount, nextLineCount } = {}) {
+  const hasPrior = Number.isFinite(priorLineCount);
+  const hasNext = Number.isFinite(nextLineCount);
+
+  if (!hasPrior && !hasNext) {
+    return "";
+  }
+
+  const before = hasPrior ? Math.max(0, priorLineCount) : 0;
+  const after = hasNext ? Math.max(0, nextLineCount) : 0;
+
+  if (!hasPrior) {
+    return `${after} renderer line${after === 1 ? "" : "s"}`;
+  }
+
+  if (!hasNext || !after) {
+    return `0 renderer lines (was ${before})`;
+  }
+
+  const delta = after - before;
+
+  if (delta === 0) {
+    return `${after} renderer lines`;
+  }
+
+  const sign = delta > 0 ? "+" : "-";
+  return `${after} renderer lines (was ${before}, ${sign}${Math.abs(delta)})`;
+}
+
 function formatWidgetOperationStatusText(widgetId, operationLabel, widgetRender, options = {}) {
   const check = cloneWidgetRenderCheck(widgetRender, widgetId);
   const verb = getWidgetOperationStatusVerb(operationLabel);
   const targetLabel = widgetId ? `Widget "${widgetId}"` : "Widget";
   const suffix = options.transientUpdated ? "loaded to TRANSIENT." : "done.";
+  const magnitude = formatWidgetOperationChangeMagnitude(options);
+  const magnitudeFragment = magnitude ? `, ${magnitude}` : "";
 
   if (check.status === "error") {
-    return `${targetLabel} ${verb}, render failed, ${suffix}`;
+    return `${targetLabel} ${verb}${magnitudeFragment}, render failed, ${suffix}`;
   }
 
   if (check.status === "ok") {
-    return `${targetLabel} ${verb}, rendered ok, ${suffix}`;
+    return `${targetLabel} ${verb}${magnitudeFragment}, rendered ok, ${suffix}`;
   }
 
-  return `${targetLabel} ${verb}, not live-tested, ${suffix}`;
+  return `${targetLabel} ${verb}${magnitudeFragment}, not live-tested, ${suffix}`;
 }
 
 function extractWidgetIdFromWidgetText(widgetText) {
@@ -1271,7 +1307,13 @@ async function buildWidgetToolResult(
         widgetText
       })
     : false;
+  const priorRendererLineCount =
+    Number.isFinite(nextResult.priorRendererLineCount) ? nextResult.priorRendererLineCount : null;
+  const nextRendererLineCount =
+    Number.isFinite(nextResult.nextRendererLineCount) ? nextResult.nextRendererLineCount : null;
   const widgetStatusText = formatWidgetOperationStatusText(normalizedWidgetId, operationLabel, widgetRender, {
+    nextLineCount: nextRendererLineCount,
+    priorLineCount: priorRendererLineCount,
     transientUpdated
   });