diff --git a/src/review/unified-comment-bridge.ts b/src/review/unified-comment-bridge.ts
index 426da542c6..e3ffcc9222 100644
--- a/src/review/unified-comment-bridge.ts
+++ b/src/review/unified-comment-bridge.ts
@@ -458,8 +458,13 @@ export function buildBeforeAfterCollapsible(routes: CaptureRoute[]): UnifiedColl
       .replace(/`/g, "\\`")
       .replace(/\|/g, "\\|")
       .replace(/[<>]/g, (char) => (char === "<" ? "&lt;" : "&gt;"))}\``;
+  // #6324: the same one-line caption UNDER the thumbnail that the screenshot-table contract itself requires
+  // of contributors (see e.g. .claude/skills/metagraphed/SKILL.md's Phase B2 in JSONbored/metagraphed) --
+  // previously only present as the invisible `alt` attribute, never rendered as visible text. <br> (not a
+  // literal newline, which would break the GFM table row) keeps the caption inside the same cell; <sub> is
+  // the same de-emphasized styling this table already uses for its own footer legend line below.
   const cell = (url: string | undefined, label: string): string =>
-    url ? `<a href="${attr(url)}" target="_blank" rel="noopener"><img width="360" alt="${attr(label)}" src="${attr(url)}"></a>` : "—";
+    url ? `<a href="${attr(url)}" target="_blank" rel="noopener"><img width="360" alt="${attr(label)}" src="${attr(url)}"></a><br><sub>${attr(label)}</sub>` : "—";
   const rows: string[] = [];
   let hasAnyDiff = false;
   for (const route of routes) {
@@ -506,8 +511,9 @@ export function buildScrollPreviewCollapsible(routes: CaptureRoute[]): UnifiedCo
       .replace(/`/g, "\\`")
       .replace(/\|/g, "\\|")
       .replace(/[<>]/g, (char) => (char === "<" ? "&lt;" : "&gt;"))}\``;
+  // #6324: same visible one-line caption as buildBeforeAfterCollapsible's own cell() -- see its doc comment.
   const cell = (url: string | undefined, label: string): string =>
-    url ? `<a href="${attr(url)}" target="_blank" rel="noopener"><img width="360" alt="${attr(label)}" src="${attr(url)}"></a>` : "—";
+    url ? `<a href="${attr(url)}" target="_blank" rel="noopener"><img width="360" alt="${attr(label)}" src="${attr(url)}"></a><br><sub>${attr(label)}</sub>` : "—";
   const rows: string[] = [];
   for (const route of routes) {
     if (!route.beforeGifUrl && !route.afterGifUrl) continue;
diff --git a/test/unit/visual-collapsible.test.ts b/test/unit/visual-collapsible.test.ts
index 2effea8005..5ad3955434 100644
--- a/test/unit/visual-collapsible.test.ts
+++ b/test/unit/visual-collapsible.test.ts
@@ -50,6 +50,19 @@ describe("buildBeforeAfterCollapsible", () => {
     expect(c?.body).toContain("| `/` | desktop | — | <a href=");
   });
 
+  it("#6324: renders a VISIBLE one-line caption under each thumbnail, matching the contributor screenshot contract's own shape", () => {
+    const c = buildBeforeAfterCollapsible(routes);
+    // The caption text is the SAME string already used as the (invisible) alt attribute -- now also visible.
+    expect(c?.body).toContain('<img width="360" alt="before /app/analytics" src="https://api.example.dev/gittensory/shot?key=gittensory/shots/abc.png"></a><br><sub>before /app/analytics</sub>');
+    expect(c?.body).toContain('<img width="360" alt="after /app/analytics" src="https://api.example.dev/gittensory/shot?key=gittensory/shots/def.png"></a><br><sub>after /app/analytics</sub>');
+  });
+
+  it("#6324: a dash cell has no caption to escape (no <br><sub> emitted for a missing slot)", () => {
+    const c = buildBeforeAfterCollapsible([{ path: "/", afterUrl: "https://api.example.dev/gittensory/shot?key=gittensory/shots/x.png" }]);
+    expect(c?.body).toContain("| `/` | desktop | — | <a href=");
+    expect(c?.body).not.toContain("—<br>");
+  });
+
   it("returns null when no route has any shot URL (no empty table)", () => {
     expect(buildBeforeAfterCollapsible([])).toBeNull();
     expect(buildBeforeAfterCollapsible([{ path: "/" }])).toBeNull();
@@ -169,6 +182,9 @@ describe("buildScrollPreviewCollapsible (#3612)", () => {
     expect(c?.body).toContain('<a href="https://api.example.dev/gittensory/shot?key=gittensory/shots/before.gif"');
     expect(c?.body).toContain('alt="before /app/analytics (scroll)"');
     expect(c?.body).toContain('alt="after /app/analytics (scroll)"');
+    // #6324: same visible caption as buildBeforeAfterCollapsible's own cell().
+    expect(c?.body).toContain("<br><sub>before /app/analytics (scroll)</sub>");
+    expect(c?.body).toContain("<br><sub>after /app/analytics (scroll)</sub>");
   });
 
   it("returns null when no route has a scroll GIF — byte-identical to pre-#3612 for every non-opted-in repo", () => {