diff --git a/app/src/renderer/src/markdown-image-renderer.js b/app/src/renderer/src/markdown-image-renderer.js
index 84c11e0..f48abdd 100644
--- a/app/src/renderer/src/markdown-image-renderer.js
+++ b/app/src/renderer/src/markdown-image-renderer.js
@@ -1,4 +1,4 @@
-import { SESSION_IMAGE_TAG } from './session-image-element.js';
+import { SESSION_IMAGE_TAG } from './session-image-contract.js';
 
 const SAFE_IMAGE_PROTOCOLS = new Set(['blob:', 'file:', 'http:', 'https:']);
 let configuredMarked = null;
@@ -26,10 +26,25 @@ function imageFallback(alt) {
   return fallback.outerHTML;
 }
 
-export function renderSessionMarkdownImage(href, title, text) {
-  const source = decodeMarkedAttribute(href).trim();
-  const alt = decodeMarkedAttribute(text);
-  const accessibleTitle = decodeMarkedAttribute(title);
+// marked <= 14 calls renderer.image(href, title, text); marked >= 15 passes the
+// image token instead. Accepting both keeps an upgrade from silently turning
+// every session image into fallback text.
+export function normalizeMarkdownImageToken(hrefOrToken, title, text) {
+  if (hrefOrToken && typeof hrefOrToken === 'object') {
+    return {
+      href: hrefOrToken.href ?? '',
+      title: hrefOrToken.title ?? '',
+      text: hrefOrToken.text ?? '',
+    };
+  }
+  return { href: hrefOrToken ?? '', title: title ?? '', text: text ?? '' };
+}
+
+export function renderSessionMarkdownImage(hrefOrToken, title, text) {
+  const token = normalizeMarkdownImageToken(hrefOrToken, title, text);
+  const source = decodeMarkedAttribute(token.href).trim();
+  const alt = decodeMarkedAttribute(token.text);
+  const accessibleTitle = decodeMarkedAttribute(token.title);
   if (!source || !isSafeImageSource(source)) return imageFallback(alt);
 
   const image = document.createElement(SESSION_IMAGE_TAG);
diff --git a/app/src/renderer/src/session-image-contract.js b/app/src/renderer/src/session-image-contract.js
new file mode 100644
index 0000000..3e6da82
--- /dev/null
+++ b/app/src/renderer/src/session-image-contract.js
@@ -0,0 +1,10 @@
+// Shared constants for the session image element. Kept free of the component
+// import so the Markdown renderer (and its tests) do not have to pull a .vue
+// module into scope just to know the tag name.
+
+export const SESSION_IMAGE_TAG = 'obelisk-session-image';
+
+// Fired from inside the session image element (composed, so it crosses the
+// shadow boundary) once the image has either decoded or failed. The virtualized
+// timeline uses it to tell real media growth apart from an estimate correction.
+export const SESSION_IMAGE_SETTLED_EVENT = 'obelisk-session-image-settled';
diff --git a/app/src/renderer/src/session-image-element.js b/app/src/renderer/src/session-image-element.js
index f365952..abaea24 100644
--- a/app/src/renderer/src/session-image-element.js
+++ b/app/src/renderer/src/session-image-element.js
@@ -1,7 +1,6 @@
 import { defineCustomElement } from 'vue';
 import SessionImage from './components/SessionImage.ce.vue';
-
-export const SESSION_IMAGE_TAG = 'obelisk-session-image';
+import { SESSION_IMAGE_TAG } from './session-image-contract.js';
 
 export function registerSessionImageElement() {
   if (customElements.get(SESSION_IMAGE_TAG)) return;
diff --git a/tests/markdown-image-renderer.test.mjs b/tests/markdown-image-renderer.test.mjs
new file mode 100644
index 0000000..cd65fe0
--- /dev/null
+++ b/tests/markdown-image-renderer.test.mjs
@@ -0,0 +1,36 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { normalizeMarkdownImageToken } from '../app/src/renderer/src/markdown-image-renderer.js';
+
+// marked <= 14 calls renderer.image(href, title, text); marked >= 15 passes the
+// token. Getting this wrong degrades silently: every session image turns into
+// fallback text because the href is no longer a string.
+test('accepts the positional renderer signature', () => {
+  assert.deepEqual(
+    normalizeMarkdownImageToken('http://example.test/a.png', 'A title', 'Alt text'),
+    { href: 'http://example.test/a.png', title: 'A title', text: 'Alt text' },
+  );
+});
+
+test('accepts the token renderer signature', () => {
+  assert.deepEqual(
+    normalizeMarkdownImageToken({
+      type: 'image',
+      href: 'http://example.test/a.png',
+      title: 'A title',
+      text: 'Alt text',
+    }),
+    { href: 'http://example.test/a.png', title: 'A title', text: 'Alt text' },
+  );
+});
+
+test('fills in the fields marked leaves null', () => {
+  assert.deepEqual(
+    normalizeMarkdownImageToken({ href: 'http://example.test/a.png', title: null, text: '' }),
+    { href: 'http://example.test/a.png', title: '', text: '' },
+  );
+  assert.deepEqual(
+    normalizeMarkdownImageToken('http://example.test/a.png', null, null),
+    { href: 'http://example.test/a.png', title: '', text: '' },
+  );
+});