diff --git a/.changeset/hydrate-session-posts.md b/.changeset/hydrate-session-posts.md
new file mode 100644
index 0000000..a9094b5
--- /dev/null
+++ b/.changeset/hydrate-session-posts.md
@@ -0,0 +1,5 @@
+---
+"sideshow": patch
+---
+
+Hydrate session post streams from the session list endpoint to avoid N+1 post detail requests on open.
diff --git a/e2e/viewer.spec.ts b/e2e/viewer.spec.ts
index 5c8fa55..d7badf9 100644
--- a/e2e/viewer.spec.ts
+++ b/e2e/viewer.spec.ts
@@ -74,13 +74,19 @@ test("a surface kind this viewer doesn't know shows a refresh hint, not a broken
   // server returns a valid surface, but rewrite the surface kind to one THIS
   // viewer build has no Match for. It must degrade to a neutral hint, never
   // the diff fallback.
-  await page.route(/\/api\/posts\/[^/?]+(\?|$)/, async (route) => {
+  await page.route(/\/api\/(posts\/[^/?]+|sessions\/[^/]+\/posts)(\?|$)/, async (route) => {
     const res = await route.fetch();
-    const surface = await res.json();
-    if (Array.isArray(surface.surfaces)) {
-      surface.surfaces = surface.surfaces.map(() => ({ kind: "futurething" }));
-    }
-    await route.fulfill({ response: res, json: surface });
+    const body = await res.json();
+    const rewrite = (post: any) => {
+      if (Array.isArray(post.surfaces)) {
+        post.surfaces = post.surfaces.map(() => ({ kind: "futurething" }));
+      }
+      return post;
+    };
+    await route.fulfill({
+      response: res,
+      json: Array.isArray(body) ? body.map(rewrite) : rewrite(body),
+    });
   });
 
   await page.goto(server.url);
@@ -94,6 +100,46 @@ test("a surface kind this viewer doesn't know shows a refresh hint, not a broken
   await expect(card.locator(".diff-error")).toHaveCount(0);
 });
 
+test("opening a session hydrates posts without N+1 post detail fetches", async ({
+  page,
+  server,
+}) => {
+  const first = await publish(server.url, {
+    html: "<p>one</p>",
+    title: "One",
+    agent: "e2e",
+    sessionTitle: "Hydrate",
+  });
+  await publish(server.url, {
+    html: "<p>two</p>",
+    title: "Two",
+    agent: "e2e",
+    session: first.sessionId,
+  });
+  await publish(server.url, {
+    html: "<p>three</p>",
+    title: "Three",
+    agent: "e2e",
+    session: first.sessionId,
+  });
+
+  const postDetailRequests: string[] = [];
+  const hydratedListRequests: string[] = [];
+  page.on("request", (req) => {
+    if (req.method() !== "GET") return;
+    const url = new URL(req.url());
+    if (/^\/api\/posts\/[^/]+$/.test(url.pathname)) postDetailRequests.push(req.url());
+    if (url.pathname === `/api/sessions/${first.sessionId}/posts`) {
+      hydratedListRequests.push(url.searchParams.get("hydrate") ?? "");
+    }
+  });
+
+  await page.goto(`${server.url}/session/${first.sessionId}`);
+  await expect(page.locator(".card:not(#whatsNew)")).toHaveCount(3);
+  expect(hydratedListRequests).toContain("1");
+  expect(postDetailRequests).toEqual([]);
+});
+
 test("resize bridge grows the iframe beyond its 120px default", async ({ page, server }) => {
   const tall = `<div style="height: 600px">tall content</div>`;
   await publish(server.url, { html: tall, title: "Tall", agent: "e2e" });
diff --git a/server/app.ts b/server/app.ts
index ed83caf..310ba55 100644
--- a/server/app.ts
+++ b/server/app.ts
@@ -1052,7 +1052,11 @@ export function createApp({
     const session = await store.getSession(c.req.param("id"));
     if (!session) return c.json({ error: "session not found" }, 404);
     const posts = await store.listPosts(session.id);
-    return c.json(posts.map(sessionPostListRowView));
+    return c.json(
+      c.req.query("hydrate") === "1"
+        ? posts.map(postDetailView)
+        : posts.map(sessionPostListRowView),
+    );
   };
   app.get("/api/sessions/:id/surfaces", listSessionPosts); // legacy alias
   app.get("/api/sessions/:id/posts", listSessionPosts);
diff --git a/test/api.test.ts b/test/api.test.ts
index 505ce5c..eabb8e2 100644
--- a/test/api.test.ts
+++ b/test/api.test.ts
@@ -2303,6 +2303,30 @@ test("GET /api/sessions/:id/posts lists lean surfaces with ids and omitted html
   assert.deepEqual(list[0].parts, list[0].surfaces, "legacy parts aliases surfaces");
 });
 
+test("GET /api/sessions/:id/posts?hydrate=1 returns full post details in one response", async () => {
+  const app = makeApp();
+  const created = (await (
+    await app.request(
+      "/api/posts",
+      json({ title: "Hydrated", surfaces: [{ kind: "html", html: "<p>heavy</p>" }] }),
+    )
+  ).json()) as any;
+  await app.request(`/api/posts/${created.id}`, {
+    ...json({ title: "Hydrated v2", surfaces: [{ kind: "html", html: "<p>new</p>" }] }),
+    method: "PUT",
+  });
+
+  const list = (await (
+    await app.request(`/api/sessions/${created.sessionId}/posts?hydrate=1`)
+  ).json()) as any[];
+  assert.equal(list.length, 1);
+  assert.equal(list[0].id, created.id);
+  assert.equal(list[0].surfaces[0].html, "<p>new</p>");
+  assert.equal(list[0].surfaces[0].index, 0);
+  assert.equal(list[0].history[0].surfaces[0].html, "<p>heavy</p>");
+  assert.equal(list[0].history[0].surfaces[0].index, 0);
+});
+
 test("read responses expose derived surface indexes and renumber after edits", async () => {
   const app = makeApp();
   const created = (await (
diff --git a/viewer/src/state.ts b/viewer/src/state.ts
index 4492986..fdb0baf 100644
--- a/viewer/src/state.ts
+++ b/viewer/src/state.ts
@@ -246,6 +246,29 @@ export async function refreshSessions(targetPostId?: string | null) {
   }
 }
 
+function isHydratedPost(value: unknown): value is Post {
+  return !!value && typeof value === "object" && Array.isArray((value as Post).history);
+}
+
+async function fetchSessionPostDetails(id: string): Promise<Post[]> {
+  const rows = await api<unknown[]>(`/api/sessions/${id}/posts?hydrate=1`).catch(() => []);
+  const hydrated: Post[] = [];
+  for (const row of rows) {
+    if (isHydratedPost(row)) hydrated.push(row);
+  }
+  if (hydrated.length === rows.length) return hydrated;
+  const details = await Promise.all(
+    rows.map((row) =>
+      row && typeof row === "object" && typeof (row as { id?: unknown }).id === "string"
+        ? api<Post>(`/api/posts/${encodeURIComponent((row as { id: string }).id)}`).catch(
+            () => null,
+          )
+        : null,
+    ),
+  );
+  return details.filter((post): post is Post => post !== null);
+}
+
 export async function select(
   id: string,
   opts?: { fromPopState?: boolean; replace?: boolean; initialPostId?: string },
@@ -272,10 +295,7 @@ export async function select(
   setCommentsInternal([]);
   setTraceStepsInternal([]);
   void fetchTrace(id);
-  const metas = await api<{ id: string }[]>(`/api/sessions/${id}/posts`).catch(() => []);
-  const details = (
-    await Promise.all(metas.map((m) => api<Post>(`/api/posts/${m.id}`).catch(() => null)))
-  ).filter((s) => s !== null);
+  const details = await fetchSessionPostDetails(id);
   if (selected() !== id) return; // user switched away mid-load
   setPostsInternal(reconcile(details, { key: "id" }));
   // Scroll to a specific post if requested (deep link).
@@ -577,8 +597,8 @@ async function resyncSelected() {
   await refreshSessions();
   if (!before || selected() !== before) return; // select() rebuilt the stream
   void fetchTrace(before);
-  const metas = await api<{ id: string }[]>(`/api/sessions/${before}/posts`).catch(() => []);
-  const ids = new Set(metas.map((m) => m.id));
+  const details = await fetchSessionPostDetails(before);
+  const ids = new Set(details.map((post) => post.id));
   setPostsInternal(
     produce((arr) => {
       for (let i = arr.length - 1; i >= 0; i--) {
@@ -586,7 +606,7 @@ async function resyncSelected() {
       }
     }),
   );
-  for (const meta of metas) await upsertPost(meta.id, { scroll: false });
+  if (selected() === before) setPostsInternal(reconcile(details, { key: "id" }));
   const res = await api<{ comments: Comment[] }>(`/api/comments?session=${before}`).catch(
     () => null,
   );