feat(api): enforce REVIEW_CAP, level overflow reviews, and display difficulty in digest

apps/api/src/email.tsx

@@ -35,6 +35,7 @@ import {
 } from "@react-email/components";
 import { render } from "@react-email/render";
 import type { CSSProperties } from "react";
+import { REVIEW_CAP } from "./srs.ts";
 
 // ── palette (GitHub dark) ────────────────────────────────────────
 const CANVAS = "#010409";
@@ -82,6 +83,14 @@ export interface DigestRow {
   failUrl: string;
 }
 
+/** A learning-day core problem — the only rows allowed a link. */
+export interface TopicRow {
+  lc: number;
+  difficulty: string;
+  url: string;
+  solved: boolean;
+}
+
 export interface DigestData {
   /** "Tuesday, August 25" */
   day: string;
@@ -89,9 +98,9 @@ export interface DigestData {
   progress: string;
   streak: number;
   rest: boolean;
-  topic?: { name: string; core: { lc: number; url: string; solved: boolean }[] };
+  topic?: { name: string; core: TopicRow[] };
   reviews: DigestRow[];
-  /** Reviews past the daily cap; they simply stay due. */
+  /** Reviews past the daily cap; levelled onto the coming days. */
   carried: number;
   drills: DigestRow[];
   gate?: { week: number; url: string };
@@ -196,6 +205,48 @@ function ProblemTable({ rows, staged }: { rows: DigestRow[]; staged: boolean })
   );
 }
 
+/**
+ * The learning day's core list as the same table shape as reviews — this is
+ * the one section allowed to link problems, and ticks replace tap buttons.
+ */
+function TopicTable({ rows }: { rows: TopicRow[] }) {
+  return (
+    <table
+      width="100%"
+      border={0}
+      cellPadding={0}
+      cellSpacing={0}
+      style={{ borderCollapse: "collapse", width: "100%" }}
+    >
+      <thead>
+        <tr>
+          <th style={th}>Problem</th>
+          <th style={th}>Level</th>
+          <th style={{ ...th, textAlign: "right" }}>Solved</th>
+        </tr>
+      </thead>
+      <tbody>
+        {rows.map((p) => {
+          const difficulty = DIFFICULTY[p.difficulty];
+          return (
+            <tr key={p.lc}>
+              <td style={{ ...td, fontWeight: 600 }}>
+                <Link href={p.url} style={{ color: p.solved ? MUTED : LINK, textDecoration: "none" }}>
+                  LC {p.lc}
+                </Link>
+              </td>
+              <td style={{ ...td, color: difficulty?.color ?? INK }}>{difficulty?.label ?? p.difficulty}</td>
+              <td style={{ ...td, color: p.solved ? GREEN : MUTED, textAlign: "right" }}>
+                {p.solved ? "✓" : "—"}
+              </td>
+            </tr>
+          );
+        })}
+      </tbody>
+    </table>
+  );
+}
+
 function Block({
   title,
   note,
@@ -265,18 +316,8 @@ function DigestEmail({ data }: { data: DigestData }) {
                     <Text style={{ color: INK, fontSize: "16px", fontWeight: 600, margin: "0 0 8px" }}>
                       {data.topic.name}
                     </Text>
-                    <Text style={{ ...hint, margin: 0 }}>
-                      Work through these — ticked ones you have already solved:{" "}
-                      {data.topic.core.map((p, i) => (
-                        <span key={p.lc}>
-                          {i > 0 ? " · " : ""}
-                          <Link href={p.url} style={{ color: p.solved ? MUTED : LINK, textDecoration: "none" }}>
-                            LC {p.lc}
-                          </Link>
-                          {p.solved ? <span style={{ color: GREEN }}> ✓</span> : null}
-                        </span>
-                      ))}
-                    </Text>
+                    <Text style={hint}>Work through these from the top — a tick means it is already solved.</Text>
+                    <TopicTable rows={data.topic.core} />
                   </Section>
                 ) : null}
 
@@ -289,8 +330,8 @@ function DigestEmail({ data }: { data: DigestData }) {
                 />
                 {data.carried > 0 ? (
                   <Text style={{ ...hint, margin: "12px 0 0" }}>
-                    {data.carried} more {data.carried === 1 ? "is" : "are"} waiting — they come back
-                    tomorrow, oldest first.
+                    {data.carried} more {data.carried === 1 ? "is" : "are"} waiting — spread over the
+                    coming days, oldest first, never more than {REVIEW_CAP} a day.
                   </Text>
                 ) : null}
 
@@ -373,8 +414,11 @@ function plainDigest(data: DigestData): string {
       out.push(
         "",
         `SOMETHING NEW TODAY — ${data.topic.name}`,
-        "Work through these; the ones marked done you have already solved.",
-        ...data.topic.core.map((p) => `  LC ${p.lc}${p.solved ? " (done)" : ""} — ${p.url}`),
+        "Work through these from the top; the ones marked done you have already solved.",
+        ...data.topic.core.map(
+          (p) =>
+            `  LC ${p.lc} — ${DIFFICULTY[p.difficulty]?.label ?? p.difficulty}${p.solved ? " (done)" : ""} — ${p.url}`,
+        ),
       );
     }
 
@@ -411,7 +455,7 @@ function plainDigest(data: DigestData): string {
     if (data.carried > 0) {
       out.push(
         "",
-        `${data.carried} more ${data.carried === 1 ? "is" : "are"} waiting — they come back tomorrow, oldest first.`,
+        `${data.carried} more ${data.carried === 1 ? "is" : "are"} waiting — spread over the coming days, oldest first, never more than ${REVIEW_CAP} a day.`,
       );
     }
     if (data.gate) {