feat(ui): render assistant replies as Markdown

s2s-client/style.css

@@ -2772,6 +2772,103 @@ button[data-reports-sidebar-toggle] {
 }
 .hist-msg.user .hist-body.partial { opacity: 0.68; }
 
+/* Markdown is confined to assistant message bodies in both themes. */
+.markdown-content {
+  min-width: 0;
+  max-width: 100%;
+  box-sizing: border-box;
+  white-space: normal !important;
+  overflow-wrap: anywhere;
+}
+.markdown-content > :first-child { margin-top: 0; }
+.markdown-content > :last-child { margin-bottom: 0; }
+.markdown-content p { margin: 0 0 0.75em; }
+.markdown-content strong { font-weight: 700; }
+.markdown-content :is(h1, h2, h3, h4, h5, h6) {
+  margin: 1em 0 0.5em;
+  font-size: 1.12em;
+  font-weight: 700;
+  line-height: 1.35;
+}
+.markdown-content :is(ul, ol) {
+  margin: 0.65em 0;
+  padding-inline-start: 1.5em;
+}
+.markdown-content ul { list-style-type: disc; }
+.markdown-content ol { list-style-type: decimal; }
+.markdown-content li + li { margin-top: 0.35em; }
+.markdown-content li > p { margin: 0.25em 0; }
+.markdown-content li :is(ul, ol) { margin: 0.3em 0; }
+.markdown-content a {
+  color: var(--brand-3);
+  text-decoration: underline;
+  text-underline-offset: 0.15em;
+}
+html[data-theme="white"] .markdown-content a { color: #1d4ed8; }
+.markdown-content :is(a, pre, .markdown-table):focus-visible {
+  outline: 2px solid var(--brand);
+  outline-offset: 3px;
+}
+.markdown-content blockquote {
+  margin: 0.75em 0;
+  padding-inline-start: 12px;
+  border-inline-start: 3px solid var(--brand);
+  color: var(--text-dim);
+}
+.markdown-content code {
+  padding: 0.15em 0.35em;
+  border-radius: 4px;
+  background: color-mix(in srgb, currentColor 8%, transparent);
+  font-family: var(--font-mono);
+  font-size: 0.9em;
+}
+.markdown-content pre {
+  max-width: 100%;
+  margin: 0.75em 0;
+  padding: 12px;
+  border: 1px solid var(--border-strong);
+  border-radius: 8px;
+  overflow: auto;
+  white-space: pre;
+}
+.markdown-content pre code {
+  display: block;
+  padding: 0;
+  background: transparent;
+  white-space: pre;
+  overflow-wrap: normal;
+  word-break: normal;
+}
+.markdown-content hr {
+  margin: 1em 0;
+  border: 0;
+  border-top: 1px solid var(--border-strong);
+}
+.markdown-content img {
+  max-width: 100%;
+  height: auto;
+}
+.markdown-content .markdown-table {
+  max-width: 100%;
+  margin: 0.75em 0;
+  overflow-x: auto;
+  overscroll-behavior-x: contain;
+}
+.markdown-content table {
+  width: 100%;
+  border-collapse: collapse;
+  font-size: 0.92em;
+}
+.markdown-content :is(th, td) {
+  padding: 7px 10px;
+  border: 1px solid var(--border-strong);
+  text-align: start;
+  vertical-align: top;
+}
+.markdown-content th { font-weight: 700; }
+.markdown-content [align="center"] { text-align: center; }
+.markdown-content [align="right"] { text-align: end; }
+
 /* ─── Tool call history item ─────────────────────────────────────────── */
 
 .hist-tool-header {