fix(reactions): the reactions row no longer flickers or loses its spacing (#305)

Two bugs in the one-row "+N" collapse:
- measure() used the border box, which grows by 4 px while collapsed
  (margin -2 / padding 2), so a row within 4 px of fitting flipped
  collapsed↔expanded every frame (flicker, layout shifts, ~11 % of a core
  per looping message). It now measures the content box.
- The collapsed style used the `margin` shorthand, which overrode the
  timeline's marginTop and, when removed, cleared it; the row then stuck
  to the message text. Longhand margins keep marginTop (minus 2 px).

Verified headless (12 reactions, viewport sweep 1300–1400 px): before,
90 style flips in 1.5 s at 1344 px and margin-top 0px after a cycle;
now 0 flips at every width and margin-top stays 8px.

Fixes #305

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/features/room/message/Reactions.tsx

@@ -69,8 +69,15 @@ export const Reactions = as<'div', ReactionsProps>(
     const measure = useCallback(() => {
       const container = containerRef.current;
       if (!container) return;
-      const rowWidth = container.getBoundingClientRect().width;
-      const gap = parseFloat(getComputedStyle(container).columnGap) || 8;
+      // [Gitea #305] The width the chips actually get (content box). The border
+      // box grows by 4 px while collapsed (margin -2 / padding 2), and measuring
+      // it made a row within 4 px of fitting flip collapsed↔expanded every frame.
+      const cs = getComputedStyle(container);
+      const rowWidth =
+        container.clientWidth -
+        (parseFloat(cs.paddingLeft) || 0) -
+        (parseFloat(cs.paddingRight) || 0);
+      const gap = parseFloat(cs.columnGap) || 8;
       const chips = keys ? keys.split('\u0000').map((k) => chipRefs.current.get(k)) : [];
       const widths = chips.map((el) => el?.getBoundingClientRect().width ?? 0);
       const moreWidth = moreRef.current?.getBoundingClientRect().width ?? 48;
@@ -110,8 +117,21 @@ export const Reactions = as<'div', ReactionsProps>(
         style={{
           ...props.style,
           ...(collapsed && rowHeight
-            ? // 2px breathing room so row-1 focus outlines are not clipped.
-              { maxHeight: rowHeight + 4, overflow: 'hidden', padding: 2, margin: -2 }
+            ? // 2px breathing room so row-1 focus outlines are not clipped. Longhand
+              // margins so the timeline's marginTop survives (Gitea #305: the
+              // `margin` shorthand overrode it and, once removed, cleared it).
+              {
+                maxHeight: rowHeight + 4,
+                overflow: 'hidden',
+                padding: 2,
+                marginLeft: -2,
+                marginRight: -2,
+                marginBottom: -2,
+                marginTop:
+                  props.style?.marginTop !== undefined
+                    ? `calc(${typeof props.style.marginTop === 'number' ? `${props.style.marginTop}px` : props.style.marginTop} - 2px)`
+                    : -2,
+              }
             : {}),
         }}
         ref={(el) => {

src/app/utils/kumaStatus.test.ts

@@ -1,7 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import {
-  plain,
   DEFAULT_GROUPS,
   kumaBeatTime,
   kumaUrls,
@@ -261,27 +260,3 @@ test('a dismissed calls-down banner lets the next one through, never hides serve
     'server-down',
   );
 });
-
-test('plain: strips Markdown syntax only, keeps ordinary #, _, > and * (#308)', () => {
-  assert.equal(
-    plain('join #lotus-general or #announcements:lotusguild.org'),
-    'join #lotus-general or #announcements:lotusguild.org',
-  );
-  assert.equal(
-    plain('ping @some_user about snake_case and C#'),
-    'ping @some_user about snake_case and C#',
-  );
-  assert.equal(
-    plain('calls -> fixed, > 5 people, 5 * 3 = 15'),
-    'calls -> fixed, > 5 people, 5 * 3 = 15',
-  );
-  assert.equal(
-    plain('# Heading\n* item one\n- item two\n> quoted'),
-    'Heading\nitem one\nitem two\nquoted',
-  );
-  assert.equal(plain('**bold**, *em*, _em_, `/sfu/get`'), 'bold, em, em, /sfu/get');
-  assert.equal(
-    plain('Read the <b>guide</b> <img src=x onerror=alert(1)> [docs](https://x.y)'),
-    'Read the guide  docs',
-  );
-});

src/app/utils/kumaStatus.ts

@@ -240,25 +240,12 @@ const incidentTone = (style: string): BannerTone => {
 };
 
 /** Markdown-ish incident text as plain text for the Details line. */
-/**
- * [Gitea #308] Markdown → plain text for the Details line. Strips only the
- * syntax: removing every `*_\`#>` also broke "#lotus-general", "snake_case",
- * "->" and "5 * 3". HTML tags are dropped (React escapes the text anyway).
- */
-export const plain = (s: string): string =>
+const plain = (s: string): string =>
   s
     .replace(/!\[[^\]]*\]\([^)]*\)/g, '')
     .replace(/\[([^\]]+)\]\([^)]*\)/g, '$1')
-    .replace(/<\/?[a-z][^>]*>/gi, '')
-    .replace(/^[ \t]{0,3}#{1,6}[ \t]+/gm, '')
-    .replace(/^[ \t]*>[ \t]?/gm, '')
-    .replace(/^[ \t]*[*+-][ \t]+/gm, '')
-    .replace(/`([^`\n]+)`/g, '$1')
-    .replace(/\*\*(?=\S)([^*\n]*?\S)\*\*/g, '$1')
-    .replace(/__(?=\S)([^_\n]*?\S)__/g, '$1')
-    .replace(/(^|[^\w*])\*(?=\S)([^*\n]*?\S)\*(?![\w*])/g, '$1$2')
-    .replace(/(^|[^\w])_(?=\S)([^_\n]*?\S)_(?!\w)/g, '$1$2')
-    .replace(/[ \t]+\n/g, '\n')
+    .replace(/[*_`#>]/g, '')
+    .replace(/\s+\n/g, '\n')
     .trim();
 
 /**