fix(workflow-renderer): remove quadratic backtracking in reference highlighting (#7672)

The env-var branch of the display-text scanner used `\{\{[^}]+\}\}`. Because
the character class admits `{`, a run of unmatched braces restarts a full
backtracking scan at every offset, making the scan quadratic — 100k braces
took 8.3s. Excluding `{` from the class makes it linear (~1ms) and matches
the `[^{}]+` form the executor's placeholder resolvers already use, so
highlighting no longer marks references the executor would never resolve.


Claude-Session: https://claude.ai/code/session_0139x4ngJzcoYrjwsS9B2ZG4

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: waleedlatif1

packages/workflow-renderer/src/formatted-text.test.tsx

@@ -104,3 +104,21 @@ describe('shared reference formatting', () => {
     expect((html.match(/class=/g) ?? []).length).toBe(2)
   })
 })
+
+describe('brace scanning', () => {
+  it('highlights the innermost environment reference inside repeated braces', () => {
+    const html = renderToStaticMarkup(
+      <>{formatDisplayText('{{{{KEY}}', { availableEnvVars: new Set(['KEY']) })}</>
+    )
+
+    expect(html).toContain('<span>{{</span>')
+    expect(html).toContain('text-[var(--brand-secondary)]')
+    expect(html).toContain('{{KEY}}')
+  })
+
+  it('scans unterminated brace runs in linear time', () => {
+    const started = performance.now()
+    formatDisplayText('{'.repeat(100_000))
+    expect(performance.now() - started).toBeLessThan(1_000)
+  })
+})

packages/workflow-renderer/src/formatted-text.tsx

@@ -107,7 +107,7 @@ function formatDisplayTextInternal(
   }
 
   const nodes: ReactNode[] = []
-  const regex = /<[^<>]+>|\{\{[^}]+\}\}/g
+  const regex = /<[^<>]+>|\{\{[^{}]+\}\}/g
   let lastIndex = 0
   let key = 0