diff --git a/src/styles/theme.css b/src/styles/theme.css
index 12b1f5ad..c907d9e1 100644
--- a/src/styles/theme.css
+++ b/src/styles/theme.css
@@ -217,6 +217,30 @@
     max-width: 100vw;
   }
 
+  /*
+   * Monospace text is what learners read and type character by character.
+   * JetBrains Mono ships programming ligatures (contextual alternates): `--`
+   * is drawn as one continuous line, `->` as an arrow, `!=` as `≠`. In a
+   * terminal course that hides the very characters being taught — a learner
+   * typing `--no-ff` saw one of the two dashes "disappear" as soon as the
+   * space was typed, and had to paste the command to succeed (reported
+   * 24 September 2026). The property is inherited, so this covers the
+   * terminal output, its input and every code block or inline code chip.
+   *
+   * Known limit: WebKit (Safari macOS / iOS) is documented as unable to turn
+   * off contextual alternates from CSS. Verified in Chrome only; if Safari
+   * still merges `--`, the fix is a ligature-free font (JetBrains Mono NL),
+   * tracked in THI-354.
+   */
+  .font-mono,
+  code,
+  kbd,
+  samp,
+  pre {
+    font-variant-ligatures: none;
+    font-feature-settings: "liga" 0, "calt" 0;
+  }
+
   /**
   * Default typography styles for HTML elements (h1-h4, p, label, button, input).
   * These are in @layer base, so Tailwind utility classes (like text-sm, text-lg) automatically override them.
diff --git a/src/test/monospaceLigatures.test.ts b/src/test/monospaceLigatures.test.ts
new file mode 100644
index 00000000..f1e309b1
--- /dev/null
+++ b/src/test/monospaceLigatures.test.ts
@@ -0,0 +1,24 @@
+/**
+ * Regression guard (24 September 2026): JetBrains Mono draws `--` as one
+ * continuous line, so a learner typing `--no-ff` saw a dash "disappear" and had
+ * to paste the command. jsdom does not apply stylesheets, so this checks the
+ * rule itself; the visual effect was verified in Chrome.
+ */
+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+
+const css = readFileSync(resolve(__dirname, '../styles/theme.css'), 'utf8');
+
+describe('monospace text shows every character as typed', () => {
+  it('JetBrains Mono is the monospace font (the reason this rule exists)', () => {
+    expect(css).toMatch(/--font-mono:\s*'JetBrains Mono'/);
+  });
+
+  it('disables ligatures and contextual alternates for .font-mono, code, kbd, samp and pre', () => {
+    const rule = css.match(/\.font-mono,\s*code,\s*kbd,\s*samp,\s*pre\s*\{([^}]*)\}/);
+    expect(rule, 'monospace ligature rule missing from theme.css').not.toBeNull();
+    expect(rule![1]).toMatch(/font-variant-ligatures:\s*none/);
+    expect(rule![1]).toMatch(/"calt"\s*0/);
+  });
+});