diff --git a/apps/web/src/terminal/ghostty/keyCodes.test.ts b/apps/web/src/terminal/ghostty/keyCodes.test.ts
index ef4b623fdfc8..053881efca72 100644
--- a/apps/web/src/terminal/ghostty/keyCodes.test.ts
+++ b/apps/web/src/terminal/ghostty/keyCodes.test.ts
@@ -14,12 +14,29 @@ describe("ghosttyKeyForCode", () => {
 describe("ghosttyConsumedMods", () => {
   const shifted = { altKey: false, ctrlKey: false, key: "@", metaKey: false, shiftKey: true };
 
-  it("only consumes a lone Shift producing a character", () => {
-    expect(ghosttyConsumedMods(shifted)).toBe(1);
-    expect(ghosttyConsumedMods({ ...shifted, ctrlKey: true })).toBe(0);
-    expect(ghosttyConsumedMods({ ...shifted, key: "Tab" })).toBe(0);
+  it("consumes a lone Shift producing a character", () => {
+    expect(ghosttyConsumedMods(shifted, "Linux")).toBe(1);
+    expect(ghosttyConsumedMods({ ...shifted, ctrlKey: true }, "MacIntel")).toBe(0);
+    expect(ghosttyConsumedMods({ ...shifted, key: "Tab" }, "MacIntel")).toBe(0);
     // Deliberate: Shift+Space collapses to Space so it still types one.
-    expect(ghosttyConsumedMods({ ...shifted, key: " " })).toBe(1);
+    expect(ghosttyConsumedMods({ ...shifted, key: " " }, "Linux")).toBe(1);
+  });
+
+  it("consumes a lone macOS Option that produced a character", () => {
+    const option = { altKey: true, ctrlKey: false, key: "@", metaKey: false, shiftKey: false };
+    expect(ghosttyConsumedMods(option, "MacIntel")).toBe(1 << 2);
+    expect(ghosttyConsumedMods({ ...option, key: "€" }, "MacIntel")).toBe(1 << 2);
+    expect(ghosttyConsumedMods({ ...option, key: "∫" }, "MacIntel")).toBe(1 << 2);
+    expect(ghosttyConsumedMods({ ...option, key: "\\", shiftKey: true }, "MacIntel")).toBe(
+      (1 << 2) | 1,
+    );
+    expect(ghosttyConsumedMods({ ...option, ctrlKey: true }, "MacIntel")).toBe(0);
+    expect(ghosttyConsumedMods({ ...option, metaKey: true }, "MacIntel")).toBe(0);
+    expect(ghosttyConsumedMods({ ...option, key: "ArrowLeft" }, "MacIntel")).toBe(0);
+    expect(ghosttyConsumedMods({ ...option, key: "Dead" }, "MacIntel")).toBe(0);
+    expect(ghosttyConsumedMods(option, "Linux")).toBe(0);
+    expect(ghosttyConsumedMods(option, "Win32")).toBe(0);
+    expect(ghosttyConsumedMods({ ...option, shiftKey: true }, "Linux")).toBe(0);
   });
 });
 
diff --git a/apps/web/src/terminal/ghostty/keyCodes.ts b/apps/web/src/terminal/ghostty/keyCodes.ts
index a643827d6f2d..8c66188f7465 100644
--- a/apps/web/src/terminal/ghostty/keyCodes.ts
+++ b/apps/web/src/terminal/ghostty/keyCodes.ts
@@ -233,13 +233,34 @@ export function loadGhosttyKeyboardLayoutMap(): Promise<GhosttyKeyboardLayoutMap
   return promise;
 }
 
-// Browsers do not expose consumed modifiers; treat Shift as consumed for
-// unchorded character input.
+const GHOSTTY_MOD_SHIFT = 1 << 0;
+const GHOSTTY_MOD_ALT = 1 << 2;
+
+/**
+ * Modifiers the layout consumed to produce `event.key`, as a GhosttyMods bitmask.
+ *
+ * The DOM does not report consumed modifiers. A lone Shift is consumed so a
+ * shifted character is encoded as text. On macOS a lone Option is consumed too,
+ * along with Shift when Shift participated. This WASM build of libghostty-vt is
+ * not macOS, so it ignores `macos-option-as-alt` and DEC 1036 prefixes Alt:
+ * German Option+L (`@`) becomes `ESC @` (readline set-mark) and the rest of the
+ * Option layer (`€`, `~`, `[]{}|`, `\`) is dropped the same way. Consuming
+ * Option makes the encoder write the composed character, matching Ghostty's
+ * default of `macos-option-as-alt = false`. Ctrl and Meta are never consumed,
+ * so those chords stay intact. Option+arrow is not a single character, so word
+ * motion is unchanged.
+ */
 export function ghosttyConsumedMods(
   event: Pick<KeyboardEvent, "altKey" | "ctrlKey" | "key" | "metaKey" | "shiftKey">,
+  platform = typeof navigator === "undefined" ? "" : (navigator.platform ?? ""),
 ): number {
-  if (!event.shiftKey || event.ctrlKey || event.altKey || event.metaKey) return 0;
-  return [...event.key].length === 1 ? 1 : 0;
+  if ([...event.key].length !== 1 || event.ctrlKey || event.metaKey) return 0;
+  const shift = event.shiftKey ? GHOSTTY_MOD_SHIFT : 0;
+  // Same host check as isMacPlatform in lib/utils.ts. Kept local so this module
+  // stays free of the app utility graph.
+  if (event.altKey && /mac|iphone|ipad|ipod/i.test(platform)) return shift | GHOSTTY_MOD_ALT;
+  if (!event.shiftKey || event.altKey) return 0;
+  return GHOSTTY_MOD_SHIFT;
 }
 
 export function ghosttyUnshiftedCodepoint(