diff --git a/lib/ui.eigs b/lib/ui.eigs
index 0f85a97..45de4bc 100644
--- a/lib/ui.eigs
+++ b/lib/ui.eigs
@@ -477,6 +477,15 @@ define push_modal(dlg, parent_w, parent_h) as:
     # moment it is pushed, and its children need absolute positions to be
     # hit-tested (#575). app_loop re-lays it every frame after this.
     _layout of [dlg, 0, 0]
+    # Scope keyboard focus to the dialog too (#631): rebuild the focus list
+    # from the dialog's own children and drop any background focus, so Tab
+    # cycles inside the modal and a stray Enter cannot fire a widget behind
+    # it before the user has Tabbed. Mouse modality already scopes via dispatch.
+    _ui.focus_list is []
+    _build_focus_list of dlg
+    _ui.focus_index is 0 - 1
+    _ui.focused_widget is null
+    _ui.focused_input is null
 
 define pop_modal() as:
     n is len of _ui.modal_stack
@@ -488,6 +497,18 @@ define pop_modal() as:
     for i in range of (n - 1):
         append of [new_stack, _ui.modal_stack[i]]
     _ui.modal_stack is new_stack
+    # Restore focus to whatever is now on top (#631): the next modal down, or
+    # the app root once the stack is empty. edit_root is null until app_loop
+    # runs, so a headless push/pop just clears focus rather than erroring.
+    focus_root is _ui.edit_root
+    if (len of new_stack) > 0:
+        focus_root is new_stack[(len of new_stack) - 1]
+    _ui.focus_list is []
+    if focus_root != null:
+        _build_focus_list of focus_root
+    _ui.focus_index is 0 - 1
+    _ui.focused_widget is null
+    _ui.focused_input is null
     return top
 
 define show_menu(menu_widget, x, y) as:
@@ -565,19 +586,21 @@ define handle_key(root, ev) as:
 # Event dispatch — registry-driven
 
 define dispatch(root, ev) as:
+    # A modal owns ALL input — pointer AND keyboard (#631). Rebind the root to
+    # the top of the stack BEFORE routing anything, so hit-testing, the
+    # registry walk, hover, drag AND keyboard focus navigation/activation all
+    # run against the dialog's subtree — nothing behind it can be reached. The
+    # keys previously returned above this rebind (mouse-only modality), which
+    # let a user Tab to a background widget and Enter-activate it through the
+    # dialog. This is also what lets a dialog host children (#575): they are
+    # dispatched to like any other widget. Escape still pops the modal —
+    # handle_key checks the stack directly, so it survives the rebind.
+    if (len of _ui.modal_stack) > 0:
+        root is _ui.modal_stack[(len of _ui.modal_stack) - 1]
     # Keys route through the same public handler app_loop uses (#563), so
     # dispatch is the single event door for mouse, wheel and keyboard.
     if ev.type == "keydown" or ev.type == "keyup":
         return handle_key of [root, ev]
-    # A modal owns the pointer: the top of the stack becomes the root for
-    # this event, so everything below — hit-testing, the registry walk,
-    # focus, hover, drag — runs against the dialog's subtree and nothing
-    # behind it can be reached. This is also what lets a dialog host
-    # children (#575): they are dispatched to like any other widget
-    # instead of through a special-case click handler that knew only
-    # about the dialog's own buttons.
-    if (len of _ui.modal_stack) > 0:
-        root is _ui.modal_stack[(len of _ui.modal_stack) - 1]
     mx is 0
     my is 0
     if ev.type == "mousemove" or ev.type == "mousedown" or ev.type == "mouseup":
diff --git a/tests/test_ui.eigs b/tests/test_ui.eigs
index 92ff623..c085fd6 100644
--- a/tests/test_ui.eigs
+++ b/tests/test_ui.eigs
@@ -1205,6 +1205,62 @@ remove_file of "/tmp/eigs_fd_probe/a.wav"
 remove_file of "/tmp/eigs_fd_probe/sub/inner.txt"
 _ui.modal_stack is []
 
+# ============================================================
+# #631: a modal owns the keyboard, not just the pointer
+# ============================================================
+# Before the fix, dispatch returned keys with the real root above the modal
+# rebind, so Tab escaped to a background widget and Enter activated it — an
+# "Are you sure? [Cancel]" dialog could fire the destructive action behind it.
+_ui.modal_stack is []
+_ui.focus_list is []
+_ui.focused_widget is null
+_ui.focused_input is null
+_ui.focus_index is 0 - 1
+
+m631_root is panel of ["m631_root", 0, 0, 800, 600]
+m631_fired is [0]
+define m631_boom(b) as:
+    m631_fired[0] is m631_fired[0] + 1
+m631_bg is button of ["M631_BEHIND", 0, 0, 100, 30, "danger", m631_boom]
+add_child of [m631_root, m631_bg]
+_layout of [m631_root, 0, 0]
+_ui.edit_root is m631_root
+_build_focus_list of m631_root
+
+# A dialog hosting two focusable children of its own (#575).
+m631_dlg is dialog of ["m631_dlg", 400, 300, "Modal", "", ["OK"], null]
+m631_hit is [0]
+define m631_ok(b) as:
+    m631_hit[0] is m631_hit[0] + 1
+m631_c1 is button of ["M631_C1", 0, 0, 60, 24, "One", m631_ok]
+m631_c2 is button of ["M631_C2", 0, 0, 60, 24, "Two", m631_ok]
+add_child of [m631_dlg, m631_c1]
+add_child of [m631_dlg, m631_c2]
+push_modal of [m631_dlg, 800, 600]
+
+# Tab scopes to the dialog, never the background.
+dispatch of [m631_root, {"type": "keydown", "key": "tab", "shift": 0, "ctrl": 0, "alt": 0}]
+assert_true of [_ui.focused_widget != null, "#631 Tab under a modal focuses a dialog child, not nothing"]
+assert_eq of [_ui.focused_widget.id, "M631_C1", "#631 Tab lands on the dialog's first child"]
+
+# Enter fires the DIALOG child, never the button behind the modal.
+dispatch of [m631_root, {"type": "keydown", "key": "return", "shift": 0, "ctrl": 0, "alt": 0}]
+assert_eq of [m631_fired[0], 0, "#631 Enter does not fire the button behind the modal"]
+assert_eq of [m631_hit[0], 1, "#631 Enter fires the focused dialog child"]
+
+# Tab again cycles within the dialog (C1 -> C2), still not the background.
+dispatch of [m631_root, {"type": "keydown", "key": "tab", "shift": 0, "ctrl": 0, "alt": 0}]
+assert_eq of [_ui.focused_widget.id, "M631_C2", "#631 Tab cycles between the dialog's own children"]
+
+# After pop, focus returns to the background list.
+pop_modal of null
+dispatch of [m631_root, {"type": "keydown", "key": "tab", "shift": 0, "ctrl": 0, "alt": 0}]
+assert_eq of [_ui.focused_widget.id, "M631_BEHIND", "#631 after pop_modal, Tab returns to the background widget"]
+assert_eq of [m631_fired[0], 0, "#631 the background button never fired via keyboard"]
+
+_ui.modal_stack is []
+_ui.edit_root is null
+
 # ============================================================
 # Summary
 # ============================================================