patches: review fixes — memory leak, dead code, unwind-protect, protocol conformance

B1: Fix memory leak in ns_ax_scan_interactive_spans — [spans copy]
    returned +1 retained object never released by caller.
    Now returns [[spans copy] autorelease].

B2: Remove dead function ns_ax_utf16_length_for_buffer_range —
    defined but never called anywhere in the patch.

B3: Add specpdl unwind protection in
    EmacsAccessibilityInteractiveSpan setAccessibilityFocused: —
    if Fselect_window signals, block_input is now always matched
    by unblock_input via record_unwind_protect_void.

W2: Document ns_ax_event_is_line_nav_key fragility in README
    Known Limitations (raw keycodes vs command symbols).

W4: Add comment for #include intervals.h (TEXT_PROP_MEANS_INVISIBLE).

M3: accessibilityBoundsForRange: on EmacsView now delegates to the
    focused EmacsAccessibilityBuffer for accurate per-range geometry,
    with cursor-rect fallback for Zoom.

M4: Add <NSAccessibility> protocol conformance to
    EmacsAccessibilityBuffer @interface declaration.

W1: Expanded commit message listing all new types, functions, DEFSYM
    additions, and threading model.

patches/README.txt

@@ -131,7 +131,9 @@ THREADING MODEL
       - postAccessibilityNotificationsForFrame: (full notify logic)
       - setAccessibilitySelectedTextRange: (SET_PT_BOTH, marker moves)
       - setAccessibilityFocused: on EmacsAccessibilityInteractiveSpan
-        (dispatches to main queue via dispatch_async)
+        (dispatches to main queue via dispatch_async; uses specpdl
+         unwind protection so block_input is always matched by
+         unblock_input even if Fselect_window signals an error)
       - ns_draw_phys_cursor partial update (lastAccessibilityCursorRect,
         UAZoomChangeFocus)
 
@@ -343,8 +345,9 @@ INTERACTIVE SPANS
   and referenced directly -- no repeated intern() calls.
 
   Each span is allocated, configured, added to the spans array, then
-  released (the array retains it).  Label priority: completion--string
-  > buffer substring > help-echo.
+  released (the array retains it).  The function returns an autoreleased
+  immutable copy of the spans array.  Label priority:
+  completion--string > buffer substring > help-echo.
 
   Tab navigation: -accessibilityChildrenInNavigationOrder returns the
   cached span array, rebuilt lazily when interactiveSpansDirty is set.
@@ -381,9 +384,13 @@ ZOOM INTEGRATION
   2. EmacsView -accessibilityBoundsForRange: /
      -accessibilityFrameForRange:
      AT tools (including Zoom) call these with the selectedTextRange
-     to locate the insertion point.  The implementation returns the
-     screen rect stored in lastAccessibilityCursorRect, with a minimum
-     size of 1x8 pixels.  The legacy parameterized-attribute API
+     to locate the insertion point.  The implementation first delegates
+     to the focused EmacsAccessibilityBuffer element for accurate
+     per-range geometry via its accessibilityFrameForRange: method.
+     If the buffer element returns an empty rect (no valid window or
+     glyph data), the fallback uses the cached cursor rect stored in
+     lastAccessibilityCursorRect (minimum size 1x8 pixels).  The legacy
+     parameterized-attribute API
      (NSAccessibilityBoundsForRangeParameterizedAttribute) is supported
      via -accessibilityAttributeValue:forParameter: for older AT
      clients.
@@ -479,6 +486,13 @@ KNOWN LIMITATIONS
   - GNUstep is explicitly excluded (#ifdef NS_IMPL_COCOA).  GNUstep
     has a different accessibility model and requires separate work.
 
+  - Line navigation detection (ns_ax_event_is_line_nav_key) checks
+    raw key codes (C-n = 14, C-p = 16, Tab = 9, backtab symbol).
+    Users who remap keys to navigation commands (e.g. C-j -> next-line)
+    will not get forced line-granularity announcements for those
+    bindings.  A future improvement would inspect Vthis_command
+    against known navigation command symbols instead.
+
   - UAZoomChangeFocus always uses kUAZoomFocusTypeInsertionPoint
     regardless of cursor style (box, bar, hbar).  This is cosmetically
     imprecise but functionally correct.