fix: alloc free off by one

include/ghostty.h

@@ -353,6 +353,7 @@ typedef struct {
 typedef struct {
   const char* ptr;
   uintptr_t len;
+  uintptr_t cap;
 } ghostty_string_s;
 
 typedef struct {

src/config/CApi.zig

@@ -130,7 +130,8 @@ export fn ghostty_config_open_path() c.String {
         return .empty;
     };
 
-    return .fromSlice(path);
+    // Capacity is len + 1 due to sentinel
+    return .fromSlice(path, path.len + 1);
 }
 
 /// Sync with ghostty_diagnostic_s

src/main_c.zig

@@ -63,16 +63,19 @@ const Info = extern struct {
 pub const String = extern struct {
     ptr: ?[*]const u8,
     len: usize,
+    cap: usize,
 
     pub const empty: String = .{
         .ptr = null,
         .len = 0,
+        .cap = 0,
     };
 
-    pub fn fromSlice(slice: []const u8) String {
+    pub fn fromSlice(slice: []const u8, cap: usize) String {
         return .{
             .ptr = slice.ptr,
             .len = slice.len,
+            .cap = cap,
         };
     }
 };
@@ -129,5 +132,5 @@ pub export fn ghostty_translate(msgid: [*:0]const u8) [*:0]const u8 {
 
 /// Free a string allocated by Ghostty.
 pub export fn ghostty_string_free(str: String) void {
-    state.alloc.free(str.ptr.?[0..str.len]);
+    state.alloc.free(str.ptr.?[0..str.cap]);
 }