Add explicit job output panel

src/session.zig

@@ -144,7 +144,7 @@ pub const Session = struct {
     pub fn openFixtureAt(self: *Session, fixture: []const u8, cursor_byte: usize) !void {
         if (self.buffer) |*buffer| buffer.deinit();
         var buffer = try Buffer.openFromBytes(self.allocator, fixture);
-        buffer.cursor.byte = previousBoundary(buffer.bytes.items, @min(cursor_byte, buffer.bytes.items.len));
+        buffer.cursor.byte = boundaryAtOrBefore(buffer.bytes.items, @min(cursor_byte, buffer.bytes.items.len));
         buffer.refreshCell();
         self.buffer = buffer;
     }
@@ -227,6 +227,13 @@ pub const Session = struct {
     }
 };
 
+pub fn boundaryAtOrBefore(bytes: []const u8, cursor: usize) usize {
+    var i = @min(cursor, bytes.len);
+    if (i == bytes.len) return i;
+    while (i > 0 and isContinuation(bytes[i])) : (i -= 1) {}
+    return i;
+}
+
 pub fn previousBoundary(bytes: []const u8, cursor: usize) usize {
     if (cursor == 0) return 0;
     var i = @min(cursor, bytes.len) - 1;
@@ -298,6 +305,15 @@ fn isWide(cp: u21) bool {
         (cp >= 0x20000 and cp <= 0x3fffd);
 }
 
+test "regular: opening a fixture at a cursor byte keeps exact utf8 boundary" {
+    var session = Session.init(std.testing.allocator);
+    defer session.deinit();
+
+    try session.openFixtureAt("one\nabcdTARGET\n", 8);
+    const snap = try session.snapshot();
+    try std.testing.expectEqual(@as(usize, 8), snap.cursor_byte);
+}
+
 test "regular: session opens fixture and dispatches multibyte edits" {
     var session = Session.init(std.testing.allocator);
     defer session.deinit();