fix(tools): skip degenerate identical hunks in V4A validation

The apply phase already skips a hunk whose -/+ lines are identical
(patch_parser.py '(search_lines == replace_lines): continue'), but the
validation phase lacked the guard: such a hunk reached
fuzzy_find_and_replace, whose identical-strings error names
old_string/new_string — parameters that don't exist in patch mode — and
failed the whole atomic patch that apply would have accepted. Mirror
the apply-phase skip in validation; regression test drives a mixed
degenerate+live patch end-to-end (short text dodges the
is_already_applied >=8-char rescue).

tools/patch_parser.py

@@ -323,6 +323,14 @@ def _validate_operations(
                 replace_lines = [l.content for l in hunk.lines if l.prefix in {' ', '+'}]
                 replacement = '\n'.join(replace_lines)
 
+                if search_lines == replace_lines:
+                    # Degenerate hunk whose -/+ lines are identical: the apply
+                    # phase skips it as a no-op, so validation must not fail it
+                    # — fuzzy_find_and_replace would reject the identical
+                    # search/replacement with old_string/new_string guidance
+                    # that has no meaning in V4A patch mode.
+                    continue
+
                 new_simulated, count, _strategy, match_error = fuzzy_find_and_replace(
                     simulated, search_pattern, replacement, replace_all=False
                 )