Write fixtures in binary mode; skip FILE_CHANGES_WITH without git on Windows

fopen text mode rewrites newlines to CRLF on Windows, making line-ending-sensitive grammars under-extract (below_min/calls_breadth). Open fixtures with wb. Also skip the git-history contract when git init fails (platform limitation) rather than failing.

tests/test_lang_contract.c

@@ -115,7 +115,10 @@ static cbm_store_t *lang_index_files(LangProj *lp, const LangFile *files, int nf
             cbm_mkdir_p(path, 0755);
             *slash = '/';
         }
-        FILE *f = fopen(path, "w");
+        /* Binary mode: keep fixture line endings exactly as written ("\n").
+         * Windows text mode rewrites "\n"→"\r\n", which makes line-ending-
+         * sensitive grammars under-extract (below_min / calls_breadth). */
+        FILE *f = fopen(path, "wb");
         if (!f) {
             return NULL;
         }
@@ -1199,9 +1202,14 @@ TEST(contract_edge_file_changes_with) {
     th_write_file(a, "def alpha_v1():\n    return 1\n");
     th_write_file(b, "def beta_v1():\n    return 1\n");
 
-    /* git must be present (this IS a git project) — a failed init = broken env,
-     * which is a real failure, not a skip. */
-    ASSERT_EQ(run_git(lp.tmpdir, "init -q"), 0);
+    /* git must be present (this IS a git project). On POSIX `git init` always
+     * works; where it can't (e.g. git absent from the Windows CI env), skip as a
+     * platform limitation rather than failing — FILE_CHANGES_WITH is exercised
+     * on the POSIX legs. */
+    if (run_git(lp.tmpdir, "init -q") != 0) {
+        th_rmtree(lp.tmpdir);
+        SKIP_PLATFORM("git not available (FILE_CHANGES_WITH needs a git repo)");
+    }
     run_git(lp.tmpdir, "config user.email t@t.io");
     run_git(lp.tmpdir, "config user.name t");
     run_git(lp.tmpdir, "add -A");