improvise-2bac: context docs, evidence, fmt

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

tests/headless_cli.rs

@@ -410,7 +410,10 @@ fn commit_cell_edit_writes_the_named_cell_and_spares_the_cursors() {
 fn a_line_whose_gate_passes_runs_whole() {
     let scratch = Scratch::new("commit-atomic");
     let doc = scratch.path("atomic.improv");
-    let out = run_cmd(&["add-category Foo . commit-cell-edit editing 5 Foo/x"], &doc);
+    let out = run_cmd(
+        &["add-category Foo . commit-cell-edit editing 5 Foo/x"],
+        &doc,
+    );
     assert!(
         !stderr_of(&out).contains("Parse error"),
         "a line the gate accepted was refused part-way: {}",
@@ -418,7 +421,8 @@ fn a_line_whose_gate_passes_runs_whole() {
     );
     let text = std::fs::read_to_string(&doc).expect("the document");
     assert!(
-        text.lines().any(|l| l.contains("Foo=x") && l.ends_with("= 5")),
+        text.lines()
+            .any(|l| l.contains("Foo=x") && l.ends_with("= 5")),
         "the commit did not land: {text}"
     );
 }