feat(viewer): Markdown and plain-text documents are drawn as text

A text/markdown file (or text/x-markdown) is drawn as formatted text by
egui_commonmark, with no image loading, so a document never makes the
viewer read a file or the network; any other text/* type as its
selectable text. UTF-8 only (a leading byte-order mark dropped), at most
2 MiB; past that or not UTF-8, the viewer says why. The documents page's
tile shows the text's first lines. The SHA-256 row is cut to its column
(it ran off the panel and widened the page under it).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-gui/tests/text_documents.rs

@@ -0,0 +1,123 @@
+//! Text documents in the viewer: a Markdown file is drawn as formatted
+//! text, a plain-text file as its text, both on the document's page and
+//! on its tile; a text file that isn't UTF-8 says so rather than show
+//! half of it.
+
+use egui_kittest::Harness;
+use egui_kittest::kittest::Queryable;
+use ledger_core::Currency;
+use ledger_gui::nav::Route;
+use ledger_gui::{App, Source, data};
+use ledger_store::Store;
+use std::path::PathBuf;
+
+struct TempDir(PathBuf);
+
+impl TempDir {
+    fn new(tag: &str) -> TempDir {
+        let d = std::env::temp_dir().join(format!("ledger-gui-text-{tag}-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&d);
+        std::fs::create_dir_all(&d).unwrap();
+        TempDir(d)
+    }
+}
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_dir_all(&self.0);
+    }
+}
+
+const PLAN: &str = "\u{feff}# Studio plan\n\nThe studio's goal is **ten apps** that earn.\n\n\
+- Chess openings\n- Route planner\n";
+
+fn open(dir: &TempDir, route: Route) -> Harness<'static, App> {
+    let books = data::load_once(&Source {
+        data_dir: dir.0.join("books-data"),
+        today: Some(chrono::NaiveDate::from_ymd_opt(2026, 10, 23).unwrap()),
+    })
+    .unwrap();
+    let mut h = Harness::builder()
+        .with_size(egui::vec2(1100.0, 900.0))
+        .build_eframe(|cc| App::with_books(&cc.egui_ctx, books, false, route));
+    h.run_steps(3);
+    let ctx = h.ctx.clone();
+    h.state_mut().settle(&ctx);
+    h.run_steps(3);
+    h
+}
+
+/// SHOT_DIR set: the page as drawn, to look at.
+fn shot(h: &mut Harness<'static, App>, name: &str) {
+    if let Ok(out) = std::env::var("SHOT_DIR") {
+        let out = PathBuf::from(out);
+        std::fs::create_dir_all(&out).unwrap();
+        h.render()
+            .unwrap()
+            .save(out.join(format!("{name}.png")))
+            .unwrap();
+    }
+}
+
+#[test]
+fn a_markdown_document_is_drawn_as_formatted_text() {
+    let dir = TempDir::new("md");
+    let mut s = Store::create(&dir.0.join("books-data"), Currency::USD).unwrap();
+    let (md, _, _) = s
+        .file_document(
+            "other",
+            "plan.md",
+            "text/markdown",
+            PLAN.as_bytes(),
+            Some("Plan for the studio"),
+        )
+        .unwrap();
+    drop(s);
+    let mut h = open(&dir, Route::Document(md));
+    shot(&mut h, "markdown-document");
+    // The heading is its own text, without the "#" or the byte-order mark;
+    // the list items are there; nothing says it can't be shown.
+    assert!(h.query_by_label("Studio plan").is_some());
+    assert!(h.query_by_label_contains("# Studio").is_none());
+    assert!(h.query_by_label_contains("Chess openings").is_some());
+    assert!(h.query_by_label_contains("Route planner").is_some());
+    assert!(h.query_by_label_contains("can't be previewed").is_none());
+    assert!(h.query_by_label_contains("Can't show").is_none());
+}
+
+#[test]
+fn a_plain_text_document_is_its_text_and_bad_text_says_so() {
+    let dir = TempDir::new("txt");
+    let mut s = Store::create(&dir.0.join("books-data"), Currency::USD).unwrap();
+    let (txt, _, _) = s
+        .file_document(
+            "other",
+            "notes.txt",
+            "text/plain; charset=utf-8",
+            b"Meeting notes\nall agreed",
+            None,
+        )
+        .unwrap();
+    let (bad, _, _) = s
+        .file_document("other", "bad.md", "text/markdown", b"caf\xe9", None)
+        .unwrap();
+    drop(s);
+    let h = open(&dir, Route::Document(txt));
+    assert!(h.query_by_label_contains("Meeting notes").is_some());
+    assert!(h.query_by_label_contains("Can't show").is_none());
+    let h = open(&dir, Route::Document(bad));
+    assert!(h.query_by_label_contains("the text isn't UTF-8").is_some());
+}
+
+#[test]
+fn the_documents_page_draws_text_tiles() {
+    let dir = TempDir::new("tiles");
+    let mut s = Store::create(&dir.0.join("books-data"), Currency::USD).unwrap();
+    s.file_document("other", "plan.md", "text/markdown", PLAN.as_bytes(), None)
+        .unwrap();
+    drop(s);
+    let mut h = open(&dir, Route::Documents);
+    h.run_steps(2);
+    shot(&mut h, "text-tiles");
+    assert_eq!(h.state_mut().route(), &Route::Documents);
+}