Viewer: clickable breadcrumbs

Every crumb above the page you're on links to where it names: the
section goes to its home (Parties › Tobin Harlow → Parties), and a
reconciliation's trail runs Accounts › its account › it. Same look; a
pointer and "Go to …" on hover. A crumb naming the current page isn't a
link.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

crates/ledger-gui/tests/breadcrumbs.rs

@@ -0,0 +1,107 @@
+//! The breadcrumb links back up: every crumb but the page you're on goes
+//! where it names.
+//!
+//! ```text
+//! GOAL: from Parties › Tobin Harlow, clicking "Parties" goes back to the
+//!       directory; deeper trails link each level.
+//! SOURCE: DECISION (owner, 2026-10-16: "I should be able to click
+//!         parties and it takes me back there ... when it goes deeper").
+//! INVARIANTS: palette::crumbs 1-3, and
+//!   4. Clicking a crumb goes to its route (a history step, so Back
+//!      returns).
+//! ```
+
+use egui_kittest::Harness;
+use egui_kittest::kittest::Queryable;
+use ledger_gui::nav::{ReportKind, Route, Section};
+use ledger_gui::palette::{crumbs, describe};
+use ledger_gui::{App, Source, data};
+
+fn demo(tag: &str) -> Source {
+    let dir = std::env::temp_dir().join(format!("ledger-gui-crumbs-{tag}-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    let today = chrono::NaiveDate::from_ymd_opt(2026, 10, 12).unwrap();
+    ledger_gui::demo::build(&dir, today).unwrap();
+    Source {
+        data_dir: dir.join("books-data"),
+        books_toml: Some(dir.join("wanderbooks.toml")),
+        today: Some(today),
+    }
+}
+
+/// INVARIANTS 1-3 on every kind of page in the demo books.
+#[test]
+fn crumbs_link_every_level_but_the_last() {
+    let b = data::load_once(&demo("unit")).unwrap();
+    let party = b.ledger.parties().next().unwrap().id;
+    let rec = b.reconciliations.first().expect("the demo reconciles");
+    let entry = b.entries.first().unwrap().id;
+    let mut routes = vec![
+        Route::Party(party),
+        Route::Reconciliation(rec.id),
+        Route::Entry(entry),
+        Route::Reports(ReportKind::ProfitAndLoss),
+        Route::Reports(ReportKind::BalanceSheet),
+    ];
+    routes.extend(Section::ALL.iter().map(|s| s.home()));
+    for r in &routes {
+        let c = crumbs(Some(&b), r);
+        assert_eq!(c[0].0, r.section().title(), "{r:?}");
+        assert!(c.last().unwrap().1.is_none(), "{r:?}: the page you're on");
+        for (_, to) in &c {
+            assert_ne!(to.as_ref(), Some(r), "{r:?} links to itself");
+        }
+        // Every crumb above is a link, except one naming this very page
+        // (Reports on Profit and loss, the Reports section's home).
+        for (i, (_, to)) in c[..c.len() - 1].iter().enumerate() {
+            let home_here = i == 0 && r.section().home() == *r;
+            assert_eq!(to.is_some(), !home_here, "{r:?}: crumb {i}");
+        }
+        let here = describe(&b, r);
+        if !here.is_empty() {
+            assert_eq!(c.last().unwrap().0, here);
+        }
+    }
+    assert_eq!(
+        crumbs(Some(&b), &Route::Party(party)),
+        [
+            ("Parties".to_string(), Some(Route::Parties)),
+            (b.party_label(party), None),
+        ]
+    );
+    // A reconciliation sits under its account.
+    let account = Route::Account(rec.account_id);
+    let c = crumbs(Some(&b), &Route::Reconciliation(rec.id));
+    assert_eq!(c.len(), 3);
+    assert_eq!(c[0].1, Some(Route::Accounts));
+    assert_eq!(c[1], (describe(&b, &account), Some(account)));
+    // A section's own page is one crumb, not a link.
+    assert_eq!(
+        crumbs(Some(&b), &Route::Parties),
+        [("Parties".to_string(), None)]
+    );
+    // P&L is the Reports section's home, so "Reports" there isn't a link.
+    assert_eq!(
+        crumbs(Some(&b), &Route::Reports(ReportKind::ProfitAndLoss))[0].1,
+        None
+    );
+}
+
+/// INVARIANT 4, through the top bar.
+#[test]
+fn clicking_a_crumb_goes_there() {
+    let source = demo("click");
+    let b = data::load_once(&source).unwrap();
+    let rec = b.reconciliations.first().unwrap().clone();
+    let account = describe(&b, &Route::Account(rec.account_id));
+    let mut h = Harness::builder()
+        .with_size(egui::vec2(1280.0, 900.0))
+        .build_eframe(|cc| App::with_books(&cc.egui_ctx, b, false, Route::Reconciliation(rec.id)));
+    h.run_steps(3);
+    h.get_all_by_label(&account).next().unwrap().click();
+    h.run_steps(3);
+    assert_eq!(h.state().route(), &Route::Account(rec.account_id));
+    h.get_by_label("Accounts").click();
+    h.run_steps(3);
+    assert_eq!(h.state().route(), &Route::Accounts);
+}