Add current-draft diagnostic underlines and passive hover

Preserve raw include diagnostic provenance and derive bands from the existing shaped editor. Retain deferred tooltip paragraphs through rendering. Include source, regression, failure and native-trial evidence; corrected native acceptance remains pending.

crates/oa-desktop/src/source_annotations/tests.rs

@@ -0,0 +1,83 @@
+use super::*;
+use oa_core::{
+    language::{Diagnostic, Span},
+    validation::Severity,
+};
+
+fn diagnostic(path: &str, start: usize, end: usize) -> SourceDiagnostic {
+    SourceDiagnostic {
+        path: path.into(),
+        diagnostic: Diagnostic {
+            severity: Severity::Error,
+            code: "test".into(),
+            message: "synthetic admission fixture".into(),
+            object_id: None,
+            field: None,
+            line: 999,
+            column: 999,
+            span: Span { start, end },
+        },
+        related: Vec::new(),
+    }
+}
+
+#[test]
+fn exact_path_and_utf8_range_admission_keep_valid_neighbor() {
+    let index = Index::new(
+        Arc::from("雨 x"),
+        "a.arcadia",
+        &[
+            diagnostic("b.arcadia", 0, 3),
+            diagnostic("a.arcadia", 1, 3),
+            diagnostic("a.arcadia", 4, 2),
+            diagnostic("a.arcadia", 0, 99),
+            diagnostic("a.arcadia", 4, 5),
+        ],
+    );
+    assert_eq!(index.parts.len(), 1);
+    let parts = &index.parts[&0];
+    assert_eq!(parts.len(), 1);
+    assert_eq!((parts[0].diagnostic, parts[0].bytes.clone()), (4, 4..5));
+}
+
+#[test]
+fn mixed_endings_use_actual_paragraphs_and_preserve_eof() {
+    let index = Index::new(
+        Arc::from("a\r\n雨\rb\n\rc\n"),
+        "a",
+        &[
+            diagnostic("a", 3, 6),
+            diagnostic("a", 7, 8),
+            diagnostic("a", 12, 12),
+        ],
+    );
+    assert_eq!(index.lines, vec![0..1, 3..6, 7..8, 10..11, 12..12]);
+    assert_eq!(index.parts[&1][0].bytes, 0..3);
+    assert_eq!(index.parts[&2][0].bytes, 0..1);
+    assert_eq!(index.parts[&4][0].bytes, 0..0);
+}
+
+#[test]
+fn half_open_next_line_excluded_separator_only_and_empty_line_anchored() {
+    let index = Index::new(
+        Arc::from("ab\r\n\r\ncd"),
+        "a",
+        &[
+            diagnostic("a", 0, 4),
+            diagnostic("a", 2, 4),
+            diagnostic("a", 4, 6),
+        ],
+    );
+    assert_eq!(index.parts.len(), 2);
+    assert_eq!(index.parts[&0][0].bytes, 0..2);
+    assert_eq!(index.parts[&0][1].bytes, 2..2);
+    assert_eq!(index.parts[&1][0].bytes, 0..0);
+    assert!(!index.parts.contains_key(&2));
+}
+
+#[test]
+fn empty_source_has_real_zero_width_marker() {
+    let index = Index::new(Arc::from(""), "a", &[diagnostic("a", 0, 0)]);
+    assert_eq!(index.lines, vec![0..0]);
+    assert_eq!(index.parts[&0][0].bytes, 0..0);
+}