feat(lsp): wire diary/auto_toc/links_space_char/list_margin; drop client-side keys

Consume several per-wiki config keys that the server deserialized but
ignored, and remove keys whose effect is purely client-side:

- diagnostics: re-publish open-doc diagnostics on
  didChangeConfiguration so a link_severity change takes effect
  immediately; fix the single-key unwrap in apply_change so a minimal
  `{ diagnostic: {...} }` payload isn't mistaken for a namespace wrapper.
- auto_toc: rebuild an existing TOC section on save (new
  ops::toc_rebuild_edit, no-op when the page has no TOC).
- diary index: honour diary_header, diary_sort and diary_caption_level
  when rendering the diary index body.
- links_space_char: apply on rename so spaces in the link target and
  the on-disk path become the configured glyph (default " " = verbatim).
- list_margin: thread the per-wiki value into render_page_html.
- remove nested_syntaxes, maxhi and diary_start_week_day from the server
  config: nested-syntax and heading highlighting are client-side, and
  the weekly diary is ISO-week based so a custom week start has no clean
  server-side meaning.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/nuwiki-lsp/tests/index_and_config.rs

@@ -267,16 +267,13 @@ fn defaults_carry_vimwiki_per_wiki_keys() {
     let cfg = WikiConfig::empty();
     assert_eq!(cfg.index, "index");
     assert_eq!(cfg.diary_frequency, "daily");
-    assert_eq!(cfg.diary_start_week_day, "monday");
     assert_eq!(cfg.diary_caption_level, 1);
     assert_eq!(cfg.diary_sort, "desc");
     assert_eq!(cfg.diary_header, "Diary");
-    assert_eq!(cfg.maxhi, 1);
     assert_eq!(cfg.listsyms, " .oOX");
     assert!(cfg.listsyms_propagate);
     assert_eq!(cfg.list_margin, -1);
     assert_eq!(cfg.links_space_char, " ");
-    assert!(cfg.nested_syntaxes.is_empty());
     assert!(!cfg.auto_toc);
 }
 
@@ -287,35 +284,26 @@ fn raw_wiki_parses_every_new_key() {
             "root": "/tmp/w",
             "index": "home",
             "diary_frequency": "weekly",
-            "diary_start_week_day": "sunday",
             "diary_caption_level": 2,
             "diary_sort": "asc",
             "diary_header": "Journal",
-            "maxhi": 6,
             "listsyms": "abcde",
             "listsyms_propagate": false,
             "list_margin": 2,
             "links_space_char": "_",
-            "nested_syntaxes": { "python": "python", "ruby": "ruby" },
             "auto_toc": true,
         }],
     }));
     let w = &cfg.wikis[0];
     assert_eq!(w.index, "home");
     assert_eq!(w.diary_frequency, "weekly");
-    assert_eq!(w.diary_start_week_day, "sunday");
     assert_eq!(w.diary_caption_level, 2);
     assert_eq!(w.diary_sort, "asc");
     assert_eq!(w.diary_header, "Journal");
-    assert_eq!(w.maxhi, 6);
     assert_eq!(w.listsyms, "abcde");
     assert!(!w.listsyms_propagate);
     assert_eq!(w.list_margin, 2);
     assert_eq!(w.links_space_char, "_");
-    assert_eq!(
-        w.nested_syntaxes.get("python").map(String::as_str),
-        Some("python")
-    );
     assert!(w.auto_toc);
 }
 
@@ -367,6 +355,77 @@ fn apply_change_preserves_severity_on_partial_update() {
     assert_eq!(cfg.diagnostic.link_severity, LinkSeverity::Error);
 }
 
+#[test]
+fn apply_change_minimal_diagnostic_payload_is_not_unwrapped() {
+    // A lone `{ "diagnostic": { … } }` is a real flat payload, not a
+    // `{ "nuwiki": { … } }` namespace wrapper. The single-key unwrap must
+    // skip it (it's a recognised top-level key) so the severity applies.
+    let mut cfg = config_from_json(json!({ "wiki_root": "/tmp/w" }));
+    assert_eq!(cfg.diagnostic.link_severity, LinkSeverity::Warning);
+
+    cfg.apply_change(&json!({ "diagnostic": { "link_severity": "error" } }));
+    assert_eq!(cfg.diagnostic.link_severity, LinkSeverity::Error);
+
+    // The Neovim namespace wrapper still unwraps correctly.
+    cfg.apply_change(&json!({ "nuwiki": { "diagnostic": { "link_severity": "hint" } } }));
+    assert_eq!(cfg.diagnostic.link_severity, LinkSeverity::Hint);
+}
+
+#[test]
+fn severity_change_via_apply_change_is_observable_in_collected_diagnostics() {
+    // Contract behind `did_change_configuration`'s diagnostic re-publish:
+    // once `apply_change` updates the severity, re-running `collect_diagnostics`
+    // (what the handler does for every open doc) must emit broken-link
+    // diagnostics at the *new* severity. Guards the data path the handler
+    // depends on — apply_change writing the severity AND collect_diagnostics
+    // reading it.
+    use nuwiki_core::syntax::vimwiki::VimwikiSyntax;
+    use nuwiki_core::syntax::SyntaxPlugin;
+    use nuwiki_lsp::index::WorkspaceIndex;
+    use tower_lsp::lsp_types::DiagnosticSeverity;
+
+    let root = "/tmp/cfgchange";
+    let src = "[[GhostPage]]\n";
+    let ast = VimwikiSyntax::new().parse(src);
+    let mut idx = WorkspaceIndex::new(Some(PathBuf::from(root)));
+    let uri = Url::from_file_path(format!("{root}/Home.wiki")).unwrap();
+    idx.upsert(uri.clone(), &ast);
+
+    let mut cfg = config_from_json(json!({
+        "wiki_root": root,
+        "diagnostic": { "link_severity": "warn" },
+    }));
+    let warn = collect_diagnostics(
+        &ast,
+        src,
+        Some(&uri),
+        Some(&idx),
+        Some("Home"),
+        &cfg.diagnostic,
+        true,
+    );
+    assert_eq!(warn.len(), 1, "broken link should warn");
+    assert_eq!(warn[0].severity, Some(DiagnosticSeverity::WARNING));
+
+    // Simulate the client raising severity via didChangeConfiguration.
+    cfg.apply_change(&json!({ "diagnostic": { "link_severity": "error" } }));
+    let err = collect_diagnostics(
+        &ast,
+        src,
+        Some(&uri),
+        Some(&idx),
+        Some("Home"),
+        &cfg.diagnostic,
+        true,
+    );
+    assert_eq!(err.len(), 1);
+    assert_eq!(
+        err[0].severity,
+        Some(DiagnosticSeverity::ERROR),
+        "re-collected diagnostics must reflect the new severity"
+    );
+}
+
 #[test]
 fn vim_flat_and_neovim_wrapped_payloads_desugar_identically() {
     // Parity guard for the two client shapes: