refactor: DRY cleanup — extract shared helpers, remove duplication across tools, LSP, overlays, and runtime

Eliminate ~500 lines of duplicate code across 31 files by extracting
shared functions, helpers, and consolidating repeated patterns.

Highlights:
- Toast helpers (toast_info/success/warning/error) on AppStateRest
- push_event() helper for turn-event queue (19 callers consolidated)
- log_write_edit_tool() shared fn (turn.rs + engine.rs ~50 lines saved)
- resolve_api_key() shared fn (spawn.rs + provider.rs)
- LSP call_positional() helper on LspClient
- lsp_cursor_params() shared schema for 4 tool files
-overlay_block() helper for consistent overlay title/border styling
- cycle_selected_index(), path_not_found/a_directory() helpers
- mark_dirty(), save_settings() on AppStateRest
- Remove redundant Err(e) => Err(e) arms in LSP tools
- Consolidate generate_workspace_tree (turn.rs → workspace.rs)
- Simplify background-review wrapper args in auto/mod.rs

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/zesdex-backend/src/app/lsp/client.rs

@@ -303,24 +303,35 @@ impl LspClient {
         )
     }
 
+    /// Call a textDocument/positional method (hover, completion, definition, references).
+    ///
+    /// Builds the standard `{ textDocument: { uri }, position: { line, character } }` body
+    /// and delegates to `self.call`. `extra` is merged into the body when present (used by
+    /// `references` to include the `context` block).
+    fn call_positional(
+        &mut self,
+        method: &str,
+        uri: &str,
+        line: u32,
+        character: u32,
+        extra: Option<serde_json::Value>,
+    ) -> anyhow::Result<Value> {
+        let mut body = json!({
+            "textDocument": { "uri": uri },
+            "position": { "line": line, "character": character },
+        });
+        if let Some(ref extra) = extra {
+            merge_json(&mut body, extra);
+        }
+        self.call(method, &body)
+    }
+
     pub fn hover(&mut self, uri: &str, line: u32, character: u32) -> anyhow::Result<Value> {
-        self.call(
-            "textDocument/hover",
-            &json!({
-                "textDocument": { "uri": uri },
-                "position": { "line": line, "character": character }
-            }),
-        )
+        self.call_positional("textDocument/hover", uri, line, character, None)
     }
 
     pub fn completion(&mut self, uri: &str, line: u32, character: u32) -> anyhow::Result<Value> {
-        self.call(
-            "textDocument/completion",
-            &json!({
-                "textDocument": { "uri": uri },
-                "position": { "line": line, "character": character }
-            }),
-        )
+        self.call_positional("textDocument/completion", uri, line, character, None)
     }
 
     pub fn goto_definition(
@@ -329,25 +340,13 @@ impl LspClient {
         line: u32,
         character: u32,
     ) -> anyhow::Result<Value> {
-        self.call(
-            "textDocument/definition",
-            &json!({
-                "textDocument": { "uri": uri },
-                "position": { "line": line, "character": character }
-            }),
-        )
+        self.call_positional("textDocument/definition", uri, line, character, None)
     }
 
     pub fn references(&mut self, uri: &str, line: u32, character: u32) -> anyhow::Result<Value> {
-        self.call(
-            "textDocument/references",
-            &json!({
-                "textDocument": { "uri": uri },
-                "position": { "line": line, "character": character },
-                "context": {
-                    "includeDeclaration": true
-                }
-            }),
+        self.call_positional(
+            "textDocument/references", uri, line, character,
+            Some(json!({"context": { "includeDeclaration": true }})),
         )
     }
 
@@ -384,6 +383,19 @@ impl Drop for LspClient {
     }
 }
 
+/// Merge the fields of `b` into the object `a` (mutating `a` in place).
+///
+/// Used by `LspClient::call_positional` to layer extra fields (e.g. `context`)
+/// onto the standard positional-query body. When `a` is not an object or `b`
+/// is not an object this is a no-op.
+fn merge_json(a: &mut serde_json::Value, b: &serde_json::Value) {
+    if let (Some(map), Some(extra)) = (a.as_object_mut(), b.as_object()) {
+        for (k, v) in extra {
+            map.insert(k.clone(), v.clone());
+        }
+    }
+}
+
 pub fn path_to_lsp_uri(path: &str) -> String {
     file_path_to_uri(path)
 }