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/mode/effort.rs

@@ -47,9 +47,6 @@ pub fn cycle_effort(state: &mut AppStateRest) {
     let current = current_effort(state);
     state.misc.effort_level = (current + 1) % EFFORT_LEVELS.len();
     let label = current_effort_str(state);
-    state.push_toast(crate::app::state::types::Toast::new(
-        crate::app::state::types::ToastKind::Info,
-        format!("Effort: {label}"),
-    ));
+    state.toast_info(format!("Effort: {label}"));
     state.dirty = true;
 }

crates/zesdex-backend/src/app/mode/mod.rs

@@ -11,3 +11,22 @@ pub mod quit_confirm;
 pub mod rewind;
 pub mod settings;
 pub mod todo;
+
+/// Cycle `current` in the range `[0, len)`.
+///
+/// * `forward = true` — increment (wrap at len)
+/// * `forward = false` — decrement (wrap at 0), saturating at 0 when len is 0
+///
+/// Return: `0` when `len == 0`, otherwise the wrapped index.
+pub fn cycle_selected_index(current: usize, len: usize, forward: bool) -> usize {
+    if len == 0 {
+        return 0;
+    }
+    if forward {
+        (current + 1) % len
+    } else if current == 0 {
+        len.saturating_sub(1)
+    } else {
+        current - 1
+    }
+}

crates/zesdex-backend/src/app/mode/rewind.rs

@@ -27,10 +27,7 @@ pub fn rewind_to(state: &mut AppStateRest, index: usize) {
     let conn = match open_session_db(&state.session_dir) {
         Ok(c) => c,
         Err(e) => {
-            state.push_toast(crate::app::state::types::Toast::new(
-                crate::app::state::types::ToastKind::Error,
-                format!("Failed to open session DB: {e}"),
-            ));
+            state.toast_error(format!("Failed to open session DB: {e}"));
             state.dirty = true;
             return;
         }
@@ -39,20 +36,14 @@ pub fn rewind_to(state: &mut AppStateRest, index: usize) {
     let keys = match crate::model::msglog::blobs::list_blob_keys(&conn, &state.session_id) {
         Ok(k) => k,
         Err(e) => {
-            state.push_toast(crate::app::state::types::Toast::new(
-                crate::app::state::types::ToastKind::Error,
-                format!("Failed to list snapshots: {e}"),
-            ));
+            state.toast_error(format!("Failed to list snapshots: {e}"));
             state.dirty = true;
             return;
         }
     };
 
     if keys.is_empty() || index >= keys.len() {
-        state.push_toast(crate::app::state::types::Toast::new(
-            crate::app::state::types::ToastKind::Warning,
-            "No snapshot available at that index".to_string(),
-        ));
+        state.toast_warning("No snapshot available at that index".to_string());
         state.dirty = true;
         return;
     }
@@ -62,18 +53,12 @@ pub fn rewind_to(state: &mut AppStateRest, index: usize) {
     {
         Ok(Some(b)) => b,
         Ok(None) => {
-            state.push_toast(crate::app::state::types::Toast::new(
-                crate::app::state::types::ToastKind::Error,
-                "Snapshot data not found".to_string(),
-            ));
+            state.toast_error("Snapshot data not found".to_string());
             state.dirty = true;
             return;
         }
         Err(e) => {
-            state.push_toast(crate::app::state::types::Toast::new(
-                crate::app::state::types::ToastKind::Error,
-                format!("Failed to retrieve snapshot: {e}"),
-            ));
+            state.toast_error(format!("Failed to retrieve snapshot: {e}"));
             state.dirty = true;
             return;
         }
@@ -87,16 +72,10 @@ pub fn rewind_to(state: &mut AppStateRest, index: usize) {
 
     match std::fs::write(&restore_path, &bytes) {
         Ok(()) => {
-            state.push_toast(crate::app::state::types::Toast::new(
-                crate::app::state::types::ToastKind::Success,
-                format!("Restored {} from snapshot", restore_path.display()),
-            ));
+            state.toast_success(format!("Restored {} from snapshot", restore_path.display()));
         }
         Err(e) => {
-            state.push_toast(crate::app::state::types::Toast::new(
-                crate::app::state::types::ToastKind::Error,
-                format!("Failed to write restored file: {e}"),
-            ));
+            state.toast_error(format!("Failed to write restored file: {e}"));
         }
     }