# Plan 04-02: Path and Model File Validation

**Wave:** 1  
**Phase:** 4  
**Requirements addressed:** MODL-02

---

## Objective

Add path existence validation and model file scanning integration so users receive immediate feedback when their selected model path or models directory is invalid.

---

## Read First

- `tauri-app/src-tauri/src/model_files.rs` — scan_models, pick_models_dir commands
- `tauri-app/src/features/runtime/api.ts` — invoke wrappers for Tauri commands
- `tauri-app/src/features/runtime/runtime-settings-form.ts` — RuntimeSettingsFormState, scanned models
- `tauri-app/src/features/runtime/types.ts` — RuntimeModelFile, RuntimePickDirResult
- `.planning/phases/04-model-source-validation/04-RESEARCH.md` — path validation patterns

---

## Action

1. **Add Tauri command wrappers** in `api.ts`:

   ```typescript
   export interface ScannedModelsResult {
     dir: string;
     models: RuntimeModelFile[];
   }
   
   export async function scanModelsDir(dirPath: string): Promise<RuntimeModelFile[]> {
     return await invoke<RuntimeModelFile[]>("scan_models", { dir: dirPath });
   }
   
   export async function pickModelsDirectory(): Promise<ScannedModelsResult> {
     return await invoke<ScannedModelsResult>("pick_models_dir");
   }
   ```

2. **Extend runtime-utils.ts with path validation**:

   ```typescript
   import { scanModelsDir } from "./api";
   
   export async function validateModelsDirectory(
     path: string | null
   ): Promise<{ valid: boolean; modelCount: number; error: string | null }> {
     if (!path) {
       return { valid: false, modelCount: 0, error: "No models directory selected" };
     }
     try {
       const models = await scanModelsDir(path);
       return { 
         valid: true, 
         modelCount: models.length, 
         error: null 
       };
     } catch (e) {
       return { 
         valid: false, 
         modelCount: 0, 
         error: e instanceof Error ? e.message : String(e) 
       };
     }
   }
   
   export async function validateModelFile(
     path: string | null,
     scannedModels: RuntimeModelFile[]
   ): Promise<{ valid: boolean; exists: boolean; error: string | null }> {
     if (!path) {
       return { valid: false, exists: false, error: "No model selected" };
     }
     const exists = scannedModels.some(m => m.path === path);
     return {
       valid: exists,
       exists,
       error: exists ? null : "Model file not found in current models directory"
     };
   }
   ```

3. **Add model scanning to runtime-settings-form.ts**:

   - Add `scannedModels: RuntimeModelFile[]` to RuntimeSettingsFormState
   - Add `scanModels(dir: string)` function that calls api.scanModelsDir
   - Update `resolveDraftModelSelection` to use scanned models for validation

4. **Integrate into useRuntimeManager.ts**:

   - Add `scannedModels` to draft state
   - When `models_dir` field changes, trigger rescan
   - When rescan completes, validate `model_path` against new scan results
   - Update field validation state with path-specific errors

5. **Add validation display in UI components**:

   - In runtime settings form, show validation message when models_dir is invalid
   - Show "X models found" when scan succeeds
   - Show "Model not in directory" when selected model is invalid after scan

---

## Acceptance Criteria

- [ ] `api.ts` exports `scanModelsDir(path)` and `pickModelsDirectory()`
- [ ] `runtime-utils.ts` exports async validators that check directory and file existence
- [ ] Changing `models_dir` triggers rescan and updates validation state
- [ ] Selected model is validated against scanned models list
- [ ] Invalid paths show clear error messages in the UI
- [ ] User can see "X models found" feedback after scanning

---

## Notes

- Reuse existing scan_models Rust command - no backend changes needed
- Keep validation async to support filesystem checks
- Show appropriate loading state during scan
- Handle scan errors gracefully (directory not found, permission denied)