refactor: route exhaustiveness guards through assertNever

- sync mode/scope, conflict mode, setup-requirement kind, credential type 5개 throw 가드 → assertNever(x, label) (에러 메시지 보존)
- migration.ts: 가짜 `type as never` → 진짜 `credType satisfies never` 가드로 업그레이드 (컴파일타임 exhaustiveness 확보, return undefined 동작 유지)
- settings-tab filterMode는 non-throw fallback이라 satisfies never 유지

src/core/conflict-resolver.ts

@@ -7,7 +7,7 @@
  */
 
 import { Notice } from "obsidian";
-import { areValuesEqual } from '../utils';
+import { areValuesEqual, assertNever } from '../utils';
 import type { LegacySettings, ConflictInfo, SyncResult, DatabaseProvider } from '../types';
 
 /**
@@ -80,10 +80,8 @@ export class ConflictResolver {
       case 'manual':
         return this.resolveManual(conflicts, recordId);
 
-      default: {
-        const _exhaustive: never = this.settings.conflictResolution;
-        throw new Error(`Unknown conflict resolution mode: ${_exhaustive}`);
-      }
+      default:
+        return assertNever(this.settings.conflictResolution, 'Unknown conflict resolution mode');
     }
   }
 

src/core/sync-orchestrator.ts

@@ -22,7 +22,7 @@ import { FieldCache } from '../services';
 import { ConflictResolver } from './conflict-resolver';
 import { FrontmatterParser, FileWatcher } from '../file-operations';
 import { parseTemplate, buildMarkdownContent, generateBasesContent, resolveBasesFilePath, collectFieldNames } from '../builders';
-import { sanitizeFileName, sanitizeSubfolderValue, validateAndSanitizeFilename } from '../utils';
+import { sanitizeFileName, sanitizeSubfolderValue, validateAndSanitizeFilename, assertNever } from '../utils';
 
 export interface StatusBarHandle {
   setText(text: string): void;
@@ -126,10 +126,8 @@ export class SyncOrchestrator {
           break;
         }
 
-        default: {
-          const _exhaustive: never = mode;
-          throw new Error(`Unknown sync mode: ${_exhaustive}`);
-        }
+        default:
+          assertNever(mode, 'Unknown sync mode');
       }
     } catch (error) {
       const message = error instanceof Error ? error.message : 'Unknown error';
@@ -166,10 +164,8 @@ export class SyncOrchestrator {
         return this.collectMarkdownFiles(folder);
       }
 
-      default: {
-        const _exhaustive: never = scope;
-        throw new Error(`Unknown sync scope: ${_exhaustive}`);
-      }
+      default:
+        return assertNever(scope, 'Unknown sync scope');
     }
   }
 

src/ui/settings-tab.ts

@@ -34,6 +34,7 @@ import { FolderSuggest, FileSuggest } from './suggest';
 import { generateId } from '../utils/object-utils';
 import { validateFolderPath } from '../utils/validation';
 import { debounce } from '../utils/debounce';
+import { assertNever } from '../utils/assert';
 
 /**
  * Interface for the plugin that the settings tab needs.
@@ -1410,10 +1411,8 @@ export class AutoNoteImporterSettingTab extends PluginSettingTab {
         }
         return;
       }
-      default: {
-        const _exhaustive: never = needsSetup.kind;
-        throw new Error(`Unhandled setup requirement kind: ${String(_exhaustive)}`);
-      }
+      default:
+        return assertNever(needsSetup.kind, 'Unhandled setup requirement kind');
     }
   }
 
@@ -1531,10 +1530,8 @@ export class AutoNoteImporterSettingTab extends PluginSettingTab {
           return [credential.type, credential.integrationToken];
         case 'custom-api':
           return [credential.type, credential.baseUrl, credential.authHeader, credential.authValue];
-        default: {
-          const _exhaustive: never = credential;
-          throw new Error(`Unknown credential type: ${String(_exhaustive)}`);
-        }
+        default:
+          return assertNever(credential, 'Unknown credential type');
       }
     })();
     return AutoNoteImporterSettingTab.hashCredentialFingerprint(parts.map(p => p.trim()).join('\0'));

src/utils/migration.ts

@@ -155,7 +155,8 @@ function buildCredentialFromRecord(raw: Record<string, unknown>): Credential | u
   }
 
   const base = { id, name: readString(raw, 'name', '') };
-  switch (type as CredentialType) {
+  const credType = type as CredentialType;
+  switch (credType) {
     case 'airtable':
       return { ...base, type: 'airtable', apiKey: readString(raw, 'apiKey', '') };
     case 'seatable':
@@ -180,9 +181,11 @@ function buildCredentialFromRecord(raw: Record<string, unknown>): Credential | u
         authValue: readString(raw, 'authValue', ''),
       };
     default: {
-      // Compile-time exhaustiveness guard — unreachable at runtime (CREDENTIAL_TYPES.includes guards above).
-      const _exhaustive: never = type as never;
-      void _exhaustive;
+      // Real compile-time exhaustiveness guard: credType narrows to never once
+      // every CredentialType has a case. Returns undefined (not throw) so a
+      // malformed legacy setting is skipped rather than fatal — the
+      // CREDENTIAL_TYPES.includes() check above already gates the runtime path.
+      credType satisfies never;
       return undefined;
     }
   }