fix(artifact-graph): normalize paths for cross-platform glob compatibility

Add FileSystemUtils.toPosixPath() utility and consolidate scattered
path normalization patterns. This fixes Windows test failures where
fast-glob couldn't match paths containing backslashes.

Root cause: path.join() uses backslashes on Windows, but fast-glob
requires forward slashes for glob patterns on all platforms.

Changes:
- Add toPosixPath() to FileSystemUtils for cross-platform path handling
- Update artifact-graph/state.ts to normalize glob patterns
- Consolidate path normalization in update.ts, validator.ts, and
  json-converter.ts to use the new utility

src/core/artifact-graph/state.ts

@@ -3,6 +3,7 @@ import * as path from 'node:path';
 import fg from 'fast-glob';
 import type { CompletedSet } from './types.js';
 import type { ArtifactGraph } from './graph.js';
+import { FileSystemUtils } from '../../utils/file-system.js';
 
 /**
  * Detects which artifacts are completed by checking file existence in the change directory.
@@ -54,8 +55,10 @@ function isGlobPattern(pattern: string): boolean {
 
 /**
  * Checks if a glob pattern has any matches.
+ * Normalizes Windows backslashes to forward slashes for cross-platform glob compatibility.
  */
 function hasGlobMatches(pattern: string): boolean {
-  const matches = fg.sync(pattern, { onlyFiles: true });
+  const normalizedPattern = FileSystemUtils.toPosixPath(pattern);
+  const matches = fg.sync(normalizedPattern, { onlyFiles: true });
   return matches.length > 0;
 }

src/core/converters/json-converter.ts

@@ -3,6 +3,7 @@ import path from 'path';
 import { MarkdownParser } from '../parsers/markdown-parser.js';
 import { ChangeParser } from '../parsers/change-parser.js';
 import { Spec, Change } from '../schemas/index.js';
+import { FileSystemUtils } from '../../utils/file-system.js';
 
 export class JsonConverter {
   convertSpecToJson(filePath: string): string {
@@ -43,7 +44,7 @@ export class JsonConverter {
   }
 
   private extractNameFromPath(filePath: string): string {
-    const normalizedPath = filePath.replaceAll('\\', '/');
+    const normalizedPath = FileSystemUtils.toPosixPath(filePath);
     const parts = normalizedPath.split('/');
     
     for (let i = parts.length - 1; i >= 0; i--) {

src/core/update.ts

@@ -107,7 +107,7 @@ export class UpdateCommand {
 
     if (updatedSlashFiles.length > 0) {
       // Normalize to forward slashes for cross-platform log consistency
-      const normalized = updatedSlashFiles.map((p) => p.replace(/\\/g, '/'));
+      const normalized = updatedSlashFiles.map((p) => FileSystemUtils.toPosixPath(p));
       summaryParts.push(`Updated slash commands: ${normalized.join(', ')}`);
     }
 

src/core/validation/validator.ts

@@ -5,12 +5,13 @@ import { SpecSchema, ChangeSchema, Spec, Change } from '../schemas/index.js';
 import { MarkdownParser } from '../parsers/markdown-parser.js';
 import { ChangeParser } from '../parsers/change-parser.js';
 import { ValidationReport, ValidationIssue, ValidationLevel } from './types.js';
-import { 
+import {
   MIN_PURPOSE_LENGTH,
   MAX_REQUIREMENT_TEXT_LENGTH,
-  VALIDATION_MESSAGES 
+  VALIDATION_MESSAGES
 } from './constants.js';
 import { parseDeltaSpec, normalizeRequirementName } from '../parsers/requirement-blocks.js';
+import { FileSystemUtils } from '../../utils/file-system.js';
 
 export class Validator {
   private strictMode: boolean;
@@ -359,7 +360,7 @@ export class Validator {
   }
 
   private extractNameFromPath(filePath: string): string {
-    const normalizedPath = filePath.replaceAll('\\', '/');
+    const normalizedPath = FileSystemUtils.toPosixPath(filePath);
     const parts = normalizedPath.split('/');
     
     // Look for the directory name after 'specs' or 'changes'

src/utils/file-system.ts

@@ -42,6 +42,14 @@ function findMarkerIndex(
 }
 
 export class FileSystemUtils {
+  /**
+   * Converts a path to use forward slashes (POSIX style).
+   * Essential for cross-platform compatibility with glob libraries like fast-glob.
+   */
+  static toPosixPath(p: string): string {
+    return p.replace(/\\/g, '/');
+  }
+
   private static isWindowsBasePath(basePath: string): boolean {
     return /^[A-Za-z]:[\\/]/.test(basePath) || basePath.startsWith('\\');
   }