fix(rules-core): fall back to workspace directory when no project root marker is found

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/rules-injector/injector.test.ts

@@ -339,6 +339,7 @@ describe("createRuleInjectionProcessor", () => {
 				contentHashes: new Set<string>(),
 				realPaths: new Set<string>([ruleRealPath]),
 			}),
+			homedir: () => homeRoot,
 		});
 
 		// when

src/hooks/rules-injector/injector.ts

@@ -137,6 +137,9 @@ export function createRuleInjectionProcessor(deps: {
 	} = deps;
 
 	const matchDecisionCache: MatchDecisionCache = new Map();
+	const finderOptions: FindRuleFilesOptions = ruleFinderOptions
+		? { ...ruleFinderOptions, workspaceDirectory }
+		: { workspaceDirectory };
 
 	function getParsedRule(filePath: string, realPath: string): ParsedRule {
 		try {
@@ -189,7 +192,7 @@ export function createRuleInjectionProcessor(deps: {
 			projectRoot,
 			home,
 			resolved,
-			ruleFinderOptions,
+			finderOptions,
 			ruleScanCache,
 		);
 		const toInject: RuleToInject[] = [];