fix(rules-core): restore .sisyphus/rules discovery with deprecation warning (planned removal v4.3.0)

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

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

packages/rules-core/src/finder.ts

@@ -5,6 +5,11 @@ import { GLOBAL_DISTANCE, OPENCODE_USER_RULE_DIRS, PROJECT_RULE_FILES, PROJECT_R
 import { sortCandidates } from "./ordering";
 import { findRuleFilesRecursive, safeRealpathSync } from "./scanner";
 import type { DirectoryScanEntry, FindRuleFilesOptions, RuleFileCandidate, RuleScanCache, RuleSource } from "./types";
+import { log } from "../../../src/shared/logger";
+
+const SISYPHUS_DEPRECATION_MESSAGE = "[rules] .sisyphus/rules is deprecated and will be removed in v4.3.0; migrate to .omo/rules";
+const SISYPHUS_LEGACY_RULE_SOURCES: ReadonlySet<RuleSource> = new Set([".sisyphus/rules", "~/.sisyphus/rules"]);
+const warnedSisyphusRuleDirectories = new Set<string>();
 
 export function findRuleFiles(
   projectRoot: string | null,
@@ -62,6 +67,7 @@ function addProjectRuleCandidates(
       for (const entry of scanDirectoryWithCache(ruleDir, cache)) {
         if (seenRealPaths.has(entry.realPath)) continue;
         seenRealPaths.add(entry.realPath);
+        warnSisyphusRuleDeprecation(source, entry.path);
         candidates.push({
           path: entry.path,
           realPath: entry.realPath,
@@ -115,6 +121,7 @@ function addUserRuleCandidates(
     for (const entry of scanDirectoryWithCache(userRuleDir, cache)) {
       if (seenRealPaths.has(entry.realPath)) continue;
       seenRealPaths.add(entry.realPath);
+      warnSisyphusRuleDeprecation(source, entry.path);
       candidates.push({
         path: entry.path,
         realPath: entry.realPath,
@@ -136,6 +143,17 @@ function scanDirectoryWithCache(dir: string, cache: RuleScanCache | undefined):
   return entries;
 }
 
+function warnSisyphusRuleDeprecation(source: RuleSource, path: string): void {
+  if (!SISYPHUS_LEGACY_RULE_SOURCES.has(source)) return;
+  const warningKey = dirname(path);
+  if (warnedSisyphusRuleDirectories.has(warningKey)) return;
+  warnedSisyphusRuleDirectories.add(warningKey);
+  log(SISYPHUS_DEPRECATION_MESSAGE, {
+    event: "rules-sisyphus-deprecated",
+    path,
+  });
+}
+
 function validFileRealPath(filePath: string): string | null {
   if (!existsSync(filePath)) return null;
   try {