fix(shared): add ancestor project discovery helpers

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

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

src/shared/project-discovery-dirs.ts

@@ -0,0 +1,52 @@
+import { existsSync } from "node:fs"
+import { dirname, join, resolve } from "node:path"
+
+function findAncestorDirectories(
+  startDirectory: string,
+  targetPaths: ReadonlyArray<ReadonlyArray<string>>,
+): string[] {
+  const directories: string[] = []
+  const seen = new Set<string>()
+  let currentDirectory = resolve(startDirectory)
+
+  while (true) {
+    for (const targetPath of targetPaths) {
+      const candidateDirectory = join(currentDirectory, ...targetPath)
+      if (!existsSync(candidateDirectory) || seen.has(candidateDirectory)) {
+        continue
+      }
+
+      seen.add(candidateDirectory)
+      directories.push(candidateDirectory)
+    }
+
+    const parentDirectory = dirname(currentDirectory)
+    if (parentDirectory === currentDirectory) {
+      return directories
+    }
+
+    currentDirectory = parentDirectory
+  }
+}
+
+export function findProjectClaudeSkillDirs(startDirectory: string): string[] {
+  return findAncestorDirectories(startDirectory, [[".claude", "skills"]])
+}
+
+export function findProjectAgentsSkillDirs(startDirectory: string): string[] {
+  return findAncestorDirectories(startDirectory, [[".agents", "skills"]])
+}
+
+export function findProjectOpencodeSkillDirs(startDirectory: string): string[] {
+  return findAncestorDirectories(startDirectory, [
+    [".opencode", "skills"],
+    [".opencode", "skill"],
+  ])
+}
+
+export function findProjectOpencodeCommandDirs(startDirectory: string): string[] {
+  return findAncestorDirectories(startDirectory, [
+    [".opencode", "commands"],
+    [".opencode", "command"],
+  ])
+}