feat(shared): add findProjectOpencodePluginConfigFiles walker

Walks up the directory tree from a start directory looking for
.opencode/oh-my-openagent.json[c] (or legacy basename) files. Returns
detected paths in nearest-first order, optionally stopping at a
caller-provided directory.

Reuses detectPluginConfigFile so canonical/legacy basename detection,
caching, and JSONC vs JSON precedence stay consistent with existing
config loading. Foundation for #417 hierarchical config discovery.

src/shared/project-discovery-dirs.test.ts

@@ -1,5 +1,5 @@
 import { afterEach, beforeEach, describe, expect, it, mock } from "bun:test"
-import { mkdirSync, realpathSync, rmSync } from "node:fs"
+import { mkdirSync, realpathSync, rmSync, writeFileSync } from "node:fs"
 import { tmpdir } from "node:os"
 import { join } from "node:path"
 
@@ -121,4 +121,94 @@ describe("project-discovery-dirs", () => {
     expect(directories).toEqual([canonicalPath(join(projectDir, ".opencode", "skills"))])
   })
 
+  it("#given nested .opencode plugin config files #when finding plugin config files #then returns nearest-first canonical paths", async () => {
+    // given
+    const grandparentDir = join(TEST_DIR, "grandparent")
+    const parentDir = join(grandparentDir, "parent")
+    const projectDir = join(parentDir, "project")
+    mkdirSync(join(grandparentDir, ".opencode"), { recursive: true })
+    mkdirSync(join(parentDir, ".opencode"), { recursive: true })
+    mkdirSync(join(projectDir, ".opencode"), { recursive: true })
+    writeFileSync(join(grandparentDir, ".opencode", "oh-my-openagent.jsonc"), "{}")
+    writeFileSync(join(parentDir, ".opencode", "oh-my-openagent.jsonc"), "{}")
+    writeFileSync(join(projectDir, ".opencode", "oh-my-openagent.jsonc"), "{}")
+
+    const { clearPluginConfigFileDetectionCache } = await import("./jsonc-parser")
+    clearPluginConfigFileDetectionCache()
+    const { findProjectOpencodePluginConfigFiles } = await import("./project-discovery-dirs")
+
+    // when
+    const paths = findProjectOpencodePluginConfigFiles(projectDir, TEST_DIR)
+
+    // then
+    expect(paths).toEqual([
+      canonicalPath(join(projectDir, ".opencode", "oh-my-openagent.jsonc")),
+      canonicalPath(join(parentDir, ".opencode", "oh-my-openagent.jsonc")),
+      canonicalPath(join(grandparentDir, ".opencode", "oh-my-openagent.jsonc")),
+    ])
+  })
+
+  it("#given a stop directory #when finding plugin config files #then walking halts at the stop boundary inclusive", async () => {
+    // given
+    const stopDir = join(TEST_DIR, "stop")
+    const childDir = join(stopDir, "child")
+    mkdirSync(join(TEST_DIR, ".opencode"), { recursive: true })
+    mkdirSync(join(stopDir, ".opencode"), { recursive: true })
+    mkdirSync(join(childDir, ".opencode"), { recursive: true })
+    writeFileSync(join(TEST_DIR, ".opencode", "oh-my-openagent.jsonc"), "{}")
+    writeFileSync(join(stopDir, ".opencode", "oh-my-openagent.jsonc"), "{}")
+    writeFileSync(join(childDir, ".opencode", "oh-my-openagent.jsonc"), "{}")
+
+    const { clearPluginConfigFileDetectionCache } = await import("./jsonc-parser")
+    clearPluginConfigFileDetectionCache()
+    const { findProjectOpencodePluginConfigFiles } = await import("./project-discovery-dirs")
+
+    // when
+    const paths = findProjectOpencodePluginConfigFiles(childDir, stopDir)
+
+    // then
+    expect(paths).toEqual([
+      canonicalPath(join(childDir, ".opencode", "oh-my-openagent.jsonc")),
+      canonicalPath(join(stopDir, ".opencode", "oh-my-openagent.jsonc")),
+    ])
+  })
+
+  it("#given a legacy basename in an ancestor #when finding plugin config files #then detection picks up the legacy path", async () => {
+    // given
+    const projectDir = join(TEST_DIR, "project")
+    mkdirSync(join(TEST_DIR, ".opencode"), { recursive: true })
+    mkdirSync(join(projectDir, ".opencode"), { recursive: true })
+    writeFileSync(join(TEST_DIR, ".opencode", "oh-my-opencode.jsonc"), "{}")
+    writeFileSync(join(projectDir, ".opencode", "oh-my-openagent.jsonc"), "{}")
+
+    const { clearPluginConfigFileDetectionCache } = await import("./jsonc-parser")
+    clearPluginConfigFileDetectionCache()
+    const { findProjectOpencodePluginConfigFiles } = await import("./project-discovery-dirs")
+
+    // when
+    const paths = findProjectOpencodePluginConfigFiles(projectDir, TEST_DIR)
+
+    // then
+    expect(paths).toEqual([
+      canonicalPath(join(projectDir, ".opencode", "oh-my-openagent.jsonc")),
+      canonicalPath(join(TEST_DIR, ".opencode", "oh-my-opencode.jsonc")),
+    ])
+  })
+
+  it("#given no .opencode directories along the walk #when finding plugin config files #then returns an empty list", async () => {
+    // given
+    const projectDir = join(TEST_DIR, "project", "deep")
+    mkdirSync(projectDir, { recursive: true })
+
+    const { clearPluginConfigFileDetectionCache } = await import("./jsonc-parser")
+    clearPluginConfigFileDetectionCache()
+    const { findProjectOpencodePluginConfigFiles } = await import("./project-discovery-dirs")
+
+    // when
+    const paths = findProjectOpencodePluginConfigFiles(projectDir, TEST_DIR)
+
+    // then
+    expect(paths).toEqual([])
+  })
+
 })

src/shared/project-discovery-dirs.ts

@@ -2,6 +2,8 @@ import { execFileSync } from "node:child_process"
 import { existsSync, realpathSync } from "node:fs"
 import { dirname, join, resolve } from "node:path"
 
+import { detectPluginConfigFile } from "./jsonc-parser"
+
 const worktreePathCache = new Map<string, string | undefined>()
 
 function normalizePath(path: string): string {
@@ -114,3 +116,35 @@ export function findProjectOpencodeCommandDirs(startDirectory: string, stopDirec
     stopDirectory ?? detectWorktreePath(startDirectory),
   )
 }
+
+export function findProjectOpencodePluginConfigFiles(
+  startDirectory: string,
+  stopDirectory?: string,
+): string[] {
+  const paths: string[] = []
+  const seen = new Set<string>()
+  let currentDirectory = normalizePath(startDirectory)
+  const resolvedStopDirectory = stopDirectory ? normalizePath(stopDirectory) : undefined
+
+  while (true) {
+    const opencodeDirectory = join(currentDirectory, ".opencode")
+    if (existsSync(opencodeDirectory)) {
+      const detected = detectPluginConfigFile(opencodeDirectory)
+      if (detected.format !== "none" && !seen.has(detected.path)) {
+        seen.add(detected.path)
+        paths.push(detected.path)
+      }
+    }
+
+    if (resolvedStopDirectory === currentDirectory) {
+      return paths
+    }
+
+    const parentDirectory = dirname(currentDirectory)
+    if (parentDirectory === currentDirectory) {
+      return paths
+    }
+
+    currentDirectory = normalizePath(parentDirectory)
+  }
+}