feat(files): native instance-scoped file browser (replaces broken VueFinder)

FileManagerView rewritten as a native DS browser on the per-instance
file bridge: instance selector, breadcrumb nav, dir-first listing
(name/size/modified), folder drill-down, inline file editor (read/save),
toolbar (new folder/file/refresh), per-row rename + delete-confirm.
New files store wraps the /instances/:id/files* endpoints. VueFinder
import + RemoteDriver fully removed — no more retired-protocol /api/files.
Honest empty (no instance -> Server page) + error (retry) states, never
the global error boundary.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/stores/files.ts

@@ -0,0 +1,136 @@
+import { defineStore } from 'pinia'
+import { ref } from 'vue'
+import { useApi } from '@/composables/useApi'
+import { useInstancesStore } from '@/stores/instances'
+
+export interface FileEntry {
+  name: string
+  path: string
+  is_dir: boolean
+  size: number
+  modified: string
+}
+
+/**
+ * Per-instance file browser store.
+ * All operations target `/api/instances/{id}/...` — jailed to instance root.
+ * Guard: if no current instance, list() sets error and bails out early.
+ */
+export const useFilesStore = defineStore('files', () => {
+  const api = useApi()
+
+  const cwd = ref<string>('')
+  const entries = ref<FileEntry[]>([])
+  const loading = ref(false)
+  const error = ref<string | null>(null)
+
+  /** Join two relative path segments with a single forward slash. */
+  function joinPath(base: string, name: string): string {
+    if (!base) return name
+    return `${base}/${name}`
+  }
+
+  function currentId(): string | null {
+    // Retrieve fresh from the store each call — avoids stale closure.
+    return useInstancesStore().currentId
+  }
+
+  /** List a directory. Sets cwd + entries. Does NOT throw — sets error. */
+  async function list(path: string): Promise<void> {
+    const id = currentId()
+    if (!id) {
+      error.value = 'No instance — connect the host agent'
+      entries.value = []
+      return
+    }
+    loading.value = true
+    error.value = null
+    try {
+      const data = await api.get<{ entries: FileEntry[] }>(
+        `/instances/${id}/files?path=${encodeURIComponent(path)}`,
+      )
+      cwd.value = path
+      entries.value = data.entries ?? []
+    } catch (e) {
+      error.value = e instanceof Error ? e.message : 'Failed to load directory'
+    } finally {
+      loading.value = false
+    }
+  }
+
+  /** Read a text file. Returns content string. Throws on error (binary/too big/not found). */
+  async function readFile(path: string): Promise<string> {
+    const id = currentId()
+    if (!id) throw new Error('No instance selected')
+    const data = await api.get<{ content: string }>(
+      `/instances/${id}/file?path=${encodeURIComponent(path)}`,
+    )
+    return data.content ?? ''
+  }
+
+  /** Write / overwrite a text file. Throws on error. */
+  async function writeFile(path: string, content: string): Promise<void> {
+    const id = currentId()
+    if (!id) throw new Error('No instance selected')
+    await api.put(`/instances/${id}/file`, { path, content })
+  }
+
+  /** Delete a file or directory (recursive). Throws on error. */
+  async function del(path: string): Promise<void> {
+    const id = currentId()
+    if (!id) throw new Error('No instance selected')
+    await api.post(`/instances/${id}/files/delete`, { path })
+  }
+
+  /** Rename within the same parent. `name` is the bare new filename. Throws on error. */
+  async function rename(path: string, name: string): Promise<void> {
+    const id = currentId()
+    if (!id) throw new Error('No instance selected')
+    await api.post(`/instances/${id}/files/rename`, { path, name })
+  }
+
+  /** Create a directory (and all missing ancestors). Throws on error. */
+  async function mkdir(path: string): Promise<void> {
+    const id = currentId()
+    if (!id) throw new Error('No instance selected')
+    await api.post(`/instances/${id}/files/mkdir`, { path })
+  }
+
+  /** Create an empty file. Throws on error. */
+  async function mkfile(path: string): Promise<void> {
+    const id = currentId()
+    if (!id) throw new Error('No instance selected')
+    await api.post(`/instances/${id}/files/mkfile`, { path })
+  }
+
+  /** Move a file or directory. Both paths are relative to the instance root. Throws on error. */
+  async function move(path: string, dest: string): Promise<void> {
+    const id = currentId()
+    if (!id) throw new Error('No instance selected')
+    await api.post(`/instances/${id}/files/move`, { path, dest })
+  }
+
+  /** Copy a file or directory. Both paths are relative to the instance root. Throws on error. */
+  async function copy(path: string, dest: string): Promise<void> {
+    const id = currentId()
+    if (!id) throw new Error('No instance selected')
+    await api.post(`/instances/${id}/files/copy`, { path, dest })
+  }
+
+  return {
+    cwd,
+    entries,
+    loading,
+    error,
+    joinPath,
+    list,
+    readFile,
+    writeFile,
+    del,
+    rename,
+    mkdir,
+    mkfile,
+    move,
+    copy,
+  }
+})