feat(desktop): open attachments in active project

[Hona]

TLDR;

• Desktop file attachments now open from the project you are currently working in.
• Project folder selection consistently uses the native picker for local desktop projects and the server picker for web and remote projects.

Changelog

Fixed

• Choosing Add files in the desktop app with a local server now opens the native file picker in the active project instead of reusing a previously visited project folder.
• Switching projects before choosing Add files now updates the file picker's starting folder to match the newly selected project.
• Native attachment picker failures now show an error instead of surfacing as an unhandled rejection.
• Starting another attachment selection while earlier files are still processing no longer invalidates the earlier selection.

Changed

• Project folder selection now follows one consistent routing path across the home screen, project sidebar, and new-session project selector.
• Desktop attachments are read and processed one at a time, with selections limited to 20 MB total to keep memory use bounded.

[Copilot]

Pull request overview

This PR updates the desktop attachment workflow so that “Add files” (when connected to a local server) opens a native file picker rooted at the currently active project directory, avoiding reuse of a previously visited folder.

Changes:

• Added a desktop-only native attachment picker (open-attachment-picker) that reads selected files and returns them to the renderer.
• Extended the app Platform interface with openAttachmentPickerDialog and wired PromptInput to use it for local servers (with fallback to the browser file input when unavailable).
• Added a small helper (pickAttachmentFiles) plus tests to ensure the picker’s defaultPath is re-evaluated on each invocation (e.g., after switching projects).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/desktop/src/renderer/index.tsx	Adds openAttachmentPickerDialog to the desktop Platform implementation and converts IPC results into File objects.
packages/desktop/src/preload/types.ts	Extends the preload API typings with openAttachmentPicker.
packages/desktop/src/preload/index.ts	Exposes openAttachmentPicker via ipcRenderer.invoke.
packages/desktop/src/main/ipc.ts	Implements open-attachment-picker IPC handler using Electron’s open dialog + file reads.
packages/app/src/context/platform.tsx	Adds openAttachmentPickerDialog to the shared Platform type.
packages/app/src/components/prompt-input/files.ts	Introduces pickAttachmentFiles helper used by PromptInput to pass defaultPath per invocation.
packages/app/src/components/prompt-input/attachments.test.ts	Adds unit tests for pickAttachmentFiles behavior and fallback.
packages/app/src/components/prompt-input.tsx	Switches local-server attach flow to native picker (with fallback) and adds attachments from returned files.

Comments suppressed due to low confidence (1)

packages/desktop/src/main/ipc.ts:142

• open-attachment-picker reads each selected file with readFile inside Promise.all(...) but does not handle per-file read failures. If the user selects a file that can't be read (permissions, transient FS errors), the entire IPC invoke will reject and can bubble up as an unhandled rejection in the renderer. Consider catching read errors per file and returning null (or filtering unreadable files) instead of rejecting the whole request.

        defaultPath: opts?.defaultPath,
      })
      if (result.canceled) return null
      return result.filePath ?? null
    },
  )

  ipcMain.on("open-link", (_event: IpcMainEvent, url: string) => {
    void shell.openExternal(url)

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