fix(sharing): download file before "Send copy to"

[ToteMeiSter]

Problem

Closes #17619

The "Send copy to" button on the sharing tab of the file details builds the send intent with OCFile.getExposedFileUri(). That method returns null when the file has no local copy. The sharing tab can be opened for a file that was never downloaded, so Telegram, WhatsApp and other apps receive ACTION_SEND without EXTRA_STREAM and show "Unsupported content" or send nothing. For a file that is already on the device the button works.

The button was added in #16183 without a download step. The previous share entry went through SendShareDialog, which downloads the file first.

Change

FileDetailSharingFragment: when the file is not on the device, the button calls FileOperationsHelper.sendShareFile(file, true). This is the same call the "Send/share" menu entry of the details screen uses. SendShareDialog lists the apps, downloads the file through the host's SendShareDialogDownloader (FileDisplayActivity, DOWNLOAD_SEND) and sends it to the chosen app. A downloaded file still opens the system chooser. The download path is used only when the host activity implements SendShareDialogDownloader; ShareActivity also hosts the fragment and does not implement it, so it keeps the old behaviour.

Notes

• Every other send entry (image, text and media previews, the details menu) already goes through SendShareDialog. "Send copy to" was the only one that called IntentUtil.createSendIntent directly.
• No new download logic: the existing SendShareDialog / SendShareDialogDownloader path is reused. The host of the sharing tab, FileDisplayActivity, already implements SendShareDialogDownloader.
• SendShareDialog sends a not downloaded image as the cached preview (sendCachedImage), not as the original. The menu entry behaves the same way today. Changing that is out of scope here.
• No unit test: the change is a click handler in a fragment, and the unit tests run without the Android SDK.
• Touches only FileDetailSharingFragment. No file overlap with the other three PRs (fix(auto-upload): restart folder runs that stay enqueued on rescan #17805, fix(auto-upload): start auto upload right after resuming global upload pause #17806, fix(share): send original file instead of cached thumbnail #17808); trial merge of all four is clean. Logically it goes together with fix(share): send original file instead of cached thumbnail #17808 (SendShareDialog): with both merged, a not downloaded picture from "Send copy to" is downloaded and sent as the original.

How to test

• Unit: no new test. The existing unit tests pass (jacocoTestGplayDebugUnitTest).
• Device: Checked on a HUAWEI Mate X7 (DEL-LX9, EMUI 15.0.0, Android 12) with a test build: works, "Send copy to" for a file that was not downloaded downloads it and sends it.
• Manual steps:
  1. Open the details of a file that is not downloaded, go to the sharing tab.
  2. Tap "Send copy to", pick an app.
  3. The file is downloaded and sent to the app.
  4. Repeat with a downloaded file: the system chooser opens as before.

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI

The change was drafted with Claude Code (Assisted-by: Claude-Code:claude-opus-5-5).

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...d/android/ui/fragment/FileDetailSharingFragment.kt	0.00%	5 Missing ⚠️

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