feat: implement MoveFile and CopyItem across all providers (stub audit follow-up)

[brunolnetto]

Background

An audit of the CloudFS codebase identified several unimplemented or stub operations across the 6 cloud storage providers. This issue tracks each gap and links to the implementing PR.

Audit Results

🔴 P0 — Critical Blockers

#	Feature	File	Status
1	MoveFile()	cloud_filesystem.cpp:446	🟡 In Progress (this branch)
2	Google Drive JWT RS256 Signing	gdrive_auth.cpp:120	✅ Fixed in PR #4

🟠 P1 — Important

#	Feature	Providers Missing	Status
3	CopyItem()	OneDrive ❌, SFTP ❌	🟡 In Progress (OneDrive added this branch)
4	ListFolderRecursive() native API	GDrive, OneDrive, SharePoint, SFTP, VFS	⏳ Pending

🟢 P2 — Nice-to-have

#	Feature	Providers Missing	Status
5	RefreshDownloadUrl()	GDrive ❌, SFTP ❌	⏳ Pending
6	AbortUpload()	All providers	⏳ Pending

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Provider Coverage Matrix (After This PR)

                    GDrive  Dropbox  OneDrive  SharePoint  SFTP   VFS
MoveFile()           ✅       ✅        ✅         ✅         ✅     ✅
CopyItem()           ✅       ✅        ✅         ✅         ❌     ❌
ListFolderRecursive  📊       ✅        📊         📊         📊    📊
RefreshDownloadUrl   ❌       ✅        ✅         ✅         ❌     ❌
AbortUpload          ❌       ❌        ❌         ❌         ❌     ❌

✅ = Implemented | ❌ = Not implemented | 📊 = Software fallback (suboptimal)

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Implementation Approach for MoveFile

Each provider uses its native move/rename API:

• SharePoint/OneDrive: PATCH /drives/{root}/items/{id} with parentReference + name
• Google Drive: GET /files/{id}?fields=parents then PATCH with addParents/removeParents
• Dropbox: POST /files/move_v2
• SFTP: libssh2_sftp_rename_ex() with OVERWRITE|ATOMIC|NATIVE flags
• VFS Agent: POST /v1/move (requires agent-side endpoint)

Acceptance Criteria

• MoveFile(src, dst) works for same-root moves on all 5 cloud providers
• CopyItem() works for OneDrive
• Cross-provider and cross-root moves return a clear error
• All existing tests pass (no regressions)
• Build: 0 errors, 0 warnings

Related

• PR feat(auth): implement client credentials and service account auth across providers #4: feat(auth): implement client credentials and service account auth
• Audit docs: docs/AUTHENTICATION_AUDIT.md, docs/INVESTIGATION_SUMMARY.md