fix: container backup should not fail entirely on mount copy errors

[jakub961241]

Summary

Fixes #12236 - Container backup fails and gets stuck in "running" state when a mounted directory is too large or disk runs out of space.

Root Cause

In stepBackupContainerMounts(), when CopyDirWithNewName or CopyFile fails for any mount, the function returns the error immediately, causing the entire backup task to fail. With large bind mounts, this is common (disk full, permissions, etc.).

Fix

Mount copy failures are now non-fatal:

• Error is logged via global.LOG.Errorf
• Mount metadata records status: "failed" with the error message
• Backup continues with remaining mounts
• Task completes successfully with partial backup data

Before:

if err := backupCtx.fileOp.CopyDirWithNewName(...); err != nil {
    return err  // entire backup fails
}

After:

if err := backupCtx.fileOp.CopyDirWithNewName(...); err != nil {
    mountMeta.Status = "failed"
    mountMeta.Message = fmt.Sprintf("copy dir failed: %v", err)
    // ... log and continue
    continue
}

Changed file

• agent/app/service/backup_container.go (+10, -2)

fix: Container backup no longer fails entirely when a mounted directory copy fails (#12236)

[f2c-ci-robot]

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