The first sign of anything strange are a set of relatively small (for space so still tens of meters across) telescopes that appear in distant orbits (far above geosynchronous) two for each of the planets and several more in the asteroid and outer cometary belts in the system to take pictures of space infrastructure.

There's a delay of about five minutes as those images are collected and evaluated. Then the next round begins, communication and mapping satellites are inserted in and among the various existing satellites all carefully placed to avoid collisions and hopefully to be able to snoop on EM communications that aren't transmitted in tight beams. These are far more likely to be noticed especially once they start transmitting a first contact package based on mathematical principles in their best guess at a compatible transmission range from a few seconds of observation.

A close observer may notice that simultanaity as evidence of superluminal capabilities.

Space is big, and telescope coverage is spotty. But the Deep Space Network cannot miss an intentional radio transmission made from inside the solar system, actually.

Highly periodic transmission detected. 
No recognized packet header.
No scheduled transmissions expected.

Hey mission control I think you might want to see this. Relaying transmission ...

Those are prime numbers!

A different civilization might panic, or have to race to come up with a response. But the thing is, Þereminia planned for this. There are festivals where people dress up in silly makeup and explore this exact scenario.

So Director Ŋaceta makes an announcement on behalf of Larger Continent Emergency Services and mathematicians and linguists and (not-so) speculative xenoanthropologists are woken by urgent phone notifications. A Network-wide protocol announcement goes out, and the Network shifts to 'oh shoot our encryption is probably broken' mode and suddenly all RF communication audible from space is encrypted with one-time keys.

And the Emergency Services of two continents compose a response.

"Lunar Mapping Orbiter, stand by to relay a verbatim radio message at best power."

New verbatim relay request acknowledged.
Destination coordinates acknowledged.

Standing by for relay.

Ready when you are, mission control!

The þereminian first-contact package has its own set of math problems and carefully built physics-based translation. But if the aliens made it here, they might be Sufficiently Advanced, so it also contains a plain-language message. In text, audio, and video, in LCTL and SCOL:

Three diplomats in black and purple uniforms stand behind a podium. One has a beaming smile. One needs to keep surreptitiously wiping their eyes.

"Greetings, on behalf of the people of þereminia. To one who has come an incredible distance: we[ex] convey our[ex] sincerest greetings and well-wishes. It is our[ex] utmost hope to come to know you and greet you as friends, and to arrange for peaceful contact and mutually beneficial trade between our[in] civilizations."

Them deciding to switch to one time keys is inconvenient. It will make learning about them take longer and they might need to consider more... invasive actions eventually.

But for now it's more important to act in good faith. They'll work through the mutual first contact packages and try to get to mutually intelligible conversations as soon as they can. With only a couple minutes of corpus that's all encrypted there isn't much acceleration so it'll be around a full rotation of the planet before they can respond in kind.

"We[ex], the people of the rings, greet you in turn and convey our[ex] own sincere greetings and well-wishes. We[ex] share your hopes for peaceful contact and mutual benefit and learning. Our people seek to offer infrastructure and biological maintenance support once we[ex] are confident these will benefit you."

"Okay — Jarnegh, you said that the linguists have a report on their probable computing power based on how long it took them to reply? Let's go through that."

"So we[in]'re dealing with FTL-capable ships, with orders of magnitude more computing power than our[in] whole planet. How does that impact the contingency plans?"

"Damn it, I know that you swore to — no, head Archivist, I don't want to see an uncoordinated release — look, there are security concerns ..."

If the visitors had not demonstrated FTL capability, then Emergency Services would have executed the planned contingency and sent out a last warning, to any other alien civilizations listening, before fully committing to cooperation. But it looks like their understanding of physics was even wronger than expected, and þereminia will not have a chance to get one last word in.

Instead, the head of the Archive, the world's oldest (and probably most soft-power-having) institution, sends a message via the Deep Space Network.

"Hello, people of the rings! I am Head Archivist Zamerast, the coordinator in charge of ensuring that our civilization's written and creative works are preserved in the long-term. I have gotten an agreement to share our[ex] corpus with you. I would be immensely grateful if you were to store a copy. Please stand by for a transmission of the index, and protocol documentation on how to make prioritized requests. Transmit bandwidth on this frequency is somewhat constrained; are you able to pick up the test broadcast originating at the attached coordinates?"

"Greetings Head Archivist and associated team. We[ex] would be pleased to store such information. If it would be more efficient and desirable we[ex] could retrieve a physical storage medium if you specify its position and dimensions in this same coordinate system. If EM transmission is preferred, we[ex] are receiving the transmissions from the specified sites."

"Thank you. What are your limits on lifting capacity to orbit? You could take the entire Smaller Continent Secondary Archive, located at the attached coordinates. It is quite large, however, because it's optimized for storage durability and not for storage density. If it would be more efficient, we can prepare a site with denser physical storage, although that will take approximately 10 days to arrange. In the meantime, we will continue transmitting in that same band from available sites."

With most Network traffic having gone to physical links, the Archive has no particular difficulty bidding on the unused radio spectrum and getting volunteers to set up planet-wide transmitters for better bandwidth.

"Our[ex] lifting capacity is sufficient to relocate that complex but we[ex] do not presently have a suitable location to place it and according to your own archives it is an inhabited complex. We[ex] would be happy to arrange a transfer of denser storage media.

"We[ex] could also offer higher bandwidth transmission interfaces capable of transferring up to 1.3 TBs over optical feeds or electrical feeds per second, full specifications attached. We[ex] can supply as many such interfaces as you can make use of up to a limit of 3 million. We[ex] will leave it to your discretion what combination of methods we[in] will use for this process."

The promised technical specs show small devices about ten centimeters cube that have an internal power feed and no discernable antenna that can have a number of data lines attached at the specified ports.

It's going to be a lot faster and less expensive to just hook a box into the Archive's existing high-speed Network connection, compared to purchasing and transferring enough high-density storage media.

The head archivist requests 20 such boxes (a primary and a backup for each of the six Archive sites on the planet), and can get them hooked up in short order.

The boxes appear at the specified coordinates promptly after the request comes through. There's no sign they can easily detect heralding their arrival, they just become present where previously there was empty air.

Sweet!

AAaaaaaahhh!

"People of the rings, we should have everything hooked up on our end in another few hours. Thanks!"

"People of the rings, I am Diplomat Tatenika. My job is to facilitate coordination and understanding between people of different polities and cultures. I have a number of people here who are worried about the implications of your arrival, and have been working to put together a single question packet," a different transmission comes.

"Could you please elaborate on what you mean by 'infrastructure and biological support' and what criteria you would be using to decide whether it is good for us[ex]? And could you share a copy of whatever rules of engagement you have for interacting with us[ex]? I have attached a copy of our[ex] Global Minimum Standards (the rules to which every person of our[ex] civilization is subject, and that we[ex] hope to be able to continue to enforce planet-wide, although the relevant standards body is capable of renegotiating them), and our[ex] Standards for the Behavior of Diplomats and Ambassadors, to which I am bound (but that we[ex] don't expect you to follow unless you choose to become a signatory)."

"We[ex] hope to offer improved infrastructure to facilitate space travel and space habitats to be scaled based on need and preference. We[ex] may also offer planetside infrastructure for scaling food, sanitation, power production or housing structures as needed but the intervention standard for those is higher as there's a greater risk of unduly destabilizing or reinforcing existing power structures.

"Biological support consists of using our[ex] imaging and computer modelling capabilities to make breakthroughs in extant adverse biological conditions and to facilitate changes to individual's body plans where such changes are sustainably scalable and again are not unduly destabilizing or reinforcing existing power structures.

"Our[ex] standards for engagement are to avoid deliberate deception except where necessary for information gathering purposes or to prevent early disclosure of advanced technological capabilities, and to minimize it when needed for those purposes.

"In addition, we[ex] should avoid destabilizing any existing power structures to the point of prompting large scale interpersonal violent conflict, with certain exceptions where the existing actions of the power structures are evaluated to have similar harm profiles to such conflict.

"Further, we[ex] should avoid substantially reinforcing power structures which are causing substantial harm if possible and avoid if possible incentivizing peoples we are in contact with towards becoming substantially more homogenized or otherwise making it less likely for new opinions and patterns of life to emerge.

"We[ex] have no substantive objections to our best understanding of your provided Global Minimum Standards and will take your standards for Diplomats and Ambassadors under advisement."

Well, that is a pretty promising response, all things considered! It makes sense that the aliens must like something about the status quo ante, since they have teleporters and yet the planet remains unconquered.

Tatenika workshops responses with her colleagues.

"It sounds like one of your biggest concerns, that informs your other priorities, is not interfering with existing power structures. Could you elaborate on why, please? Is it that those kinds of interferences tend to provoke other harms, or is it that you prefer governmental systems to remain stable as an intrinsic end?"

"Also — we[ex] are curious about more details of your culture and language. Do you have a general civilizational history, or some set of relevant popular cultural outputs that you would be willing to share so that we[ex] can get a better understanding of your culture, purpose, and attitudes?"

"Social structures are potentially delicate. Yours have most likely been substantially impacted by our arrival in ways that won't be clear for quite some time. It isn't our[ex] goal to make no change to your social and power structures it is to allow you collectively to continue to choose your path rather than forcing you to assume a shape to our[ex] liking or to empower one or more groups among you to claim an unassailable position of control over all others.

"We[ex] are not inclined to share cultural outputs at present, the majority of those we possess are generated by other civilizations like your own that we have made comparable contact with. To the extent that we can be said to have our own language it is challenging to translate as we share experiences and knowledge in lieu of more compressed concepts such as those used in your own language."

Well, in the presence of actual aliens and absence of actual facts, the speculation is going to be wild. This, too, is something that þereminian authors have prepared for, even if writing alien-abduction slashfic is not, maybe, the most adaptive response to this situation.

"I believe that I understand. Thank you for sharing. If your worry is about exerting undue influence on our[ex] culture, would it be helpful for us[ex] to try generating our[ex] own suggestions for how you might go about providing space-based infrastructure, so that we[in] end up building something primarily shaped by our[ex] designs?"

Diplomat Tatenika can't actually stop some enthusiastic people with software defined radios who are listening in on their conversation from chipping in with links to various designs for O'Neill cylinders, even if she wanted to. Hopefully the aliens just interpret it as willing.

"We[ex] would welcome such inputs."

"Attached is a general prospectus on types of space infrastructure and their properties."

The attached document has material constraints on how large they can make structures under various levels of force and also goes into the various tradeoffs in power consumption, maintenance, size and performance of active support structures.

They will receive a flood of suggestions. "Design your ideal space habitat" is the sort of dinner-party conversation that everyone has an opinion on. A substantial subset of those designs are even proper engineering diagrams that take their expressed material constraints into account.

As a general trend, the þereminian designs tend to completely eschew active support structures. They overwhelmingly prefer spin gravity and solar power, although some smaller designs have backup thermal radioisotope generators. They also have a strong dispreference for things that involve a lot of maintenance.

When freed from budgetary constraints, þereminian designs tend to be overbuilt, with huge safety margins and multiple redundant systems. A few people submit six variations on the same design, expressing different points on the tradeoff between assumed-construction-cost and redundancy.

Also in evidence: big windows for natural sunlight, deep soil beds for growing trees, dubiously practical space-efficient micro-gravity hydroponics, and bedrooms that consist entirely of cushions.

Each design will get replies with notes about practical issues they might have missed like potentially wanting static wrappers to protect rotating habitats from space debris and also how large windows may be undesirable given now fast even large habitats rotate if they are built in proximity to other objects such as planets or if they have direct exposure to sunlight.

The minimal use of active support structures is acceptable though they are the only available surface to orbit option that doesn't require independent aerospace craft or teleportation.

Teleportation is actually preferable, if they're offering? But mainly people are planning to just make every space-habitat self-sustaining, since the aliens seem happy to build quite large structures for them. If they're all self-sustaining, then there will be a lot fewer urgent rescues, and they can probably cover that with rocket-based infrastructure, at least in near-planet orbit.

They definitely, absolutely can't have a space elevator. A space fountain is similarly bad.

Sure, it would be way more efficient for lifting things to orbit, but have you seen the calculations of what would happen if one of those had a structural failure? That would be species-ending. They've only got one habitable planet at the moment and they intend to keep it that way. Maybe once there are 6 independent self-sustaining colonies they could do a space elevator. But teleportation just seems better in every way.

Active support structures are extremely reliable with reasonable maintenance (have some figures about the details of that) and some structure designs have much less catastrophic failure modes than balanced tensile lift structures (see attached calculations for this). That said it's entirely reasonable to prefer to minimize risks with even relatively low likelihoods.

Teleportation in particular is one of the things they're least willing to part with, because of how easy it is to abuse.

Hmm.

There are now Network arguments about skyhooks versus magnetic launch solutions versus other stranger designs.

One group of people have gotten together to collaborate on designing a large space city intended to house a million people and the infrastructure necessary to support them.

"Hi — super excited about space, thanks for the opportunity — we[ex] were wondering whether you just object to giving us[ex] teleporters on an ongoing basis? Like, even if you're going to build something to our[ex] specifications, we[ex] still don't really have the launch capacity to handle initial relocations, even if we[ex] can probably handle ongoing resupply. So if we[ex] got everyone who wants to settle in Space City to get together in a particular location with our[ex] belongings, would you be willing to teleport us[ex] up?"

"We[ex] will offer support with relocating people and materials if there is a plan for supporting them though reasonable contingencies without our[ex] direct intervention. Gathering all of the materials and individuals to be moved is not required so long as adequate assurances are made that their relocation is uncoerced."

That's ... a slightly baffling response. Putting someone who doesn't want to be there on your space station sounds like a great way to stop having a useful space station. They're building in as much redundancy as they can, but that's not going to stop a dedicated saboteur.

... maybe the aliens just don't think the average þereminian will be capable of making their presence on the station an obvious net negative?

The Space City Planning group responds with a new design that includes prominent, well-marked, accessible levers for wedging the airlocks open and venting sections of the city to space.

It takes markedly longer than usual for a response to be formulated. "We[in] appear to be having a substantial miscommunication. Allowing individuals to end their lives and those of substantial numbers of individuals around them is not a response we[ex] expected. The worst case of mass forced displacement does not seem likely given your communication thus far, but making it easy to shift that into mass death does not address it. We[ex] will seek confirmation from individuals before relocating them."

A miscommunication seems pretty likely, yeah! The aliens clearly think death is bad ... so they either don't believe that þereminians believe that, or they think þereminians are sufficiently bad at planning that thinking that won't be sufficient incentive to take steps to make it not happen?

Ouch. That feels really rude, actually.

But the correct thing to do when someone from a foreign culture seems to have given you a grave insult is get a specialist involved. Diplomatic Corps! We choose you!

Diplomat Tatenika has been having an extraordinarily busy day. Maybe when first contact is over she should retire and take up a nice relaxing hobby like herding cats.

"Speaking on behalf of the Space City Planning Group: We[ex] apologize for the inadvertent miscommunication. SCPG is an initiative to found a new city. Historically, we[ex] have found that attempts to found new cities with non-volunteers doesn't work, and often ends up with everyone having wasted a lot of time and resources. See the attached Archive references for historical accounts. This makes sense from the perspective of game theory: if someone doesn't want to be involved in founding a new city, they are incentivized to make including them in the process as difficult and unpleasant as possible. That way, when the city-founders are rational, they don't involve those people in the plan."

"As a result of this historical knowledge, modern attempts to found cities are traditionally done only with volunteers. There is no actual law against not doing that, for the same reason that there isn't a law against lighting your own face on fire — people mostly know not to try. There is a law against forcing people to belong to a political group or forcing them to work when they do not choose to. See the global minimum standards that were previously shared. If the SCPG had attempted to do those things, they would have been subject to a GMSB tribunal, which is an additional disincentive."

"When you said that you were worried about people who didn't want to be part of Space City being added to the transport list, the planning committee inferred that either you didn't believe that their screening procedures for volunteers were sufficiently robust, or that you didn't believe the cultural disincentives from our existing institutions were strong enough, in the face of getting to live in space. But since you have evinced a preference for not informing our decision making, they assumed that you wouldn't be willing to improve screening procedures. So they added additional ways to disincentivize the use of involuntary colonization, so that you could see that they were trying their best to avoid involving non-volunteers, even if you didn't trust our[ex] established legal system."

"When you responded negatively to that and said that you would implement your own screening procedures, the planning committee took that to mean that you didn't think that they were rational beings capable of responding to incentives. I have assured them that this is almost certainly not the case, and that, in my professional opinion, this is very likely a miscommunication caused by missing cultural context. I have encouraged them to assume that aliens are even weirder than they were assuming, and that they should avoid making assumptions about what you will or will not be able to infer from our[ex] transmissions."

"In that spirit: I do not believe that you have done anything incorrectly, and I have done my best to convey to the planning committee that they have not been insulted. But we[ex] have multiple probably-evolutionarily-designed* involuntary decision-making procedures in our brains, and while the committee is rationally committed to continuing to work productively toward our[in] goal of seeing peaceful settlement of space, some members of the committee would be emotionally reassured if you would confirm my assessment. It would, in my opinion as a diplomat, smooth further relations if you were to compose and issue a brief apology. See On the Purpose and Composition of Apologies for an explanation of the underlying psychology and how to compose an apology that will be correctly received."

*i.e. stupid.

"Thank you for your thorough evaluation of this miscommunication. It is a standard part of our[ex] procedures to seek confirmation from individuals before relocating them and ensure that their relocation is freely chosen. We[ex] apologize for our[ex] lack of care in communicating this such that it seemed this was an expression of mistrust particular to that group or to the people of your world in general.

"Our[ex] procedures are built on the assumption that those we[ex] are communicating with may be attempting to deceive us[ex] and while we[ex] have no reason to believe that is the case here, and indeed the evidence so far made available to us suggests the opposite, we[ex] will continue to follow those procedures out of an abundance of caution. We[ex] hope you will not take this caution, especially at this relatively early stage as further insult.

"The suggestion of making it easy for individuals to vent large sections of a habitat does make sense under the assumption that individuals consistently behave rationally. If your people can be modelled under that assumption, that is an exceedingly unusual trait. Most societies we[ex] encounter have at least some significant portion of the the population, typically more than one person in one thousand, have at least one emotional episode which makes them a danger to themselves and those around them during their lifetime. Typically this dangerous behavior is not something they would endorse outside of that episode.

"To clarify our[ex] earlier statement regarding allowing you to select your own path we[ex] have an interest in not directly facilitating harms such as forced relocation. We[ex] do not consider checking for consent when moving individuals to be an example of influencing your decision making process over and above the influence already entailed by offering such relocation."