The various tubers and rhizomes all turn out to be edible. ...Edible-ish. They're not full of heavy metals or any toxin she has equipment to detect, and logically there's no reason for de novo plant sugars to bioaccumulate organic toxins present in the water, they're like the opposite of apex predators. Her gut bacteria grow on samples. They don't taste like something she should spit out instantly. 

The starchy bulbwrack root is a good staple food, in that Merrin cannot find a dose at which it gives her any upset-stomach symptoms. She is of course unsure if she's digesting all of it, she's pretty sure a bunch of it is insoluble fiber, but at least her gut bacteria can't break that down either and so it doesn't give her horrible gas.

It's a pain to process but she can make a reflective sun-powered oven from gear she has and bake it all afternoon, rather than boiling it with her precious electricity. And then mash it, pull out as many of the long fibers as she can (and set them aside in case she ever feels like trying to spin them into textiles), sun-bake the paste again until it's dry, sift the resulting grainy powder to get rid of the smaller bits of fiber, and she has something like flour. If she wets it again and mixes it with a bit of bladdersac syrup and re-bakes it a third time, it's not even terrible. 

She can even check her blood sugar after a huge meal of it, once she's confident that huge meals are something she can tolerate, and confirm that it rises just like it ought to. 

The other tubers both give her an upset stomach if she has too much, but like, that would ALSO happen if she tried to eat a 2000-calorie meal consisting entirely of garlic. There's no obvious serious toxicity, just a bit of nausea and gas that pass within six hours. 

...She thinks to check her liver enzymes with one of her limited number of test strips, and they're not elevated. So probably not toxic, just again full of sugar alcohol she digests poorly or something. 

The larger snails turn out to be process-able into about 5-6 kg of muscle meat each. Assuming it has the same nutritional breakdown as dath ilan snails and she can actually digest all of the protein, that's probably almost 1000 grams of protein. Way more than she needs in even a 64-hour day. 

Plus like 4kg each of organs. 

Merrin drains the oil-storage organ and processes it, and then sun-cooks everything else and renders it to melt out the fat and skim it off the surface of her pot, because she might as well. She's pretty sure the main problem with her local-biomass-based diet is that it's really, really low in fat. And she's noticing it, even with some supplementation from her reduced dath ilani rations. 

...Her gut bacteria do grow on the oil. Not with a ton of eagerness? But they can metabolize it at all. 

Merrin will cautiously test eating some.

Sheeeeee can eat up to about 25 grams at once. More than that, and it's the same deal as the bladdersac syrup: it's not that it's obviously toxic, her liver enzymes don't budge, but she has. Regrets. 

...She's pretty sure it's full of wax esters or something. There's a fish species like that in dath ilan, and eating too much of it has the same rather unmistakeable GI side effects. Meaning that 25 grams is probably getting her, like, half that amount of fatty acids her body can actually use. 

...Well, it's not nothing. She can use it to cook with and make her staple snail rations and bulbwrack-flour crackers more palatable. 

And dath ilani plants contain small amounts of oils, she's probably getting a little bit from plant sources.

She...is pretty sure that her body is still unhappy about the macronutrient ratios, even while she's still filling out some of her diet with meal bars. She never really feels full or totally satisfied, anymore. 

But she's now only eating 2.5 meal bars per 64h day – sometimes mixing it up with the other rations, she's started taking meal powder in her suit bladder for ocean trips now that she has more freshwater to wash her drinking bladder with afterward – and she's not obviously running a huge deficit in total calories. 

She does another ocean harvest trip in the daytime of Day 19. And, again, a later-shifted trip on Day 20, getting back well after dark. She refills her cache with a lot of snails - smaller ones, this time, the large ones are actually annoying because she doesn't trust her current sketchy refrigeration setup (the emptied rations box, packed with ice each morning from freshwater she left out overnight to freeze into bricks) to keep the meat good for three planetary days, so she ends up having to dry it, and dried-and-rehydrated snail is worse. She harvests a wider range of various weird worms and anemones, this time, to test if those are edible. 

She finally has more than enough strapwrack fronds stashed to build her shelter design. 

Day 21 is the spring equinox. Dawn is at 16:02, sunset is at 47:58, and the day and night are exactly the same length.

Overnight it's only dropping to between -30° and -32° C, now. It still takes nine or ten hours into the morning for the temperature to pass freezing, but that's less than a third of the total day length. Early-afternoon is hitting 40° C. On Day 21, Merrin records eleven hours of absolute temperature above 30° C, and of course it's always fairly humid right by the ocean. The period during which Merrin would be risking heatstroke if she were working outdoors lasts fourteen hours. 

With cool air piped in from underground, her cave is at least peaking at only 25-26° C inside, even in the hottest parts of the day. And the relative humidity in it is lower; the cave air is humid, but it's also cold enough that its absolute water content is a lot lower.

She can afford to run her ventilation for ten hours a day, now. She's banking more than 2000 Wh of solar power per daily cycle. 

...Even if Merrin arrived literally the day after the winter solstice - which isn't possible, she doesn't think, it would make no sense for the year to be anywhere near that short - her extremely sketchy made-up-math climate model makes it seem likely the summer highs would reach 50° C. In fact, with a 240-day year (rounded down for nice math) her model spits out highs of at least 55° C. 

The "wet-bulb" temperature (literally what it sounds like, she wraps the temp sensor in wet gauze to measure how much it drops from evaporative cooling) was already 34° C today, and it was a lower-humidity day than the peaks she's recorded. Humans flat-out cannot survive wet-bulb temperatures much above 35° C for very long, even resting. 

Well. She's still going to make an AWESOME CAVE SHELTER. If she can keep it down to 35° C inside, her suit can climate-control that to something she can tolerate for ten hours. Maybe. 

She finishes it on Day 25, right before her next block of harvest missions. 

[AUTHOR'S NOTE: please ignore any discrepancy in the structure from the two inside views, I have spent like 50 image model generations on this already and I give up.]

...And then she's just going to put the reflective tarp right back over, which is a lot less pretty but that is, in fact, what the tarp is for, and she's not going to be able to get anything made of local materials that works nearly as well.

And she can keep iterating on insulating the ceiling. Her next idea is layering some of the giant sailweed leaves over the woven strapwrack and under the tarp, possibly on top of a layer of natural fibre if she can process anywhere near enough of it. 

She's considering trying to enlarge the deeper-cave tunnel at the back of her cave. Right now the problem is that, while it miiiight just baaaarely fit Merrin herself, it will absolutely not fit Merrin plus her power armor, and it's a really bad idea to explore caves on a known high-uranium planet without having first gone in with a protective suit of armor and closed-loop air supply to check for radioactivity alarms.

(She has a CO2 detector and radioactivity sensor permanently configured to her ventilator-fan. The cave air is on average about the same CO2 content as her interior - both a little higher than ambient outside but not dangerous - but her ventilation, if it's running at the time, will switch itself off if the cave does somehow develop a CO2-accumulation problem, maybe because some internal passage collapses and it's no longer "breathing" as much with the outside air.) 

Eh. She'll need to explore for additional entrances to the same cave system, that might let her map it out from there and determine the radon risk. And if it's low, then it might be worth the sheer labor of enlarging the entrance without any tool more powerful than a drill. 

Of course, she's only going to have to worry about the heat if she solves all of the many nutritional deficits in her local-biomass diet before she runs out of supplementary food. 

She's down to 36 meal bars (and down by two more sugary-meal-replacement-powder pouches and two micronutrient-supplement-only pouches). She can stretch that to another 26 planetary days. 

Maybe the snail protein has all of her essential amino acids, and maybe she'll miraculously discover a rare seaweed or burrowing land-arthropod or some sort of edible cave fungus that's packed full of the essential fatty acids she's failing to get from anywhere else because all of the marine animal life she can find insists on being full of wax esters! Maybe she'll solve purifying out the digestible fat component by then! 

Maybe she won't. 

The summer solstice is probably not for at least another 60 days. 

But she's going to keep going.

She's going to explore the coast and look for caves, and she's going to keep bringing back and testing possible-food samples every time she finds a new species, and she's going to experiment with burning her waxy oil for lighting and cooking, though to do that safely for periods longer than a three-minute test she really needs some sort of heatproof receptacle with a ventilation flue to pipe the slightly-toxic smoke and also all the CO2 produced out of her cave, and she needs better O2 tracking indoors even when she's asleep.

She's going to point her X-ray spectrometer at cool rocks, and she's going to collect a growing pile of enormous armored snail shells and mull on what to do with them, and she's going to experiment with spinning the bulbwrack-bulb fiber into rope and see if she can make it well enough to stand in for her limited supply of paracord.

She's going to swim in the beautiful ocean and frolic in the strapwrack forests for imaginary Kalorm, though she has drawn a hard line at his suggestion that she COULD leap off the tall rocks directly into the incoming tidal bore, nobody can STOP her.  

She's going to walk around in the middle of the night - it's now taking ten or eleven hours for the temperature to drop as far as freezing, so it's not too uncomfortable to go for walks after her first sleep block - and talk to Laeirthe from her fanfiction about how someday, in 500 million years, maybe a sapient species will evolve on this planet, and maybe they'll find the fossilized remains of her Exception Handling gear, and maybe it'll give their scientists a remarkably fascinating puzzle and solving that puzzle will incidentally give them SPACE TRAVEL.

She's going to finish her EPIC DOOMPUNK SUN ROBE.