The word sure[-]fast does show up occasionally in all-lowercase letters in books and periodicals, although its meaning seems to vary considerably from one occurrence to another. Here are some examples that I found in Google Books and Elephind searches.
From Jane Austin, Standish of Standish: A Story of the Pilgrims (1890):
"Peace, peace, dear child. Thou wastest thy strength in talking overmuch. Sleep, canst thou not, dear heart?"
"Dost think that Barbara will come hither? She promised me surefast that she would so soon as there was a company ready. She said it was so lonely there in Man when I was gone. Will she come, think you, Myles?"
In this stilted dialogue, surefast seems to mean something like "solemnly" or "with firm commitment."
From U.S. Army Ordnance Department, Report of the Chief of Ordnance (1893):
The surefast girth fastening, invented by H. M. Tileston, Kansas City, Mo. This fastening holds the cincha strap very firmly, and has the advantage that the girth can be tightened without dismounting. The cavalry officers who tried this device were not in favor of it, and it was not recommended. Mr. Tileson has since made an improvement on the surefast and 40 of his girths are now being tried by the Sixth and Ninth cavalry.
The sense here is approximately "reliably fastening." Although this instance of the word appears in lowercase, Mr. Tileson ran a company in Duluth, Minnesota, called Tileson Surefast that produced various types of straps—for example, for girths, luggage, and ladies' skirts—and in its advertisements the company consistently spelled the word (when it appeared as an adjective) as Surefast.
From "Labor," in the Sydney [New South Wales] International Socialist (January 7, 1911):
For Labor bears no luck in dower, / Sweat needs must run for man's increase / In health and wealth that merge to power / 'Mid sure-fast guarantees of peace.
Sure-fast here seems to be standing in for sure-fire—that is "certain," "trustworthy," or "thoroughly reliable."
From "The Soul of a Suit," an advertisement in the Lebanon [Indiana] Daily Reporter (February 17, 1917):
Just as the body of a suit is made up of the fabric and trimmings, so the soul is the design and cut. KHAN MADE TO MEASURE CLOTHES $20 TO $40 are builded of pure all-wool fabrics, dyed sure-fast and so guaranteed. In design and and cut they are eloquent of apparel artistry.
Here, sure-fast means "with assurance of being colorfast" or perhaps "using a reliable process for colorfastness."
From "Saturday Specials," an advertisement in the Orange [Texas] Leader (February 14, 1929):
Men's surefast dress shirts fast colors. $1.39
Although this advertisement spells surefast in all-lowercase letters, an instance in the same newspaper a year later suggests that Surefast was a proprietary or category name for a type of shirt. From "A New Opportunity for the People of Orange," an advertisement in the Orange [Texas] Leader (January 29, 1930):
Men's better grade Dress Shirts Surefast and Perfectos in prices ranging from $1.39 to $1.95
From "New Type Supporter Belt Will Take Inches off Your Waistline," an advertisement in the San Bernardino [California] Sun (September 6, 1938):
Knitted from two-way stretch Lastex, The Bracer is scientifically tailored by Bauer & Black, makers of the famous Pal supporter, to give the maximum in support — wear — and comfort. No buckles or buttons — special fly front construction — seams made "sure-fast" with live rubber. Try The Bracer now! PRICE $2
Here sure-fast means something like "reliably sealed."
From Addison Burbank, Guatemala Profile (1939) [combined snippets]:
The broad rainbow-hued bands of her silk corte were varied by intricate designs, and the belt that supplemented the usual sure[-]fast twist had in the middle a large purple ball exactly like the one over her forehead. She stood as stiffly as an image on her tiny bare feet, and in her right hand she held a bouquet of lilies of the valley.
Here sure[-]fast evidently refers to a style of tying a belt securely in place.
From Safety, volumes 34–35 (1947) [text not visible in snippet window]:
Stainless steel "surefast" headband slides for corrosion resistance.
The sense of the term as used here may be "sure-fastening," although the limited context makes the meaning difficult to identify with confidence.
From James Joyce, Scribbledehobble: The Ur-workbook for Finnegans Wake (1961) [combined snippets]:
... disease from mummy, attached a weight to his neck, noble character, ivorine surefast, clothes hung out to salute tram, Hothaun [?], masculine headgear, sorting bell, four fire windows, screen struck,
From Proceedings - Canadian Society for Civil Engineering, volume 4 (1991) [snippet view]:
... surefast connectors and receptacles. A digital display indicates the voltage from -100 to +100 μV in the 100-μV position and voltages from -1000 μV to +1000 in the 1000-μV position.
From Art and AsiaPacific, volume 1 (1994) [combined snippets]:
The early decision by Central Australian batik communities to use only Napthol dyes, technically the simplest and most surefast, has been one of the important factors determining style.
Assuming the word here is indeed surefast (which is not a certainty, owing to the cropping of the text snippet), the meaning seems to be "ensuring colorfastness."
From Ekaterini Georgoudaki, Women, Creators of Culture (1997) [combined snippets]:
It is significant that the selves asserted by Baby Suggs (and Morrison) are constituted in relation to a community of shifting character but surefast existence in the past, present, and future of "rememory" and history.
Here surefast seems to mean "permanent," "fixed," or "certain."
From Michael Power, Jesuit in the Legislative Gallery: A Life of Father Carl Matthews, S.J. (2005) [combined snippets]:
Fot Catholics born in the first half of the century, priest and people were close allies in the Church Militant. Religion was so integral to one's private and public life that life without religion would have been unimaginable. Catholicism was an all-enveloping reality. It was one's sure[-]fast identity and a badge of honour worn not on one's sleeve but on one's heart. The faith kept Catholics whole and set them apart.
The word here seems to mean "certain" or "unvarying."
Surefast appears in various commercial settings as a descriptive term (often capitalized) indicating "fastening firmly and reliably" in the context of a belt or strap, "colorfast" in the context of dyes or clothing, or "swift and sure" in the context of a process.
Outside commercial contexts, the word appears rarely but for the most part with roughly the same meaning of "firm, stable, fixed" that the OED (cited in Greybeard's answer) attributes to it. Although the OED considers the word obsolete, examples of it (sometimes in hyphenated form) appear in published writings from 1890, 1911, 1939, 1997, and 2005. The two examples cited in the posted question can be understood as signifying, in a figurative sense, "firm, stable, fixed," too—that is, as meaning "certain, reliable, trustworthy, guaranteed." That is clearly the sense of sure-fast in the 1911 poem "Labor" and it is no great jump from the self-consciously archaic use of surefast in Standish of Standish to the modernistic appearance of sure-fast in "Labor."