Conto em que uma realidade flexível endurece para uma imutável

É possível que isso seja "O mundo petrificado" (1968) de Robert Sheckley? Estava em sua coleção Você pode sentir alguma coisa quando faço isso? (1973).

O protagonista, Lanigan, é de um mundo muito mais mutável que o nosso:

Lanigan looked at his watch. "Six-fifteen." But as he said it, the hour hand jumped convulsively forward. "No, it's five to seven."

Ele conversa com seu vizinho Torstein, no qual observamos mudanças normais em seu mundo:

"Well, Tom, how's the boy?" Torstein greeted him."

"Fine," Lanigan said, "just fine." He nodded pleasantly and began to walk away under a melting green sky. [...]

"I can't really afford a vacation this month," Lanigan said. (The sky was ochre and pink now-, three pines had withered; an aged oak had turned into a youthful cactus.)

É Torstein quem menciona montanhas em um céu dourado:

"Trees and lakes," Torstein was rhapsodizing. "The feel of grass growing under your feet, the sight of tall black mountains marching across a golden sky--"

Lanigan finalmente acaba preso em seu pesadelo; nosso mundo "petrificado" (imutável).

The street at first seemed like any normal city street. There were paving stones, cars, people, buildings, a sky overhead, a sun in the sky. All perfectly normal. Except that nothing was happening.

The pavement never once yielded beneath his feet. Over there was the First National City Bank; it had been here yesterday, which was bad enough; but worse it would be there without fail tomorrow, and the day after that, and the year after that. The First National City Bank (Founded 1892) was grotesquely devoid of possibilities. It would never become a tomb, an airplane, the bones of a prehistoric monster. Sullenly it would remain a building of concrete and steel, madly persisting in its fixity until men with tools came and tediously tore it down.

Lanigan walked through this petrified world, under a blue sky that oozed a sly white around the edges, teasingly promising something that was never delivered. Traffic moved implacably to the right, people crossed at crossings, clocks were within minutes of agreement.

A história foi publicada originalmente em If, Fevereiro 1968; você pode leia-o em archive.org.

Isso soa um pouco como Os homens retornam por Jack Vance, anteriormente identificado como a resposta para Conto - terra em um bolso de não-causalidade. Como foi escrito em 1957, ele se ajusta ao seu período de tempo e corresponde de algumas maneiras, mas difere de outras.

Nas palavras da história:

Then came the terrible hour when Earth swam into a pocket of non-causality, and all the ordered tensions of cause-effect dissolved.

O resultado é aleatoriedade, assim como você descreve. Por exemplo, ele tem superfícies que ficam líquidas e depois sólidas novamente:

He tested the surface of the plain with his foot. The glassy surface (though it likewise seemed a construction of red and gray-green pyramids) accepted his weight, then suddenly sucked at his leg. In a frenzy he tore himself free, jumped back, squatted on the temporarily solid rock.

E comida se tornando aleatoriamente venenosa:

The Relict cared nothing for this; he needed food and out on the plain were plants. They would suffice in lieu of anything better. They grew in the ground, or sometimes on a floating lump of water, or surrounding a core of hard black gas. There were dank black flaps of leaf, clumps of haggard thorn, pale green bulbs, stalks with leaves and contorted flowers. There were no recognizable species, and the Relict had no means of knowing if the leaves and tendrils he had eaten yesterday would poison him today.

No final da história, a Terra deixa o bolso da não-causalidade:

The shrouded sky was gone; the sun rode proud and bright in a sea of blue. The ground below churned, cracked, heaved, solidified. They felt the obsidian harden under their feet; its color shifted to glossy black. The Earth, the sun, the galaxy, had departed the region of freedom; the other time with its restrictions and logic was once more with them.

O problema é que a história não é narrada e não há nada sobre o narrador se sentir entediado com a nova permanência. Também não consigo encontrar nenhuma referência a montanhas em marcha, em um céu dourado ou não. Finalmente, a aleatoriedade não é algo que os humanos levam em consideração. De fato, reduziu a humanidade (os relatados acima) para apenas cinco sobreviventes. Portanto, nesses aspectos, a história não corresponde à sua descrição.