Heart Sūtra root in Pali Canon?

Not quite on the topic of Kassaka Sutta, but regarding Heart Sutra roots in Pali Canon, one line of thinking traditionally connects the prajna-paramita genesis with Shrenika the Wanderer, also known as Vacchagotta of Pali Canon. Here I will post a couple of relevant quotes:

(from Aṣṭasāhasrikā Prajñāpāramitā Sūtra)

...
Also, not of body, nor feelings, nor thoughts, nor volitions,
Nor of consciousness, position even a little do not bother him.
Thus, to all dharmas not getting stuck, not getting caught into traps of abstractions (aniketacari)
Not clinging, he attains awakening of the Lucky Ones.

As venerable Shrenika the wandering beggar,
Realization acquired, without precisely grasping the skandhas,
Just so bodhisattva, intuits real nature of things (dharmas).
And does not seek cessation (nirvritti) but abides in wisdom.

(from Conze's notes on Aṣṭasāhasrikā Prajñāpāramitā Sūtra)

Shrenika Vatsagotra was a “Wanderer,” i.e. a non-Buddhist ascetic, whose conversations with the Buddha form one section of the Samyuktägama of the Sarvastivadins. On one occasion (SA 105, MN 72, SN 44.8) Shrenika raised the question of the “true self,” which he identified with the Tathagata. The Buddha told him that the Tathagata could not be found in the skandhas, outside the skandhas, or in the absence of the skandhas. In a supreme act of faith Shrenika was willing to accept the Tathagata in spite of the fact that he could not be related to any of the skandhas.

(from MN 72)

"Does Master Gotama have any position at all?"
"A 'position,' Vaccha, is something that a Tathagata has done away with. What a Tathagata sees is this: 'Such is form, such its origin, such its disappearance; such is feeling, such its origin, such its disappearance; such is perception… such are mental fabrications… such is consciousness, such its origin, such its disappearance.' Because of this, I say, a Tathagata — with the ending, fading out, cessation, renunciation, & relinquishment of all construings, all excogitations, all I-making & mine-making & obsession with conceit — is, through lack of clinging/sustenance, released."
...
"Even so, Vaccha, any physical form [Any feeling... Any perception... Any fabrication... Any consciousness] by which one describing the Tathagata would describe him: That the Tathagata has abandoned, its root destroyed, made like a palmyra stump, deprived of the conditions of development, not destined for future arising. Freed from the classification of form [feeling, perception, fabrication, consciousness], Vaccha, the Tathagata is deep, boundless, hard to fathom, like the sea.

Some thoughts and bibliography on Shrenika can be found in THE BRAHMACĀRIN ŚREṆIKA: EARLY SŪTRA SOURCES OF THE PRAJÑĀPĀRAMITĀ work by M.B. Orsborn (釋慧峰) here (I hope the link works).

Another work connecting this topic (of skahdhas/conceit/I-making/anatta/non-abiding) with the roots of Prajna-Paramita and Shunyata in early texts, is "The Concept of Emptiness in Pali Literature" by Medawachchiye Dhammajothi Thero. You can download it here (scroll down for the Download button). Here is what it says in conclusion:

It has been shown that "Anatta" as used in early Suttas, did not merely mean the absence of an individual soul, but meant also the absence of any entity in both compounded (Samkhata/Samskrta) elements as well as in uncompounded (Asamskhata, Asamskrta) elements, that is Nibbana. Thus, it has been clearly shown that Anatta means "emptiness" of everything, including Nibbana (Nirnvana).
...
A chapter was denoted to the study of various meditational practices recommended in early Buddhism, that lead to the realization of Sunna. Special focus was laid on two suttas namely Cula-Sunnata and Maha-Sunnata, both of the Majjhimanikaya. These while showing that the Buddha emphasized internalization of the understanding of the voidness of everything describes also how this could be done. This chapter will be of interest to those who wish to understand how meditative practice could be utilized to personally experience the voidness of all phenomena.

(from Cula-Sunnata Sutta)

"Further, Ananda, the monk — not attending to the perception of the dimension of nothingness, not attending to the perception of the dimension of neither perception nor non-perception — attends to the singleness based on the theme-less concentration of awareness.

(from SA 926, which explains Shrenika's meditation)

He meditates not leaning on Earth, Water, Fire, Air, the place of Infinity of Space, the place of the Infinity of Consciousness, the place of Nothingness, the place of Neither-Perception-nor-non-Perception; he meditates not leaning on this world, the world hereafter, the sun or moon, on whatever is seen, heard, sensed, cognized, obtained, sought after, followed after by mind, without leaning on them he meditates, because he has un-done the notion of Earth, Water... etc. -- he meditates not leaning on anything at all (na sarvam sarvam iti nisritya dhyayati).

(from Cula-Sunnata Sutta)

"He discerns that '[Even] This theme-less concentration of awareness is fabricated & mentally fashioned.' And he discerns that 'Whatever is fabricated & mentally fashioned is inconstant & subject to cessation.' For him — thus knowing, thus seeing — the mind is released from the effluent of sensuality, the effluent of becoming, the effluent of ignorance. With release, there is the knowledge, 'Released.' He discerns that 'Birth is ended, the holy life fulfilled, the task done. There is nothing further for this world.'

(from Maha-nidana Sutta)

This is the extent to which there is birth, aging, death, passing away, and re-arising. This is the extent to which there are means of designation, expression, and delineation. This is the extent to which the sphere of discernment extends, the extent to which the cycle revolves for the manifesting of this world — i.e., name-and-form together with consciousness.
...
Having directly known the extent of designation and the extent of the objects of designation, the extent of expression and the extent of the objects of expression, the extent of description and the extent of the objects of description, the extent of discernment and the extent of the objects of discernment, the extent to which the cycle revolves: Having directly known that, the monk is released.