I am reading the passage below for the 1st time and sense the Pali grammar rules probably might determine the correct translation; particularly for the two phrases "tulamatulañca sambhavaṃ" & "attasambhavan".
I am intuitively drawn to Bhikkhu Sujato's translation for guidance however I suppose the proper translation must fit the grammar rules, particularly the two phrases: "tulamatulañca sambhavaṃ" & "attasambhavan". Following my mere intuition, I think the verse could be as follows:DN 16 wrote:So at the Cāpāla tree shrine the Buddha, mindful and aware, surrendered the life force.
Atha kho bhagavā cāpāle cetiye sato sampajāno āyusaṅkhāraṃ ossaji.
Weighing up the incomparable against an extension of life,
the sage surrendered the life force.
Happy inside, serene,
he burst out of this self-made chain like a suit of armor.”
Measurable and immeasurable continuity,
And the continuation-process the Sage relinquished.
Content in himself, and concentrated,
He broke continuity of self like a coat of mail.
What causes life, unbounded or confined  —
His process of becoming  — this the Sage
Renounces. With inward calm and joy he breaks,
As though a coat of mail, his own life's cause .
Sister Vajira & Francis Story
24. Tulam atulañca sambhavam: lit. "the measurable and immeasurable productive cause (of life)," i.e., the volitional action causing rebirth in the confined, or limited sense-sphere, or in the unbounded fine-material and immaterial spheres.
25. Bhavasankhara: the formative force of becoming, in the sense of what forms existence.
26. Kavacam iv'attasambhavam. Comy.: "He breaks through the entire net of defilements that envelops individual existence like a coat of mail; he breaks the defilements as a great warrior breaks his armor after a battle." The Sanskrit version has "like an egg shell" (kosam iv' anda-sambhavam).
* Tulamatulañca sambhavaṃ = coming-to-be compared to the incomparable
* Bhavasaṅkhāramavassaji muni = the sage surrendered the will for continued existence
* Ajjhattarato samāhito = happy inside, serene
* Abhindi kavacamivattasambhavan = bursting out of the suit-of-armor-like-self-produced-continued-existence.
I think the "continued existence" and the "suit-of-armour-like-self-made-continued-existence" is the following from the sutta:
What do we think?Whoever has developed and cultivated the four bases of psychic power—made them a vehicle and a basis, kept them up, consolidated them, and properly implemented them—may, if they wish, live on for the eon or what’s left of the eon.
Sometimes the Realized One, not focusing on any signs, and with the cessation of certain feelings, enters and remains in the signless immersion of the heart. Only then does the Realized One’s body become more comfortable.