Mifkad Pakid (non-Circulatory Blood)

Tosafos (Shabbos 75a) in the name of Rabbeinu Tam is very clear that techeiles does not come from the regular circulatory blood.

Besides the Meiri, none of the other Rishonim mentioned in the question say that techeiles is from the life-blood. All they do is give an alternative answer for the question that forced Rabbeinu Tam to say that it is not life-blood. In other words, they are saying that what Rabbeinu Tam says is not מוכרח because there is another answer, but they are not saying that it can’t be.

Furthermore, it has been suggested by the Radzyner Rebbe )עין התכלת עמ’ ר”צ ( that perhaps the other Rishonim needed to provide a different answer to the question of Rabbeinu Tam not because they doubted his answer, rather because they had to deal with another question of why there is no מלאכ ה of חובל as one pierces through the skin and flesh of the chilazon in order to access the pouch containing the dye-blood.5

“סיכום: ‘דם החלזון… הוא דם ממש’… ולא מצינו בראשונים חולק.”
English: “Summary: The blood of the Chilazon is literal blood. No Rishon holds it’s merely secretion.”
📖 Source: חלזון התכלת במשנת הראשונים, סימן ז

“…אפילו ר״ת ודעימיה… לא פליגי ש’דם החלזון שצובעים ממנו’ הוא לשון ‘דם’—השאלה היא מיפקד פקיד או חבורי מחבר…”
English: “Even Rabbeinu Tam agrees it is called blood. The question is whether it’s stored separately or bound — relevant for Hilchos Shabbos.”
📖 Source: תגובה לקונטרס לחלזון במשנת הראשונים, עמ’ 8