Fair Value Measurements - Contingent Consideration and Contingent Founder Shares (Successor) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Apr. 27, 2023	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Class of Stock [Line Items]
Number of additional shares to be issued	222,653
Threshold increase in Episodic Migraine Contingent Consideration Shares	152,998
Number of Chronic Migraine Contingent Consideration Shares by increase in Episodic Migraine Contingent Consideration Shares	0
Number of Contingent Consideration Shares to be issued upon Threshold Increase in Episodic Migraine Contingent Consideration Shares	0
Reduction in number of Chronic Migraine Contingent Consideration Shares	13,996
Minimum number of Chronic Migraine Contingent Consideration Shares after Reduction	0
Income related to the change in fair value of contingent consideration		$ (3,500)		$ (3,500)
Income related to the change in fair value of contingent consideration		16	$ (161,233)	(3,472)	$ (97,464)
Contingent consideration liability		$ 69		$ 69		$ 3,541
Maximum
Class of Stock [Line Items]
Number of additional shares to be issued	222,653
Reduction in Episodic Migraine Contingent Consideration Shares	13,996
Founder Shares
Class of Stock [Line Items]
Percentage of shares unvested and subject to the restrictions and forfeiture provisions	50.00%
Number of founder shares subject to vesting and forfeiture conditions.	47,921
Percentage of shares not subject to restrictions and forfeiture provisions	50.00%
Migraine Phase 3 Contingent Founder Shares | Upon the achievement of the conditions for the issuance of the Migraine Phase 3 Contingent Consideration Shares on or prior to the Migraine Phase 3 Outside Date
Class of Stock [Line Items]
Number of additional shares to be issued	13,890
Number of founder shares subject to vesting and forfeiture conditions.	13,996
Migraine Phase 3 Contingent Founder Shares | Upon the achievement of the conditions for the issuance of the CD BLA Contingent Consideration Shares on or prior to the CD BLA Outside Date
Class of Stock [Line Items]
Number of founder shares subject to vesting and forfeiture conditions.	13,890
Migraine Phase 3 Contingent Founder Shares | Upon the earlier of (x) the achievement of the conditions for the issuance of the Episodic Migraine Contingent Consideration Shares on or before the Episodic Migraine Outside Date and (y) the achievement of the conditions for the issuance of the Chronic Migraine Contingent Consideration Shares on or before the Chronic Migraine Outside Date
Class of Stock [Line Items]
Number of founder shares subject to vesting and forfeiture conditions.	20,141
CD BLA Contingent Founder Shares
Class of Stock [Line Items]
Number of additional shares to be issued	55,659
Number of founder shares subject to vesting and forfeiture conditions.	55,659
Episodic/Chronic Migraine Contingent Founder Shares
Class of Stock [Line Items]
Number of additional shares to be issued	152,998
Number of common shares become due and payable	27,992
Episodic/Chronic Migraine Contingent Founder Shares | Maximum
Class of Stock [Line Items]
Reduction in Episodic Migraine Contingent Consideration Shares	27,992
Episodic Migraine Contingent Consideration Shares
Class of Stock [Line Items]
Number of additional shares to be issued	55,659
Chronic Migraine Contingent Consideration Shares
Class of Stock [Line Items]
Number of additional shares to be issued	97,339