swiftly self-update 1.1.1 -> 1.1.2 fails

I first ran into this issue: #560 / #539

❯ swiftly list-available 6.4-snapshot
-----------------------------
A new release of swiftly is available.
Please run `swiftly self-update` to update.
-----------------------------
Error: Unexpected response, expected status code: ok, response: undocumented(statusCode: 404, OpenAPIRuntime.UndocumentedPayload(headerFields: [(field: Server: Apple, next: 65535), (field: Date: Tue, 16 Jun 2026 18:14:51 GMT, next: 65535), (field: Content-Type: text/html, next: 65535), (field: Content-Length: 146, next: 65535), (field: Strict-Transport-Security: max-age=31536000; includeSubdomains, next: 65535), (field: X-Frame-Options: SAMEORIGIN, next: 65535), (field: X-XSS-Protection: 1; mode=block, next: 65535), (field: Age: 0, next: 65535), (field: Via: https/1.1 usqas3-xdc-mx-001.ts.apple.com (acdn/302.16436), https/1.1 usqas2-edge-fx-023.ts.apple.com (acdn/302.16436), next: 65535), (field: X-Cache: miss, miss, next: 65535), (field: CDNUUID: 498b8b67-5e22-4984-a1cc-6f4da565525e-3332554284, next: 65535), (field: Connection: keep-alive, next: 65535)], body: Optional(OpenAPIRuntime.HTTPBody)))

But trying to self-update encounters another issue:

❯ swiftly self-update
Checking for swiftly updates...
Checking for swiftly updates...
A new version of swiftly is available: 1.1.2
                                                                                  Downloading swiftly 1.1.2
100% [=========================================================================================================================================================================]
Downloaded 9.8 MiB of 9.8 MiB

Extracting the swiftly package...
installer: Error - the package path specified was invalid: '/var/folders/2w/07485fvx44lc0v3q_fz83jpc0000gn/T/swiftly-C1F111B3-A886-4CBE-9AAF-417E718AF9E4'.
Error: RunProgramError(exitCode: 1, program: "installer", arguments: ["-pkg", "/var/folders/2w/07485fvx44lc0v3q_fz83jpc0000gn/T/swiftly-C1F111B3-A886-4CBE-9AAF-417E718AF9E4", "-target", "CurrentUserHomeDirectory"])

Start by reproducing swiftly self-update from version 1.1.1 and trace the self-update flow through package extraction to the macOS installer invocation shown in the report. Done means updating to 1.1.2 completes successfully without the invalid package-path error.