And of course tickets can be private, so even if the data survived migration, you may not have access to it (principle of least privilege and all that).
What you're describing here is a design. The most important parts of a design are the decisions and their reasoning.
e.g. "we decided on tool/library pattern X over tool/library/pattern Y because Z" – that is a design, usually discussed outside (and before) a commit message.
You discuss these decisions with others, document the discussion and decision, and then you have a design and can start writing code.
Let me ask you this: suppose you have a task that needs to be done eventually, and you want to write down some ideas for it, but don't want to start coding right now. Where do you put those ideas? How do you link them to that specific task?
Random example:
Provide a new syscall which has the only purpose to yield the CPU after the kernel granted a time slice extension.
sched_yield() is not suitable for that because it unconditionally schedules, but the end of the time slice extension is not required to schedule when the task was already preempted. This also allows to have a strict check for termination to catch user space invoking random syscalls including sched_yield() from a time slice extension region.
From 99d2592023e5d0a31f5f5a83c694df48239a1e6c
In your example, for example, where was the issue tracked before the code was written? The format you linked makes it difficult to get the history of the issue.
Let me ask you this: suppose you have a task that needs to be done eventually, and you want to write down some ideas for it, but don't want to start coding right now. Where do you put those ideas? How do you link them to that specific task?