Backport #3073 to 4.1: Avoid eagerly inspecting call traces in type assertions - #3076

The Backports section explains what `-x` buys — that the changelog
reaches the pull request the change was written and reviewed in — but
not what the entry ends up looking like, so the annotation naming the
backport was rediscovered while preparing 4.1.3, and got it wrong first.

`gem:changelog` now prints the form rather than leaving it to be
remembered. It already had both halves: `changelog_origins` resolves the
`-x` trailer to where the change was written, and the `fallbacks` path
already looked the cherry-pick's own pull request up, calling it in
passing "at least the backport that brought it here". Both ends are now
asked for together — one query rather than two, since the second was
only ever a retry — and the cherry-pick's becomes the entry's second
link instead of being discarded.

A backport also stops appearing beside the entries it carried. Its merge
commit is in the history too and has no `-x` trailer to resolve, so it
read as an ordinary commit of its own pull request: dispatching this on
the 4.1.3 cycle listed #3076 as a change of its own, above the entry it
annotates. A backport is how a change arrived rather than a change, so
the ones that annotate something are dropped from the list.

On the development line there are no origins, so entries keep the single
link they have today. A backport carrying several changes at once falls
out of the same handling: each entry names its own origin and shares the
one backport link, which is what 4.0.3 should have looked like.

docs/release.md loses the procedure it carried for assembling the
changelog by hand, which existed because the task could not run from a
Claude Code on the web session. `changelog.yml` runs it on a runner now,
so the section says to dispatch that instead — and the traps it
documented, all of them about hand-rolling the match, go with it. What
replaces them is the one thing the workflow adds: the ref picks the copy
of the task as well as the history, so a release branch needs the file
on it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QAgPhpLrU9Z4bENCR9RUub