The Telegram Desktop proof previously built the candidate from the raw PR
head, so a head behind main failed for reasons main already fixed
(observed on #127770: 59 commits behind, hitting the Unknown-model defect
fixed by #127952). GitHub's cached PR test merge cannot be the candidate
either: it was observed 50 commits / 12 hours stale and never refreshed.
The workflow now resolves the live refs/heads/main tip and merge base at
dispatch, requires a main-targeting PR, and builds a deterministic local
merge (merge-tree --merge-base + commit-tree with pinned identity/date) as
the candidate; conflicts fail with a direct rebase message and there is no
fallback to the raw head. Lane labels and docs now say the candidate is
the PR merged onto main.
Ayaan Zaidi
6917a15bce
