Re-fold feat/contextvars onto upstream master ebb6468 (post-#703 base)

[coreyleavitt]

What this is

Re-fold the feat/contextvars series onto the advanced upstream master. Upstream moved b71392a to ebb6468 (2026-08-13 sync), which includes our own status-im#703 testsoon fix plus docs and mobile-CI changes. Rebasing the four-commit series onto a base that already contains the status-im#703 fix removes the one known upstream flake from the series' CI baseline.

Procedure reminders (from the fold discipline)

• The series is re-folded, never appended: reset to the new base, four staged commits, commit messages preserved from the log before any reset.
• Commit 1 requires the authored intermediate state of asyncengine.nim (queue swap without capture); the fold is not pure whole-file staging for that file.
• verify/ is never in the fold allow-list and stays branch-local to worktree-contextvars-rebase.
• After the fold: ladder legs plus matrix, then force-push feat/contextvars and update the PR contextvars: continuation-local storage status-im/nim-chronos#702 base expectations; fresco-pin merge and downstream lock bumps follow the usual order.

Timing

Not urgent while status-im#702 sits in review; the right moment is either just before review re-engages (freshest possible base) or when upstream CI runs on the PR against a base that has drifted enough to matter. Coordinate with any review feedback that lands first.

[coreyleavitt]

PR status-im#702 is being left open for posterity rather than active review; the re-fold's purpose (freshest review base) is moot. The fork's development lineage moved to coreyleavitt/tonalli, already rebased onto ebb6468.