Order PR stack tables by base chain

[fjord-oai]

Summary

Order PR stack tables from the explicit base chain instead of relying on the current commit_range.group_list order.

This fixes cases where the stack table in PR descriptions can appear reversed or otherwise misordered after sync. range() still returns groups in git-log-oriented order, but the PR body update path needs base-to-tip stack order. Since each stack group already records its intended base, we can derive the display order directly from those base links.

Details

• Updates CommitMetadata.stack_order(...) to derive canonical stack order from group.base relationships.
• Uses that canonical order when building the PR URL list rendered into stack tables.
• Preserves all groups even if a base link is missing or incomplete, falling back to the original input order for disconnected groups.
• Aligns ManualRebase and rebase_order() with the new canonical ordering semantics so callers do not reinterpret stack_order() inconsistently.
• Adds a regression test that reproduces the user-visible bug: even if group_list is reversed, the rendered stack table rows still come out in base-chain order.

Test plan

• bun test src/app/SyncGithub.test.ts src/core/CommitMetadata.order.test.ts
• ./node_modules/.bin/tsc

[magus]

Do you have a repro? I spent some time thinking about this and I don't think it's possible for things to ever be out of order actually they are always the order of the commits in the local branch.

a7b8d27
ca13756
5b3b3ef

I added some instructions for running locally, maybe you move your fork to master briefly, build it and run it locally for awhile and see

2e966d5

Either we will get a repro or we might have confidence the coverage landed is sufficient now.