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 the concrete pre-push fixup failure mode where SyncGithub starts with an ordered range from ManualRebase, but then --pre-push-fixup folds hook-created changes and replaces that range with a fresh CommitMetadata.range(...). That fresh range is in git-log/display order, which can be tip-before-base. When the existing PR body also has stale preserved stack rows, the table can become:

1. stale old PR
2. current tip PR
3. current base PR

The stack table should always render the current stack in base-to-tip order, regardless of the incidental array order returned by range().

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 regression coverage for the real bug shape: stale rows from the previous PR body are preserved, while the current stack is rendered in base-chain order even when group_list is tip-before-base.

Test plan

• bun test src/app/SyncGithub.test.ts src/core/CommitMetadata.order.test.ts src/core/StackSummaryTable.test.ts
• ./node_modules/.bin/tsc
• pnpm run build

[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.