A test pins `revertCommit`: undoing a shipped commit keeps later changes, reports a real conflict, and refuses a merge commit with two parents #6703

revertCommit and commitParents now have tests in test/git-revert.test.ts. All 6 pass, and the push went through. bun x tsc --noEmit couldn't run here: it reported a missing bun type definition (TS2688) even after bun install ran, so the type check is unconfirmed until the forge's check runs. src/git/revert.ts is unchanged.

Each test builds a throwaway repository in $TMPDIR:

• Later work stays: reverting B with C on top removes only B's line, and C's edit survives.
• Conflict: when C rewrote B's lines, the result is {kind: "conflict", files: ["f.txt"]}, and the refs are identical before and after.
• New commit: its only parent is ontoOid, and it carries the given message and author (name and email, for both author and committer).
• Parents: commitParents returns [] for a root, one oid for a squash, and two for a merge. It returns undefined for a malformed oid.
• What revertCommit does with each:

- A root commit is refused with a git error. - A merge commit with two parents is reverted against its first parent, so the side branch's file goes and main's edit stays. - Anything over two parents returns {kind: "octopus", parents: n}. - An unsafe oid returns unsafe.

The issue title says a merge commit with two parents should be refused, but the code reverts it against the first parent, as git revert -m 1 does. I pinned the code's behaviour, not the title's, and only octopus merges are refused. If you want two-parent merges refused too, that is a code change in src/git/revert.ts.

To try it, run bun test test/git-revert.test.ts.

Closes #6702

revertCommit and commitParents now have tests in test/git-revert.test.ts. All 6 pass, and the push went through. bun x tsc --noEmit couldn't run here: it reported a missing bun type definition (TS2688) even after bun install ran, so the type check is unconfirmed until the forge's check runs. src/git/revert.ts is unchanged.

Each test builds a throwaway repository in $TMPDIR:

• Later work stays: reverting B with C on top removes only B's line, and C's edit survives.
• Conflict: when C rewrote B's lines, the result is {kind: "conflict", files: ["f.txt"]}, and the refs are identical before and after.
• New commit: its only parent is ontoOid, and it carries the given message and author (name and email, for both author and committer).
• Parents: commitParents returns [] for a root, one oid for a squash, and two for a merge. It returns undefined for a malformed oid.
• What revertCommit does with each:

- A root commit is refused with a git error. - A merge commit with two parents is reverted against its first parent, so the side branch's file goes and main's edit stays. - Anything over two parents returns {kind: "octopus", parents: n}. - An unsafe oid returns unsafe.

The issue title says a merge commit with two parents should be refused, but the code reverts it against the first parent, as git revert -m 1 does. I pinned the code's behaviour, not the title's, and only octopus merges are refused. If you want two-parent merges refused too, that is a code change in src/git/revert.ts.

To try it, run bun test test/git-revert.test.ts.