fix: preserve upstream compat merge bases

script/upstream/merge.ts

@@ -536,7 +536,7 @@ async function main() {
   const compatMessage = `refactor: kilo compat for ${targetVersion.tag}`
   if (prior) {
     const tree = await git.writeTree()
-    const commit = await git.commitTree(tree, compatMessage, [targetVersion.commit, prior.commit])
+    const commit = await git.createMergeCommit(tree, compatMessage, targetVersion.commit, prior.commit)
     await git.updateBranch(opencodeBranch, commit)
     await git.checkout(opencodeBranch)
   } else {

script/upstream/utils/git.test.ts

@@ -0,0 +1,55 @@
+import { afterEach, beforeEach, expect, test } from "bun:test"
+import { mkdtemp, rm } from "node:fs/promises"
+import { join } from "node:path"
+import { tmpdir } from "node:os"
+import { $ } from "bun"
+import { createMergeCommit, findLatestCompatCommit, getCommitHash, updateBranch, writeTree } from "./git"
+
+const cwd = process.cwd()
+let dir = ""
+
+async function commit(message: string) {
+  await $`git add -A`.quiet()
+  await $`git -c user.name=Test -c user.email=test@example.com commit -m ${message}`.quiet()
+  return getCommitHash("HEAD")
+}
+
+beforeEach(async () => {
+  dir = await mkdtemp(join(tmpdir(), "kilo-upstream-git-"))
+  process.chdir(dir)
+  await $`git init -b upstream`.quiet()
+  await $`git config user.name Test`.quiet()
+  await $`git config user.email test@example.com`.quiet()
+})
+
+afterEach(async () => {
+  process.chdir(cwd)
+  await rm(dir, { recursive: true, force: true })
+})
+
+test("finds previous compatibility commit for transformed merge base", async () => {
+  await Bun.write("brand.txt", "opencode A\n")
+  const old = await commit("release: v1.0.0")
+
+  await Bun.write("brand.txt", "opencode B\n")
+  const target = await commit("release: v1.0.1")
+
+  await $`git checkout -b main ${old}`.quiet()
+  await Bun.write("brand.txt", "kilo A\n")
+  const prior = await commit("refactor: kilo compat for v1.0.0")
+
+  const found = await findLatestCompatCommit("main", target)
+  expect(found?.commit).toBe(prior)
+  expect(found?.upstream).toBe(old)
+
+  await $`git checkout ${target}`.quiet()
+  await $`git checkout -b opencode-v1.0.1`.quiet()
+  await Bun.write("brand.txt", "kilo B\n")
+  await $`git add -A`.quiet()
+  const tree = await writeTree()
+  const next = await createMergeCommit(tree, "refactor: kilo compat for v1.0.1", target, prior)
+  await updateBranch("opencode-v1.0.1", next)
+
+  const base = (await $`git merge-base main opencode-v1.0.1`.text()).trim()
+  expect(base).toBe(prior)
+})

script/upstream/utils/git.ts

@@ -196,9 +196,8 @@ export async function writeTree(): Promise<string> {
   return result.trim()
 }
 
-export async function commitTree(tree: string, message: string, parents: string[]): Promise<string> {
-  const args = parents.flatMap((parent) => ["-p", parent])
-  const result = await $`git commit-tree ${tree} ${args} -m ${message}`.text()
+export async function createMergeCommit(tree: string, message: string, first: string, second: string): Promise<string> {
+  const result = await $`git commit-tree ${tree} -p ${first} -p ${second} -m ${message}`.text()
   return result.trim()
 }