fix: resolve compat bases from version tags

script/upstream/utils/git.test.ts

@@ -33,8 +33,10 @@ test("finds previous compatibility commit for transformed base", async () => {
 
   await Bun.write("brand.txt", "opencode B\n")
   const target = await commit("release: v1.0.1")
+  await $`git tag v1.0.1 ${target}`.quiet()
 
   await $`git checkout -b main ${old}`.quiet()
+  await $`git tag v1.0.0 ${old}`.quiet()
   await Bun.write("brand.txt", "kilo A\n")
   const prior = await commit("refactor: kilo compat for v1.0.0")
 

script/upstream/utils/git.ts

@@ -205,6 +205,19 @@ export async function updateBranch(name: string, commit: string): Promise<void>
   await $`git update-ref refs/heads/${name} ${commit}`
 }
 
+async function compatUpstream(message: string): Promise<string | null> {
+  const prefix = "refactor: kilo compat for "
+  if (!message.startsWith(prefix)) return null
+
+  const tag = message.slice(prefix.length).trim().split(/\s+/)[0]
+  if (!tag) return null
+
+  const ref = `${tag}^{commit}`
+  const result = await $`git rev-parse ${ref}`.quiet().nothrow()
+  if (result.exitCode !== 0) return null
+  return result.stdout.toString().trim()
+}
+
 export async function findLatestCompatCommit(base: string, target: string): Promise<CompatBase | null> {
   const grep = "^refactor: kilo compat for "
   const result = await $`git log --format=%H%x00%s --grep=${grep} ${base}`.quiet().nothrow()
@@ -222,6 +235,9 @@ export async function findLatestCompatCommit(base: string, target: string): Prom
     const [commit, message = ""] = line.split("\0")
     if (!commit) continue
 
+    const upstream = await compatUpstream(message)
+    if (upstream && (await isAncestor(upstream, target))) return { commit, upstream, message }
+
     const parents = await getCommitParents(commit)
     for (const parent of parents) {
       if (await isAncestor(parent, target)) return { commit, upstream: parent, message }