feat(cli): show which upstream versions are already merged in list-versions

Uses 'git merge-base --is-ancestor' per tag (parallelized) to mark
upstream versions reachable from HEAD with a '✓ merged' annotation.
Kilo's own package version no longer tracks upstream, so semver
comparison isn't reliable; the ancestor check is the source of truth
and handles non-linear merge history correctly.

script/upstream/list-versions.ts

@@ -7,7 +7,7 @@
  */
 
 import { getAvailableUpstreamVersions, getCurrentKiloVersion } from "./utils/version"
-import { fetchUpstream, hasUpstreamRemote } from "./utils/git"
+import { fetchUpstream, hasUpstreamRemote, isAncestor } from "./utils/git"
 import { header, info, success, warn, error } from "./utils/logger"
 
 async function main() {
@@ -34,11 +34,15 @@ async function main() {
   console.log()
 
   const limit = process.argv.includes("--all") ? versions.length : 20
+  const shown = versions.slice(0, Math.min(limit, versions.length))
 
-  for (let i = 0; i < Math.min(limit, versions.length); i++) {
-    const v = versions[i]
+  // Check merge status in parallel — fast because is-ancestor short-circuits.
+  const merged = await Promise.all(shown.map((v) => isAncestor(v.commit, "HEAD")))
+
+  for (let i = 0; i < shown.length; i++) {
+    const v = shown[i]
     if (!v) continue
-    const marker = i === 0 ? " (latest)" : ""
+    const marker = merged[i] ? " ✓ merged" : i === 0 ? " (latest)" : ""
     console.log(`  ${v.tag.padEnd(12)} ${v.commit.slice(0, 8)}${marker}`)
   }
 

script/upstream/utils/git.ts

@@ -172,6 +172,16 @@ export async function getCommitHash(ref: string): Promise<string> {
   return result.trim()
 }
 
+/**
+ * Check if `commit` is an ancestor of `ref` (i.e. reachable from `ref`).
+ * Uses `git merge-base --is-ancestor`, which exits 0 for yes, 1 for no.
+ * Any other exit code (e.g. unknown commit) is treated as "not an ancestor".
+ */
+export async function isAncestor(commit: string, ref = "HEAD"): Promise<boolean> {
+  const result = await $`git merge-base --is-ancestor ${commit} ${ref}`.quiet().nothrow()
+  return result.exitCode === 0
+}
+
 export async function getTagsForCommit(commit: string): Promise<string[]> {
   const result = await $`git tag --points-at ${commit}`.text()
   return result