Auto-resolve merge conflicts using Claude when merging branches

src/cli.ts

@@ -143,8 +143,50 @@ program
   .action(async (branch: string) => {
     const root = await git.repoRoot()
 
-    await git.merge(branch, root)
+    const conflicts = await git.merge(branch, root)
-    console.log(`Merged ${branch} into current branch`)
+
+    if (conflicts.length === 0) {
+      console.log(`Merged ${branch} into current branch`)
+      await closeAction(branch)
+      return
+    }
+
+    // Resolve conflicts with Claude
+    console.log(`Merge conflicts in ${conflicts.length} file(s). Resolving with Claude...`)
+    const spin = spinner("Starting container")
+
+    try {
+      await vm.ensure((msg) => { spin.text = msg })
+
+      for (const file of conflicts) {
+        spin.text = `Resolving ${file}`
+        const content = await Bun.file(join(root, file)).text()
+
+        const tmpPath = join(homedir(), '.sandlot', '.conflict-tmp')
+        await Bun.write(tmpPath, content)
+
+        const resolved = await vm.exec(
+          join(homedir(), '.sandlot'),
+          'cat /sandlot/.conflict-tmp | claude -p "resolve this merge conflict. output ONLY the resolved file content with no markdown fences, no explanation, no surrounding text."',
+        )
+
+        await Bun.file(tmpPath).unlink().catch(() => {})
+
+        if (resolved.exitCode !== 0) {
+          throw new Error(`Claude failed to resolve ${file}: ${resolved.stderr}`)
+        }
+
+        await Bun.write(join(root, file), resolved.stdout + "\n")
+        await git.stageFile(file, root)
+      }
+
+      await git.commitMerge(root)
+      spin.succeed(`Resolved ${conflicts.length} conflict(s) and merged ${branch}`)
+    } catch (err) {
+      spin.fail(String((err as Error).message ?? err))
+      await git.abortMerge(root)
+      process.exit(1)
+    }
 
     await closeAction(branch)
   })

src/git.ts

@@ -81,10 +81,34 @@ export async function checkout(branch: string, cwd: string): Promise<void> {
   }
 }
 
-/** Merge a branch into the current branch. */
+/** Merge a branch into the current branch. Returns conflicted file paths, or empty array if clean. */
-export async function merge(branch: string, cwd: string): Promise<void> {
+export async function merge(branch: string, cwd: string): Promise<string[]> {
   const result = await $`git merge ${branch}`.cwd(cwd).nothrow().quiet()
+  if (result.exitCode === 0) return []
+
+  // Check for unmerged (conflicted) files
+  const unmerged = await $`git diff --name-only --diff-filter=U`.cwd(cwd).nothrow().quiet().text()
+  const files = unmerged.trim().split("\n").filter(Boolean)
+  if (files.length > 0) return files
+
+  // Not a conflict — some other merge failure
+  throw new Error(`Failed to merge branch "${branch}": ${result.stderr.toString().trim()}`)
+}
+
+/** Stage a file. */
+export async function stageFile(file: string, cwd: string): Promise<void> {
+  await $`git add ${file}`.cwd(cwd).nothrow().quiet()
+}
+
+/** Finalize a merge commit after resolving conflicts. */
+export async function commitMerge(cwd: string): Promise<void> {
+  const result = await $`git commit --no-edit`.cwd(cwd).nothrow().quiet()
   if (result.exitCode !== 0) {
-    throw new Error(`Failed to merge branch "${branch}": ${result.stderr.toString().trim()}`)
+    throw new Error(`Failed to commit merge: ${result.stderr.toString().trim()}`)
   }
 }
+
+/** Abort an in-progress merge. */
+export async function abortMerge(cwd: string): Promise<void> {
+  await $`git merge --abort`.cwd(cwd).nothrow().quiet()
+}