Rework squash command to collapse commits in-place

Instead of squash-merging into main, `sandlot squash` now soft-resets
to the merge base and recommits, keeping the branch independent.
This removes the --force flag and all squash-merge logic from
mergeAndClose, which goes back to being a plain merge.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli.ts

@@ -141,9 +141,8 @@ program
 program
   .command("squash")
   .argument("<branch>", "branch name")
-  .option("-f, --force", "allow merging into a non-main branch")
-  .description("Squash-merge a branch into main and close the session")
-  .action((branch: string, opts: { force?: boolean }) => squashAction(branch, opts))
+  .description("Squash all commits on a branch into a single commit")
+  .action((branch: string) => squashAction(branch))
 
 program
   .command("rebase")

src/commands/helpers.ts

@@ -106,8 +106,8 @@ export async function resolveConflicts(
   }
 }
 
-/** Merge (or squash-merge) a branch into main, resolve conflicts if needed, and close the session. */
-export async function mergeAndClose(branch: string, opts?: { squash?: boolean; force?: boolean }): Promise<void> {
+/** Merge a branch into main, resolve conflicts if needed, and close the session. */
+export async function mergeAndClose(branch: string, opts?: { force?: boolean }): Promise<void> {
   const root = await git.repoRoot()
   const main = await git.mainBranch(root)
   const current = await git.currentBranch(root)
@@ -120,18 +120,11 @@ export async function mergeAndClose(branch: string, opts?: { squash?: boolean; f
     die(`Branch "${branch}" has unsaved changes. Run "sandlot save ${branch}" first.`)
   }
 
-  const label = opts?.squash ? "Squash-merged" : "Merged"
   const spin = spinner("Merging", branch)
-  const conflicts = await git.merge(branch, root, opts?.squash ? { squash: true } : undefined)
+  const conflicts = await git.merge(branch, root)
 
   if (conflicts.length === 0) {
-    if (opts?.squash) {
-      spin.text = "Starting container"
-      await vm.ensure((msg) => { spin.text = msg })
-      spin.text = "Generating commit message"
-      await squashCommit(branch, root)
-    }
-    spin.succeed(`${label} ${branch} into ${current}`)
+    spin.succeed(`Merged ${branch} into ${current}`)
     if (session) await teardownSession(root, branch, session.worktree)
     await git.deleteLocalBranch(branch, root).catch(() => {})
     return
@@ -147,12 +140,8 @@ export async function mergeAndClose(branch: string, opts?: { squash?: boolean; f
       spin.text = total > 1 ? `(${i}/${total}) Resolving ${file}` : `Resolving ${file}`
     })
 
-    if (opts?.squash) {
-      await squashCommit(branch, root)
-    } else {
-      await git.commitMerge(root)
-    }
-    spin.succeed(`Resolved ${conflicts.length} conflict(s) and ${label.toLowerCase()} ${branch}`)
+    await git.commitMerge(root)
+    spin.succeed(`Resolved ${conflicts.length} conflict(s) and merged ${branch}`)
   } catch (err) {
     const message = err instanceof Error ? err.message : String(err)
     spin.fail(message)
@@ -166,25 +155,6 @@ export async function mergeAndClose(branch: string, opts?: { squash?: boolean; f
   await git.deleteLocalBranch(branch, root).catch(() => {})
 }
 
-/** Generate a commit message for a squash-merge via Claude and commit. */
-async function squashCommit(branch: string, cwd: string): Promise<void> {
-  const diff = await git.diffStaged(cwd)
-
-  if (diff.trim()) {
-    const gen = await vm.claudePipe(
-      diff,
-      "Write a commit message summarizing all changes in this squash merge. Subject line: imperative mood, max 72 characters, no period. Add a blank line then a concise body with the key changes as bullet points. Output only the raw commit message, no quotes or markdown.",
-    )
-    if (gen.exitCode === 0 && gen.stdout.trim()) {
-      await git.commit(gen.stdout.trim(), cwd)
-      return
-    }
-  }
-
-  // Fallback if diff is empty or Claude fails
-  await git.commit(`squash ${branch}`, cwd)
-}
-
 /** Stage all changes, generate a commit message, and commit. Returns true on success. */
 export async function saveChanges(worktree: string, branch: string, message?: string): Promise<boolean> {
   const spin = spinner("Staging changes", branch)

src/commands/squash.ts

@@ -1,5 +1,47 @@
-import { mergeAndClose } from "./helpers.ts"
+import { $ } from "bun"
+import * as git from "../git.ts"
+import * as vm from "../vm.ts"
+import { spinner } from "../spinner.ts"
+import { die } from "../fmt.ts"
+import { requireSession } from "./helpers.ts"
 
-export async function action(branch: string, opts?: { force?: boolean }) {
-  await mergeAndClose(branch, { squash: true, force: opts?.force })
+export async function action(branch: string) {
+  const { session } = await requireSession(branch)
+  const worktree = session.worktree
+
+  const main = await git.mainBranch(worktree)
+  const base = await git.mergeBase(main, "HEAD", worktree)
+  const head = (await $`git rev-parse HEAD`.cwd(worktree).nothrow().quiet().text()).trim()
+
+  if (head === base) {
+    die(`Branch "${branch}" has no commits beyond ${main}.`)
+  }
+
+  const spin = spinner("Squashing", branch)
+
+  await git.resetSoft(base, worktree)
+
+  spin.text = "Starting container"
+  await vm.ensure((msg) => { spin.text = msg })
+
+  spin.text = "Generating commit message"
+  const diff = await git.diffStaged(worktree)
+
+  if (!diff.trim()) {
+    spin.fail("No changes after squash")
+    return
+  }
+
+  const gen = await vm.claudePipe(
+    diff,
+    "Write a commit message summarizing all changes. Subject line: imperative mood, max 72 characters, no period. Add a blank line then a concise body with the key changes as bullet points. Output only the raw commit message, no quotes or markdown.",
+  )
+
+  if (gen.exitCode === 0 && gen.stdout.trim()) {
+    await git.commit(gen.stdout.trim(), worktree)
+  } else {
+    await git.commit(`squash ${branch}`, worktree)
+  }
+
+  spin.succeed(`Squashed ${branch} into a single commit`)
 }

src/git.ts

@@ -151,6 +151,14 @@ export async function abortMerge(cwd: string): Promise<void> {
   await $`git merge --abort`.cwd(cwd).nothrow().quiet()
 }
 
+/** Soft-reset to a given ref (keeps changes staged). */
+export async function resetSoft(ref: string, cwd: string): Promise<void> {
+  const result = await $`git reset --soft ${ref}`.cwd(cwd).nothrow().quiet()
+  if (result.exitCode !== 0) {
+    throw new Error(`Failed to reset to "${ref}": ${result.stderr.toString().trim()}`)
+  }
+}
+
 /** Rebase the current branch onto another. Returns conflicted file paths, or empty array if clean. */
 export async function rebase(onto: string, cwd: string): Promise<string[]> {
   // Bail early if a rebase is already in progress (check for rebase state directories, not REBASE_HEAD which can be stale)