feat: support commit hash in --base flag for bt add

The --base flag previously only accepted branch names (local or remote).
Now it also accepts commit hashes (full or short SHA), falling back to
git rev-parse verification when branch resolution fails.

Author: amaya382

README.md

@@ -326,7 +326,7 @@ cp examples/rules/working-directory-on-git-worktree-with-baretree.md .cursor/rul
 
 | Command | Description |
 |---------|-------------|
-| `bt add <branch>` | Add worktree (`-b` for new branch, auto-fetches remotes, `--no-fetch` to skip) |
+| `bt add <branch>` | Add worktree (`-b` for new branch, `--base` for base branch/commit, auto-fetches remotes) |
 | `bt list` / `bt ls` | List worktrees |
 | `bt remove` / `bt rm` | Remove worktree (`--with-branch` to delete branch) |
 | `bt cd <name>` | Switch to worktree (`@` for default, `-` for previous) |

cmd/bt/add.go

@@ -44,6 +44,7 @@ Branch resolution order:
 
 Examples:
   bt add -b feature/auth           # Creates new branch and worktree
+  bt add -b feature/new --base abc123  # Creates new branch based on a commit
   bt add existing-local-branch     # Uses existing local branch
   bt add feature/remote            # Auto-detects and tracks origin/feature/remote
   bt add upstream/feature/test     # Tracks upstream/feature/test
@@ -54,7 +55,7 @@ Examples:
 
 func init() {
 	addCmd.Flags().BoolVarP(&addNewBranch, "branch", "b", false, "Create new branch")
-	addCmd.Flags().StringVar(&addBaseBranch, "base", "", "Base branch for new branch (default: HEAD)")
+	addCmd.Flags().StringVar(&addBaseBranch, "base", "", "Base branch or commit hash for new branch (default: HEAD)")
 	addCmd.Flags().BoolVar(&addDetach, "detach", false, "Create detached HEAD worktree")
 	addCmd.Flags().BoolVar(&addForce, "force", false, "Force creation even if worktree exists")
 	addCmd.Flags().BoolVar(&addNoFetch, "no-fetch", false, "Skip auto-fetch from remotes")
@@ -114,6 +115,13 @@ func runAdd(cmd *cobra.Command, args []string) error {
 		} else if baseInfo.IsRemote {
 			resolvedBaseBranch = baseInfo.RemoteRef
 			baseDisplayInfo = baseInfo.RemoteRef + " (remote)"
+		} else if wtMgr.Executor.IsCommitHash(addBaseBranch) {
+			resolvedBaseBranch = addBaseBranch
+			shortHash := addBaseBranch
+			if len(shortHash) > 7 {
+				shortHash = shortHash[:7]
+			}
+			baseDisplayInfo = shortHash + " (commit)"
 		} else {
 			return fmt.Errorf("base branch '%s' not found locally or on any remote", addBaseBranch)
 		}

e2e/README.md

@@ -134,6 +134,7 @@ Remote branch operation tests.
 | `TestAddNewBranchWithLocalBase` | `--base` with local branch works correctly |
 | `TestAddNewBranchWithNonexistentBase` | Error when `--base` specifies non-existent branch |
 | `TestAddNewBranchShowsBaseInfo` | Display of base branch information (HEAD fallback) |
+| `TestAddNewBranchWithCommitBase` | `--base` with commit hash (full and short) works correctly |
 
 ### journey_rename_test.go
 

e2e/journey_remote_test.go

@@ -459,3 +459,48 @@ func TestAddNewBranchShowsBaseInfo(t *testing.T) {
 		assertOutputContains(t, stdout, "Worktree created")
 	})
 }
+
+// TestAddNewBranchWithCommitBase tests --base with a commit hash
+func TestAddNewBranchWithCommitBase(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping e2e test in short mode")
+	}
+
+	tempDir := createTempDir(t, "commit-base")
+
+	runBtSuccess(t, tempDir, "repo", "init", "test-repo")
+	projectDir := filepath.Join(tempDir, "test-repo")
+	bareDir := filepath.Join(projectDir, ".git")
+
+	// Get the full commit hash of HEAD
+	cmd := exec.Command("git", "rev-parse", "HEAD")
+	cmd.Dir = bareDir
+	output, err := cmd.Output()
+	if err != nil {
+		t.Fatalf("failed to get commit hash: %v", err)
+	}
+	fullHash := strings.TrimSpace(string(output))
+
+	t.Run("new branch based on full commit hash", func(t *testing.T) {
+		stdout := runBtSuccess(t, projectDir, "add", "-b", "feat/from-commit", "--base", fullHash)
+
+		assertOutputContains(t, stdout, "(commit)")
+		assertOutputContains(t, stdout, "Worktree created")
+		assertFileExists(t, filepath.Join(projectDir, "feat", "from-commit"))
+	})
+
+	t.Run("new branch based on short commit hash", func(t *testing.T) {
+		shortHash := fullHash[:7]
+		stdout := runBtSuccess(t, projectDir, "add", "-b", "feat/from-short-commit", "--base", shortHash)
+
+		assertOutputContains(t, stdout, "(commit)")
+		assertOutputContains(t, stdout, "Worktree created")
+		assertFileExists(t, filepath.Join(projectDir, "feat", "from-short-commit"))
+	})
+
+	t.Run("error when base is invalid commit hash", func(t *testing.T) {
+		_, stderr := runBtExpectError(t, projectDir, "add", "-b", "feat/bad-hash", "--base", "deadbeef00deadbeef00")
+
+		assertOutputContains(t, stderr, "not found")
+	})
+}

internal/git/branch.go

@@ -168,3 +168,9 @@ func (e *Executor) GetUpstreamBehindCount(localBranch string) (int, error) {
 	}
 	return count, nil
 }
+
+// IsCommitHash checks if the given string resolves to a valid commit object
+func (e *Executor) IsCommitHash(ref string) bool {
+	_, err := e.Execute("rev-parse", "--verify", "--quiet", ref+"^{commit}")
+	return err == nil
+}