fix: upgrade to go-git v6 to support worktreeConfig repos

AGENTS.md

@@ -24,10 +24,9 @@ The flow is: `pro.go` (CLI wiring) → `command/` (orchestration + user-facing o
   - `list.go` — interactive PR/MR picker using `ktr0731/go-fuzzyfinder`.
   - `auth.go` — prompts for and saves a personal access token.
 
-- **`repository/`** — wraps `go-git` to find the repo and read the origin URL. Two things are done manually rather than through go-git:
-  - **Worktree support**: `CurrentBranchName` reads and parses the `.git/HEAD` file directly because go-git does not resolve branches correctly inside external worktrees. `makeRepository` detects the `.git/worktrees` path and tracks both the worktree git dir and the real git dir separately.
-  - **Parent traversal**: `FindInParents` recurses up the directory tree until it finds a git repo or hits the filesystem root.
-  - Typed errors live in `errors.go` (`ErrNoRemoteOrigin`, `ErrNoActiveBranch`) and are matched with `errors.Is` in `command/`.
+- **`repository/`** — wraps `go-git` to find the repo, read the current branch, and read the origin URL. `FindInParents` opens the repo with `PlainOpenWithOptions{DetectDotGit: true}`, which walks up parent directories itself, so no manual traversal is needed. Linked worktrees need no special handling — go-git resolves both HEAD and the shared config from inside a worktree.
+  - Typed errors live in `errors.go` (`ErrNoRepository`, `ErrNoRemoteOrigin`, `ErrNoActiveBranch`) and are matched with `errors.Is` in `command/`. A detached HEAD or a branch without commits yields `ErrNoActiveBranch`.
+  - **go-git is pinned to a v6 alpha on purpose.** v5 cannot open any repository whose config sets the `worktreeConfig` extension (git enables it automatically for per-worktree config): v5's `extensionsValidForV0` allow-list keys are camelCase while lookups are lowercased, so `worktreeconfig` misses and `Open` rejects the repo. v5.19.1 is the last v5, and `verifyExtensions` is unconditional, so v6 is the only fix. Don't downgrade to v5.
 
 - **`provider/github/` and `provider/gitlab/`** — one file each, self-contained REST clients built on `net/http` (no SDK). Each finds the PR/MR for a branch and lists remote branches, handles pagination, and returns typed sentinel errors (e.g. `ErrNotFound`/`ErrUnauthorized`, `ErrMergeRequestNotFound`/`ErrProjectNotFound`/`ErrTokenExpired`). The two providers do not share an interface — `command/` switches on host and calls each directly.
 

command/list.go

@@ -18,8 +18,12 @@ import (
 func List(repoPath string, print bool, copy bool) {
 	repo, err := repository.FindInParents(repoPath)
 	if err != nil {
-		fmt.Fprintln(os.Stderr, color.RedString("Unable to find git repository in given directory or any of parent directories."))
-		fmt.Fprintln(os.Stderr, "Please make sure you are in the project directory.")
+		if errors.Is(err, repository.ErrNoRepository) {
+			fmt.Fprintln(os.Stderr, color.RedString("Unable to find git repository in given directory or any of parent directories."))
+			fmt.Fprintln(os.Stderr, "Please make sure you are in the project directory.")
+		} else {
+			fmt.Fprintln(os.Stderr, color.RedString("Unable to open git repository: %s", err.Error()))
+		}
 		os.Exit(1)
 	}
 
@@ -28,10 +32,10 @@ func List(repoPath string, print bool, copy bool) {
 		if errors.Is(err, repository.ErrNoRemoteOrigin) {
 			fmt.Fprintln(os.Stderr, color.RedString("No remote named \"origin\" found."))
 			fmt.Fprintln(os.Stderr, "Please make sure you have a remote named \"origin\".")
-			os.Exit(1)
 		} else {
 			fmt.Fprintln(os.Stderr, color.RedString("Unable to get origin URL: %s", err.Error()))
 		}
+		os.Exit(1)
 	}
 
 	gitURL, err := giturl.Parse(originURL)

command/open.go

@@ -21,8 +21,12 @@ import (
 func Open(repoPath string, print bool, copy bool) {
 	repo, err := repository.FindInParents(repoPath)
 	if err != nil {
-		fmt.Fprintln(os.Stderr, color.RedString("Unable to find git repository in given directory or any of parent directories."))
-		fmt.Fprintln(os.Stderr, "Please make sure you are in the project directory.")
+		if errors.Is(err, repository.ErrNoRepository) {
+			fmt.Fprintln(os.Stderr, color.RedString("Unable to find git repository in given directory or any of parent directories."))
+			fmt.Fprintln(os.Stderr, "Please make sure you are in the project directory.")
+		} else {
+			fmt.Fprintln(os.Stderr, color.RedString("Unable to open git repository: %s", err.Error()))
+		}
 		os.Exit(1)
 	}
 
@@ -31,10 +35,10 @@ func Open(repoPath string, print bool, copy bool) {
 		if errors.Is(err, repository.ErrNoRemoteOrigin) {
 			fmt.Fprintln(os.Stderr, color.RedString("No remote named \"origin\" found."))
 			fmt.Fprintln(os.Stderr, "Please make sure you have a remote named \"origin\".")
-			os.Exit(1)
 		} else {
 			fmt.Fprintln(os.Stderr, color.RedString("Unable to get origin URL: %s", err.Error()))
 		}
+		os.Exit(1)
 	}
 
 	gitURL, err := giturl.Parse(originURL)

go.mod

@@ -5,8 +5,7 @@ go 1.26.4
 require (
 	github.com/atotto/clipboard v0.1.4
 	github.com/fatih/color v1.19.0
-	github.com/go-git/go-billy/v5 v5.9.0
-	github.com/go-git/go-git/v5 v5.19.1
+	github.com/go-git/go-git/v6 v6.0.0-alpha.4
 	github.com/ktr0731/go-fuzzyfinder v0.9.0
 	github.com/mitchellh/go-homedir v1.1.0
 	github.com/urfave/cli/v2 v2.27.7
@@ -15,21 +14,19 @@ require (
 )
 
 require (
-	dario.cat/mergo v1.0.2 // indirect
 	github.com/Microsoft/go-winio v0.6.2 // indirect
 	github.com/ProtonMail/go-crypto v1.4.1 // indirect
 	github.com/clipperhouse/uax29/v2 v2.7.0 // indirect
 	github.com/cloudflare/circl v1.6.3 // indirect
 	github.com/cpuguy83/go-md2man/v2 v2.0.7 // indirect
-	github.com/cyphar/filepath-securejoin v0.6.1 // indirect
 	github.com/emirpasic/gods v1.18.1 // indirect
 	github.com/gdamore/encoding v1.0.1 // indirect
 	github.com/gdamore/tcell/v2 v2.13.10 // indirect
-	github.com/go-git/gcfg v1.5.1-0.20230307220236-3a3c6141e376 // indirect
-	github.com/golang/groupcache v0.0.0-20241129210726-2c02b8208cf8 // indirect
-	github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 // indirect
+	github.com/go-git/gcfg/v2 v2.0.2 // indirect
+	github.com/go-git/go-billy/v6 v6.0.0-alpha.1 // indirect
 	github.com/kevinburke/ssh_config v1.6.0 // indirect
 	github.com/klauspost/cpuid/v2 v2.3.0 // indirect
+	github.com/kr/pretty v0.3.1 // indirect
 	github.com/ktr0731/go-ansisgr v0.1.0 // indirect
 	github.com/lucasb-eyer/go-colorful v1.4.0 // indirect
 	github.com/mattn/go-colorable v0.1.15 // indirect
@@ -39,14 +36,14 @@ require (
 	github.com/pjbgf/sha1cd v0.6.0 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
+	github.com/rogpeppe/go-internal v1.14.1 // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/sergi/go-diff v1.4.0 // indirect
-	github.com/skeema/knownhosts v1.3.2 // indirect
-	github.com/xanzy/ssh-agent v0.3.3 // indirect
 	github.com/xrash/smetrics v0.0.0-20250705151800-55b8f293f342 // indirect
 	golang.org/x/crypto v0.52.0 // indirect
 	golang.org/x/net v0.55.0 // indirect
+	golang.org/x/sync v0.20.0 // indirect
 	golang.org/x/sys v0.46.0 // indirect
 	golang.org/x/text v0.37.0 // indirect
-	gopkg.in/warnings.v0 v0.1.2 // indirect
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
 )