feat(cmd): implement push, diff, and commit commands

Implement three previously-stubbed commands following the existing
parallel execution pattern used by clone/pull/fetch:

- push: pushes all refs to origin for all configured repos
- diff: shows file-level uncommitted changes across all repos
- commit: commits staged changes across all repos with a shared message (-m)

All commands support parallel execution via -j flag.
Update AGENTS.md to reflect current implementation status.

AGENTS.md

@@ -44,11 +44,11 @@ mg/
 │   │       ├── register.go  # Register repo (implemented)
 │   │       ├── unregister.go# Unregister repo (implemented)
 │   │       ├── import.go    # Merge configs (implemented)
-│   │       ├── push.go      # Stub
-│   │       ├── fetch.go     # Stub
-│   │       ├── status.go    # Stub
-│   │       ├── diff.go      # Stub
-│   │       ├── commit.go    # Stub
+│   │       ├── push.go      # Push all repos (implemented)
+│   │       ├── fetch.go     # Fetch all repos (implemented)
+│   │       ├── status.go    # Status all repos (implemented)
+│   │       ├── diff.go      # Diff all repos (implemented)
+│   │       ├── commit.go    # Commit staged changes (implemented)
 │   │       └── config.go    # Stub
 │   └── paths/
 │       └── mrpaths.go       # Utility to list repo paths from mrconfig
@@ -67,11 +67,11 @@ mg/
 | `register`   | Implemented | Detects git root, stores `$HOME`  |
 | `unregister` | Implemented | By path or current dir             |
 | `import`     | Implemented | Merge configs, supports stdin `-` |
-| `push`       | Stub        | Prints "push called"               |
-| `fetch`      | Stub        | Prints "fetch called"              |
-| `status`     | Stub        | Prints "status called"             |
-| `diff`       | Stub        | Prints "diff called"               |
-| `commit`     | Stub        | Prints "commit called"             |
+| `push`       | Implemented | Parallel via `-j`, pushes all refs |
+| `fetch`      | Implemented | Parallel via `-j`                  |
+| `status`     | Implemented | Parallel via `-j`, sorted output   |
+| `diff`       | Implemented | Parallel via `-j`, file-level diff |
+| `commit`     | Implemented | Parallel via `-j`, `-m` message    |
 | `config`     | Stub        | Prints "config called"             |
 
 ## Configuration
@@ -221,10 +221,9 @@ go test ./...
 
 ## Known Issues / TODOs
 
-1. Several commands are stubs (push, fetch, status, diff, commit, config)
-2. `parse/mgconf.go:61` has a hint about inefficient string concatenation in a loop
-3. Test coverage is minimal
-4. `unregister` command short description incorrectly says "add current path" (copy-paste error)
+1. `config` command is still a stub
+2. Test coverage is minimal for cmd package (parse package has good coverage)
+3. No integration tests for commands that interact with git repos
 
 ## Error Handling Pattern
 

cmd/mg/cmd/commit.go

@@ -2,19 +2,122 @@ package cmd
 
 import (
 	"fmt"
+	"log"
+	"os"
+	"sync"
 
+	git "github.com/go-git/go-git/v5"
 	"github.com/spf13/cobra"
 )
 
+var commitMessage string
+
 // commitCmd represents the commit command
 var commitCmd = &cobra.Command{
 	Use:   "commit",
-	Short: "commit all current repos with the same message",
+	Short: "commit staged changes across all repos with the same message",
 	Run: func(_ *cobra.Command, args []string) {
-		fmt.Println("commit called")
+		type RepoError struct {
+			Error error
+			Repo  string
+		}
+		if jobs < 1 {
+			log.Println("jobs must be greater than 0")
+			os.Exit(1)
+		}
+		if commitMessage == "" {
+			log.Println("commit message is required (-m)")
+			os.Exit(1)
+		}
+		conf := GetConfig()
+		if len(args) > 0 {
+			log.Println("too many arguments")
+			os.Exit(1)
+		}
+		repoChan := make(chan string, len(conf.Repos))
+		var (
+			errs    []RepoError
+			skipped int
+			mutex   sync.Mutex
+			wg      sync.WaitGroup
+		)
+		wg.Add(len(conf.Repos))
+		for i := 0; i < jobs; i++ {
+			go func() {
+				for repo := range repoChan {
+					r, err := git.PlainOpenWithOptions(repo, &git.PlainOpenOptions{DetectDotGit: true})
+					if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						wg.Done()
+						continue
+					}
+					w, err := r.Worktree()
+					if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						wg.Done()
+						continue
+					}
+					st, err := w.Status()
+					if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						wg.Done()
+						continue
+					}
+					// Check if there are any staged changes
+					hasStagedChanges := false
+					for _, s := range st {
+						if s.Staging != git.Unmodified && s.Staging != git.Untracked {
+							hasStagedChanges = true
+							break
+						}
+					}
+					if !hasStagedChanges {
+						mutex.Lock()
+						skipped++
+						mutex.Unlock()
+						fmt.Printf("repo %s: nothing staged to commit\n", repo)
+						wg.Done()
+						continue
+					}
+					_, err = w.Commit(commitMessage, &git.CommitOptions{})
+					if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						log.Printf("commit failed for %s: %v\n", repo, err)
+						wg.Done()
+						continue
+					}
+					fmt.Printf("successfully committed in %s\n", repo)
+					wg.Done()
+				}
+			}()
+		}
+		for _, repo := range conf.Repos {
+			repoChan <- repo.Path
+		}
+		close(repoChan)
+		wg.Wait()
+		for _, err := range errs {
+			log.Printf("error committing %s: %s\n", err.Repo, err.Error)
+		}
+		lenErrs := len(errs)
+		committed := len(conf.Repos) - lenErrs - skipped
+		fmt.Println()
+		fmt.Printf("successfully committed %d/%d repos\n", committed, len(conf.Repos))
+		fmt.Printf("%d repos had nothing staged\n", skipped)
+		fmt.Printf("failed to commit %d/%d repos\n", lenErrs, len(conf.Repos))
 	},
 }
 
 func init() {
 	rootCmd.AddCommand(commitCmd)
+	commitCmd.Flags().IntVarP(&jobs, "jobs", "j", 1, "number of jobs to run in parallel")
+	commitCmd.Flags().StringVarP(&commitMessage, "message", "m", "", "commit message")
 }

cmd/mg/cmd/diff.go

@@ -2,19 +2,140 @@ package cmd
 
 import (
 	"fmt"
+	"log"
+	"os"
+	"sort"
+	"sync"
 
+	git "github.com/go-git/go-git/v5"
 	"github.com/spf13/cobra"
 )
 
+type repoDiff struct {
+	Path    string
+	Changes []string
+}
+
 // diffCmd represents the diff command
 var diffCmd = &cobra.Command{
 	Use:   "diff",
-	Short: "compute a collective diff",
-	Run: func(cmd *cobra.Command, args []string) {
-		fmt.Println("diff called")
+	Short: "show uncommitted changes across all repos",
+	Run: func(_ *cobra.Command, args []string) {
+		type RepoError struct {
+			Error error
+			Repo  string
+		}
+		if jobs < 1 {
+			log.Println("jobs must be greater than 0")
+			os.Exit(1)
+		}
+		conf := GetConfig()
+		if len(args) > 0 {
+			log.Println("too many arguments")
+			os.Exit(1)
+		}
+		repoChan := make(chan string, len(conf.Repos))
+		var (
+			errs  []RepoError
+			diffs []repoDiff
+			mutex sync.Mutex
+			wg    sync.WaitGroup
+		)
+		wg.Add(len(conf.Repos))
+		for i := 0; i < jobs; i++ {
+			go func() {
+				for repo := range repoChan {
+					r, err := git.PlainOpenWithOptions(repo, &git.PlainOpenOptions{DetectDotGit: true})
+					if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						wg.Done()
+						continue
+					}
+					w, err := r.Worktree()
+					if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						wg.Done()
+						continue
+					}
+					st, err := w.Status()
+					if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						wg.Done()
+						continue
+					}
+					if st.IsClean() {
+						wg.Done()
+						continue
+					}
+					rd := repoDiff{Path: repo}
+					for file, status := range st {
+						code := status.Worktree
+						if code == git.Unmodified {
+							code = status.Staging
+						}
+						var prefix string
+						switch code {
+						case git.Modified:
+							prefix = "M"
+						case git.Added:
+							prefix = "A"
+						case git.Deleted:
+							prefix = "D"
+						case git.Renamed:
+							prefix = "R"
+						case git.Copied:
+							prefix = "C"
+						case git.Untracked:
+							prefix = "?"
+						default:
+							continue
+						}
+						rd.Changes = append(rd.Changes, fmt.Sprintf("  %s %s", prefix, file))
+					}
+					sort.Strings(rd.Changes)
+					mutex.Lock()
+					diffs = append(diffs, rd)
+					mutex.Unlock()
+					wg.Done()
+				}
+			}()
+		}
+		for _, repo := range conf.Repos {
+			repoChan <- repo.Path
+		}
+		close(repoChan)
+		wg.Wait()
+
+		sort.Slice(diffs, func(i, j int) bool {
+			return diffs[i].Path < diffs[j].Path
+		})
+
+		for _, rd := range diffs {
+			fmt.Printf("%s:\n", rd.Path)
+			for _, change := range rd.Changes {
+				fmt.Println(change)
+			}
+			fmt.Println()
+		}
+
+		for _, err := range errs {
+			log.Printf("error reading %s: %s\n", err.Repo, err.Error)
+		}
+
+		fmt.Printf("%d/%d repos have changes\n", len(diffs), len(conf.Repos))
+		if len(errs) > 0 {
+			fmt.Printf("failed to read %d/%d repos\n", len(errs), len(conf.Repos))
+		}
 	},
 }
 
 func init() {
 	rootCmd.AddCommand(diffCmd)
+	diffCmd.Flags().IntVarP(&jobs, "jobs", "j", 1, "number of jobs to run in parallel")
 }

cmd/mg/cmd/push.go

@@ -2,7 +2,12 @@ package cmd
 
 import (
 	"fmt"
+	"log"
+	"os"
+	"sync"
 
+	git "github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/config"
 	"github.com/spf13/cobra"
 )
 
@@ -10,11 +15,81 @@ import (
 var pushCmd = &cobra.Command{
 	Use:   "push",
 	Short: "push all git repos",
-	Run: func(cmd *cobra.Command, args []string) {
-		fmt.Println("push called")
+	Run: func(_ *cobra.Command, args []string) {
+		type RepoError struct {
+			Error error
+			Repo  string
+		}
+		if jobs < 1 {
+			log.Println("jobs must be greater than 0")
+			os.Exit(1)
+		}
+		conf := GetConfig()
+		if len(args) > 0 {
+			log.Println("too many arguments")
+			os.Exit(1)
+		}
+		repoChan := make(chan string, len(conf.Repos))
+		var (
+			errs            []RepoError
+			alreadyUpToDate int
+			mutex           sync.Mutex
+			wg              sync.WaitGroup
+		)
+		wg.Add(len(conf.Repos))
+		for i := 0; i < jobs; i++ {
+			go func() {
+				for repo := range repoChan {
+					log.Printf("attempting push: %s\n", repo)
+					r, err := git.PlainOpenWithOptions(repo, &git.PlainOpenOptions{DetectDotGit: true})
+					if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						log.Printf("push failed for %s: %v\n", repo, err)
+						wg.Done()
+						continue
+					}
+					err = r.Push(&git.PushOptions{
+						RefSpecs: []config.RefSpec{"refs/heads/*:refs/heads/*"},
+					})
+					if err == git.NoErrAlreadyUpToDate {
+						mutex.Lock()
+						alreadyUpToDate++
+						mutex.Unlock()
+						fmt.Printf("repo %s: already up to date\n", repo)
+						wg.Done()
+						continue
+					} else if err != nil {
+						mutex.Lock()
+						errs = append(errs, RepoError{Error: err, Repo: repo})
+						mutex.Unlock()
+						log.Printf("push failed for %s: %v\n", repo, err)
+						wg.Done()
+						continue
+					}
+					fmt.Printf("successfully pushed %s\n", repo)
+					wg.Done()
+				}
+			}()
+		}
+		for _, repo := range conf.Repos {
+			repoChan <- repo.Path
+		}
+		close(repoChan)
+		wg.Wait()
+		for _, err := range errs {
+			log.Printf("error pushing %s: %s\n", err.Repo, err.Error)
+		}
+		lenErrs := len(errs)
+		fmt.Println()
+		fmt.Printf("successfully pushed %d/%d repos\n", len(conf.Repos)-lenErrs, len(conf.Repos))
+		fmt.Printf("%d repos already up to date\n", alreadyUpToDate)
+		fmt.Printf("failed to push %d/%d repos\n", lenErrs, len(conf.Repos))
 	},
 }
 
 func init() {
 	rootCmd.AddCommand(pushCmd)
+	pushCmd.Flags().IntVarP(&jobs, "jobs", "j", 1, "number of jobs to run in parallel")
 }