Add --force flag to update command for dev builds (#116)

## Summary
- Dev builds are no longer replaced by default during `roborev update`
- Add `--force`/`-f` flag to explicitly install official release over
dev build
- Show full download details before prompting for `--force`

This prevents accidental replacement of dev builds when testing, while
still making it easy to switch back to official releases.

## Test plan
- [x] `roborev update --check` on dev build shows "Use --force to
install..."
- [x] `roborev update` on dev build shows details then "Use --force to
install..."
- [x] `roborev update --force` on dev build proceeds to download/install
- [x] `roborev update` on official release works as before (no --force
needed)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: wesm

cmd/roborev/main.go

@@ -1928,14 +1928,18 @@ it only updates existing installations. Used by 'roborev update'.`,
 func updateCmd() *cobra.Command {
 	var checkOnly bool
 	var yes bool
+	var force bool
 
 	cmd := &cobra.Command{
 		Use:   "update",
 		Short: "Update roborev to the latest version",
 		Long: `Check for and install roborev updates.
 
 Shows exactly what will be downloaded and where it will be installed.
-Requires confirmation before making changes (use --yes to skip).`,
+Requires confirmation before making changes (use --yes to skip).
+
+Dev builds are not replaced by default. Use --force to install the latest
+official release over a dev build.`,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			fmt.Println("Checking for updates...")
 
@@ -1952,7 +1956,7 @@ Requires confirmation before making changes (use --yes to skip).`,
 			fmt.Printf("\n  Current version: %s\n", info.CurrentVersion)
 			fmt.Printf("  Latest version:  %s\n", info.LatestVersion)
 			if info.IsDevBuild {
-				fmt.Println("\nYou're running a dev build. Latest stable release available.")
+				fmt.Println("\nYou're running a dev build. Latest official release available.")
 			} else {
 				fmt.Println("\nUpdate available!")
 			}
@@ -1975,6 +1979,15 @@ Requires confirmation before making changes (use --yes to skip).`,
 			fmt.Printf("  %s\n", binDir)
 
 			if checkOnly {
+				if info.IsDevBuild {
+					fmt.Println("\nUse --force to install the latest official release.")
+				}
+				return nil
+			}
+
+			// Dev builds require --force to update
+			if info.IsDevBuild && !force {
+				fmt.Println("\nUse --force to install the latest official release.")
 				return nil
 			}
 
@@ -2082,6 +2095,7 @@ Requires confirmation before making changes (use --yes to skip).`,
 
 	cmd.Flags().BoolVar(&checkOnly, "check", false, "only check for updates, don't install")
 	cmd.Flags().BoolVarP(&yes, "yes", "y", false, "skip confirmation prompt")
+	cmd.Flags().BoolVarP(&force, "force", "f", false, "replace dev build with latest official release")
 
 	return cmd
 }

internal/update/update.go

@@ -76,7 +76,7 @@ type cachedCheck struct {
 // Uses a 1-hour cache to avoid hitting GitHub API too often
 func CheckForUpdate(forceCheck bool) (*UpdateInfo, error) {
 	currentVersion := strings.TrimPrefix(version.Version, "v")
-	isDevBuild := extractBaseSemver(currentVersion) == ""
+	isDevBuild := isDevBuildVersion(currentVersion)
 
 	// Check cache first (unless forced)
 	// Use shorter cache for dev builds so they learn about releases sooner
@@ -561,6 +561,24 @@ func extractBaseSemver(v string) string {
 	return v
 }
 
+// gitDescribePattern matches git describe format: v0.16.1-2-gabcdef
+// The -N-gHASH suffix indicates N commits after the tag
+var gitDescribePattern = regexp.MustCompile(`-\d+-g[0-9a-f]+$`)
+
+// isDevBuildVersion returns true if the version is a dev build.
+// Dev builds are either:
+// - Pure hashes with no semver (e.g., "9c2baf2", "dev")
+// - Git describe format with commits after tag (e.g., "v0.16.1-2-gabcdef")
+func isDevBuildVersion(v string) bool {
+	v = strings.TrimPrefix(v, "v")
+	// Pure hash or "dev" - no semver base
+	if extractBaseSemver(v) == "" {
+		return true
+	}
+	// Git describe format: has commits after a tag
+	return gitDescribePattern.MatchString(v)
+}
+
 // isNewer returns true if v1 is newer than v2
 // Assumes semver format: major.minor.patch
 // Handles git describe format (v0.4.0-5-gabcdef) by extracting base version.

internal/update/update_test.go

@@ -257,6 +257,44 @@ func TestExtractBaseSemver(t *testing.T) {
 	}
 }
 
+func TestIsDevBuildVersion(t *testing.T) {
+	tests := []struct {
+		version string
+		want    bool
+	}{
+		// Official releases - NOT dev builds
+		{"0.16.1", false},
+		{"v0.16.1", false},
+		{"1.0.0", false},
+		{"v1.0.0", false},
+
+		// Git describe format - ARE dev builds
+		{"0.16.1-2-g75d300a", true},
+		{"v0.16.1-2-g75d300a", true},
+		{"0.4.0-5-gabcdef", true},
+		{"1.2.3-100-gdeadbeef", true},
+
+		// Pure hash/dev - ARE dev builds
+		{"dev", true},
+		{"abc1234", true},
+		{"88be010", true},
+
+		// Prerelease tags - NOT dev builds (intentional releases)
+		{"0.16.1-rc1", false},
+		{"v1.0.0-beta.1", false},
+		{"0.4.0-alpha", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.version, func(t *testing.T) {
+			got := isDevBuildVersion(tt.version)
+			if got != tt.want {
+				t.Errorf("isDevBuildVersion(%q) = %v, want %v", tt.version, got, tt.want)
+			}
+		})
+	}
+}
+
 func TestIsNewer(t *testing.T) {
 	tests := []struct {
 		v1, v2 string