fix(gen): skip claude invocation in proto Gen() when buf produces no changes

The meta gen-nodiff CI job runs mage gen:all and checks for drift. Each
proto client's Gen() function unconditionally called claude after buf
generate/export, which always failed in CI (claude binary not available).

Add a git diff check immediately after buf generate/export: if the
generated proto files have no changes, skip the claude boilerplate step
and return nil. When proto API hasn't changed (the normal case for
gen-nodiff), Gen() is now a clean no-op that does not require claude.

Idiomatic client Gen() functions already have an equivalent guard (they
diff against a stored baseline ref), so Gen().Client() was already safe.

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

Author: josephschorr

proto-clients/spicedb-csharp-proto/Magefile.go

@@ -21,6 +21,12 @@ func Gen() error {
 		return fmt.Errorf("buf generate failed: %w", err)
 	}
 
+	diff, _ := sh.Output("git", "diff", "--name-only", ".")
+	if strings.TrimSpace(diff) == "" {
+		fmt.Println("==> No proto changes detected after buf generate, skipping Claude step.")
+		return nil
+	}
+
 	fmt.Println("==> Invoking Claude to add boilerplate...")
 	if err := runClaude(
 		"Read DESIGN.md. Review the generated code under gen/. " +

proto-clients/spicedb-go-proto/Magefile.go

@@ -14,13 +14,20 @@ import (
 const maxRetries = 3
 
 // Gen regenerates the proto client: runs buf generate, then invokes Claude
-// to add boilerplate per DESIGN.md.
+// to add boilerplate per DESIGN.md. If buf generate produces no changes,
+// the Claude step is skipped (so gen-nodiff CI passes without claude).
 func Gen() error {
 	fmt.Println("==> Running buf generate...")
 	if err := sh.Run("buf", "generate"); err != nil {
 		return fmt.Errorf("buf generate failed: %w", err)
 	}
 
+	diff, _ := sh.Output("git", "diff", "--name-only", ".")
+	if strings.TrimSpace(diff) == "" {
+		fmt.Println("==> No proto changes detected after buf generate, skipping Claude step.")
+		return nil
+	}
+
 	fmt.Println("==> Invoking Claude to add boilerplate...")
 	if err := runClaude(
 		"Read DESIGN.md. Review the generated code under gen/. " +

proto-clients/spicedb-java-proto/Magefile.go

@@ -21,6 +21,12 @@ func Gen() error {
 		return fmt.Errorf("buf generate failed: %w", err)
 	}
 
+	diff, _ := sh.Output("git", "diff", "--name-only", ".")
+	if strings.TrimSpace(diff) == "" {
+		fmt.Println("==> No proto changes detected after buf generate, skipping Claude step.")
+		return nil
+	}
+
 	fmt.Println("==> Invoking Claude to add boilerplate...")
 	if err := runClaude(
 		"Read DESIGN.md. Review the generated code under gen/. " +

proto-clients/spicedb-python-proto/Magefile.go

@@ -20,6 +20,12 @@ func Gen() error {
 		return fmt.Errorf("buf generate failed: %w", err)
 	}
 
+	diff, _ := sh.Output("git", "diff", "--name-only", ".")
+	if strings.TrimSpace(diff) == "" {
+		fmt.Println("==> No proto changes detected after buf generate, skipping Claude step.")
+		return nil
+	}
+
 	fmt.Println("==> Syncing Python deps...")
 	if err := sh.RunV("uv", "sync"); err != nil {
 		return fmt.Errorf("uv sync failed: %w", err)

proto-clients/spicedb-ruby-proto/Magefile.go

@@ -21,6 +21,12 @@ func Gen() error {
 		return fmt.Errorf("buf generate failed: %w", err)
 	}
 
+	diff, _ := sh.Output("git", "diff", "--name-only", ".")
+	if strings.TrimSpace(diff) == "" {
+		fmt.Println("==> No proto changes detected after buf generate, skipping Claude step.")
+		return nil
+	}
+
 	fmt.Println("==> Installing Ruby dependencies...")
 	if err := sh.Run("bundle", "install"); err != nil {
 		return fmt.Errorf("bundle install failed: %w", err)

proto-clients/spicedb-rust-proto/Magefile.go

@@ -20,6 +20,12 @@ func Gen() error {
 		return fmt.Errorf("buf export failed: %w", err)
 	}
 
+	diff, _ := sh.Output("git", "diff", "--name-only", "proto")
+	if strings.TrimSpace(diff) == "" {
+		fmt.Println("==> No proto changes detected after buf export, skipping Claude step.")
+		return nil
+	}
+
 	fmt.Println("==> Invoking Claude to wire up generated code...")
 	if err := runClaude(
 		"Read DESIGN.md. The proto/ directory has been populated by buf export. " +

proto-clients/spicedb-typescript-proto/Magefile.go

@@ -20,6 +20,12 @@ func Gen() error {
 		return fmt.Errorf("buf generate failed: %w", err)
 	}
 
+	diff, _ := sh.Output("git", "diff", "--name-only", ".")
+	if strings.TrimSpace(diff) == "" {
+		fmt.Println("==> No proto changes detected after buf generate, skipping Claude step.")
+		return nil
+	}
+
 	fmt.Println("==> Installing deps...")
 	if err := sh.RunV("pnpm", "install"); err != nil {
 		return fmt.Errorf("pnpm install failed: %w", err)