Independent client/engine versioning with compatibility check

Split release.sh into release-client.sh and release-engine.sh for
independent release cadences. Client checks engine version on first
API call and hard-fails if engine is below MinEngineVersion.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/internal/api/version_test.go

@@ -0,0 +1,136 @@
+package api
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestSemverAtLeast(t *testing.T) {
+	tests := []struct {
+		version  string
+		minimum  string
+		expected bool
+	}{
+		{"2.1.0", "2.0.0", true},
+		{"2.0.0", "2.0.0", true},
+		{"2.0.5", "2.0.0", true},
+		{"2.1.5", "2.1.0", true},
+		{"2.0.9", "2.1.0", false},
+		{"1.9.9", "2.0.0", false},
+		{"3.0.0", "2.9.9", true},
+		{"2.0.0", "2.0.1", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.version+">="+tt.minimum, func(t *testing.T) {
+			got := semverAtLeast(tt.version, tt.minimum)
+			if got != tt.expected {
+				t.Errorf("semverAtLeast(%q, %q) = %v, want %v", tt.version, tt.minimum, got, tt.expected)
+			}
+		})
+	}
+}
+
+func TestCheckEngineVersion_Compatible(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]string{"version": "2.1.0"})
+	}))
+	defer srv.Close()
+
+	clientVersion = "2.2.0"
+	minEngineVersion = "2.1.0"
+	defer func() { clientVersion = ""; minEngineVersion = "" }()
+
+	c := &Client{
+		baseURL:    srv.URL,
+		httpClient: &http.Client{},
+	}
+
+	// Should not panic or exit
+	c.checkEngineVersion()
+
+	if !c.versionChecked {
+		t.Error("versionChecked should be true after check")
+	}
+}
+
+func TestCheckEngineVersion_SkipsWhenDev(t *testing.T) {
+	clientVersion = "dev"
+	minEngineVersion = "dev"
+	defer func() { clientVersion = ""; minEngineVersion = "" }()
+
+	c := &Client{
+		baseURL:    "http://localhost:99999",
+		httpClient: &http.Client{},
+	}
+
+	// Should not attempt connection
+	c.checkEngineVersion()
+
+	if !c.versionChecked {
+		t.Error("versionChecked should be true after skipping")
+	}
+}
+
+func TestCheckEngineVersion_SkipsWhenEmpty(t *testing.T) {
+	clientVersion = "1.0.0"
+	minEngineVersion = ""
+	defer func() { clientVersion = ""; minEngineVersion = "" }()
+
+	c := &Client{
+		baseURL:    "http://localhost:99999",
+		httpClient: &http.Client{},
+	}
+
+	c.checkEngineVersion()
+
+	if !c.versionChecked {
+		t.Error("versionChecked should be true after skipping")
+	}
+}
+
+func TestCheckEngineVersion_SkipsWhenUnreachable(t *testing.T) {
+	clientVersion = "2.0.0"
+	minEngineVersion = "2.0.0"
+	defer func() { clientVersion = ""; minEngineVersion = "" }()
+
+	c := &Client{
+		baseURL:    "http://localhost:99999",
+		httpClient: &http.Client{},
+	}
+
+	// Should not panic — just skip
+	c.checkEngineVersion()
+
+	if !c.versionChecked {
+		t.Error("versionChecked should be true even when unreachable")
+	}
+}
+
+func TestCheckEngineVersion_CachedAfterFirstCall(t *testing.T) {
+	callCount := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		callCount++
+		json.NewEncoder(w).Encode(map[string]string{"version": "2.1.0"})
+	}))
+	defer srv.Close()
+
+	clientVersion = "2.1.0"
+	minEngineVersion = "2.0.0"
+	defer func() { clientVersion = ""; minEngineVersion = "" }()
+
+	c := &Client{
+		baseURL:    srv.URL,
+		httpClient: &http.Client{},
+	}
+
+	c.checkEngineVersion()
+	c.checkEngineVersion()
+	c.checkEngineVersion()
+
+	if callCount != 1 {
+		t.Errorf("expected 1 status call, got %d", callCount)
+	}
+}