diff --git a/internal/cli/frontdoor.go b/internal/cli/frontdoor.go
index 43284d08..8af6e012 100644
--- a/internal/cli/frontdoor.go
+++ b/internal/cli/frontdoor.go
@@ -217,7 +217,10 @@ func realpath(path string) string {
 // would otherwise slip through as "compatible". gateHost prints the actionable
 // remedy for every non-Compatible verdict EXCEPT NoPluginFound, whose message the
 // caller owns (it auto-installs by default and only refuses under --no-install,
-// so the right wording depends on the caller's choice).
+// so the right wording depends on the caller's choice). On Compatible it stays
+// silent on the bare OK line but surfaces the opt-in upgrade hint when the plugin
+// is contract-compatible yet behind a strictly-newer binary; the hint never
+// blocks — the caller still proceeds to launch.
 func gateHost(ops hostOps, host string, stderr io.Writer) contract.Verdict {
 	manifestPath, err := ops.ResolveManifest(host)
 	if err != nil {
@@ -235,6 +238,13 @@ func gateHost(ops hostOps, host string, stderr io.Writer) contract.Verdict {
 	}
 	if res.Verdict != contract.Compatible {
 		fmt.Fprintln(stderr, res.Message)
+		return res.Verdict
+	}
+	// Compatible but behind: surface the opt-in upgrade hint (the front door
+	// stays silent on the bare OK line). The hint never blocks — the caller still
+	// proceeds to launch on Compatible.
+	if res.Hint != "" {
+		fmt.Fprintln(stderr, res.Hint)
 	}
 	return res.Verdict
 }
diff --git a/internal/cli/frontdoor_test.go b/internal/cli/frontdoor_test.go
index eddbb34e..5505ae81 100644
--- a/internal/cli/frontdoor_test.go
+++ b/internal/cli/frontdoor_test.go
@@ -70,6 +70,17 @@ func withExecutablePath(t *testing.T, path string, err error) {
 	t.Cleanup(func() { executablePath = orig })
 }
 
+// withVersion stamps the package Version (the binary display semver the gate
+// feeds to the upgrade-hint compare), restoring it after the test. The package
+// default is the `dev` sentinel, which suppresses the hint, so a test that
+// exercises the behind-plugin hint must stamp a real semver.
+func withVersion(t *testing.T, v string) {
+	t.Helper()
+	orig := Version
+	Version = v
+	t.Cleanup(func() { Version = orig })
+}
+
 func executableFixture(t *testing.T) string {
 	t.Helper()
 	p := filepath.Join(t.TempDir(), "spacedock")
@@ -111,6 +122,71 @@ func TestClaudeFrontDoorLaunchesOnCompatible(t *testing.T) {
 	}
 }
 
+// TestFrontDoorUpgradeHintOnBehindPlugin is AC-4: the front-door gate prints the
+// opt-in upgrade hint to stderr when the resolved plugin is contract-compatible
+// but behind the binary, then proceeds to launch (the hint never blocks). The
+// compatible.json fixture is plugin 0.12.1; stamping the binary Version to a
+// strictly-newer semver makes it behind-but-compatible. A paired equal-version
+// case (binary == plugin) asserts the gate stays silent. Both arms observe the
+// recorded launch + stderr, never a source grep.
+func TestFrontDoorUpgradeHintOnBehindPlugin(t *testing.T) {
+	cases := []struct {
+		name string
+		host string
+		run  func(args []string, dir string, fake *fakeHost, stderr *bytes.Buffer) int
+	}{
+		{"claude", "claude", func(args []string, dir string, fake *fakeHost, stderr *bytes.Buffer) int {
+			var stdout bytes.Buffer
+			return runClaude(context.Background(), args, dir, fake, lookFound, &stdout, stderr)
+		}},
+		{"codex", "codex", func(args []string, dir string, fake *fakeHost, stderr *bytes.Buffer) int {
+			var stdout bytes.Buffer
+			return runCodex(context.Background(), args, dir, fake, lookFound, &stdout, stderr)
+		}},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name+" behind-plugin hints + launches", func(t *testing.T) {
+			withVersion(t, "0.20.0") // strictly newer than the fixture plugin 0.12.1
+			fake := &fakeHost{manifest: compatibleManifest(t)}
+			var stderr bytes.Buffer
+
+			code := tc.run(nil, t.TempDir(), fake, &stderr)
+
+			if code != 0 {
+				t.Fatalf("exit = %d, want 0 (the hint must not block launch) (stderr=%q)", code, stderr.String())
+			}
+			if fake.launchedArg == nil {
+				t.Fatalf("launch seam not invoked — the hint must not change the launch path")
+			}
+			out := stderr.String()
+			if !strings.Contains(out, "newer plugin") {
+				t.Fatalf("stderr missing the behind-plugin upgrade hint: %q", out)
+			}
+			if !strings.Contains(out, "spacedock install --host "+tc.host) {
+				t.Fatalf("stderr hint missing host install command for %s: %q", tc.host, out)
+			}
+		})
+
+		t.Run(tc.name+" equal-version stays silent", func(t *testing.T) {
+			withVersion(t, "0.12.1") // exactly the fixture plugin version
+			fake := &fakeHost{manifest: compatibleManifest(t)}
+			var stderr bytes.Buffer
+
+			code := tc.run(nil, t.TempDir(), fake, &stderr)
+
+			if code != 0 {
+				t.Fatalf("exit = %d, want 0 (stderr=%q)", code, stderr.String())
+			}
+			if fake.launchedArg == nil {
+				t.Fatalf("launch seam not invoked on an equal-version compatible plugin")
+			}
+			if strings.Contains(stderr.String(), "newer plugin") || strings.Contains(stderr.String(), "spacedock install") {
+				t.Fatalf("equal-version gate must stay silent (no upgrade hint): %q", stderr.String())
+			}
+		})
+	}
+}
+
 // TestClaudeFrontDoorFailFastOnMismatch: on a mismatch verdict the launch seam is
 // NOT invoked and the process exits non-zero with the pinned remedy on stderr.
 func TestClaudeFrontDoorInjectsResolvedLauncherBin(t *testing.T) {
diff --git a/internal/cli/init.go b/internal/cli/init.go
index 9bac79e7..c1fb3888 100644
--- a/internal/cli/init.go
+++ b/internal/cli/init.go
@@ -44,11 +44,22 @@ func runInit(ctx context.Context, args []string, ops hostOps, stdout, stderr io.
 			fmt.Fprintf(stderr, "spacedock init: could not resolve the installed codex plugin: %v\n", err)
 			return 1
 		}
-		if resolved != "" || check {
-			code := contract.RunDoctor(resolved, "codex", devBranch, Version, stdout, stderr)
-			if code != 0 || resolved != "" || check {
-				return code
+		if check {
+			return contract.RunDoctor(resolved, "codex", devBranch, Version, stdout, stderr)
+		}
+		if resolved != "" {
+			// An already-present plugin is refreshed on `install` like the claude
+			// arm — drive the install seam, then run doctor. Without this the codex
+			// arm was a doctor-only no-op that left a behind plugin in place.
+			out, err := ops.Install("codex", marketplaceSource, devBranch)
+			if err != nil {
+				fmt.Fprintf(stderr, "spacedock install: host install failed: %v\n", err)
+				return 1
+			}
+			if out != "" {
+				fmt.Fprintln(stdout, out)
 			}
+			return runDoctor(ctx, []string{"--host", "codex"}, ops, stdout, stderr)
 		}
 
 		// Codex install is documented prose when no installed plugin resolves: the
diff --git a/internal/cli/init_test.go b/internal/cli/init_test.go
index 888579a3..56e96be7 100644
--- a/internal/cli/init_test.go
+++ b/internal/cli/init_test.go
@@ -102,6 +102,12 @@ func TestInitCheckRunsDoctorWithoutInstalling(t *testing.T) {
 }
 
 func TestInitCodexInstallReadiness(t *testing.T) {
+	// compatible-installed: `spacedock install --host codex` re-installs an
+	// already-present compatible plugin instead of short-circuiting to a
+	// doctor-only no-op. The codex arm must drive the install seam exactly like
+	// the claude arm — the recorded {host, source, branch} call is the
+	// independent source of truth that the refresh actually fired, not the
+	// no-op the prior assertion codified.
 	t.Run("compatible-installed", func(t *testing.T) {
 		fake := &fakeHost{manifest: compatibleManifest(t)}
 		var stdout, stderr bytes.Buffer
@@ -111,14 +117,33 @@ func TestInitCodexInstallReadiness(t *testing.T) {
 		if code != 0 {
 			t.Fatalf("exit = %d, want 0 (stderr=%q)", code, stderr.String())
 		}
+		wantInstall := []string{"codex", marketplaceSource, devBranch}
+		if !equalArgv(fake.installCmds, wantInstall) {
+			t.Fatalf("install seam = %v, want %v — codex init on a present plugin must refresh, not no-op", fake.installCmds, wantInstall)
+		}
+		// After install, init runs doctor — a compatible report on stdout.
 		out := stdout.String()
 		if !strings.Contains(out, "OK: spacedock binary "+Version+" and plugin 0.12.1") {
-			t.Fatalf("codex init should report compatible installed plugin first; stdout = %q", out)
+			t.Fatalf("codex init should run doctor after install and report compatible; stdout = %q", out)
 		}
-		for _, banned := range []string{"codex plugin marketplace add", "codex plugin add spacedock@spacedock"} {
-			if strings.Contains(out, banned) {
-				t.Errorf("compatible codex init must not print manual add command %q:\n%s", banned, out)
-			}
+	})
+
+	// compatible-installed-check: `--check` keeps the no-install report — it runs
+	// doctor without driving the install seam.
+	t.Run("compatible-installed-check", func(t *testing.T) {
+		fake := &fakeHost{manifest: compatibleManifest(t)}
+		var stdout, stderr bytes.Buffer
+
+		code := runInit(context.Background(), []string{"--host", "codex", "--check"}, fake, &stdout, &stderr)
+
+		if code != 0 {
+			t.Fatalf("exit = %d, want 0 (stderr=%q)", code, stderr.String())
+		}
+		if len(fake.installCmds) != 0 {
+			t.Fatalf("--check must not install: %v", fake.installCmds)
+		}
+		if !strings.Contains(stdout.String(), "OK") {
+			t.Fatalf("--check should print the doctor report; stdout = %q", stdout.String())
 		}
 	})
 
diff --git a/internal/cli/install_behavior_codex_test.go b/internal/cli/install_behavior_codex_test.go
index 0e1c5877..0c003690 100644
--- a/internal/cli/install_behavior_codex_test.go
+++ b/internal/cli/install_behavior_codex_test.go
@@ -77,12 +77,84 @@ func TestCodexPluginInstallIsHostNative(t *testing.T) {
 	}
 }
 
+// TestCodexInitRefreshAdvancesBehindPlugin is the AC-2 live proof for the wired
+// codex arm: seed an older plugin (0.0.1) via the production Install seam, then
+// run that same seam against a newer (0.0.2) local marketplace — the path
+// runInit's codex arm now drives on a present plugin. The resolved cache
+// manifest must advance to 0.0.2, read from the on-disk manifest (not the
+// install command's claim). This pins the spike's finding as a regression test
+// on the production refresh path. Skips when `codex` is not on PATH; hermetic
+// via CODEX_HOME isolation + local-path marketplaces (empty branch → no --ref →
+// offline).
+func TestCodexInitRefreshAdvancesBehindPlugin(t *testing.T) {
+	if _, err := exec.LookPath("codex"); err != nil {
+		t.Skip("codex not on PATH; refresh-advances smoke requires the host CLI")
+	}
+
+	tmp := t.TempDir()
+	behind := buildCodexMarketplaceAtVersion(t, filepath.Join(tmp, "behind"), "0.0.1")
+	newer := buildCodexMarketplaceAtVersion(t, filepath.Join(tmp, "newer"), "0.0.2")
+	codexHomeDir := filepath.Join(tmp, "codexhome")
+	mustMkdir(t, codexHomeDir)
+	t.Setenv("CODEX_HOME", codexHomeDir)
+
+	// Seed the behind install (0.0.1) through the production seam.
+	if out, err := (execHost{}).Install("codex", behind, ""); err != nil {
+		t.Fatalf("seed Install(codex, 0.0.1) failed: %v\nout=%q", err, out)
+	}
+	if got := resolvedCodexManifestVersion(t); got != "0.0.1" {
+		t.Fatalf("after seed, resolved manifest version = %q, want 0.0.1", got)
+	}
+
+	// Refresh-on-present (0.0.2) — the wired runInit codex arm calls exactly this
+	// Install seam when a plugin is already resolved.
+	if out, err := (execHost{}).Install("codex", newer, ""); err != nil {
+		t.Fatalf("refresh Install(codex, 0.0.2) failed: %v\nout=%q", err, out)
+	}
+	if got := resolvedCodexManifestVersion(t); got != "0.0.2" {
+		t.Fatalf("after refresh, resolved manifest version = %q, want 0.0.2 (refresh did not advance the behind plugin)", got)
+	}
+}
+
+// resolvedCodexManifestVersion resolves the cached spacedock@spacedock manifest
+// via the production resolver and returns its on-disk version field — the
+// independent source of truth that an install advanced the plugin, not the
+// command's stdout.
+func resolvedCodexManifestVersion(t *testing.T) string {
+	t.Helper()
+	manifest, err := execHost{}.resolveCodexManifest()
+	if err != nil {
+		t.Fatalf("resolveCodexManifest: %v", err)
+	}
+	if manifest == "" {
+		t.Fatalf("resolveCodexManifest returned empty after an install")
+	}
+	data, err := os.ReadFile(manifest)
+	if err != nil {
+		t.Fatalf("read resolved manifest %s: %v", manifest, err)
+	}
+	var m struct {
+		Version string `json:"version"`
+	}
+	if err := json.Unmarshal(data, &m); err != nil {
+		t.Fatalf("parse resolved manifest %s: %v", manifest, err)
+	}
+	return m.Version
+}
+
 // buildLocalCodexMarketplace writes a minimal valid local-path marketplace under
 // root and returns the marketplace directory. Codex reads the marketplace
 // manifest from .claude-plugin/marketplace.json (it reuses the claude manifest
 // layout) and the plugin manifest from the plugin's .codex-plugin/plugin.json.
 // The plugin manifest carries a requires-contract bracketing CONTRACT_VERSION.
 func buildLocalCodexMarketplace(t *testing.T, root string) string {
+	return buildCodexMarketplaceAtVersion(t, root, "0.0.0")
+}
+
+// buildCodexMarketplaceAtVersion is buildLocalCodexMarketplace parameterized by
+// the plugin's display version, so a test can seed a behind plugin then refresh
+// it from a newer marketplace and observe the resolved version advance.
+func buildCodexMarketplaceAtVersion(t *testing.T, root, version string) string {
 	t.Helper()
 	marketplace := filepath.Join(root, "marketplace")
 	plugin := filepath.Join(marketplace, "spacedock")
@@ -98,7 +170,8 @@ func buildLocalCodexMarketplace(t *testing.T, root string) string {
   ]
 }
 `)
-	mustWrite(t, filepath.Join(plugin, ".codex-plugin", "plugin.json"), `{ "name": "spacedock", "version": "0.0.0", "requires-contract": ">=1,<2", "skills": "./skills/" }
+	mustWrite(t, filepath.Join(plugin, ".codex-plugin", "plugin.json"),
+		`{ "name": "spacedock", "version": "`+version+`", "requires-contract": ">=1,<2", "skills": "./skills/" }
 `)
 	mustWrite(t, filepath.Join(plugin, "skills", "demo", "SKILL.md"), "---\nname: demo\ndescription: demo skill\n---\ndemo\n")
 	return marketplace
diff --git a/internal/contract/contract.go b/internal/contract/contract.go
index 7aafff4d..1261720d 100644
--- a/internal/contract/contract.go
+++ b/internal/contract/contract.go
@@ -68,10 +68,14 @@ func (v Verdict) String() string {
 
 // Result carries a comparison's verdict and the operator-facing message. For
 // Compatible the message is a one-line "OK" report; for every mismatch it is the
-// shared-shape actionable message with the per-class remedy.
+// shared-shape actionable message with the per-class remedy. Hint is the opt-in
+// upgrade hint for a compatible-but-behind plugin — empty unless the binary is a
+// strictly-newer semver than the plugin. Doctor folds it into Message; the front
+// door surfaces Hint alone (it stays silent on the bare OK line).
 type Result struct {
 	Verdict Verdict
 	Message string
+	Hint    string
 }
 
 // ParseRange parses a requires-contract value of the form ">=N,<M" into its
@@ -145,8 +149,81 @@ func compareWithManifest(c int, raw, host, branch, manifestPath, pluginVersion,
 	case c >= hi:
 		return Result{Verdict: TooOldPlugin, Message: mismatchMessage(binaryVersion, pluginVersion, "Update the plugin to continue.", tooOldPluginRemedy(host))}
 	default:
-		return Result{Verdict: Compatible, Message: fmt.Sprintf("OK: spacedock binary %s and plugin %s are compatible.", binaryVersion, pluginVersion)}
+		msg := fmt.Sprintf("OK: spacedock binary %s and plugin %s are compatible.", binaryVersion, pluginVersion)
+		hint := upgradeHint(host, pluginVersion, binaryVersion)
+		if hint != "" {
+			msg += "\n" + hint
+		}
+		return Result{Verdict: Compatible, Message: msg, Hint: hint}
+	}
+}
+
+// upgradeHint returns the opt-in upgrade hint appended to a Compatible message
+// when the binary's display semver is strictly newer than the plugin's — a
+// plugin that still works (the contract is compatible) but is behind. It returns
+// "" (no hint) unless BOTH versions are valid dotted-int semver and the binary
+// is strictly greater: an unstamped `dev` binary, a non-semver, or an
+// equal/older binary emits nothing, so the gate never fires a false "you must
+// upgrade". The hint names the host-specific refresh command.
+func upgradeHint(host, pluginVersion, binaryVersion string) string {
+	if semverCompare(binaryVersion, pluginVersion) <= 0 {
+		return ""
+	}
+	return fmt.Sprintf(
+		"A newer plugin is available — run spacedock install --host %s to refresh.",
+		host)
+}
+
+// semverCompare orders two dotted-int versions (e.g. `0.20.0`), returning -1, 0,
+// or 1. It returns 0 (treat as not-greater, so no hint) when EITHER side is not
+// a valid dotted-int version — the defensive gate that keeps a non-semver (`dev`)
+// or empty value from triggering the upgrade hint. Unlike the cli resolver's
+// lexical fallback, a non-integer component here is a parse failure, not a
+// lexical tiebreak: the hint must not fire on anything but a clean semver skew.
+func semverCompare(a, b string) int {
+	an, aok := parseDottedInts(a)
+	bn, bok := parseDottedInts(b)
+	if !aok || !bok {
+		return 0
+	}
+	for i := 0; i < len(an) || i < len(bn); i++ {
+		var av, bv int
+		if i < len(an) {
+			av = an[i]
+		}
+		if i < len(bn) {
+			bv = bn[i]
+		}
+		if av != bv {
+			if av < bv {
+				return -1
+			}
+			return 1
+		}
+	}
+	return 0
+}
+
+// parseDottedInts splits a dotted version into its integer components, reporting
+// ok=false when the string is empty or any component is not a non-negative
+// integer. A pre-release/build suffix (e.g. `-rc1`) makes its component
+// non-integer and so fails the parse — the conservative read for the upgrade
+// hint, which only fires on a clean numeric skew.
+func parseDottedInts(v string) ([]int, bool) {
+	v = strings.TrimSpace(v)
+	if v == "" {
+		return nil, false
+	}
+	parts := strings.Split(v, ".")
+	out := make([]int, len(parts))
+	for i, p := range parts {
+		n, err := strconv.Atoi(p)
+		if err != nil || n < 0 {
+			return nil, false
+		}
+		out[i] = n
 	}
+	return out, true
 }
 
 // mismatchMessage assembles the shared-shape mismatch message: a header naming
diff --git a/internal/contract/contract_test.go b/internal/contract/contract_test.go
index 3a0a8b31..adfce674 100644
--- a/internal/contract/contract_test.go
+++ b/internal/contract/contract_test.go
@@ -96,6 +96,109 @@ func TestCompare(t *testing.T) {
 	}
 }
 
+// TestCompatibleUpgradeHint locks AC-3: when the binary and plugin display
+// versions are both valid semver and the binary is strictly newer while the
+// contract is compatible, the Compatible message carries an opt-in upgrade hint
+// naming a newer plugin AND the host-specific `spacedock install --host {host}`
+// command — but the verdict stays Compatible and the OK line is preserved. The
+// hint NEVER fires on equal versions or a non-semver (`dev`) binary version. The
+// trigger (the semver skew) comes from the version inputs, not the message.
+func TestCompatibleUpgradeHint(t *testing.T) {
+	t.Run("behind-plugin-hints", func(t *testing.T) {
+		for _, host := range []string{"claude", "codex"} {
+			res := Compare(CONTRACT_VERSION, ">=1,<2", host, "", "0.19.8", "0.20.0")
+			if res.Verdict != Compatible {
+				t.Fatalf("host %s: verdict = %v, want Compatible (the hint must not change the verdict)", host, res.Verdict)
+			}
+			if !strings.Contains(res.Message, "OK: spacedock binary 0.20.0 and plugin 0.19.8 are compatible.") {
+				t.Fatalf("host %s: OK line not preserved alongside the hint: %q", host, res.Message)
+			}
+			if !strings.Contains(res.Message, "newer plugin") {
+				t.Fatalf("host %s: hint missing newer-plugin notice: %q", host, res.Message)
+			}
+			if !strings.Contains(res.Message, "spacedock install --host "+host) {
+				t.Fatalf("host %s: hint missing host install command: %q", host, res.Message)
+			}
+		}
+	})
+
+	// Negative: equal versions carry no hint — there is nothing to upgrade to.
+	t.Run("equal-version-no-hint", func(t *testing.T) {
+		res := Compare(CONTRACT_VERSION, ">=1,<2", "claude", "", "0.20.0", "0.20.0")
+		if res.Verdict != Compatible {
+			t.Fatalf("verdict = %v, want Compatible", res.Verdict)
+		}
+		if strings.Contains(res.Message, "newer plugin") || strings.Contains(res.Message, "spacedock install") {
+			t.Fatalf("equal versions must not emit an upgrade hint: %q", res.Message)
+		}
+	})
+
+	// Negative: an unstamped `dev` binary version is not valid semver — the hint
+	// must not fire (no false "you must upgrade" against a dev build).
+	t.Run("dev-binary-no-hint", func(t *testing.T) {
+		res := Compare(CONTRACT_VERSION, ">=1,<2", "claude", "", "0.19.8", "dev")
+		if res.Verdict != Compatible {
+			t.Fatalf("verdict = %v, want Compatible", res.Verdict)
+		}
+		if strings.Contains(res.Message, "newer plugin") || strings.Contains(res.Message, "spacedock install") {
+			t.Fatalf("dev binary version must not emit an upgrade hint: %q", res.Message)
+		}
+	})
+
+	// Negative: a binary OLDER than the plugin (but still contract-compatible)
+	// carries no hint — the hint is for a behind plugin, not a behind binary.
+	t.Run("older-binary-no-hint", func(t *testing.T) {
+		res := Compare(CONTRACT_VERSION, ">=1,<2", "claude", "", "0.21.0", "0.20.0")
+		if res.Verdict != Compatible {
+			t.Fatalf("verdict = %v, want Compatible", res.Verdict)
+		}
+		if strings.Contains(res.Message, "newer plugin") {
+			t.Fatalf("a newer plugin than the binary must not emit the behind-plugin hint: %q", res.Message)
+		}
+	})
+
+	// Positive across the single-vs-double-digit boundary: binary 0.10.0 is
+	// numerically NEWER than plugin 0.9.0 and MUST hint — but lexically "0.10.0"
+	// sorts BEFORE "0.9.0" ("1" < "9"), so a lexical-compare regression of
+	// semverCompare would wrongly suppress the hint here. Pins the integer compare.
+	t.Run("behind-plugin-double-digit-minor-hints", func(t *testing.T) {
+		res := Compare(CONTRACT_VERSION, ">=1,<2", "claude", "", "0.9.0", "0.10.0")
+		if res.Verdict != Compatible {
+			t.Fatalf("verdict = %v, want Compatible", res.Verdict)
+		}
+		if !strings.Contains(res.Message, "newer plugin") {
+			t.Fatalf("binary 0.10.0 is numerically newer than plugin 0.9.0 — the hint MUST fire: %q", res.Message)
+		}
+	})
+
+	// Negative mirror across the boundary: binary 0.9.0 is numerically OLDER than
+	// plugin 0.10.0 and MUST NOT hint — but lexically "0.9.0" sorts AFTER "0.10.0",
+	// so a lexical-compare regression would wrongly FIRE the hint on this older
+	// binary. The two boundary cases together RED any lexical compare.
+	t.Run("older-binary-double-digit-minor-no-hint", func(t *testing.T) {
+		res := Compare(CONTRACT_VERSION, ">=1,<2", "claude", "", "0.10.0", "0.9.0")
+		if res.Verdict != Compatible {
+			t.Fatalf("verdict = %v, want Compatible", res.Verdict)
+		}
+		if strings.Contains(res.Message, "newer plugin") {
+			t.Fatalf("binary 0.9.0 is numerically older than plugin 0.10.0 — the hint MUST NOT fire: %q", res.Message)
+		}
+	})
+
+	// Negative: a pre-release binary version (e.g. 0.20.0-rc1) is not clean
+	// dotted-int semver — the conservative gate emits no hint. Pins that
+	// parseDottedInts rejects a `-rc1` suffix rather than stripping it.
+	t.Run("prerelease-binary-no-hint", func(t *testing.T) {
+		res := Compare(CONTRACT_VERSION, ">=1,<2", "claude", "", "0.19.8", "0.20.0-rc1")
+		if res.Verdict != Compatible {
+			t.Fatalf("verdict = %v, want Compatible", res.Verdict)
+		}
+		if strings.Contains(res.Message, "newer plugin") || strings.Contains(res.Message, "spacedock install") {
+			t.Fatalf("a pre-release binary version must not emit an upgrade hint: %q", res.Message)
+		}
+	})
+}
+
 // TestCompareMessageShape locks the shared mismatch-message shape: the leading
 // "Spacedock version mismatch" line names both display versions, and the message
 // ends with the "Run spacedock doctor" pointer — for every mismatch class except