fix(wasmguest): expose host services during register

docs/adr/0007-register-sees-the-current-guest-host-services.md

@@ -0,0 +1,36 @@
+# Register sees the current guest host services
+
+Go guest plugins can declare capability-backed runtime surfaces from their
+`Register` callback. Bridge providers are the first such surface: the provider
+stores its invokable value in the guest-local bridge stub while the stub tells
+the CMS host that the named service exists.
+
+`Serve` previously assigned the package-level guest runtime only after
+`newGuest` returned. Because `newGuest` runs `Register` synchronously,
+`HostServices()` returned an empty `CoreServices` value during registration.
+Plugins that correctly nil-checked the bridge silently skipped registration.
+The CMS could therefore mark a Wasm plugin loaded while consumers failed with
+`bridge: no service registered` during a later load hook.
+
+`newGuest` now makes the guest under construction current for the synchronous
+registration pass and restores the previous runtime before returning. `Serve`
+then installs the completed guest as before. This keeps construction isolated
+for native tests while making the documented `HostServices()` escape hatch
+truthful during `Register` on every pooled Wasm instance.
+
+Alternatives rejected were moving bridge registration into `Load`, which runs
+on only one pooled instance, and adding bridge names only to the manifest,
+which would advertise host availability without installing the guest-local
+`BridgeInvokable` value needed by `HOOK_BRIDGE_CALL`.
+
+Consequences:
+
+- Bridge services registered from `Register` exist on every pooled guest
+  instance and remain callable after CMS startup and hot swap.
+- A regression test exercises the observable `Serve` plus
+  `HOOK_BRIDGE_CALL` contract instead of relying on initialization internals.
+- No ABI or protobuf change is required; consumers need a plugin SDK release
+  containing the corrected Go guest runtime.
+
+Keywords: wasmguest.Serve, newGuest, HostServices, PluginRegistration.Register,
+plugin bridge, RegisterService, BridgeInvokable, HOOK_BRIDGE_CALL, wiki content

plugin/wasmguest/dispatch.go

@@ -100,7 +100,15 @@ func newGuest(reg plugin.PluginRegistration) *guest {
 	// Pool whose calls fail cleanly, matching the capability stubs.
 	g.services.Pool = bnwasm.NewPool(bnwasm.Transport(capTransport))
 	g.rag, _ = g.services.RAGService.(*caps.RAGStub)
+	// Register callbacks may use HostServices for capability-backed surfaces
+	// that are not passed as Register parameters, such as bridge services.
+	// Publish this partially initialized guest only for the synchronous
+	// registration pass, then restore the previous runtime. Serve installs g
+	// permanently after newGuest returns.
+	previous := current
+	current = g
 	g.registerErr = runRegister(reg, g.templates, g.blocks)
+	current = previous
 	return g
 }
 

plugin/wasmguest/dispatch_test.go

@@ -130,6 +130,43 @@ func TestServeInstallsRuntime(t *testing.T) {
 	}
 }
 
+func TestServeExposesHostServicesDuringRegister(t *testing.T) {
+	previous := current
+	t.Cleanup(func() { current = previous })
+
+	Serve(plugin.PluginRegistration{
+		Name:    "bridge-provider",
+		Version: "0.1.0",
+		Register: func(_ templates.TemplateRegistry, _ blocks.BlockRegistry) error {
+			bridge := HostServices().Bridge
+			if bridge == nil {
+				return fmt.Errorf("HostServices bridge is unavailable during Register")
+			}
+			bridge.RegisterService("bridge-provider", "content", bridgeInvokableFunc(
+				func(_ context.Context, _ string, _ []byte) ([]byte, error) {
+					return []byte("registered"), nil
+				},
+			))
+			return nil
+		},
+	})
+
+	resp := invokeHook(t, current, abiv1.Hook_HOOK_BRIDGE_CALL, &abiv1.BridgeCallRequest{
+		ServiceName: "content",
+		Method:      "apply",
+	})
+	if resp.GetError() != nil {
+		t.Fatalf("bridge call returned error: %v", resp.GetError())
+	}
+	bridgeResp := &abiv1.BridgeCallResponse{}
+	if err := proto.Unmarshal(resp.GetPayload(), bridgeResp); err != nil {
+		t.Fatalf("unmarshal BridgeCallResponse: %v", err)
+	}
+	if got := string(bridgeResp.GetPayload()); got != "registered" {
+		t.Fatalf("bridge payload = %q, want registered", got)
+	}
+}
+
 func TestBridgeCallProvidesAuthenticatedCallerContext(t *testing.T) {
 	g := newGuest(fixtureRegistration())
 	g.services.Bridge.RegisterService("fixture", "content", bridgeInvokableFunc(