scheduler: Add CheckLightningAvailability feature gate

libs/gl-client-py/Makefile

@@ -10,6 +10,19 @@ PYVERSION=$(shell cd libs && cargo metadata --format-version 1 | jq -r '.package
 PYDIR=${REPO}/libs/gl-client-py
 PROTODIR=${REPO}/libs/proto
 
+# The protobuf gencode embeds a hard assertion that the runtime is at
+# least as new as the protoc that produced it, so regenerating with a
+# newer toolchain than the deployed runtime breaks every consumer at
+# import time. Pin the generator and run it isolated from the ambient
+# venv, so the checked-in stubs do not depend on who regenerated them.
+# Bump deliberately, together with the `protobuf` runtime bound in
+# pyproject.toml.
+PROTOC_TOOLCHAIN = \
+	uv run --no-project \
+	--with grpcio-tools==1.78.0 \
+	--with mypy-protobuf==5.0.0 \
+	python -m grpc_tools.protoc
+
 PYPROTOC_OPTS = \
 	-I ${PROTODIR} \
 	--python_out=${PYDIR} \
@@ -35,8 +48,8 @@ ${PYPROTOS}: pygrpc
 pygrpc: ${PROTOSRC}
 	cp ${PYDIR}/../proto/glclient/scheduler.proto ${PYDIR}/glclient/
 	cp ${PYDIR}/../proto/glclient/greenlight.proto ${PYDIR}/glclient/
-	cd ${PYDIR}; uv run python -m grpc_tools.protoc ${PYPROTOC_OPTS} glclient/scheduler.proto
-	cd ${PYDIR}; uv run python -m grpc_tools.protoc ${PYPROTOC_OPTS} glclient/greenlight.proto
+	cd ${PYDIR}; ${PROTOC_TOOLCHAIN} ${PYPROTOC_OPTS} glclient/scheduler.proto
+	cd ${PYDIR}; ${PROTOC_TOOLCHAIN} ${PYPROTOC_OPTS} glclient/greenlight.proto
 
 check-py:
 	#uv run --reinstall-package='gl-sdk' --all-packages mypy ${PYDIR}/glclient

libs/gl-client-py/glclient/scheduler.proto

@@ -26,8 +26,10 @@ import "glclient/greenlight.proto";
 // Users are authenticated using mTLS authentication. Applications are
 // provisioned with an anonymous keypair that is not bound to a node,
 // allowing access only to the unauthenticated endpoints
-// `Scheduler.GetChallenge`, `Scheduler.Register` and
-// `Scheduler.Recover`. This allows them to register or recover a
+// `Scheduler.GetChallenge`, `Scheduler.Register`,
+// `Scheduler.Recover` and
+// `Scheduler.CheckLightningAvailability`. This allows them to
+// register or recover a
 // node, but doesn't give access to the node itself. Upon registering
 // or recovering an account the user receives a keypair that is bound
 // to the specific node. Once the user receives their personal mTLS
@@ -82,6 +84,25 @@ service Scheduler {
 	// error being returned.
 	rpc GetChallenge(ChallengeRequest) returns (ChallengeResponse) {}
 
+	// Reports whether the Lightning account backed by `node_id` may
+	// be surfaced to the user. This is a feature gate for downstream
+	// applications: greenlight relays the question to its Lightning
+	// Service Provider, which answers based on whether it has
+	// previously granted this node a slot (grants are sticky) or has
+	// the capacity to grant one now.
+	//
+	// Unlike the other node-scoped calls this one is deliberately
+	// available *before* registration, since an application has to
+	// decide whether to offer Lightning at all before it creates a
+	// node. There is therefore no mTLS identity to derive the node
+	// from, and the caller names the `node_id` it is asking about.
+	//
+	// The answer is advisory and may change: a node that is not
+	// available today may become available once the LSP has capacity
+	// again. Applications should treat an error as "unknown" rather
+	// than as a negative answer.
+	rpc CheckLightningAvailability(CheckLightningAvailabilityRequest) returns (CheckLightningAvailabilityResponse) {}
+
 	// Scheduling takes a previously registered node, locates a
 	// free slot in greenlight's infrastructure and allocates it
 	// to run the node. The node then goes through the startup
@@ -248,6 +269,18 @@ enum ChallengeScope {
 	RECOVER = 1;
 }
 
+message CheckLightningAvailabilityRequest {
+	// 33 bytes node public key. The node need not be registered
+	// with greenlight yet.
+	bytes node_id = 1;
+};
+
+message CheckLightningAvailabilityResponse {
+	// Whether the Lightning account backed by this node may be
+	// surfaced to the user.
+	bool available = 1;
+};
+
 message RegistrationRequest {
 	// 33 bytes node public key.
 	bytes node_id = 1;