refactor: extract host runtime controller for connection management

packages/app/src/utils/connection-selection.test.ts

@@ -25,7 +25,7 @@ function probes(
 }
 
 describe("selectBestConnection", () => {
-  it("picks the available connection with lowest latency regardless of transport type", () => {
+  it("picks the available connection with lowest latency regardless of transport", () => {
     const candidates: ConnectionCandidate[] = [
       { connectionId: "direct:a", connection: makeDirect("direct:a", "a:6767") },
       {
@@ -36,7 +36,6 @@ describe("selectBestConnection", () => {
 
     const selected = selectBestConnection({
       candidates,
-      preferredConnectionId: "direct:a",
       probeByConnectionId: probes({
         "direct:a": { status: "available", latencyMs: 84 },
         "relay:b": { status: "available", latencyMs: 34 },
@@ -46,6 +45,28 @@ describe("selectBestConnection", () => {
     expect(selected).toBe("relay:b");
   });
 
+  it("picks the lowest-latency connection among mixed transport candidates", () => {
+    const candidates: ConnectionCandidate[] = [
+      { connectionId: "direct:a", connection: makeDirect("direct:a", "a:6767") },
+      { connectionId: "direct:c", connection: makeDirect("direct:c", "c:6767") },
+      {
+        connectionId: "relay:b",
+        connection: makeRelay("relay:b", "relay.example:443"),
+      },
+    ];
+
+    const selected = selectBestConnection({
+      candidates,
+      probeByConnectionId: probes({
+        "direct:a": { status: "available", latencyMs: 84 },
+        "direct:c": { status: "available", latencyMs: 41 },
+        "relay:b": { status: "available", latencyMs: 12 },
+      }),
+    });
+
+    expect(selected).toBe("relay:b");
+  });
+
   it("ignores unavailable and pending probes", () => {
     const candidates: ConnectionCandidate[] = [
       { connectionId: "direct:a", connection: makeDirect("direct:a", "a:6767") },
@@ -58,7 +79,6 @@ describe("selectBestConnection", () => {
 
     const selected = selectBestConnection({
       candidates,
-      preferredConnectionId: "direct:a",
       probeByConnectionId: probes({
         "direct:a": { status: "pending", latencyMs: null },
         "relay:b": { status: "unavailable", latencyMs: null },
@@ -69,7 +89,7 @@ describe("selectBestConnection", () => {
     expect(selected).toBe("direct:c");
   });
 
-  it("falls back to preferred connection when no candidates are available", () => {
+  it("returns null when no candidates are available", () => {
     const candidates: ConnectionCandidate[] = [
       { connectionId: "direct:a", connection: makeDirect("direct:a", "a:6767") },
       {
@@ -80,17 +100,16 @@ describe("selectBestConnection", () => {
 
     const selected = selectBestConnection({
       candidates,
-      preferredConnectionId: "relay:b",
       probeByConnectionId: probes({
         "direct:a": { status: "pending", latencyMs: null },
         "relay:b": { status: "unavailable", latencyMs: null },
       }),
     });
 
-    expect(selected).toBe("relay:b");
+    expect(selected).toBeNull();
   });
 
-  it("falls back to first candidate when preferred is missing and none are available", () => {
+  it("returns null when no probes are available even if candidates exist", () => {
     const candidates: ConnectionCandidate[] = [
       { connectionId: "direct:a", connection: makeDirect("direct:a", "a:6767") },
       {
@@ -101,13 +120,12 @@ describe("selectBestConnection", () => {
 
     const selected = selectBestConnection({
       candidates,
-      preferredConnectionId: "missing",
       probeByConnectionId: probes({
         "direct:a": { status: "unavailable", latencyMs: null },
         "relay:b": { status: "pending", latencyMs: null },
       }),
     });
 
-    expect(selected).toBe("direct:a");
+    expect(selected).toBeNull();
   });
 });

packages/app/src/utils/connection-selection.ts

@@ -12,14 +12,13 @@ export type ConnectionProbeState =
 
 export type SelectBestConnectionInput = {
   candidates: ConnectionCandidate[];
-  preferredConnectionId: string | null;
   probeByConnectionId: Map<string, ConnectionProbeState>;
 };
 
 export function selectBestConnection(
   input: SelectBestConnectionInput
 ): string | null {
-  const { candidates, preferredConnectionId, probeByConnectionId } = input;
+  const { candidates, probeByConnectionId } = input;
   if (candidates.length === 0) {
     return null;
   }
@@ -29,8 +28,9 @@ export function selectBestConnection(
     .filter(({ candidate }) => {
       const probe = probeByConnectionId.get(candidate.connectionId);
       return probe?.status === "available";
-    })
-    .sort((left, right) => {
+    });
+
+  const byLatency = (left: { candidate: ConnectionCandidate; index: number }, right: { candidate: ConnectionCandidate; index: number }) => {
       const leftProbe = probeByConnectionId.get(left.candidate.connectionId);
       const rightProbe = probeByConnectionId.get(right.candidate.connectionId);
 
@@ -48,18 +48,12 @@ export function selectBestConnection(
       }
 
       return leftLatency - rightLatency;
-    });
+    };
 
-  if (available.length > 0) {
-    return available[0]!.candidate.connectionId;
+  if (available.length === 0) {
+    return null;
   }
 
-  const preferred = candidates.find(
-    (candidate) => candidate.connectionId === preferredConnectionId
-  );
-  if (preferred) {
-    return preferred.connectionId;
-  }
-
-  return candidates[0]!.connectionId;
+  const sorted = available.sort(byLatency);
+  return sorted[0]!.candidate.connectionId;
 }