fix(clients): dropped connections say why in the client trace

packages/client-runtime/src/connection/supervisor.ts

@@ -802,7 +802,30 @@ export const make = Effect.fn("EnvironmentSupervisor.make")(function* (
         resetRetry: connectedExit.value,
       } satisfies AttemptOutcome;
     }
-    return failureFromExit(target, connectedExit, true, connectedForMs >= BACKOFF_RESET_AFTER_MS);
+    const outcome = failureFromExit(
+      target,
+      connectedExit,
+      true,
+      connectedForMs >= BACKOFF_RESET_AFTER_MS,
+    );
+    if (outcome._tag === "Failure") {
+      // A live session ending is otherwise invisible in the client trace, so
+      // record why, and how long it lasted, as its own root span.
+      yield* Effect.void.pipe(
+        Effect.withSpan("EnvironmentSupervisor.connectionLost", {
+          root: true,
+          attributes: {
+            "environment.id": target.environmentId,
+            "environment.label": target.label,
+            "environment.target.kind": target._tag,
+            "connection.connected_ms": connectedForMs,
+            "connection.failure.reason": outcome.failure.error.reason,
+            "connection.failure.detail": outcome.failure.error.detail,
+          },
+        }),
+      );
+    }
+    return outcome;
   }, Effect.ensuring(clearLease));
 
   const waitForRetrySignal = Effect.fnUntraced(function* (delayMs: number) {

packages/client-runtime/src/errors/transport.test.ts

@@ -22,6 +22,7 @@ describe("isTransportConnectionErrorMessage", () => {
 
   it("recognizes connection errors emitted by the Effect RPC session", () => {
     expect(isTransportConnectionErrorMessage("Test environment disconnected.")).toBe(true);
+    expect(isTransportConnectionErrorMessage("Test environment stopped responding.")).toBe(true);
     expect(
       isTransportConnectionErrorMessage(
         "Test environment could not establish a WebSocket connection.",
@@ -34,6 +35,7 @@ describe("isTransportConnectionErrorMessage", () => {
   it("recognizes relay connection errors that carry the network hint", () => {
     for (const sentence of [
       "Relay environment disconnected.",
+      "Relay environment stopped responding.",
       "Relay environment could not establish a WebSocket connection.",
     ]) {
       expect(isTransportConnectionErrorMessage(`${sentence} ${NETWORK_BLOCKING_HINT}`)).toBe(true);

packages/client-runtime/src/errors/transport.ts

@@ -10,7 +10,7 @@ const TRANSPORT_ERROR_PATTERNS = [
   // The RPC session appends the network hint for relay connections. Any other
   // trailing text means a different error that the user should still see.
   new RegExp(
-    `\\b(?:is not connected|disconnected|could not establish a WebSocket connection)\\.(?: ${escapeRegExp(NETWORK_BLOCKING_HINT)})?$`,
+    `\\b(?:is not connected|disconnected|stopped responding|could not establish a WebSocket connection)\\.(?: ${escapeRegExp(NETWORK_BLOCKING_HINT)})?$`,
     "i",
   ),
   /\bClientProtocolError\b/i,

packages/client-runtime/src/rpc/session.test.ts

@@ -1108,7 +1108,10 @@ describe("RpcSessionFactory", () => {
       yield* TestClock.adjust("5 seconds");
       const error = yield* Fiber.join(closedFiber);
       expect(error).toBeInstanceOf(ConnectionTransientError);
-      expect(error).toMatchObject({ reason: "transport" });
+      expect(error).toMatchObject({
+        reason: "transport",
+        detail: "Test environment stopped responding.",
+      });
     }).pipe(Effect.scoped, Effect.provide(TestClock.layer())),
   );
 

packages/client-runtime/src/rpc/session.ts

@@ -170,18 +170,24 @@ export const make = Effect.fn("RpcSessionFactory.make")(function* (
 
     const connected = yield* Deferred.make<void>();
     const disconnected = yield* Deferred.make<never, ConnectionTransientError>();
+    // Set when the socket closes because pongs stopped, so the failure says so
+    // instead of looking like the server closed the connection.
+    const pingTimedOut = yield* Ref.make(false);
     const hooks = RpcClient.ConnectionHooks.of({
       onConnect: Deferred.succeed(connected, undefined).pipe(Effect.asVoid),
-      onDisconnect: Deferred.isDone(connected).pipe(
-        Effect.flatMap((wasConnected) =>
+      onPingTimeout: Ref.set(pingTimedOut, true),
+      onDisconnect: Effect.all([Deferred.isDone(connected), Ref.get(pingTimedOut)]).pipe(
+        Effect.flatMap(([wasConnected, timedOut]) =>
           Deferred.fail(
             disconnected,
             new ConnectionTransientErrorClass({
               reason: "transport",
               detail: `${
-                wasConnected
-                  ? `${connection.label} disconnected.`
-                  : `${connection.label} could not establish a WebSocket connection.`
+                !wasConnected
+                  ? `${connection.label} could not establish a WebSocket connection.`
+                  : timedOut
+                    ? `${connection.label} stopped responding.`
+                    : `${connection.label} disconnected.`
               }${networkHint}`,
             }),
           ),

patches/effect@4.0.1.patch

@@ -1,5 +1,5 @@
 diff --git a/dist/ai/McpServer.js b/dist/ai/McpServer.js
-index 2da5941..9fada51 100644
+index 2da594107273980144e84ab9b53636ef34043f6b..9fada51944f58fd0d988ae8f6b18f83e79583a25 100644
 --- a/dist/ai/McpServer.js
 +++ b/dist/ai/McpServer.js
 @@ -1093,7 +1093,7 @@ export const layerHttp = options => {
@@ -30,7 +30,7 @@ index 2da5941..9fada51 100644
  }));
  const mcpHttpSerialization = /*#__PURE__*/(() => {
 diff --git a/dist/ai/internal/mcpRuntime.js b/dist/ai/internal/mcpRuntime.js
-index 06370fd..baa945b 100644
+index 06370fd1341ae7a6b681c513a3a3c2866a414b7b..baa945b8b4763b5472c4a900b90b817209caa4bf 100644
 --- a/dist/ai/internal/mcpRuntime.js
 +++ b/dist/ai/internal/mcpRuntime.js
 @@ -336,6 +336,7 @@ export const make = /*#__PURE__*/Effect.fnUntraced(function* (protocols) {
@@ -42,7 +42,7 @@ index 06370fd..baa945b 100644
      canDeliver: (clientId, headers, notification, fallback) => stateful?.canDeliver(clientId, headers, notification, fallback) ?? true,
      installHandlers: Effect.fnUntraced(function* (options) {
 diff --git a/dist/ai/internal/mcpStatefulRuntime.js b/dist/ai/internal/mcpStatefulRuntime.js
-index 9471bdf..4558603 100644
+index 9471bdfbcff0643b44df3a08c3701f743a299638..455860316ddfccaf98ff95f9f05da500c331869c 100644
 --- a/dist/ai/internal/mcpStatefulRuntime.js
 +++ b/dist/ai/internal/mcpStatefulRuntime.js
 @@ -46,6 +46,7 @@ export const make = () => {
@@ -54,7 +54,7 @@ index 9471bdf..4558603 100644
        const session = resolveSession(clientId, headers);
        if (session !== undefined) {
 diff --git a/dist/http/HttpClientResponse.js b/dist/http/HttpClientResponse.js
-index 42fba67..2b4981b 100644
+index 42fba673de3b6bdc089c305f2e87ad56c3bfc374..2b4981b8a88606fb93d62a29f21f9556803307c4 100644
 --- a/dist/http/HttpClientResponse.js
 +++ b/dist/http/HttpClientResponse.js
 @@ -195,7 +195,7 @@ class WebHttpClientResponse extends Inspectable.Class {
@@ -66,10 +66,37 @@ index 42fba67..2b4981b 100644
    }
    get remoteAddress() {
      return Option.none();
+diff --git a/dist/rpc/RpcClient.d.ts b/dist/rpc/RpcClient.d.ts
+index c498ff74510b784dcba791dbf6b8f23dac40a71d..8be9c910a8112a5289159251846128cd27cf32aa 100644
+--- a/dist/rpc/RpcClient.d.ts
++++ b/dist/rpc/RpcClient.d.ts
+@@ -302,6 +302,8 @@ export declare const layerProtocolWorker: (options: {
+ declare const ConnectionHooks_base: Context.ServiceClass<ConnectionHooks, "effect/rpc/RpcClient/ConnectionHooks", {
+     readonly onConnect: Effect.Effect<void>;
+     readonly onDisconnect: Effect.Effect<void>;
++    /** Runs when the socket is dropped because pongs stopped, before `onDisconnect`. */
++    readonly onPingTimeout?: Effect.Effect<void> | undefined;
+ }>;
+ /**
+  * Represents optional client protocol hooks that run when a transport connects
 diff --git a/dist/rpc/RpcClient.js b/dist/rpc/RpcClient.js
-index 8af2e2e..65acae4 100644
+index 8af2e2efa9311d582add61fef131fd39fd459ab4..723649f05baa61ac33c9bc3634d106caa9641164 100644
 --- a/dist/rpc/RpcClient.js
 +++ b/dist/rpc/RpcClient.js
+@@ -679,11 +679,11 @@ export const makeProtocolSocket = options => Protocol.make(Effect.fnUntraced(fun
+           yield* processData(frames[i]);
+         }
+       }
+-    }).pipe(Effect.scoped, Effect.raceFirst(Effect.flatMap(pinger.timeout, () => Effect.fail(new Socket.SocketError({
++    }).pipe(Effect.scoped, Effect.raceFirst(Effect.flatMap(pinger.timeout, () => (Option.isSome(hooks) && hooks.value.onPingTimeout ? hooks.value.onPingTimeout : Effect.void).pipe(Effect.andThen(Effect.fail(new Socket.SocketError({
+       reason: new Socket.SocketReadError({
+         cause: new Error("ping timeout")
+       })
+-    })))));
++    })))))));
+   }).pipe(Option.isSome(hooks) ? Effect.ensuring(hooks.value.onDisconnect) : identity, Effect.tapCause(cause => {
+     const error = Cause.findError(cause);
+     const hasError = Result.isSuccess(error);
 @@ -726,17 +726,25 @@ export const makeProtocolSocket = options => Protocol.make(Effect.fnUntraced(fun
  const defaultRetryPolicy = /*#__PURE__*/Schedule.min([/*#__PURE__*/Schedule.exponential(500, 1.5), /*#__PURE__*/Schedule.spaced(5000)]);
  const makePinger = /*#__PURE__*/Effect.fnUntraced(function* (writePing) {
@@ -98,7 +125,7 @@ index 8af2e2e..65acae4 100644
    }).pipe(Effect.delay("5 seconds"), Effect.ignore, Effect.forever, Effect.interruptible, Effect.forkScoped);
    return {
 diff --git a/src/http/HttpClientResponse.ts b/src/http/HttpClientResponse.ts
-index c037015..a8b0d8b 100644
+index c037015185da1e0c664653b5a496832a9449f3c1..a8b0d8be28bbbd3a0d0d3f1a222c2f074d2d3ad5 100644
 --- a/src/http/HttpClientResponse.ts
 +++ b/src/http/HttpClientResponse.ts
 @@ -341,7 +341,7 @@ class WebHttpClientResponse extends Inspectable.Class implements HttpClientRespo