Surface stderr from failing proxy command

[spikecurtis]

Some users are reporting trouble connecting to their workspaces, and receive an error "Server closed connection during identification exchange" on the "Choose IDE and project for workspace ... " screen.

Stack trace is:

java.lang.Throwable: Failed to retrieve IDEs (attempt 1; will retry in 5000 ms)
	at com.intellij.openapi.diagnostic.Logger.error(Logger.java:370)
	at com.coder.gateway.views.steps.CoderLocateRemoteProjectStepView$onInit$1$ides$2.invoke(CoderLocateRemoteProjectStepView.kt:212)
	at com.coder.gateway.views.steps.CoderLocateRemoteProjectStepView$onInit$1$ides$2.invoke(CoderLocateRemoteProjectStepView.kt:186)
	at com.coder.gateway.sdk.RetryKt.suspendingRetryWithExponentialBackOff(Retry.kt:63)
	at com.coder.gateway.sdk.RetryKt$suspendingRetryWithExponentialBackOff$1.invokeSuspend(Retry.kt)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:104)
	at com.intellij.openapi.application.impl.DispatchedRunnable.run(DispatchedRunnable.kt:43)
	at com.intellij.openapi.application.TransactionGuardImpl.runWithWritingAllowed(TransactionGuardImpl.java:208)
	at com.intellij.openapi.application.TransactionGuardImpl.access$100(TransactionGuardImpl.java:21)
	at com.intellij.openapi.application.TransactionGuardImpl$1.run(TransactionGuardImpl.java:190)
	at com.intellij.openapi.application.impl.ApplicationImpl.runIntendedWriteActionOnCurrentThread(ApplicationImpl.java:861)
	at com.intellij.openapi.application.impl.ApplicationImpl$4.run(ApplicationImpl.java:478)
	at com.intellij.openapi.application.impl.FlushQueue.doRun(FlushQueue.java:79)
	at com.intellij.openapi.application.impl.FlushQueue.runNextEvent(FlushQueue.java:121)
	at com.intellij.openapi.application.impl.FlushQueue.flushNow(FlushQueue.java:41)
	at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:318)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:792)
	at java.desktop/java.awt.EventQueue$3.run(EventQueue.java:739)
	at java.desktop/java.awt.EventQueue$3.run(EventQueue.java:733)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:761)
	at com.intellij.ide.IdeEventQueue.defaultDispatchEvent(IdeEventQueue.kt:690)
	at com.intellij.ide.IdeEventQueue._dispatchEvent$lambda$10(IdeEventQueue.kt:593)
	at com.intellij.openapi.application.impl.ApplicationImpl.runWithoutImplicitRead(ApplicationImpl.java:1485)
	at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.kt:593)
	at com.intellij.ide.IdeEventQueue.access$_dispatchEvent(IdeEventQueue.kt:67)
	at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1$1.compute(IdeEventQueue.kt:369)
	at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1$1.compute(IdeEventQueue.kt:368)
	at com.intellij.openapi.progress.impl.CoreProgressManager.computePrioritized(CoreProgressManager.java:787)
	at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1.invoke(IdeEventQueue.kt:368)
	at com.intellij.ide.IdeEventQueue$dispatchEvent$processEventRunnable$1$1.invoke(IdeEventQueue.kt:363)
	at com.intellij.ide.IdeEventQueueKt.performActivity$lambda$1(IdeEventQueue.kt:997)
	at com.intellij.openapi.application.TransactionGuardImpl.performActivity(TransactionGuardImpl.java:105)
	at com.intellij.ide.IdeEventQueueKt.performActivity(IdeEventQueue.kt:997)
	at com.intellij.ide.IdeEventQueue.dispatchEvent$lambda$7(IdeEventQueue.kt:363)
	at com.intellij.openapi.application.impl.ApplicationImpl.runIntendedWriteActionOnCurrentThread(ApplicationImpl.java:861)
	at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.kt:405)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:207)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:92)

[code-asher]

We identified that the issue was the proxy command failed because the header command provided to the plugin was failing.

I wonder if it is possible to surface a better error instead of just "server closed", but I think it depends on whether the error returned by the Gateway API contains that information in some way or if it really is just "server closed".

If it does not, maybe there is something else we can do to suss out problems with the header command, like running SSH ourselves just as a sanity check before we call out to Gateway's stuff.

[code-asher]

Renamed the issue to somehow surface an error from running the proxy command. We had another issue where it was failing because the agent was shutting down but this was not being shown directly to the user.