refactor(ec2): improve error information in telemetry. (aws#6624)

## Problem
Within telemetry, there are a large group of fatal errors within EC2
Connect being grouped together under the same general error code.
Additionally, there is very little information in the error message to
determine the source of this error. Specifically, it appears the the
test SSM connection done before attempting to pass the connection to VS
Code, implemented
[here](https://github.com/aws/aws-toolkit-vscode/blob/b9af56c3097242fb796995479f864d95098bf713/packages/core/src/shared/extensions/ssh.ts#L133-L155),
can fail, and gives us a general error code with little information
about its root cause.

## Solution
- Add a specific error code for this connection type. (reused an old
unused one)
- Pipe the error from the child process into the error message so that
we get it in telemetry.
- Add a docstring to test connect function, since its not obvious whats
happening as it involves both ssh and ssm.

Example Error:
<img width="465" alt="image"
src="https://github.com/user-attachments/assets/8b27746d-9291-48a4-a125-dcea761a2c13"
/>

---

- Treat all work as PUBLIC. Private `feature/x` branches will not be
squash-merged at release time.
- Your code changes must meet the guidelines in
[CONTRIBUTING.md](https://github.com/aws/aws-toolkit-vscode/blob/master/CONTRIBUTING.md#guidelines).
- License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

---------

Co-authored-by: Justin M. Keyes <[email protected]>

Author: Hweinstock

packages/core/src/awsService/ec2/model.ts

@@ -36,7 +36,7 @@ import { SshKeyPair } from './sshKeyPair'
 import { Ec2SessionTracker } from './remoteSessionManager'
 import { getEc2SsmEnv } from './utils'
 
-export type Ec2ConnectErrorCode = 'EC2SSMStatus' | 'EC2SSMPermission' | 'EC2SSMConnect' | 'EC2SSMAgentStatus'
+export type Ec2ConnectErrorCode = 'EC2SSMStatus' | 'EC2SSMPermission' | 'EC2SSMTestConnect' | 'EC2SSMAgentStatus'
 
 export interface Ec2RemoteEnv extends VscodeRemoteConnection {
     selection: Ec2Selection
@@ -221,8 +221,8 @@ export class Ec2Connecter implements vscode.Disposable {
                 remoteUser.name
             )
         } catch (err) {
-            const message = err instanceof SshError ? 'Testing SSH connection to instance failed' : ''
-            this.throwConnectionError(message, selection, err as Error)
+            const message = err instanceof SshError ? `Testing SSM connection to instance failed: ${err.message}` : ''
+            this.throwConnectionError(message, selection, { ...(err as Error), code: 'EC2SSMTestConnect' })
         } finally {
             await this.ssmClient.terminateSession(testSession)
         }

packages/core/src/shared/extensions/ssh.ts

@@ -130,27 +130,34 @@ export class RemoteSshSettings extends Settings.define('remote.SSH', remoteSshTy
     }
 }
 
+/**
+ * Test a SSH connection over SSM.
+ * @param ProcessClass given process to test the connection within.
+ * @param hostname
+ * @param sshPath
+ * @param user
+ * @param session SSM session credentials. These cannot be reused, so it may be required to create a seperate session for the test connection.
+ * @returns
+ */
 export async function testSshConnection(
     ProcessClass: typeof ChildProcess,
     hostname: string,
     sshPath: string,
     user: string,
     session: SSM.StartSessionResponse
 ): Promise<ChildProcessResult | never> {
+    const env = { SESSION_ID: session.SessionId, STREAM_URL: session.StreamUrl, TOKEN: session.TokenValue }
+    const process = new ProcessClass(sshPath, ['-T', `${user}@${hostname}`, 'echo "test connection succeeded" && exit'])
     try {
-        const env = { SESSION_ID: session.SessionId, STREAM_URL: session.StreamUrl, TOKEN: session.TokenValue }
-        const result = await new ProcessClass(sshPath, [
-            '-T',
-            `${user}@${hostname}`,
-            'echo "test connection succeeded" && exit',
-        ]).run({
+        return await process.run({
             spawnOptions: {
                 env,
             },
         })
-        return result
     } catch (error) {
-        throw new SshError('SSH connection test failed', { cause: error as Error })
+        throw new SshError(process.result()?.stderr ?? 'An unknown error occurred when testing the connection', {
+            cause: error as Error,
+        })
     }
 }