fix(sagemaker): Fix host identification issue after restarting a Space (#8249)

## Problem
Users will face a host identification issue when reconnecting to a Space
after restarting it, if the Space name has capital letters. This occurs
because the Space's hostname is written to the known_hosts file in
lowercase, but hostname matching during reconnection is case-sensitive.

## Solution
When removing the Space hostname from the known_hosts file, ensure to
remove lines that match the lowercase variant of the Space hostname.

---

- 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: Laxman Reddy <[email protected]>

Author: dylanraws

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

@@ -226,7 +226,13 @@ export async function removeKnownHost(hostname: string): Promise<void> {
         throw ToolkitError.chain(err, 'Failed to read known_hosts file')
     }
 
-    const updatedLines = lines.filter((line) => !line.split(' ')[0].split(',').includes(hostname))
+    const updatedLines = lines.filter((line) => {
+        const entryHostname = line.split(' ')[0].split(',')
+        // Hostnames in the known_hosts file seem to be always lowercase, but keeping the case-sensitive check just in
+        // case. Originally we were only doing the case-sensitive check which caused users to get a host
+        // identification error when reconnecting to a Space after it was restarted.
+        return !entryHostname.includes(hostname) && !entryHostname.includes(hostname.toLowerCase())
+    })
 
     if (updatedLines.length !== lines.length) {
         try {

packages/core/src/test/awsService/sagemaker/model.test.ts

@@ -211,6 +211,28 @@ describe('SageMaker Model', () => {
             assertLogsContain(`Removed '${hostname}' from known_hosts`, false, 'debug')
         })
 
+        it('removes case-sensitive hostname when entry in known_hosts is lowercase', async function () {
+            const mixedCaseHostname = 'Test.Host.Com'
+
+            sandbox.stub(fs, 'existsFile').resolves(true)
+
+            const inputContent = `test.host.com ssh-rsa AAAA\nsome.other.com ssh-rsa BBBB`
+            const expectedOutput = `some.other.com ssh-rsa BBBB`
+
+            sandbox.stub(fs, 'readFileText').resolves(inputContent)
+            const writeStub = sandbox.stub(fs, 'writeFile').resolves()
+
+            await removeKnownHost(mixedCaseHostname)
+
+            sinon.assert.calledWith(
+                writeStub,
+                path.join(os.homedir(), '.ssh', 'known_hosts'),
+                sinon.match((value: string) => value.trim() === expectedOutput),
+                { atomic: true }
+            )
+            assertLogsContain(`Removed '${mixedCaseHostname}' from known_hosts`, false, 'debug')
+        })
+
         it('handles hostname in comma-separated list', async function () {
             sandbox.stub(fs, 'existsFile').resolves(true)