fix(amazonq /dev): unpredictable placement of LLM-created files aws#5672

## Problem
In VS Code, when user add 2 different folders in the workspace which
contain different root paths, RTS/LLM cannot decide where to place a
generated file.

## Solution
This fix add the default first folder selected as its default for
orphaned root created files, not blocking user to receive an empty patch
but also support better the workspace usage.

Author: tverney

packages/amazonq/.changes/next-release/Bug Fix-93a879d3-5fa1-47d3-a908-77fcbce9335d.json

@@ -0,0 +1,4 @@
+{
+	"type": "Bug Fix",
+	"description": "Amazon Q /dev: define first folder as a root path for LLM-created files when using workspaces"
+}

packages/core/src/amazonqFeatureDev/session/sessionState.ts

@@ -68,7 +68,13 @@ function registerNewFiles(
         fs.registerProvider(uri, new VirtualMemoryFile(contents))
         const prefix =
             workspaceFolderPrefixes === undefined ? '' : zipFilePath.substring(0, zipFilePath.indexOf(path.sep))
-        const folder = workspaceFolderPrefixes === undefined ? workspaceFolders[0] : workspaceFolderPrefixes[prefix]
+        const folder =
+            workspaceFolderPrefixes === undefined
+                ? workspaceFolders[0]
+                : workspaceFolderPrefixes[prefix] ??
+                  workspaceFolderPrefixes[
+                      Object.values(workspaceFolderPrefixes).find((val) => val.index === 0)?.name ?? ''
+                  ]
         if (folder === undefined) {
             getLogger().error(`No workspace folder found for file: ${zipFilePath} and prefix: ${prefix}`)
             continue
@@ -78,7 +84,9 @@ function registerNewFiles(
             fileContent,
             virtualMemoryUri: uri,
             workspaceFolder: folder,
-            relativePath: zipFilePath.substring(workspaceFolderPrefixes === undefined ? 0 : prefix.length + 1),
+            relativePath: zipFilePath.substring(
+                workspaceFolderPrefixes === undefined ? 0 : prefix.length > 0 ? prefix.length + 1 : 0
+            ),
             rejected: false,
         })
     }

packages/core/src/amazonqFeatureDev/util/files.ts

@@ -63,15 +63,18 @@ export async function prepareRepoData(
         const iterator = ignoredExtensionMap.entries()
 
         for (let i = 0; i < ignoredExtensionMap.size; i++) {
-            const [key, value] = iterator.next().value
-            await amznTelemetry.amazonq_bundleExtensionIgnored.run(async (bundleSpan) => {
-                const event = {
-                    filenameExt: key,
-                    count: value,
-                }
+            const iteratorValue = iterator.next().value
+            if (iteratorValue) {
+                const [key, value] = iteratorValue
+                await amznTelemetry.amazonq_bundleExtensionIgnored.run(async (bundleSpan) => {
+                    const event = {
+                        filenameExt: key,
+                        count: value,
+                    }
 
-                bundleSpan.record(event)
-            })
+                    bundleSpan.record(event)
+                })
+            }
         }
 
         telemetry.setRepositorySize(totalBytes)
@@ -117,7 +120,9 @@ export function getPathsFromZipFilePath(
     }
     // otherwise the first part of the zipPath is the prefix
     const prefix = zipFilePath.substring(0, zipFilePath.indexOf(path.sep))
-    const workspaceFolder = workspacesByPrefix[prefix]
+    const workspaceFolder =
+        workspacesByPrefix[prefix] ??
+        (workspacesByPrefix[Object.values(workspacesByPrefix).find((val) => val.index === 0)?.name ?? ''] || undefined)
     if (workspaceFolder === undefined) {
         throw new ToolkitError(`Could not find workspace folder for prefix ${prefix}`)
     }