fix(types): flip residual T | null declarations to T | undefined

Cleanup of null→undefined autofix fallout (task #52 / related). The
autofix changed assignment sites (`return null` → `return undefined`,
`= null` → `= undefined`) but didn't update the type unions, leaving 17
TS2322 errors where `undefined` was assigned to a `T | null` slot.

Fixes:
* src/auth.ts: getOrganizations() return type → Promise<X | undefined>
* src/data/editor-config.ts: onDidChangeConfigurationDisposable union
* src/data/go/mod-parser.ts: parseGoMod() return type
* src/data/go/wasm-executor.ts: _pendingEvent union; fsync callback
  uses the (null, undefined) Node-style "no error, void result"
  pattern (the null IS the API contract here — inline rule disable).
* src/ui/decorations.ts: packageData union
* src/ui/externals/parse-externals.ts: parseExternals() return type
* src/ui/purl-alerts-and-scores/manager.ts: pkgData/error unions

No behavior change — only type-side adjustments to match the assignment
shape the autofix already chose. tsgo check now passes (0 errors).

Author: jdalton

src/auth.ts

@@ -320,7 +320,7 @@ export function getAuthHeader(apiKey: string) {
 
 export async function getOrganizations(
   apiKey: string,
-): Promise<OrganizationsRecord | null> {
+): Promise<OrganizationsRecord | undefined> {
   const authHeader = getAuthHeader(apiKey)
   const orgReq = https.get('https://api.socket.dev/v0/organizations', {
     method: 'GET',

src/data/editor-config.ts

@@ -44,7 +44,8 @@ export function activate(context: vscode.ExtensionContext) {
       })
     context.subscriptions.push(onDidChangeConfigurationDisposable)
   }
-  let onDidChangeConfigurationDisposable: vscode.Disposable | null = null
+  let onDidChangeConfigurationDisposable: vscode.Disposable | undefined =
+    undefined
   function getValuesForListener(listener: Listener) {
     return getConfigValues(listener.sections)
   }

src/data/go/mod-parser.ts

@@ -122,7 +122,7 @@ interface GoParseError {
 const isParseError = (data: unknown): data is GoParseError =>
   typeof (data as GoParseError).Error === 'string'
 
-export async function parseGoMod(src: string): Promise<GoModFile | null> {
+export async function parseGoMod(src: string): Promise<GoModFile | undefined> {
   if (!goWASM) {
     // WebAssembly.instantiate has two overloads. TypeScript can't tell
     // a Uint8Array from a `WebAssembly.Module` (both fit the second

src/data/go/wasm-executor.ts

@@ -52,7 +52,7 @@ class GoExecutor<T extends Record<string, unknown> = Record<string, unknown>> {
   private exitCode: number | undefined
   private instance: GoInstance | undefined
   private mem: DataView | undefined
-  _pendingEvent: GoPendingEvent | null
+  _pendingEvent: GoPendingEvent | undefined
 
   constructor() {
     this._pendingEvent = undefined
@@ -102,7 +102,8 @@ class GoExecutor<T extends Record<string, unknown> = Record<string, unknown>> {
           callback(enosys())
         },
         fsync(_fd: number, callback: GoCallback<void>) {
-          callback(undefined)
+          // oxlint-disable-next-line socket/prefer-undefined-over-null -- GoCallback uses Node-style `(err, result)` signature; null signals "no error".
+          callback(null, undefined)
         },
         ftruncate(_fd: number, _length: number, callback: GoCallback) {
           callback(enosys())

src/ui/decorations.ts

@@ -214,7 +214,7 @@ class DecorationManagerForPURL {
     this.documentManagersForDocumentsWithThisPURL.delete(manager)
   }
   purl: SimPURL
-  packageData: PURLPackageData | null = undefined
+  packageData: PURLPackageData | undefined = undefined
   decorationType: vscode.TextEditorDecorationType
   decorationTypes: DecorationTypes
   isBuiltin: boolean

src/ui/externals/parse-externals.ts

@@ -71,7 +71,9 @@ export function hydrateJSONRefs(src: string): ExternalRef[] {
 
 export async function parseExternals(
   doc: vscode.TextDocument,
-): Promise<Map<SimPURL, { builtin: boolean; ranges: vscode.Range[] }> | null> {
+): Promise<
+  Map<SimPURL, { builtin: boolean; ranges: vscode.Range[] }> | undefined
+> {
   const languageId = doc.languageId
   const src = doc.getText()
   const results = new ExternalPurlRangeManager()

src/ui/purl-alerts-and-scores/manager.ts

@@ -43,9 +43,9 @@ export type PackageScoreAndAlerts = {
 export class PURLPackageData {
   purl: SimPURL
   watchers: Set<(pkgData: PURLPackageData) => void> = new Set()
-  pkgData!: PackageScoreAndAlerts | null
+  pkgData: PackageScoreAndAlerts | undefined = undefined
   mtime: number = -Infinity
-  error: string | null = undefined
+  error: string | undefined = undefined
   setError(reason: string) {
     this.error = reason
     if (!this.pkgData) {