diff --git a/frontend/src/lib/components/Editor.svelte b/frontend/src/lib/components/Editor.svelte
index 8563190a89..67dff11d07 100644
--- a/frontend/src/lib/components/Editor.svelte
+++ b/frontend/src/lib/components/Editor.svelte
@@ -41,7 +41,6 @@
 
 	import { editorConfig, registerWebviewPaste, updateOptions } from '$lib/editorUtils'
 	import { editorFontSize } from '$lib/editorFontSize.svelte'
-	import { createHash as randomHash } from '$lib/editorLangUtils'
 	import { workspaceStore } from '$lib/stores'
 	import DdlMigrationGuard from './DdlMigrationGuard.svelte'
 	import {
@@ -109,7 +108,8 @@
 	import type { ScriptLintResult } from './copilot/chat/shared'
 	import FakeMonacoPlaceHolder from './FakeMonacoPlaceHolder.svelte'
 	import { editorPositionMap } from '$lib/utils'
-	import { extToLang, langToExt } from '$lib/editorLangUtils'
+	import { extToLang } from '$lib/editorLangUtils'
+	import { computeModelPath, computeModelUri } from './lint/monacoUri'
 	import { aiChatManager } from './copilot/chat/AIChatManager.svelte'
 	import type { Selection } from 'monaco-editor'
 	import { canHavePreprocessor, getPreprocessorModuleCode } from '$lib/script_helpers'
@@ -252,7 +252,12 @@
 		cmdEnterAction?.()
 	}
 
-	let filePath = $state(computePath(untrack(() => path)))
+	let filePath = $state(
+		computeModelPath(
+			untrack(() => path),
+			untrack(() => scriptLang)
+		)
+	)
 
 	let initialPath: string | undefined = $state(untrack(() => path))
 
@@ -269,41 +274,14 @@
 	let dbSchema: DBSchema | undefined = $state(undefined)
 
 	let destroyed = false
-	const uri = computeUri(
+	const uri = computeModelUri(
 		untrack(() => filePath),
-		untrack(() => scriptLang)
+		untrack(() => scriptLang),
+		untrack(() => lang)
 	)
 
 	console.log('uri', uri)
 
-	function computeUri(filePath: string, scriptLang: string | undefined) {
-		let file
-		if (filePath.includes('.')) {
-			file = filePath
-		} else {
-			file = `${filePath}.${scriptLang == 'tsx' ? 'tsx' : langToExt(lang)}`
-		}
-		if (file.startsWith('/')) {
-			file = file.slice(1)
-		}
-		return !['deno', 'go', 'python3'].includes(scriptLang ?? '')
-			? `file:///${file}`
-			: `file:///tmp/monaco/${file}`
-	}
-
-	function computePath(path: string | undefined): string {
-		if (
-			['deno', 'go', 'python3'].includes(scriptLang ?? '') ||
-			path == '' ||
-			path == undefined //||path.startsWith('/')
-		) {
-			return randomHash()
-		} else {
-			// console.log('path', path)
-			return path as string
-		}
-	}
-
 	export function switchToFile(path: string, value: string, lang: string) {
 		if (editor) {
 			const uri = mUri.parse(path)
@@ -2035,7 +2013,7 @@
 	})
 
 	$effect(() => {
-		filePath = computePath(path)
+		filePath = computeModelPath(path, scriptLang)
 	})
 	$effect(() => {
 		path != initialPath &&
diff --git a/frontend/src/lib/components/lint/monacoUri.test.ts b/frontend/src/lib/components/lint/monacoUri.test.ts
new file mode 100644
index 0000000000..87390b65c2
--- /dev/null
+++ b/frontend/src/lib/components/lint/monacoUri.test.ts
@@ -0,0 +1,43 @@
+import { describe, it, expect } from 'vitest'
+import { scriptLangToEditorLang } from '$lib/scripts'
+import { computeModelPath, computeModelUri } from './monacoUri'
+
+// Mirrors what Editor.svelte does: path -> filePath -> uri.
+function uriFor(path: string | undefined, scriptLang: string) {
+	const filePath = computeModelPath(path, scriptLang)
+	return computeModelUri(filePath, scriptLang, scriptLangToEditorLang(scriptLang as any))
+}
+
+describe('computeModelUri', () => {
+	it.each([
+		['u/admin/my_script', 'bun', 'file:///u/admin/my_script.ts'],
+		['u/admin/my_script', 'bunnative', 'file:///u/admin/my_script.ts'],
+		['u/admin/my_script', 'nativets', 'file:///u/admin/my_script.ts'],
+		['u/admin/component', 'tsx', 'file:///u/admin/component.tsx'],
+		['u/admin/component', 'jsx', 'file:///u/admin/component.js'],
+		['u/admin/script', 'javascript', 'file:///u/admin/script.js'],
+		// flow module and raw-app runnable derive their path as <item path>/<id>
+		['f/flows/myflow/a', 'bun', 'file:///f/flows/myflow/a.ts'],
+		['u/admin/myapp/backend_1', 'bun', 'file:///u/admin/myapp/backend_1.ts'],
+		['/u/admin/leading_slash', 'bun', 'file:///u/admin/leading_slash.ts'],
+		// a path that already carries an extension keeps it verbatim
+		['u/admin/lib.ts', 'bun', 'file:///u/admin/lib.ts']
+	])('%s (%s) -> %s', (path, scriptLang, expected) => {
+		expect(uriFor(path, scriptLang)).toBe(expected)
+	})
+
+	it.each(['deno', 'go', 'python3'])(
+		'randomizes the path and namespaces %s under /tmp/monaco',
+		(scriptLang) => {
+			const uri = uriFor('u/admin/my_script', scriptLang)
+			expect(uri.startsWith('file:///tmp/monaco/')).toBe(true)
+			expect(uri).not.toContain('my_script')
+			expect(uri).not.toBe(uriFor('u/admin/my_script', scriptLang))
+		}
+	)
+
+	it('falls back to a random path when none is given', () => {
+		expect(computeModelPath(undefined, 'bun')).not.toBe('')
+		expect(computeModelPath('', 'bun')).not.toBe('')
+	})
+})
diff --git a/frontend/src/lib/components/lint/monacoUri.ts b/frontend/src/lib/components/lint/monacoUri.ts
new file mode 100644
index 0000000000..5cdadb7562
--- /dev/null
+++ b/frontend/src/lib/components/lint/monacoUri.ts
@@ -0,0 +1,34 @@
+import { createHash as randomHash, langToExt } from '$lib/editorLangUtils'
+
+// Canonical Monaco model path/URI for a piece of Windmill code. Diagnostics are a
+// property of the model at a given URI, so any code that lints headlessly must
+// derive the URI from here — a URI that differs from the editor's yields a second,
+// independently-validated model and diverging markers.
+
+const RANDOMIZED_PATH_LANGS = ['deno', 'go', 'python3']
+
+export function computeModelPath(path: string | undefined, scriptLang: string | undefined): string {
+	if (RANDOMIZED_PATH_LANGS.includes(scriptLang ?? '') || path == '' || path == undefined) {
+		return randomHash()
+	}
+	return path
+}
+
+export function computeModelUri(
+	filePath: string,
+	scriptLang: string | undefined,
+	editorLang: string
+): string {
+	let file: string
+	if (filePath.includes('.')) {
+		file = filePath
+	} else {
+		file = `${filePath}.${scriptLang == 'tsx' ? 'tsx' : langToExt(editorLang)}`
+	}
+	if (file.startsWith('/')) {
+		file = file.slice(1)
+	}
+	return !RANDOMIZED_PATH_LANGS.includes(scriptLang ?? '')
+		? `file:///${file}`
+		: `file:///tmp/monaco/${file}`
+}