diff --git a/bun.lock b/bun.lock
index 29aa6863..37db52c4 100644
--- a/bun.lock
+++ b/bun.lock
@@ -119,6 +119,7 @@
         "react": "^19.2.3",
         "react-dom": "^19.2.3",
         "rehype-katex": "^7.0.1",
+        "remark-breaks": "^4.0.0",
         "remark-gfm": "^4.0.1",
         "remark-math": "^6.0.0",
         "shiki": "^3.20.0",
diff --git a/web/package.json b/web/package.json
index 735f38a0..f9cfc56e 100644
--- a/web/package.json
+++ b/web/package.json
@@ -38,6 +38,7 @@
         "react": "^19.2.3",
         "react-dom": "^19.2.3",
         "rehype-katex": "^7.0.1",
+        "remark-breaks": "^4.0.0",
         "remark-gfm": "^4.0.1",
         "remark-math": "^6.0.0",
         "shiki": "^3.20.0",
diff --git a/web/src/components/AssistantChat/messages/user-bubble.test.tsx b/web/src/components/AssistantChat/messages/user-bubble.test.tsx
index 586172be..150e4f9e 100644
--- a/web/src/components/AssistantChat/messages/user-bubble.test.tsx
+++ b/web/src/components/AssistantChat/messages/user-bubble.test.tsx
@@ -2,8 +2,14 @@ import { describe, expect, it, vi } from 'vitest'
 import { render, screen } from '@testing-library/react'
 
 vi.mock('@/components/LazyRainbowText', () => ({
-    LazyRainbowText: ({ text, inline }: { text: string; inline?: boolean }) => (
-        <span data-testid="lazy-rainbow-text" data-inline={inline ? 'true' : 'false'}>{text}</span>
+    LazyRainbowText: ({ text, inline, preserveSingleLineBreaks }: { text: string; inline?: boolean; preserveSingleLineBreaks?: boolean }) => (
+        <span
+            data-testid="lazy-rainbow-text"
+            data-inline={inline ? 'true' : 'false'}
+            data-preserve-single-line-breaks={preserveSingleLineBreaks ? 'true' : 'false'}
+        >
+            {text}
+        </span>
     )
 }))
 
@@ -42,6 +48,13 @@ describe('UserBubbleContent', () => {
         expect(screen.getByTestId('lazy-rainbow-text')).toHaveAttribute('data-inline', 'true')
     })
 
+    it('asks LazyRainbowText to preserve single newlines in sent prompt bodies', () => {
+        const { container } = render(<UserBubbleContent text={'Line one\nLine two\nLine three'} />)
+        const lazyText = container.querySelector('[data-testid="lazy-rainbow-text"]')
+
+        expect(lazyText).toHaveAttribute('data-preserve-single-line-breaks', 'true')
+    })
+
     it('preserves original directive casing in chip labels', () => {
         expect(formatDirectiveLabel('$DeEp-INTERVIEW')).toBe('DeEp INTERVIEW')
     })
diff --git a/web/src/components/AssistantChat/messages/user-bubble.tsx b/web/src/components/AssistantChat/messages/user-bubble.tsx
index e0995598..be9a12db 100644
--- a/web/src/components/AssistantChat/messages/user-bubble.tsx
+++ b/web/src/components/AssistantChat/messages/user-bubble.tsx
@@ -68,7 +68,7 @@ export function UserBubbleContent(props: { text: string }) {
             <div className="happy-chat-text min-w-0">
                 <div className="inline-flex min-w-0 flex-wrap items-center gap-x-1 gap-y-1.5 align-top">
                     {directives.map((directive) => <DirectiveChip key={directive} value={directive} />)}
-                    <LazyRainbowText text={body} inline />
+                    <LazyRainbowText text={body} inline preserveSingleLineBreaks />
                 </div>
             </div>
         )
@@ -81,7 +81,7 @@ export function UserBubbleContent(props: { text: string }) {
                     {directives.map((directive) => <DirectiveChip key={directive} value={directive} />)}
                 </div>
             ) : null}
-            {hasBody ? <LazyRainbowText text={body} /> : null}
+            {hasBody ? <LazyRainbowText text={body} preserveSingleLineBreaks /> : null}
         </div>
     )
 }
diff --git a/web/src/components/LazyRainbowText.tsx b/web/src/components/LazyRainbowText.tsx
index b9d5d704..120f1915 100644
--- a/web/src/components/LazyRainbowText.tsx
+++ b/web/src/components/LazyRainbowText.tsx
@@ -102,7 +102,7 @@ function processChildrenForRainbow(children: React.ReactNode): React.ReactNode {
     })
 }
 
-export function LazyRainbowText(props: { text: string; inline?: boolean }) {
+export function LazyRainbowText(props: { text: string; inline?: boolean; preserveSingleLineBreaks?: boolean }) {
     const text = props.text
     const ref = useRef<HTMLElement>(null)
     const [hasBeenVisible, setHasBeenVisible] = useState(false)
@@ -148,6 +148,7 @@ export function LazyRainbowText(props: { text: string; inline?: boolean }) {
         <MarkdownRenderer
             content={text}
             className={props.inline ? 'inline' : undefined}
+            preserveSingleLineBreaks={props.preserveSingleLineBreaks}
             components={
                 hasSpecialWord && hasBeenVisible
                     ? rainbowComponents
diff --git a/web/src/components/MarkdownRenderer.tsx b/web/src/components/MarkdownRenderer.tsx
index 280ff217..ecc71e73 100644
--- a/web/src/components/MarkdownRenderer.tsx
+++ b/web/src/components/MarkdownRenderer.tsx
@@ -3,6 +3,7 @@ import { MarkdownTextPrimitive } from '@assistant-ui/react-markdown'
 import { TextMessagePartProvider } from '@assistant-ui/react'
 import {
     MARKDOWN_PLUGINS,
+    MARKDOWN_PLUGINS_WITH_BREAKS,
     MARKDOWN_REHYPE_PLUGINS,
     MARKDOWN_COMPONENTS_BY_LANGUAGE,
     MARKDOWN_CLASSNAME,
@@ -16,6 +17,7 @@ interface MarkdownRendererProps {
     content: string
     components?: MarkdownTextPrimitiveProps['components']
     className?: string
+    preserveSingleLineBreaks?: boolean
 }
 
 function MarkdownContent(props: MarkdownRendererProps) {
@@ -27,7 +29,7 @@ function MarkdownContent(props: MarkdownRendererProps) {
         <UriConfirmProvider>
             <TextMessagePartProvider text={props.content}>
                 <MarkdownTextPrimitive
-                    remarkPlugins={MARKDOWN_PLUGINS}
+                    remarkPlugins={props.preserveSingleLineBreaks ? MARKDOWN_PLUGINS_WITH_BREAKS : MARKDOWN_PLUGINS}
                     rehypePlugins={MARKDOWN_REHYPE_PLUGINS}
                     components={mergedComponents}
                     componentsByLanguage={MARKDOWN_COMPONENTS_BY_LANGUAGE}
diff --git a/web/src/components/assistant-ui/markdown-text.test.ts b/web/src/components/assistant-ui/markdown-text.test.ts
index 43745f3d..9a7b2a32 100644
--- a/web/src/components/assistant-ui/markdown-text.test.ts
+++ b/web/src/components/assistant-ui/markdown-text.test.ts
@@ -1,7 +1,8 @@
 import { describe, expect, it } from 'vitest'
+import remarkBreaks from 'remark-breaks'
 import remarkNonHttpsAutolink from '@/lib/remark-non-https-autolink'
 import remarkStripCjkAutolink from '@/lib/remark-strip-cjk-autolink'
-import { MARKDOWN_PLUGINS } from '@/components/assistant-ui/markdown-text'
+import { MARKDOWN_PLUGINS, MARKDOWN_PLUGINS_WITH_BREAKS } from '@/components/assistant-ui/markdown-text'
 
 describe('MARKDOWN_PLUGINS integration', () => {
     it('includes remarkNonHttpsAutolink', () => {
@@ -14,4 +15,9 @@ describe('MARKDOWN_PLUGINS integration', () => {
         expect(idxAutolink).toBeGreaterThan(0) // not first (remarkGfm is first)
         expect(idxAutolink).toBeLessThan(idxCjk) // autolink before CJK strip
     })
+
+    it('keeps hard-break parsing scoped to opt-in user prompt rendering', () => {
+        expect(MARKDOWN_PLUGINS).not.toContain(remarkBreaks)
+        expect(MARKDOWN_PLUGINS_WITH_BREAKS).toContain(remarkBreaks)
+    })
 })
diff --git a/web/src/components/assistant-ui/markdown-text.tsx b/web/src/components/assistant-ui/markdown-text.tsx
index 925686cb..b07d6cc7 100644
--- a/web/src/components/assistant-ui/markdown-text.tsx
+++ b/web/src/components/assistant-ui/markdown-text.tsx
@@ -9,6 +9,7 @@ import {
     type CodeHeaderProps,
 } from '@assistant-ui/react-markdown'
 import remarkGfm from 'remark-gfm'
+import remarkBreaks from 'remark-breaks'
 import remarkMath from 'remark-math'
 import rehypeKatex from 'rehype-katex'
 import remarkDisableIndentedCode from '@/lib/remark-disable-indented-code'
@@ -33,8 +34,7 @@ import type { MarkdownTextPrimitiveProps } from '@assistant-ui/react-markdown'
 // from them. Both must come before remarkMath (to avoid treating TeX as URI).
 // remarkFilePathLinks runs last to convert file paths → links after all other
 // transforms have settled.
-export const MARKDOWN_PLUGINS = [
-    remarkGfm,
+const MARKDOWN_PLUGIN_TAIL = [
     remarkNonHttpsAutolink,
     remarkStripCjkAutolink,
     remarkMath,
@@ -42,6 +42,19 @@ export const MARKDOWN_PLUGINS = [
     remarkFilePathLinks,        // upstream — file path → link conversion, runs last
 ] satisfies NonNullable<MarkdownTextPrimitiveProps['remarkPlugins']>
 
+export const MARKDOWN_PLUGINS = [
+    remarkGfm,
+    ...MARKDOWN_PLUGIN_TAIL,
+] satisfies NonNullable<MarkdownTextPrimitiveProps['remarkPlugins']>
+
+// User-authored prompts should preserve Shift+Enter/newline intent without
+// changing assistant/tool markdown behavior globally.
+export const MARKDOWN_PLUGINS_WITH_BREAKS = [
+    remarkGfm,
+    remarkBreaks,
+    ...MARKDOWN_PLUGIN_TAIL,
+] satisfies NonNullable<MarkdownTextPrimitiveProps['remarkPlugins']>
+
 export const MARKDOWN_REHYPE_PLUGINS = [rehypeKatex] satisfies NonNullable<MarkdownTextPrimitiveProps['rehypePlugins']>
 export const MARKDOWN_CLASSNAME = 'aui-md happy-chat-text min-w-0 max-w-full break-words text-[var(--app-fg)]'
 export const MARKDOWN_COMPONENTS_BY_LANGUAGE = {