diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb205f46..16cf3df4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,16 @@
 
 ## [Unreleased]
 
+### Phase 6 — Study Buddy wired into the reader (2026-06-15)
+
+Phase 6 **AI-038, slice b** — the panel is now reachable: select a passage in the reader → "Help me understand this" → the agent investigates live.
+
+- **`SelectionToolbar`** gains a **"Help me understand this"** action (sparkles icon) next to Explain, shown only when `onStudyBuddy` is wired (catalog editions).
+- **`ReaderHighlights`** passes the whole selected passage up via a new `onStudyBuddy(passage)` prop and clears the selection.
+- **`ReaderPage`** holds the passage state and renders `StudyBuddyPanel` (catalog editions only, like Ask), threading the **current chapter number** so the agent's chapter tools have context. Opening it for a new passage re-runs.
+- i18n: `reader.selectionToolbar.studyBuddy`.
+- Verified: `tsc` + `pnpm build` clean; full web suite green (517); no e2e clicks the selection toolbar positionally (no index drift). The live agent run is exercised on prod (key + corpus).
+
 ### Phase 6 — Study Buddy web panel (2026-06-15)
 
 Phase 6 **AI-038, slice a** — the web UI for the agent: an `api` client, a streaming hook, and the panel. Wiring it into the reader's selection toolbar is slice b.
diff --git a/apps/web/src/components/reader/ReaderHighlights.tsx b/apps/web/src/components/reader/ReaderHighlights.tsx
index 041cdef6..ac835404 100644
--- a/apps/web/src/components/reader/ReaderHighlights.tsx
+++ b/apps/web/src/components/reader/ReaderHighlights.tsx
@@ -37,6 +37,8 @@ interface ReaderHighlightsProps {
   ttsSpeed?: number
   scrollToHighlightId?: string | null
   showInlineTranslations?: boolean
+  /** Open the Study Buddy panel for a highlighted passage (AI-038b). Catalog editions only. */
+  onStudyBuddy?: (passage: string) => void
   children: React.ReactNode
 }
 
@@ -67,6 +69,7 @@ export function ReaderHighlights({
   ttsSpeed = 1.0,
   scrollToHighlightId,
   showInlineTranslations = false,
+  onStudyBuddy,
   children,
 }: ReaderHighlightsProps) {
   const { nativeLanguage, setNativeLanguage, hasConfirmedLanguage } = useNativeLanguage()
@@ -401,6 +404,14 @@ export function ReaderHighlights({
     explainPopup.openFromSelection(selection.text, selection.range, selection.rect)
   }, [explainPopup, selection.text, selection.range, selection.rect])
 
+  // --- Study Buddy: hand the whole selected passage up to the reader's panel ---
+  const handleStudyBuddy = useCallback(() => {
+    const passage = selection.text?.trim()
+    if (!passage || !onStudyBuddy) return
+    onStudyBuddy(passage)
+    clearSelection()
+  }, [selection.text, onStudyBuddy, clearSelection])
+
   // --- Selection toolbar ---
   const handleHighlight = useCallback(
     async (color: HighlightColor) => {
@@ -462,6 +473,7 @@ export function ReaderHighlights({
           onHighlight={handleHighlight}
           onTranslate={handleTranslate}
           onExplain={handleExplain}
+          onStudyBuddy={onStudyBuddy ? handleStudyBuddy : undefined}
           onSpeak={() => handleSpeak(selection.text)}
           onCopy={handleCopy}
         />
diff --git a/apps/web/src/components/reader/SelectionToolbar.tsx b/apps/web/src/components/reader/SelectionToolbar.tsx
index 60bd1b28..49d6a66a 100644
--- a/apps/web/src/components/reader/SelectionToolbar.tsx
+++ b/apps/web/src/components/reader/SelectionToolbar.tsx
@@ -16,6 +16,7 @@ interface SelectionToolbarProps {
   onHighlight: (color: HighlightColor) => void
   onTranslate?: () => void
   onExplain?: () => void
+  onStudyBuddy?: () => void
   onSpeak?: () => void
   onCopy?: () => void
 }
@@ -27,6 +28,7 @@ export function SelectionToolbar({
   onHighlight,
   onTranslate,
   onExplain,
+  onStudyBuddy,
   onSpeak,
   onCopy,
 }: SelectionToolbarProps) {
@@ -130,6 +132,18 @@ export function SelectionToolbar({
           <ExplainIcon />
         </button>
       )}
+      {onStudyBuddy && (
+        <button
+          className="selection-toolbar__action"
+          onMouseDown={(e) => e.preventDefault()}
+          onTouchStart={(e) => e.preventDefault()}
+          onClick={onStudyBuddy}
+          title={t('reader.selectionToolbar.studyBuddy')}
+          aria-label={t('reader.selectionToolbar.studyBuddy')}
+        >
+          <StudyBuddyIcon />
+        </button>
+      )}
       {onSpeak && text.trim().length <= 500 && (
         <button
           className="selection-toolbar__action"
@@ -188,6 +202,16 @@ function ExplainIcon() {
   )
 }
 
+function StudyBuddyIcon() {
+  // Sparkles — "help me understand" / agent assist.
+  return (
+    <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+      <path d="M12 3l1.9 4.6L18.5 9.5 13.9 11.4 12 16l-1.9-4.6L5.5 9.5l4.6-1.9L12 3z" />
+      <path d="M19 14l.7 1.7L21.5 16.5l-1.8.8L19 19l-.7-1.7L16.5 16.5l1.8-.8L19 14z" />
+    </svg>
+  )
+}
+
 function SpeakIcon() {
   return (
     <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
diff --git a/apps/web/src/locales/en.json b/apps/web/src/locales/en.json
index 91f972e8..d20dcb22 100644
--- a/apps/web/src/locales/en.json
+++ b/apps/web/src/locales/en.json
@@ -233,6 +233,7 @@
       "highlightBlue": "Highlight blue",
       "translate": "Translate selected text",
       "explain": "Explain in context",
+      "studyBuddy": "Help me understand this",
       "listen": "Listen to pronunciation",
       "copy": "Copy selected text"
     },
diff --git a/apps/web/src/pages/ReaderPage.tsx b/apps/web/src/pages/ReaderPage.tsx
index 722f35bb..c0fac5f3 100644
--- a/apps/web/src/pages/ReaderPage.tsx
+++ b/apps/web/src/pages/ReaderPage.tsx
@@ -20,6 +20,7 @@ import { ReaderNav } from '../components/reader/ReaderNav'
 import { ReaderFooterNav } from '../components/reader/ReaderFooterNav'
 import { ReaderSettingsDrawer } from '../components/reader/ReaderSettingsDrawer'
 import { AskPanel } from '../components/reader/AskPanel'
+import { StudyBuddyPanel } from '../components/reader/StudyBuddyPanel'
 import type { AskCitation } from '../api/ask'
 import { scrollToCitation } from '../lib/citationScroll'
 import { ReaderTocDrawer } from '../components/reader/ReaderTocDrawer'
@@ -69,6 +70,7 @@ export function ReaderPage({ mode = 'public' }: ReaderPageProps) {
   const [tocOpen, setTocOpen] = useState(false)
   const [settingsOpen, setSettingsOpen] = useState(false)
   const [askOpen, setAskOpen] = useState(false)
+  const [studyBuddyPassage, setStudyBuddyPassage] = useState<string | null>(null)
   const [searchOpen, setSearchOpen] = useState(false)
 
   // Highlight ID from URL — scroll to this highlight after chapter loads
@@ -514,6 +516,7 @@ export function ReaderPage({ mode = 'public' }: ReaderPageProps) {
           ttsSpeed={settings.ttsSpeed}
           showInlineTranslations={settings.showInlineTranslations}
           scrollToHighlightId={scrollToHighlightId}
+          onStudyBuddy={askEditionId ? setStudyBuddyPassage : undefined}
         >
           <div ref={scrollContainerRef}>
             <ReaderSection
@@ -590,6 +593,18 @@ export function ReaderPage({ mode = 'public' }: ReaderPageProps) {
         />
       )}
 
+      {askEditionId && studyBuddyPassage && (
+        <StudyBuddyPanel
+          open
+          editionId={askEditionId}
+          passage={studyBuddyPassage}
+          chapterNumber={activeChapter?.chapterNumber ?? null}
+          isAuthenticated={isAuthenticated}
+          onSignIn={openAuthModal}
+          onClose={() => setStudyBuddyPassage(null)}
+        />
+      )}
+
       <ReaderSearchDrawer
         open={searchOpen}
         query={searchQuery}