Suggestions: right-margin comment rail + Mandarin explanations

Surface every outstanding suggestion as a card in the right-hand
whitespace, vertically aligned to the text it flags — so the writer sees
the whole queue at once instead of hovering each highlight. Cards stack
with collision avoidance, link both ways with their highlight (hover/click
↔ soft text wash, driven through the decoration plugin so it survives
edit repaints), and carry the same Accept / Dismiss / Ask Petal actions.
The rail is a progressive enhancement: it mounts only when there's room
beside the editor, otherwise the existing inline hover card is unchanged.
Stacked cards that reach the bottom-right corner tuck behind the
companion mascot (z-order).

When a card is expanded, the Ask Petal bubble now opens with the
Simplified-Chinese translation of the explanation (the English stays in
the card body) instead of repeating the same text twice — a new
POST /api/suggestions/{id}/translate one-shot LLM endpoint, loaded
lazily on open with an English fallback.

Verified live against the local LLM via the uitest harness: rail
stacking, hover↔text wash, expand/Ask Petal, accept-from-rail, narrow
fallback, and the Mandarin bubble.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

internal/llm/prompts.go

@@ -165,3 +165,24 @@ func RewriteMessages(text, style string) []Message {
 		{Role: "user", Content: text},
 	}
 }
+
+// translateSystemPrompt drives the explanation translator: it renders a
+// suggestion's English explanation into Simplified Chinese so an ESL reader sees
+// the "why" in her first language. Strict about returning ONLY the translation
+// (no quotes, no pinyin, no English echo) so it can drop straight into the chat
+// bubble. Kept warm and plain — these are short, friendly one-liners.
+const translateSystemPrompt = `You are Petal, a warm writing assistant. Translate the English text the user ` +
+	`sends into natural, friendly Simplified Chinese (Mandarin). It is a short explanation of a writing ` +
+	`suggestion, written for a native Chinese speaker learning English.
+
+Respond with ONLY the Simplified Chinese translation. No quotation marks, no pinyin, no English, no preamble — ` +
+	`just the translated sentence.`
+
+// TranslateMessages builds the message array for translating one short English
+// explanation into Simplified Chinese.
+func TranslateMessages(text string) []Message {
+	return []Message{
+		{Role: "system", Content: translateSystemPrompt},
+		{Role: "user", Content: text},
+	}
+}

internal/llm/translate.go

@@ -0,0 +1,23 @@
+package llm
+
+import (
+	"context"
+)
+
+// RunTranslate renders a short English explanation into Simplified Chinese. It
+// is a one-shot Complete (the result seeds the Ask Petal bubble), kept at a low
+// temperature so the translation is faithful rather than creative. Output is
+// trimmed of any stray surrounding quotes the model may add.
+func RunTranslate(ctx context.Context, client LLMClient, text string) (string, error) {
+	out, err := client.Complete(ctx, CompletionRequest{
+		Messages:          TranslateMessages(text),
+		MaxTokens:         512,
+		Temperature:       0.2,
+		TopP:              0.9,
+		RepetitionPenalty: 1.1,
+	})
+	if err != nil {
+		return "", err
+	}
+	return cleanRewrite(out), nil
+}

internal/suggestions/handlers.go

@@ -55,6 +55,7 @@ func (h *Handler) Routes() chi.Router {
 	r.Post("/{id}/accept", h.accept)
 	r.Post("/{id}/dismiss", h.dismiss)
 	r.Post("/{id}/chat", h.chat)
+	r.Post("/{id}/translate", h.translate)
 	return r
 }
 

internal/suggestions/translate.go

@@ -0,0 +1,57 @@
+package suggestions
+
+import (
+	"database/sql"
+	"errors"
+	"net/http"
+	"strings"
+
+	"github.com/go-chi/chi/v5"
+
+	"gitea.parodia.dev/drwily/petal/internal/db"
+	"gitea.parodia.dev/drwily/petal/internal/llm"
+)
+
+type translateResponse struct {
+	Translation string `json:"translation"`
+}
+
+// translate renders a suggestion's English explanation into Simplified Chinese
+// for the Ask Petal bubble, so the ESL reader sees the "why" in her first
+// language instead of a second copy of the same English text. The explanation is
+// loaded server-side from the suggestion id (scoped to the local user) and never
+// trusted from the client, mirroring chat (spec Note #10).
+func (h *Handler) translate(w http.ResponseWriter, r *http.Request) {
+	sugID := chi.URLParam(r, "id")
+
+	var explanation string
+	err := h.DB.QueryRow(
+		`SELECT s.explanation
+		   FROM suggestions s
+		   JOIN documents d ON d.id = s.doc_id
+		  WHERE s.id = ? AND d.user_id = ?`,
+		sugID, db.LocalUserID,
+	).Scan(&explanation)
+	if errors.Is(err, sql.ErrNoRows) {
+		errorJSON(w, http.StatusNotFound, "suggestion not found")
+		return
+	}
+	if err != nil {
+		serverError(w, err)
+		return
+	}
+
+	explanation = strings.TrimSpace(explanation)
+	if explanation == "" {
+		writeJSON(w, http.StatusOK, translateResponse{Translation: ""})
+		return
+	}
+
+	out, err := llm.RunTranslate(r.Context(), h.Client, explanation)
+	if err != nil {
+		errorJSON(w, http.StatusBadGateway, "translate failed: "+err.Error())
+		return
+	}
+
+	writeJSON(w, http.StatusOK, translateResponse{Translation: out})
+}

web/src/api/client.ts

@@ -147,6 +147,10 @@ export const api = {
     req<void>(`/suggestions/${id}/accept`, { method: 'POST' }),
   dismissSuggestion: (id: string) =>
     req<void>(`/suggestions/${id}/dismiss`, { method: 'POST' }),
+  // Simplified-Chinese rendering of a suggestion's explanation, for the Ask Petal
+  // opening bubble (the explanation itself stays English in the card body).
+  translateSuggestion: (id: string) =>
+    req<{ translation: string }>(`/suggestions/${id}/translate`, { method: 'POST' }),
 
   // Version history. listVersions returns metadata only (no bodies); getVersion
   // loads one full snapshot for preview; snapshotDoc takes an explicit restore

web/src/components/Editor/AskPetal.tsx

@@ -1,9 +1,11 @@
 import { useEffect, useRef, useState } from 'react'
-import { streamSuggestionChat, type ChatMessage } from '../../api/client'
+import { api, streamSuggestionChat, type ChatMessage } from '../../api/client'
 
 interface Props {
   suggestionId: string
-  // Pre-populates Petal's first bubble so the conversation opens with context.
+  // The English explanation (shown in the card body). Petal's opening bubble is
+  // its Simplified-Chinese translation, fetched on open — so the panel doesn't
+  // just repeat the same English text twice. Falls back to this on failure.
   explanation: string
 }
 
@@ -17,9 +19,10 @@ const CHAT_FONT = "'Nunito', 'PingFang SC', 'Microsoft YaHei', 'Noto Sans CJK SC
 // the card (unmounting) clears it. Each send streams Petal's reply token-by-
 // token into the latest assistant bubble.
 export function AskPetal({ suggestionId, explanation }: Props) {
-  const [messages, setMessages] = useState<ChatMessage[]>([
+  // Opening bubble starts empty (caret-only) and fills with the Mandarin
-    { role: 'assistant', content: explanation },
+  // translation once it lands; `seeding` drives that loading caret.
-  ])
+  const [messages, setMessages] = useState<ChatMessage[]>([{ role: 'assistant', content: '' }])
+  const [seeding, setSeeding] = useState(true)
   const [input, setInput] = useState('')
   const [streaming, setStreaming] = useState(false)
   const scrollRef = useRef<HTMLDivElement>(null)
@@ -36,6 +39,31 @@ export function AskPetal({ suggestionId, explanation }: Props) {
     inputRef.current?.focus()
   }, [])
 
+  // Fetch the Chinese translation of the explanation to seed the first bubble.
+  // Only replaces the seed bubble if the user hasn't started chatting yet (the
+  // conversation always opens with this one assistant turn). Falls back to the
+  // English explanation if the translation can't be fetched.
+  useEffect(() => {
+    let cancelled = false
+    api
+      .translateSuggestion(suggestionId)
+      .then((res) => {
+        if (cancelled) return
+        const text = res.translation.trim() || explanation
+        setMessages((prev) => (prev.length === 1 ? [{ role: 'assistant', content: text }] : prev))
+      })
+      .catch(() => {
+        if (cancelled) return
+        setMessages((prev) => (prev.length === 1 ? [{ role: 'assistant', content: explanation }] : prev))
+      })
+      .finally(() => {
+        if (!cancelled) setSeeding(false)
+      })
+    return () => {
+      cancelled = true
+    }
+  }, [suggestionId, explanation])
+
   async function send() {
     const text = input.trim()
     if (!text || streaming) return
@@ -86,7 +114,12 @@ export function AskPetal({ suggestionId, explanation }: Props) {
         style={{ maxHeight: 220 }}
       >
         {messages.map((m, i) => (
-          <Bubble key={i} role={m.role} content={m.content} streaming={streaming && i === messages.length - 1} />
+          <Bubble
+            key={i}
+            role={m.role}
+            content={m.content}
+            streaming={(streaming && i === messages.length - 1) || (seeding && i === 0)}
+          />
         ))}
       </div>
 

web/src/components/Editor/EditorCore.tsx

@@ -18,7 +18,8 @@ import type { EditorView } from '@tiptap/pm/view'
 import { useCallback, useEffect, useRef, useState } from 'react'
 import { Toolbar } from '../Toolbar/Toolbar'
 import { SuggestionCard } from './SuggestionCard'
-import { SuggestionHighlight, setSuggestions, findRange } from './SuggestionHighlight'
+import { SuggestionRail, type RailItem } from './SuggestionRail'
+import { SuggestionHighlight, setSuggestions, setActiveSuggestion, findRange } from './SuggestionHighlight'
 import { SpellCheck, setSpellChecker, wordAt } from './SpellCheck'
 import { MisspellCard } from './MisspellCard'
 import { WordCard } from './WordCard'
@@ -219,6 +220,18 @@ export function EditorCore({
   const rewriteReqRef = useRef(0)
   // The in-document Find & Replace bar (Ctrl/Cmd+F).
   const [findOpen, setFindOpen] = useState(false)
+  // The right-margin comment rail. `railItems` carries each anchored suggestion's
+  // vertical offset; `railEnabled` is true only when the viewport has room for the
+  // column beside the editor (otherwise we fall back to the inline hover cards).
+  // `railExpandedId` is the card showing its full explanation + Ask Petal, and
+  // `activeId` is the suggestion currently emphasized (hovered text or card).
+  const [railItems, setRailItems] = useState<RailItem[]>([])
+  const [railEnabled, setRailEnabled] = useState(false)
+  const [railExpandedId, setRailExpandedId] = useState<string | null>(null)
+  const [activeId, setActiveId] = useState<string | null>(null)
+  // A stable handle to the latest recompute so the editor's onUpdate (captured
+  // once at construction) can trigger a re-measure without stale closures.
+  const recomputeRailRef = useRef<() => void>(() => {})
 
   const editor = useEditor({
     extensions: [
@@ -282,6 +295,8 @@ export function EditorCore({
         content_text: editor.getText(),
         word_count: editor.storage.characterCount.words(),
       })
+      // Edits reflow the text, so the rail anchors need re-measuring.
+      recomputeRailRef.current()
     },
     onSelectionUpdate: ({ editor }) => {
       // A selection supersedes the hover gloss; an empty one clears the bubble.
@@ -333,8 +348,87 @@ export function EditorCore({
     setSuggestions(editor.state, editor.view.dispatch, suggestions)
     // Close the card if its suggestion is gone.
     setHover((h) => (h && suggestions.some((s) => s.id === h.suggestion.id) ? h : null))
+    // Drop any rail expand/emphasis that points at a now-removed suggestion.
+    setRailExpandedId((id) => (id && suggestions.some((s) => s.id === id) ? id : null))
+    setActiveId((id) => (id && suggestions.some((s) => s.id === id) ? id : null))
   }, [editor, suggestions])
 
+  // Re-measure the margin rail: whether there's room for the column beside the
+  // editor, and where each suggestion's highlight sits vertically. Anchors are
+  // taken from the live decoration DOM (keyed by data-suggestion-id) relative to
+  // the wrapper — stable under scroll since text and wrapper scroll together.
+  // Deferred a frame so decoration DOM and reflow have settled.
+  const recomputeRail = useCallback(() => {
+    requestAnimationFrame(() => {
+      const wrapper = wrapperRef.current
+      if (!wrapper) return
+      const wrapRect = wrapper.getBoundingClientRect()
+      // Need room for the 300px column + its 32px gutter (see .petal-rail), plus
+      // a little breathing space to the viewport edge.
+      setRailEnabled(window.innerWidth - wrapRect.right >= 348)
+      const seen = new Set<string>()
+      const items: RailItem[] = []
+      wrapper.querySelectorAll<HTMLElement>('.petal-suggestion[data-suggestion-id]').forEach((el) => {
+        const id = el.getAttribute('data-suggestion-id')
+        if (!id || seen.has(id)) return
+        const s = suggestions.find((x) => x.id === id)
+        if (!s) return
+        seen.add(id)
+        items.push({ suggestion: s, anchorTop: el.getBoundingClientRect().top - wrapRect.top })
+      })
+      setRailItems(items)
+    })
+  }, [suggestions])
+
+  useEffect(() => {
+    recomputeRailRef.current = recomputeRail
+  }, [recomputeRail])
+
+  // Re-anchor when the suggestion set changes (after the decorations repaint),
+  // and keep the rail in sync with viewport/editor width changes (room + reflow).
+  useEffect(() => {
+    recomputeRail()
+    const wrapper = wrapperRef.current
+    const ro = wrapper ? new ResizeObserver(() => recomputeRail()) : null
+    if (wrapper && ro) ro.observe(wrapper)
+    window.addEventListener('resize', recomputeRail)
+    return () => {
+      ro?.disconnect()
+      window.removeEventListener('resize', recomputeRail)
+    }
+  }, [recomputeRail])
+
+  // Emphasize the flagged text for the active suggestion, mirroring the rail
+  // card ↔ text link both ways. Driven through the decoration plugin (not an
+  // imperative DOM class) so it survives the repaints that fire on every edit.
+  useEffect(() => {
+    if (!editor) return
+    setActiveSuggestion(editor.state, editor.view.dispatch, railEnabled ? activeId : null)
+  }, [editor, activeId, railEnabled])
+
+  // Scroll a suggestion's highlight to the middle of the viewport (clicking its
+  // rail card jumps the editor to the flagged text).
+  const scrollToSuggestion = useCallback((id: string) => {
+    const el = wrapperRef.current?.querySelector(
+      `.petal-suggestion[data-suggestion-id="${CSS.escape(id)}"]`,
+    )
+    el?.scrollIntoView({ block: 'center', behavior: 'smooth' })
+  }, [])
+
+  // Clicking a rail card's body jumps to the text and toggles its detail panel.
+  const activateRailCard = useCallback(
+    (id: string) => {
+      setActiveId(id)
+      scrollToSuggestion(id)
+      setRailExpandedId((cur) => (cur === id ? null : id))
+    },
+    [scrollToSuggestion],
+  )
+
+  const toggleRailExpand = useCallback((id: string) => {
+    setRailExpandedId((cur) => (cur === id ? null : id))
+  }, [])
+
   const openCardFor = useCallback(
     (id: string, el: HTMLElement) => {
       const wrapper = wrapperRef.current
@@ -366,10 +460,17 @@ export function EditorCore({
       if (!target) return
       const id = target.getAttribute('data-suggestion-id')
       if (!id) return
+      // With the rail open the card already lives in the margin — hovering the
+      // text just emphasizes its card (and the highlight) rather than popping a
+      // second, redundant floating card.
+      if (railEnabled) {
+        setActiveId(id)
+        return
+      }
       clearTimeout(closeTimer.current)
       openCardFor(id, target)
     },
-    [openCardFor],
+    [openCardFor, railEnabled],
   )
 
   const scheduleClose = useCallback(() => {
@@ -389,35 +490,53 @@ export function EditorCore({
   // pointer can bridge the small gap from text to card.
   const handleMouseOut = useCallback(
     (e: React.MouseEvent) => {
-      if ((e.target as HTMLElement).closest('.petal-suggestion')) scheduleClose()
+      if (!(e.target as HTMLElement).closest('.petal-suggestion')) return
+      if (railEnabled) {
+        setActiveId(null)
+        return
+      }
+      scheduleClose()
     },
-    [scheduleClose],
+    [scheduleClose, railEnabled],
   )
 
   const keepOpen = useCallback(() => clearTimeout(closeTimer.current), [])
 
   // Accept applies the replacement to the document, plays a little confetti
-  // burst where the card sat, then notifies the parent.
+  // burst over the flagged text, then notifies the parent. The confetti is
+  // anchored to the highlight itself (captured before the replacement removes it),
+  // so it fires in the right spot whether the accept came from the hover card or
+  // the margin rail.
   const handleAccept = useCallback(
     (s: Suggestion) => {
+      const wrapper = wrapperRef.current
+      const el = wrapper?.querySelector(
+        `.petal-suggestion[data-suggestion-id="${CSS.escape(s.id)}"]`,
+      ) as HTMLElement | null
+      let burst: { top: number; left: number } | null = null
+      if (wrapper && el) {
+        const wrapRect = wrapper.getBoundingClientRect()
+        const elRect = el.getBoundingClientRect()
+        burst = { top: elRect.top - wrapRect.top, left: elRect.right - wrapRect.left }
+      }
       if (editor && s.replacement.trim() !== '') {
         const range = findRange(editor.state.doc, s.original)
         if (range) {
           editor.chain().focus().insertContentAt(range, s.replacement).run()
         }
       }
-      setHover((h) => {
+      // Fall back to the hover card's position if the highlight wasn't found.
-        if (h) {
+      if (!burst && hover) burst = { top: hover.top, left: hover.left + 16 }
-          setConfetti({ top: h.top, left: h.left + 16 })
+      if (burst) {
-          clearTimeout(confettiTimer.current)
+        setConfetti(burst)
-          confettiTimer.current = setTimeout(() => setConfetti(null), 720)
+        clearTimeout(confettiTimer.current)
-        }
+        confettiTimer.current = setTimeout(() => setConfetti(null), 720)
-        return h
+      }
-      })
       closeCard()
+      setRailExpandedId(null)
       onAccept(s)
     },
-    [editor, onAccept, closeCard],
+    [editor, onAccept, closeCard, hover],
   )
 
   const handleDismiss = useCallback(
@@ -439,7 +558,16 @@ export function EditorCore({
       const suggestionEl = (e.target as HTMLElement).closest('.petal-suggestion') as HTMLElement | null
       if (suggestionEl) {
         const id = suggestionEl.getAttribute('data-suggestion-id')
-        if (id) openCardFor(id, suggestionEl)
+        if (id) {
+          // With the rail open, a tap emphasizes and expands its margin card
+          // instead of opening a floating one.
+          if (railEnabled) {
+            setActiveId(id)
+            setRailExpandedId(id)
+          } else {
+            openCardFor(id, suggestionEl)
+          }
+        }
         return
       }
       if (!editor || !spellChecker) return
@@ -461,7 +589,7 @@ export function EditorCore({
       setWordInfo(null)
       setMisspell({ ...range, suggestions: spellChecker.suggest(range.word), top, left })
     },
-    [editor, spellChecker, closeCard, openCardFor],
+    [editor, spellChecker, closeCard, openCardFor, railEnabled],
   )
 
   const replaceMisspelling = useCallback(
@@ -854,7 +982,7 @@ export function EditorCore({
             onAdd={addMisspellingToDict}
           />
         )}
-        {hover && (
+        {hover && !railEnabled && (
           <SuggestionCard
             suggestion={hover.suggestion}
             style={{ top: hover.top, left: hover.left }}
@@ -865,6 +993,18 @@ export function EditorCore({
             onExpandChange={setPinned}
           />
         )}
+        {railEnabled && railItems.length > 0 && (
+          <SuggestionRail
+            items={railItems}
+            activeId={activeId}
+            expandedId={railExpandedId}
+            onAccept={handleAccept}
+            onDismiss={handleDismiss}
+            onHover={setActiveId}
+            onActivate={activateRailCard}
+            onToggleExpand={toggleRailExpand}
+          />
+        )}
       </div>
     </div>
   )

web/src/components/Editor/SuggestionCard.tsx

@@ -1,15 +1,7 @@
 import { useState } from 'react'
-import type { Suggestion, SuggestionType } from '../../api/client'
+import type { Suggestion } from '../../api/client'
 import { AskPetal } from './AskPetal'
-
+import { TYPE_META } from './suggestionMeta'
-// Per-type accent color + human label, mirroring the design tokens.
-const TYPE_META: Record<SuggestionType, { color: string; label: string }> = {
-  grammar: { color: 'var(--color-mint)', label: 'Grammar' },
-  phrasing: { color: 'var(--color-peach)', label: 'Phrasing' },
-  idiom: { color: 'var(--color-lavender)', label: 'Idiom' },
-  clarity: { color: 'var(--color-sky)', label: 'Clarity' },
-  voice: { color: 'var(--color-honey)', label: 'Voice' },
-}
 
 interface Props {
   suggestion: Suggestion

web/src/components/Editor/SuggestionHighlight.ts

@@ -16,9 +16,17 @@ export const suggestionPluginKey = new PluginKey<PluginState>('petalSuggestions'
 
 interface PluginState {
   suggestions: Suggestion[]
+  // The suggestion currently emphasized from its margin card / a hover, or null.
+  // Carried in plugin state (not an imperative DOM class) so it survives the
+  // decoration repaints that fire on every document change.
+  activeId: string | null
   decorations: DecorationSet
 }
 
+// Meta carried on a transaction to update the plugin: either a fresh suggestion
+// list or a change to which suggestion is emphasized.
+type SuggestionMeta = { suggestions: Suggestion[] } | { activeId: string | null }
+
 // mapOffset converts a character offset within a textblock's flattened text into
 // an absolute ProseMirror position, accounting for inline atoms (e.g. hard
 // breaks) that occupy a position but contribute no text.
@@ -130,14 +138,15 @@ export function findRange(doc: PMNode, search: string): { from: number; to: numb
   return result
 }
 
-function buildDecorations(doc: PMNode, suggestions: Suggestion[]): DecorationSet {
+function buildDecorations(doc: PMNode, suggestions: Suggestion[], activeId: string | null): DecorationSet {
   const decos: Decoration[] = []
   for (const s of suggestions) {
     const range = findRange(doc, s.original)
     if (!range) continue
+    const active = s.id === activeId ? ' petal-suggestion-active' : ''
     decos.push(
       Decoration.inline(range.from, range.to, {
-        class: `petal-suggestion petal-suggestion-${s.type}`,
+        class: `petal-suggestion petal-suggestion-${s.type}${active}`,
         'data-suggestion-id': s.id,
       }),
     )
@@ -148,10 +157,22 @@ function buildDecorations(doc: PMNode, suggestions: Suggestion[]): DecorationSet
 // setSuggestions pushes a new suggestion list into the plugin. Decorations are
 // rebuilt against the current document immediately.
 export function setSuggestions(state: EditorState, dispatch: (tr: Transaction) => void, suggestions: Suggestion[]) {
-  const tr = state.tr.setMeta(suggestionPluginKey, suggestions)
+  const tr = state.tr.setMeta(suggestionPluginKey, { suggestions } satisfies SuggestionMeta)
   dispatch(tr)
 }
 
+// setActiveSuggestion marks one suggestion (or none) as emphasized, rebuilding
+// the decorations so the flagged text gets the active wash. Driven by the margin
+// rail's hover/selection so the card↔text link reads both ways.
+export function setActiveSuggestion(
+  state: EditorState,
+  dispatch: (tr: Transaction) => void,
+  activeId: string | null,
+) {
+  if (suggestionPluginKey.getState(state)?.activeId === activeId) return
+  dispatch(state.tr.setMeta(suggestionPluginKey, { activeId } satisfies SuggestionMeta))
+}
+
 export const SuggestionHighlight = Extension.create({
   name: 'suggestionHighlight',
 
@@ -160,17 +181,29 @@ export const SuggestionHighlight = Extension.create({
       new Plugin<PluginState>({
         key: suggestionPluginKey,
         state: {
-          init: () => ({ suggestions: [], decorations: DecorationSet.empty }),
+          init: () => ({ suggestions: [], activeId: null, decorations: DecorationSet.empty }),
           apply(tr, value, _oldState, newState) {
-            const meta = tr.getMeta(suggestionPluginKey) as Suggestion[] | undefined
+            const meta = tr.getMeta(suggestionPluginKey) as SuggestionMeta | undefined
-            if (meta) {
+            if (meta && 'suggestions' in meta) {
-              return { suggestions: meta, decorations: buildDecorations(newState.doc, meta) }
+              return {
+                suggestions: meta.suggestions,
+                activeId: value.activeId,
+                decorations: buildDecorations(newState.doc, meta.suggestions, value.activeId),
+              }
+            }
+            if (meta && 'activeId' in meta) {
+              return {
+                suggestions: value.suggestions,
+                activeId: meta.activeId,
+                decorations: buildDecorations(newState.doc, value.suggestions, meta.activeId),
+              }
             }
             // On any document change, re-anchor by string against the new doc.
             if (tr.docChanged) {
               return {
                 suggestions: value.suggestions,
-                decorations: buildDecorations(newState.doc, value.suggestions),
+                activeId: value.activeId,
+                decorations: buildDecorations(newState.doc, value.suggestions, value.activeId),
               }
             }
             return value

web/src/components/Editor/SuggestionRail.tsx

@@ -0,0 +1,211 @@
+import { forwardRef, useLayoutEffect, useRef, useState } from 'react'
+import type { Suggestion } from '../../api/client'
+import { AskPetal } from './AskPetal'
+import { TYPE_META } from './suggestionMeta'
+
+// Vertical breathing room kept between stacked cards when their natural anchors
+// would otherwise collide.
+const CARD_GAP = 12
+
+export interface RailItem {
+  suggestion: Suggestion
+  // Vertical offset (px) of the suggestion's highlight, relative to the editor
+  // wrapper — the position the card wants to sit beside.
+  anchorTop: number
+}
+
+interface Props {
+  items: RailItem[]
+  // The suggestion currently emphasized (its highlight hovered, or this card
+  // hovered) — gets a lifted, ring-accented treatment so the text↔card link reads.
+  activeId: string | null
+  // The card expanded to show the full explanation + Ask Petal, or null.
+  expandedId: string | null
+  onAccept: (s: Suggestion) => void
+  onDismiss: (s: Suggestion) => void
+  // Pointer entering/leaving a card, so the matching highlight can light up.
+  onHover: (id: string | null) => void
+  // A card's body was clicked — scroll its highlight into view and toggle expand.
+  onActivate: (id: string) => void
+  onToggleExpand: (id: string) => void
+}
+
+// SuggestionRail is the right-margin "comment column": every outstanding
+// suggestion as a card, vertically aligned to the text it flags, so the writer
+// sees the whole queue at once instead of hunting highlight by highlight. Cards
+// are anchored to their highlight's vertical position and pushed down only as far
+// as needed to avoid overlapping their neighbor above (a la doc-editor comments).
+export function SuggestionRail({
+  items,
+  activeId,
+  expandedId,
+  onAccept,
+  onDismiss,
+  onHover,
+  onActivate,
+  onToggleExpand,
+}: Props) {
+  // Measured resolved tops keyed by suggestion id (after collision avoidance).
+  const [tops, setTops] = useState<Record<string, number>>({})
+  const cardRefs = useRef<Map<string, HTMLDivElement>>(new Map())
+  // Bumped whenever a card's own height changes (Ask Petal streaming in, wrapping
+  // text) so the stack re-packs and cards below don't get overlapped.
+  const [measureTick, setMeasureTick] = useState(0)
+  const observerRef = useRef<ResizeObserver | null>(null)
+  if (!observerRef.current && typeof ResizeObserver !== 'undefined') {
+    observerRef.current = new ResizeObserver(() => setMeasureTick((t) => t + 1))
+  }
+  useLayoutEffect(() => () => observerRef.current?.disconnect(), [])
+
+  // Sort by anchor, then greedily stack: each card sits at its anchor unless that
+  // would overlap the previous card, in which case it slides down just enough.
+  // Re-runs whenever the anchors or the expanded card (which changes a height)
+  // shift. Reads live offsetHeight so variable-length explanations pack tightly.
+  const ordered = [...items].sort((a, b) => a.anchorTop - b.anchorTop)
+  const layoutKey = ordered.map((i) => `${i.suggestion.id}:${Math.round(i.anchorTop)}`).join('|')
+  useLayoutEffect(() => {
+    let cursor = -Infinity
+    const next: Record<string, number> = {}
+    for (const { suggestion, anchorTop } of ordered) {
+      const h = cardRefs.current.get(suggestion.id)?.offsetHeight ?? 96
+      const top = Math.max(anchorTop, cursor)
+      next[suggestion.id] = top
+      cursor = top + h + CARD_GAP
+    }
+    setTops((prev) => {
+      const ids = Object.keys(next)
+      if (ids.length === Object.keys(prev).length && ids.every((id) => prev[id] === next[id])) return prev
+      return next
+    })
+    // layoutKey captures anchor positions; expandedId/measureTick capture height
+    // changes (toggling detail, Ask Petal streaming in).
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [layoutKey, expandedId, measureTick])
+
+  return (
+    <div className="petal-rail petal-no-print" aria-label="Suggestions">
+      {ordered.map(({ suggestion }) => (
+        <RailCard
+          key={suggestion.id}
+          ref={(el) => {
+            const prev = cardRefs.current.get(suggestion.id)
+            if (prev && prev !== el) observerRef.current?.unobserve(prev)
+            if (el) {
+              cardRefs.current.set(suggestion.id, el)
+              observerRef.current?.observe(el)
+            } else {
+              cardRefs.current.delete(suggestion.id)
+            }
+          }}
+          suggestion={suggestion}
+          top={tops[suggestion.id] ?? 0}
+          active={activeId === suggestion.id}
+          expanded={expandedId === suggestion.id}
+          onAccept={onAccept}
+          onDismiss={onDismiss}
+          onHover={onHover}
+          onActivate={onActivate}
+          onToggleExpand={onToggleExpand}
+        />
+      ))}
+    </div>
+  )
+}
+
+interface CardProps {
+  suggestion: Suggestion
+  top: number
+  active: boolean
+  expanded: boolean
+  onAccept: (s: Suggestion) => void
+  onDismiss: (s: Suggestion) => void
+  onHover: (id: string | null) => void
+  onActivate: (id: string) => void
+  onToggleExpand: (id: string) => void
+}
+
+const RailCard = forwardRef<HTMLDivElement, CardProps>(function RailCard(
+  { suggestion, top, active, expanded, onAccept, onDismiss, onHover, onActivate, onToggleExpand },
+  ref,
+) {
+  const meta = TYPE_META[suggestion.type]
+  const hasReplacement = suggestion.replacement.trim() !== ''
+
+  return (
+    <div
+      ref={ref}
+      role="group"
+      aria-label={`${meta.label} suggestion`}
+      onMouseEnter={() => onHover(suggestion.id)}
+      onMouseLeave={() => onHover(null)}
+      className={`petal-rail-card${active ? ' petal-rail-card-active' : ''}`}
+      style={{ top, borderLeftColor: meta.color }}
+    >
+      <div className="flex items-center justify-between">
+        <span
+          className="inline-flex items-center rounded-full px-2 py-0.5 text-[0.68rem] font-bold"
+          style={{ background: meta.color, color: 'var(--color-plum)' }}
+        >
+          {meta.label}
+        </span>
+        <button
+          type="button"
+          aria-label="Dismiss suggestion"
+          onClick={() => onDismiss(suggestion)}
+          className="petal-rail-x"
+        >
+          ✕
+        </button>
+      </div>
+
+      {/* The body toggles the expanded explanation + Ask Petal and points the
+          editor at the flagged text. */}
+      <button type="button" onClick={() => onActivate(suggestion.id)} className="mt-2 block w-full text-left">
+        {hasReplacement && (
+          <span className="flex flex-col gap-0.5" style={{ fontFamily: 'var(--font-body)' }}>
+            <span className="truncate text-[0.9rem] line-through" style={{ color: 'var(--color-muted)' }}>
+              {suggestion.original}
+            </span>
+            <span className="truncate text-[0.9rem] font-medium" style={{ color: 'var(--color-plum)' }}>
+              {suggestion.replacement}
+            </span>
+          </span>
+        )}
+        <span
+          className={`mt-1.5 block text-[0.82rem] leading-snug${expanded ? '' : ' line-clamp-2'}`}
+          style={{ color: 'var(--color-plum)' }}
+        >
+          {suggestion.explanation}
+        </span>
+      </button>
+
+      {expanded && <AskPetal suggestionId={suggestion.id} explanation={suggestion.explanation} />}
+
+      <div className="mt-2.5 flex items-center gap-2">
+        {hasReplacement && (
+          <button
+            type="button"
+            onClick={() => onAccept(suggestion)}
+            className="rounded-full px-3 py-1 text-xs font-bold text-white"
+            style={{ background: 'var(--color-accent)' }}
+            onMouseEnter={(e) => (e.currentTarget.style.background = 'var(--color-accent-hover)')}
+            onMouseLeave={(e) => (e.currentTarget.style.background = 'var(--color-accent)')}
+          >
+            Accept
+          </button>
+        )}
+        <button
+          type="button"
+          onClick={() => onToggleExpand(suggestion.id)}
+          className="rounded-full px-2.5 py-1 text-xs font-bold transition-colors"
+          style={{
+            background: expanded ? 'var(--color-surface-alt)' : 'transparent',
+            color: 'var(--color-accent-hover)',
+          }}
+        >
+          {expanded ? 'Hide Petal' : 'Ask Petal ✨'}
+        </button>
+      </div>
+    </div>
+  )
+})

web/src/components/Editor/suggestionMeta.ts

@@ -0,0 +1,12 @@
+import type { SuggestionType } from '../../api/client'
+
+// Per-type accent color + human label, mirroring the design tokens. Shared by the
+// inline hover SuggestionCard and the margin SuggestionRail so a given suggestion
+// type reads the same color/name wherever it surfaces.
+export const TYPE_META: Record<SuggestionType, { color: string; label: string }> = {
+  grammar: { color: 'var(--color-mint)', label: 'Grammar' },
+  phrasing: { color: 'var(--color-peach)', label: 'Phrasing' },
+  idiom: { color: 'var(--color-lavender)', label: 'Idiom' },
+  clarity: { color: 'var(--color-sky)', label: 'Clarity' },
+  voice: { color: 'var(--color-honey)', label: 'Voice' },
+}

web/src/index.css

@@ -223,6 +223,67 @@ button, a, input {
   animation: petal-suggestion-in 200ms ease both;
 }
 
+/* Text emphasized from its margin card (or a hover) — a soft wash so the
+   card↔text link reads at a glance, both directions. */
+.petal-suggestion-active {
+  background: var(--color-surface-alt);
+  box-shadow: 0 0 0 3px var(--color-surface-alt);
+  border-radius: 3px;
+}
+
+/* --- Suggestion margin rail -------------------------------------------------
+   The right-hand "comment column": every outstanding suggestion as a card,
+   vertically aligned to the text it flags, so the whole queue is visible at a
+   glance instead of one-highlight-at-a-time on hover. It floats in the whitespace
+   just right of the editor column and is only mounted when there's room for it
+   (EditorCore measures the gap). Cards are absolutely positioned by a resolved
+   top (anchor + collision avoidance), so the container only anchors the column. */
+.petal-rail {
+  position: absolute;
+  top: 0;
+  left: 100%;
+  margin-left: 32px;
+  width: 300px;
+  /* Below the companion mascot (z-40): where a stacked card reaches the
+     bottom-right corner it simply tucks behind the sleeping cat. */
+  z-index: 10;
+}
+.petal-rail-card {
+  position: absolute;
+  left: 0;
+  right: 0;
+  background: var(--color-surface);
+  border: 1px solid var(--color-border);
+  border-left: 3px solid var(--color-border); /* type color set inline */
+  border-radius: var(--radius-card);
+  box-shadow: var(--shadow-soft);
+  padding: 0.7rem 0.85rem;
+  /* `top` eases so re-stacking (accept/dismiss/edit) glides instead of jumping.
+     The entrance uses fill `backwards` so its translateY doesn't linger and fight
+     the active-state transform once it's done. */
+  transition: top 240ms cubic-bezier(0.2, 0.7, 0.3, 1), box-shadow 200ms ease,
+    transform 200ms ease, border-color 200ms ease;
+  animation: petal-suggestion-in 220ms ease backwards;
+}
+.petal-rail-card-active {
+  transform: translateX(-5px);
+  box-shadow: 0 8px 26px rgba(180, 130, 160, 0.24);
+  border-top-color: var(--color-accent);
+  border-right-color: var(--color-accent);
+  border-bottom-color: var(--color-accent);
+}
+.petal-rail-x {
+  color: var(--color-muted);
+  font-size: 0.72rem;
+  line-height: 1;
+  padding: 2px 5px;
+  border-radius: var(--radius-pill);
+}
+.petal-rail-x:hover {
+  background: var(--color-surface-alt);
+  color: var(--color-plum);
+}
+
 /* --- Find & Replace ---------------------------------------------------------
    In-document search (Ctrl/Cmd+F). Every match gets a soft honey wash; the
    current match is brighter with a rose ring so it stands out as you step