diff --git a/src/app/(protected)/workorders/[id].tsx b/src/app/(protected)/workorders/[id].tsx
index f7350669..e9fb5b56 100644
--- a/src/app/(protected)/workorders/[id].tsx
+++ b/src/app/(protected)/workorders/[id].tsx
@@ -31,9 +31,12 @@ import {
   Typography,
 } from "@mui/material";
 import ExpandMoreIcon from "@mui/icons-material/ExpandMore";
+import { CommentMentionComposer } from "@/components/common/comment-mention-composer";
+import { CommentTimeline } from "@/components/common/comment-timeline";
+import { mapWorkOrderCommentsToTimeline } from "@/components/common/comment-timeline-mappers";
 import { DispatchCreateModal } from "./_components/dispatch-create-modal";
 import { DispatchDetailModal } from "./_components/dispatch-detail-modal";
-import type { WorkOrderAuditEntry, WorkOrderComment } from "@/domain/work-orders/types/work-order";
+import type { WorkOrderAuditEntry } from "@/domain/work-orders/types/work-order";
 import { WORK_ORDER_STATUS_OPTIONS } from "@/domain/work-orders/types/work-order";
 import { useWorkOrderDetail } from "@/domain/work-orders/use-cases/use-work-order-detail";
 import {
@@ -45,6 +48,7 @@ import {
 import { useWorkOrderUsers } from "@/domain/work-orders/use-cases/use-work-orders-list";
 import { vendorsApi } from "@/domain/vendors/api/vendors-api";
 import type { VendorPreferredContact } from "@/domain/vendors/types/vendor";
+import { extractMentionIds } from "@/domain/work-orders/utils/comment-mentions";
 import { formatDateTime, timeSince, waitTimeColor } from "@/lib/time-utils";
 
 const STATUS_COLORS: Record<
@@ -85,57 +89,6 @@ function isVendorEditorValid(editor: VendorEditorState): boolean {
   );
 }
 
-function CommentTimeline({ comments }: { comments: WorkOrderComment[] }) {
-  const sorted = useMemo(
-    () =>
-      [...comments].sort(
-        (a, b) => new Date(a.createdDate).getTime() - new Date(b.createdDate).getTime(),
-      ),
-    [comments],
-  );
-
-  if (!sorted.length) {
-    return (
-      <Typography
-        sx={{
-          color: "text.secondary",
-        }}
-      >
-        No comments yet.
-      </Typography>
-    );
-  }
-
-  return (
-    <Stack spacing={2} className="max-h-72 overflow-y-auto">
-      {sorted.map((comment) => (
-        <Box key={String(comment.id)} className="rounded border border-border p-3">
-          <Stack
-            direction="row"
-            className="mb-1"
-            sx={{
-              justifyContent: "space-between",
-            }}
-          >
-            <Typography variant="caption" className="font-semibold">
-              {comment.userName || comment.commenter || "System"}
-            </Typography>
-            <Typography
-              variant="caption"
-              sx={{
-                color: "text.secondary",
-              }}
-            >
-              {comment.createdDate ? formatDateTime(comment.createdDate) : ""}
-            </Typography>
-          </Stack>
-          <Typography variant="body2">{comment.commenttext}</Typography>
-        </Box>
-      ))}
-    </Stack>
-  );
-}
-
 function AuditTimeline({ entries }: { entries: WorkOrderAuditEntry[] }) {
   const sorted = useMemo(
     () =>
@@ -220,6 +173,18 @@ export default function WorkOrderViewPage() {
     [wo?.comments],
   );
   const auditLog = wo?.auditLog ?? [];
+  const mentionUsers = useMemo(
+    () => users.map((user) => ({ id: user.id, name: user.name })),
+    [users],
+  );
+  const customerTimelineItems = useMemo(
+    () => mapWorkOrderCommentsToTimeline(customerComments),
+    [customerComments],
+  );
+  const internalTimelineItems = useMemo(
+    () => mapWorkOrderCommentsToTimeline(internalComments),
+    [internalComments],
+  );
 
   const handleCommentSubmit = (event: React.FormEvent) => {
     event.preventDefault();
@@ -230,8 +195,15 @@ export default function WorkOrderViewPage() {
       return;
     }
 
+    const trimmedText = commentText.trim();
+    const mentions = extractMentionIds(trimmedText);
+
     commentMutation.mutate(
-      { text: commentText.trim(), commentType: activeTab },
+      {
+        text: trimmedText,
+        mentions: mentions.length > 0 ? mentions : undefined,
+        commentType: activeTab,
+      },
       { onSuccess: () => setCommentText("") },
     );
   };
@@ -626,18 +598,20 @@ export default function WorkOrderViewPage() {
           <Tab value="audit" label={`Audit Log (${auditLog.length})`} />
         </Tabs>
 
-        {activeTab === "customer" && <CommentTimeline comments={customerComments} />}
-        {activeTab === "internal" && <CommentTimeline comments={internalComments} />}
+        {activeTab === "customer" && (
+          <CommentTimeline items={customerTimelineItems} mentionUsers={mentionUsers} />
+        )}
+        {activeTab === "internal" && (
+          <CommentTimeline items={internalTimelineItems} mentionUsers={mentionUsers} />
+        )}
         {activeTab === "audit" && <AuditTimeline entries={auditLog} />}
 
         {activeTab === "internal" && (
           <Box component="form" onSubmit={handleCommentSubmit} className="mt-4 flex flex-col gap-2">
-            <TextField
-              multiline
-              rows={2}
+            <CommentMentionComposer
               value={commentText}
-              onChange={(event) => setCommentText(event.target.value)}
-              placeholder="Type a comment..."
+              onChange={setCommentText}
+              candidates={mentionUsers}
               disabled={commentMutation.isPending}
             />
             <Button
diff --git a/src/components/common/comment-body-with-mentions.tsx b/src/components/common/comment-body-with-mentions.tsx
new file mode 100644
index 00000000..a7566e70
--- /dev/null
+++ b/src/components/common/comment-body-with-mentions.tsx
@@ -0,0 +1,44 @@
+import { useMemo } from "react";
+import { Box } from "@mui/material";
+import { Text } from "@/components/ui/text";
+import {
+  buildCommentBodySegments,
+  type MentionLookup,
+} from "@/domain/work-orders/utils/comment-mentions";
+
+type CommentBodyWithMentionsProps = {
+  text: string;
+  mentions?: string[];
+  users?: MentionLookup[];
+};
+
+export function CommentBodyWithMentions({ text, mentions, users }: CommentBodyWithMentionsProps) {
+  const segments = useMemo(
+    () => buildCommentBodySegments(text, mentions, users),
+    [text, mentions, users],
+  );
+
+  if (segments.length === 0) {
+    return null;
+  }
+
+  return (
+    <Text variant="description" as="span">
+      {segments.map((segment, index) => {
+        if (segment.type === "text") {
+          return <span key={`text-${index}`}>{segment.value}</span>;
+        }
+
+        return (
+          <Box
+            component="span"
+            key={`mention-${segment.userId}-${index}`}
+            className="font-semibold text-primary"
+          >
+            @{segment.label}
+          </Box>
+        );
+      })}
+    </Text>
+  );
+}
diff --git a/src/components/common/comment-mention-composer.tsx b/src/components/common/comment-mention-composer.tsx
new file mode 100644
index 00000000..566c1a5b
--- /dev/null
+++ b/src/components/common/comment-mention-composer.tsx
@@ -0,0 +1,173 @@
+import { useCallback, useMemo, useRef, useState } from "react";
+import {
+  Box,
+  ClickAwayListener,
+  List,
+  ListItemButton,
+  Paper,
+  Popper,
+  TextField,
+} from "@mui/material";
+import {
+  filterMentionCandidates,
+  findActiveMentionQuery,
+  insertMentionToken,
+  type MentionLookup,
+} from "@/domain/work-orders/utils/comment-mentions";
+
+type CommentMentionComposerProps = {
+  value: string;
+  onChange: (value: string) => void;
+  candidates: MentionLookup[];
+  placeholder?: string;
+  disabled?: boolean;
+  rows?: number;
+  onSubmit?: () => void;
+};
+
+export function CommentMentionComposer({
+  value,
+  onChange,
+  candidates,
+  placeholder = "Type a comment...",
+  disabled = false,
+  rows = 2,
+  onSubmit,
+}: CommentMentionComposerProps) {
+  const inputRef = useRef<HTMLTextAreaElement | HTMLInputElement>(null);
+  const [anchorEl, setAnchorEl] = useState<HTMLElement | null>(null);
+  const [cursor, setCursor] = useState(0);
+  const [menuOpen, setMenuOpen] = useState(false);
+  const [highlightIndex, setHighlightIndex] = useState(0);
+
+  const activeQuery = useMemo(() => findActiveMentionQuery(value, cursor), [value, cursor]);
+
+  const filteredCandidates = useMemo(
+    () => filterMentionCandidates(candidates, activeQuery?.query ?? ""),
+    [activeQuery?.query, candidates],
+  );
+
+  const showMenu = Boolean(menuOpen && activeQuery && filteredCandidates.length > 0);
+
+  const syncCursor = useCallback(() => {
+    const element = inputRef.current;
+    if (!element) {
+      return;
+    }
+
+    const nextCursor = element.selectionStart ?? value.length;
+    setCursor(nextCursor);
+    setMenuOpen(Boolean(findActiveMentionQuery(value, nextCursor)));
+    setHighlightIndex(0);
+  }, [value]);
+
+  const handleChange = (nextValue: string) => {
+    onChange(nextValue);
+    requestAnimationFrame(syncCursor);
+  };
+
+  const applyMention = useCallback(
+    (user: MentionLookup) => {
+      if (!activeQuery) {
+        return;
+      }
+
+      const { nextText, nextCursor } = insertMentionToken(value, activeQuery.start, cursor, user);
+      onChange(nextText);
+      setMenuOpen(false);
+      setHighlightIndex(0);
+
+      requestAnimationFrame(() => {
+        const element = inputRef.current;
+        if (!element) {
+          return;
+        }
+        element.focus();
+        element.setSelectionRange(nextCursor, nextCursor);
+        setCursor(nextCursor);
+      });
+    },
+    [activeQuery, cursor, onChange, value],
+  );
+
+  const handleKeyDown = (event: React.KeyboardEvent<HTMLDivElement>) => {
+    if (showMenu) {
+      if (event.key === "ArrowDown") {
+        event.preventDefault();
+        setHighlightIndex((current) => (current + 1) % filteredCandidates.length);
+        return;
+      }
+
+      if (event.key === "ArrowUp") {
+        event.preventDefault();
+        setHighlightIndex(
+          (current) => (current - 1 + filteredCandidates.length) % filteredCandidates.length,
+        );
+        return;
+      }
+
+      if (event.key === "Enter" && !event.shiftKey) {
+        event.preventDefault();
+        const selected = filteredCandidates[highlightIndex];
+        if (selected) {
+          applyMention(selected);
+        }
+        return;
+      }
+
+      if (event.key === "Escape") {
+        event.preventDefault();
+        setMenuOpen(false);
+        return;
+      }
+    }
+
+    if (event.key === "Enter" && (event.metaKey || event.ctrlKey) && onSubmit) {
+      event.preventDefault();
+      onSubmit();
+    }
+  };
+
+  return (
+    <ClickAwayListener onClickAway={() => setMenuOpen(false)}>
+      <Box
+        className="relative"
+        ref={(node: HTMLDivElement | null) => {
+          setAnchorEl(node);
+        }}
+      >
+        <TextField
+          inputRef={inputRef}
+          multiline
+          rows={rows}
+          fullWidth
+          value={value}
+          onChange={(event) => handleChange(event.target.value)}
+          onClick={syncCursor}
+          onKeyUp={syncCursor}
+          onSelect={syncCursor}
+          onKeyDown={handleKeyDown}
+          placeholder={placeholder}
+          disabled={disabled}
+        />
+
+        <Popper open={showMenu} anchorEl={anchorEl} placement="bottom-start" className="z-50">
+          <Paper elevation={4} className="mt-1 max-h-48 overflow-y-auto">
+            <List dense disablePadding>
+              {filteredCandidates.map((candidate, index) => (
+                <ListItemButton
+                  key={String(candidate.id)}
+                  selected={index === highlightIndex}
+                  onMouseDown={(event) => event.preventDefault()}
+                  onClick={() => applyMention(candidate)}
+                >
+                  @{candidate.name}
+                </ListItemButton>
+              ))}
+            </List>
+          </Paper>
+        </Popper>
+      </Box>
+    </ClickAwayListener>
+  );
+}
diff --git a/src/components/common/comment-timeline-mappers.ts b/src/components/common/comment-timeline-mappers.ts
index aad27c4b..324e1230 100644
--- a/src/components/common/comment-timeline-mappers.ts
+++ b/src/components/common/comment-timeline-mappers.ts
@@ -6,6 +6,7 @@ type CommentSource = {
   commenter?: string | null;
   createdDate?: string;
   commenttext: string;
+  mentions?: string[];
 };
 
 export function mapWorkOrderCommentsToTimeline(comments: CommentSource[]): CommentTimelineItem[] {
@@ -14,6 +15,7 @@ export function mapWorkOrderCommentsToTimeline(comments: CommentSource[]): Comme
     author: comment.userName || comment.commenter || "System",
     createdAt: comment.createdDate,
     body: comment.commenttext,
+    mentions: comment.mentions,
   }));
 }
 
diff --git a/src/components/common/comment-timeline.tsx b/src/components/common/comment-timeline.tsx
index d0404ba7..4f9c9dea 100644
--- a/src/components/common/comment-timeline.tsx
+++ b/src/components/common/comment-timeline.tsx
@@ -1,5 +1,8 @@
 import { useMemo } from "react";
-import { Box, Stack, Typography } from "@mui/material";
+import { Box, Stack } from "@mui/material";
+import { CommentBodyWithMentions } from "@/components/common/comment-body-with-mentions";
+import { Text } from "@/components/ui/text";
+import type { MentionLookup } from "@/domain/work-orders/utils/comment-mentions";
 import { formatDateTime } from "@/lib/time-utils";
 
 export type CommentTimelineItem = {
@@ -7,18 +10,20 @@ export type CommentTimelineItem = {
   author: string;
   createdAt?: string;
   body: string;
+  mentions?: string[];
 };
 
 type CommentTimelineProps = {
   items: CommentTimelineItem[];
   emptyMessage?: string;
   maxHeightClass?: string;
+  mentionUsers?: MentionLookup[];
 };
-
 export function CommentTimeline({
   items,
   emptyMessage = "No comments yet.",
   maxHeightClass = "max-h-72",
+  mentionUsers,
 }: CommentTimelineProps) {
   const sorted = useMemo(
     () =>
@@ -31,7 +36,7 @@ export function CommentTimeline({
   );
 
   if (!sorted.length) {
-    return <Typography color="text.secondary">{emptyMessage}</Typography>;
+    return <Text tone="muted">{emptyMessage}</Text>;
   }
 
   return (
@@ -39,14 +44,14 @@ export function CommentTimeline({
       {sorted.map((item) => (
         <Box key={String(item.id)} className="rounded border border-border p-3">
           <Stack direction="row" className="mb-1" sx={{ justifyContent: "space-between" }}>
-            <Typography variant="caption" className="font-semibold">
+            <Text variant="caption" className="font-semibold">
               {item.author}
-            </Typography>
-            <Typography variant="caption" color="text.secondary">
+            </Text>
+            <Text variant="caption" tone="muted">
               {item.createdAt ? formatDateTime(item.createdAt) : ""}
-            </Typography>
+            </Text>
           </Stack>
-          <Typography variant="body2">{item.body}</Typography>
+          <CommentBodyWithMentions text={item.body} mentions={item.mentions} users={mentionUsers} />
         </Box>
       ))}
     </Stack>
diff --git a/src/domain/work-orders/api/work-order-board-documents-api.ts b/src/domain/work-orders/api/work-order-board-documents-api.ts
index 5532459f..0560785e 100644
--- a/src/domain/work-orders/api/work-order-board-documents-api.ts
+++ b/src/domain/work-orders/api/work-order-board-documents-api.ts
@@ -20,6 +20,11 @@ import type {
 } from "@/domain/work-orders/types/work-order-board-detail";
 import type { WorkOrderComment } from "@/domain/work-orders/types/work-order";
 
+export interface CreateWorkOrderCommentPayload {
+  text: string;
+  mentions?: string[];
+}
+
 async function readResponseJson(response: Response): Promise<unknown> {
   try {
     return await response.json();
@@ -57,8 +62,17 @@ export const workOrderBoardDocumentsApi = {
     return Array.isArray(items) ? items.map(mapBoardDetailComment) : [];
   },
 
-  createComment: async (workOrderId: string | number, text: string): Promise<WorkOrderComment> => {
-    const data = await apiPost<unknown>(API_PATHS.workOrder.comments(workOrderId), { text });
+  createComment: async (
+    workOrderId: string | number,
+    text: string,
+    mentions?: string[],
+  ): Promise<WorkOrderComment> => {
+    const payload: CreateWorkOrderCommentPayload = { text };
+    if (mentions && mentions.length > 0) {
+      payload.mentions = mentions.map(String);
+    }
+
+    const data = await apiPost<unknown>(API_PATHS.workOrder.comments(workOrderId), payload);
     return mapBoardDetailComment(handleApiResponse(data));
   },
 
diff --git a/src/domain/work-orders/mappers/work-order-board-detail-mapper.ts b/src/domain/work-orders/mappers/work-order-board-detail-mapper.ts
index fffd515b..3b513279 100644
--- a/src/domain/work-orders/mappers/work-order-board-detail-mapper.ts
+++ b/src/domain/work-orders/mappers/work-order-board-detail-mapper.ts
@@ -61,6 +61,33 @@ function readBoolean(record: Record<string, unknown>, ...keys: string[]): boolea
   return false;
 }
 
+function readStringArray(record: Record<string, unknown>, ...keys: string[]): string[] {
+  for (const key of keys) {
+    const value = record[key];
+    if (!Array.isArray(value)) {
+      continue;
+    }
+
+    const mapped = value
+      .map((entry) => {
+        if (typeof entry === "string") {
+          return entry;
+        }
+        if (typeof entry === "number" || typeof entry === "boolean") {
+          return String(entry);
+        }
+        return "";
+      })
+      .filter(Boolean);
+
+    if (mapped.length > 0) {
+      return mapped;
+    }
+  }
+
+  return [];
+}
+
 function mapDocStatus(raw: unknown): CompletionDocStatus {
   const numeric = typeof raw === "number" ? raw : Number(raw);
   if (numeric === DOC_STATUS_API.Yes) return "Yes";
@@ -93,6 +120,7 @@ export function mapBoardDetailComment(raw: unknown): WorkOrderComment {
     authorId,
     commenter: readString(item, "commenter", "Commenter") || null,
     recordType: readString(item, "recordType", "RecordType") || null,
+    mentions: readStringArray(item, "mentions", "Mentions"),
   };
 }
 
diff --git a/src/domain/work-orders/mappers/work-order-mapper.ts b/src/domain/work-orders/mappers/work-order-mapper.ts
index 2b61364c..b2bb5de2 100644
--- a/src/domain/work-orders/mappers/work-order-mapper.ts
+++ b/src/domain/work-orders/mappers/work-order-mapper.ts
@@ -215,6 +215,12 @@ export { mapWorkOrderTableRow, mapWorkOrderTableRows } from "./work-order-table-
 
 export function mapWorkOrderComment(raw: unknown): WorkOrderComment {
   const item = asRecord(raw);
+  const mentionsRaw = item.mentions ?? item.Mentions;
+  const mentions = Array.isArray(mentionsRaw)
+    ? mentionsRaw
+        .map((entry) => (typeof entry === "string" ? entry : String(entry)))
+        .filter(Boolean)
+    : undefined;
 
   return {
     id: readId(item),
@@ -224,6 +230,7 @@ export function mapWorkOrderComment(raw: unknown): WorkOrderComment {
     userName: readString(item, "userName", "UserName"),
     commenter: readString(item, "commenter", "Commenter") || null,
     recordType: readString(item, "recordType", "RecordType") || null,
+    mentions,
   };
 }
 
diff --git a/src/domain/work-orders/types/work-order-board-detail.ts b/src/domain/work-orders/types/work-order-board-detail.ts
index 590aee84..ab3737b2 100644
--- a/src/domain/work-orders/types/work-order-board-detail.ts
+++ b/src/domain/work-orders/types/work-order-board-detail.ts
@@ -94,6 +94,7 @@ export interface WorkOrderBoardDetailCommentApi {
   text?: string | null;
   time?: string | null;
   documents?: unknown;
+  mentions?: string[] | null;
 }
 
 export interface WorkOrderBoardDetailAuditApi {
diff --git a/src/domain/work-orders/types/work-order-detail.ts b/src/domain/work-orders/types/work-order-detail.ts
index 8c492a99..d3d2fa87 100644
--- a/src/domain/work-orders/types/work-order-detail.ts
+++ b/src/domain/work-orders/types/work-order-detail.ts
@@ -11,6 +11,8 @@ export interface WorkOrderComment {
   authorId?: string | null;
   commenter: string | null;
   recordType: string | null;
+  /** Mentioned user ids when returned by board comments API. */
+  mentions?: string[];
 }
 
 export interface WorkOrderAuditEntry {
diff --git a/src/domain/work-orders/use-cases/use-work-order-mutations.ts b/src/domain/work-orders/use-cases/use-work-order-mutations.ts
index 82667f19..d9f447cd 100644
--- a/src/domain/work-orders/use-cases/use-work-order-mutations.ts
+++ b/src/domain/work-orders/use-cases/use-work-order-mutations.ts
@@ -40,6 +40,7 @@ function invalidateBoardDetail(
 
 interface AddWorkOrderCommentInput {
   text: string;
+  mentions?: string[];
   commentType?: "customer" | "internal";
 }
 
@@ -157,8 +158,8 @@ export function useAddWorkOrderComment(
   const queryClient = useQueryClient();
 
   return useMutation({
-    mutationFn: ({ text }: AddWorkOrderCommentInput) =>
-      workOrdersApi.createComment(workOrderId, text),
+    mutationFn: ({ text, mentions }: AddWorkOrderCommentInput) =>
+      workOrdersApi.createComment(workOrderId, text, mentions),
     onSuccess: () => {
       invalidateBoardDetail(queryClient, workOrderId);
     },
diff --git a/src/domain/work-orders/utils/comment-mentions.ts b/src/domain/work-orders/utils/comment-mentions.ts
new file mode 100644
index 00000000..7945bfb5
--- /dev/null
+++ b/src/domain/work-orders/utils/comment-mentions.ts
@@ -0,0 +1,184 @@
+/** Encoded mention token stored in comment text: `@[userId:Display Name]`. */
+export const MENTION_TOKEN_PATTERN = /@\[([^:\]]+):([^\]]+)\]/g;
+
+export type CommentBodySegment =
+  { type: "text"; value: string } | { type: "mention"; userId: string; label: string };
+
+export type MentionLookup = {
+  id: string | number;
+  name: string;
+};
+
+export function encodeMentionToken(userId: string | number, userName: string): string {
+  const trimmedName = userName.trim();
+  return `@[${String(userId)}:${trimmedName}]`;
+}
+
+export function extractMentionIds(text: string): string[] {
+  const ids: string[] = [];
+  const pattern = new RegExp(MENTION_TOKEN_PATTERN.source, "g");
+
+  for (const match of text.matchAll(pattern)) {
+    const userId = match[1];
+    if (userId && !ids.includes(userId)) {
+      ids.push(userId);
+    }
+  }
+
+  return ids;
+}
+
+export function toDisplayText(text: string): string {
+  return text.replace(MENTION_TOKEN_PATTERN, (_full, _userId: string, userName: string) => {
+    return `@${userName}`;
+  });
+}
+
+function escapeRegExp(value: string): string {
+  return value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+}
+
+function pushTextSegment(segments: CommentBodySegment[], value: string): void {
+  if (!value) {
+    return;
+  }
+
+  const last = segments.length > 0 ? segments[segments.length - 1] : undefined;
+  if (last?.type === "text") {
+    last.value += value;
+    return;
+  }
+
+  segments.push({ type: "text", value });
+}
+
+function resolveMentionNames(
+  mentionIds: string[] | undefined,
+  users: MentionLookup[] | undefined,
+): Map<string, string> {
+  const byId = new Map<string, string>();
+
+  for (const user of users ?? []) {
+    byId.set(String(user.id), user.name);
+  }
+
+  for (const mentionId of mentionIds ?? []) {
+    const id = String(mentionId);
+    if (!byId.has(id)) {
+      byId.set(id, id);
+    }
+  }
+
+  return byId;
+}
+
+function appendPlainMentionMatches(
+  segments: CommentBodySegment[],
+  plainText: string,
+  mentionNames: string[],
+): void {
+  if (!plainText || mentionNames.length === 0) {
+    pushTextSegment(segments, plainText);
+    return;
+  }
+
+  const sortedNames = [...mentionNames].sort((a, b) => b.length - a.length);
+  const namePattern = sortedNames.map((name) => escapeRegExp(name)).join("|");
+  const mentionRegex = new RegExp(`@(${namePattern})`, "g");
+
+  let cursor = 0;
+  for (const match of plainText.matchAll(mentionRegex)) {
+    const index = match.index ?? 0;
+    pushTextSegment(segments, plainText.slice(cursor, index));
+
+    const label = match[1] ?? "";
+    segments.push({ type: "mention", userId: label, label });
+    cursor = index + match[0].length;
+  }
+
+  pushTextSegment(segments, plainText.slice(cursor));
+}
+
+export function buildCommentBodySegments(
+  text: string,
+  mentionIds?: string[],
+  users?: MentionLookup[],
+): CommentBodySegment[] {
+  if (!text) {
+    return [];
+  }
+
+  const segments: CommentBodySegment[] = [];
+  const encodedPattern = new RegExp(MENTION_TOKEN_PATTERN.source, "g");
+  let cursor = 0;
+
+  for (const match of text.matchAll(encodedPattern)) {
+    const index = match.index ?? 0;
+    const plainBetween = text.slice(cursor, index);
+    appendPlainMentionMatches(segments, plainBetween, []);
+
+    const userId = match[1] ?? "";
+    const label = match[2] ?? userId;
+    segments.push({ type: "mention", userId, label });
+    cursor = index + match[0].length;
+  }
+
+  const trailingPlain = text.slice(cursor);
+  const mentionNameById = resolveMentionNames(mentionIds, users);
+  const mentionNames = [...new Set(mentionNameById.values())].filter(Boolean);
+  appendPlainMentionMatches(segments, trailingPlain, mentionNames);
+
+  return segments.length > 0 ? segments : [{ type: "text", value: text }];
+}
+
+export type ActiveMentionQuery = {
+  start: number;
+  query: string;
+};
+
+export function findActiveMentionQuery(text: string, cursor: number): ActiveMentionQuery | null {
+  const beforeCursor = text.slice(0, cursor);
+  const atIndex = beforeCursor.lastIndexOf("@");
+
+  if (atIndex < 0) {
+    return null;
+  }
+
+  const prefix = beforeCursor.slice(0, atIndex);
+  const lastPrefixChar = prefix.length > 0 ? prefix[prefix.length - 1] : "";
+  if (prefix.length > 0 && !/\s/.test(lastPrefixChar)) {
+    return null;
+  }
+
+  const query = beforeCursor.slice(atIndex + 1);
+  if (/[\n\r\t[\]]/.test(query)) {
+    return null;
+  }
+
+  return { start: atIndex, query };
+}
+
+export function filterMentionCandidates(
+  candidates: MentionLookup[],
+  query: string,
+): MentionLookup[] {
+  const normalized = query.trim().toLowerCase();
+  const filtered = normalized
+    ? candidates.filter((candidate) => candidate.name.toLowerCase().includes(normalized))
+    : candidates;
+
+  return filtered.slice(0, 8);
+}
+
+export function insertMentionToken(
+  text: string,
+  queryStart: number,
+  cursor: number,
+  user: MentionLookup,
+): { nextText: string; nextCursor: number } {
+  const token = `${encodeMentionToken(user.id, user.name)} `;
+  const nextText = `${text.slice(0, queryStart)}${token}${text.slice(cursor)}`;
+  const nextCursor = queryStart + token.length;
+
+  return { nextText, nextCursor };
+}
diff --git a/src/test/domain/work-orders/api/work-orders-api.test.ts b/src/test/domain/work-orders/api/work-orders-api.test.ts
index 7d0b91ea..6eece14e 100644
--- a/src/test/domain/work-orders/api/work-orders-api.test.ts
+++ b/src/test/domain/work-orders/api/work-orders-api.test.ts
@@ -381,6 +381,15 @@ describe("workOrdersApi.createComment", () => {
     expect(comment.authorId).toBe("guid");
     expect(comment.createdDate).toBe("2026-06-01T12:00:00.0000000Z");
   });
+
+  it("POSTs mentions when provided", async () => {
+    await workOrdersApi.createComment(55, "Ping @[u1:Jane]", ["u1"]);
+
+    expect(apiPost).toHaveBeenCalledWith(API_PATHS.workOrder.comments(55), {
+      text: "Ping @[u1:Jane]",
+      mentions: ["u1"],
+    });
+  });
 });
 
 describe("workOrdersApi.updateComment", () => {
diff --git a/src/test/domain/work-orders/utils/comment-mentions.test.ts b/src/test/domain/work-orders/utils/comment-mentions.test.ts
new file mode 100644
index 00000000..4305bcf5
--- /dev/null
+++ b/src/test/domain/work-orders/utils/comment-mentions.test.ts
@@ -0,0 +1,78 @@
+import { describe, expect, it } from "vitest";
+import {
+  buildCommentBodySegments,
+  encodeMentionToken,
+  extractMentionIds,
+  filterMentionCandidates,
+  findActiveMentionQuery,
+  insertMentionToken,
+  toDisplayText,
+} from "@/domain/work-orders/utils/comment-mentions";
+
+describe("comment-mentions", () => {
+  it("encodes and extracts mention ids from tokens", () => {
+    const token = encodeMentionToken("user-1", "Jane Doe");
+    const text = `Please review ${token} today`;
+
+    expect(text).toBe("Please review @[user-1:Jane Doe] today");
+    expect(extractMentionIds(text)).toEqual(["user-1"]);
+    expect(toDisplayText(text)).toBe("Please review @Jane Doe today");
+  });
+
+  it("builds highlight segments from encoded tokens", () => {
+    const text = `Hi ${encodeMentionToken("42", "Alex Smith")}!`;
+
+    expect(buildCommentBodySegments(text)).toEqual([
+      { type: "text", value: "Hi " },
+      { type: "mention", userId: "42", label: "Alex Smith" },
+      { type: "text", value: "!" },
+    ]);
+  });
+
+  it("highlights plain @names when response mentions are provided", () => {
+    const text = "Ping @Jane Doe about this";
+
+    expect(
+      buildCommentBodySegments(text, ["user-1"], [{ id: "user-1", name: "Jane Doe" }]),
+    ).toEqual([
+      { type: "text", value: "Ping " },
+      { type: "mention", userId: "Jane Doe", label: "Jane Doe" },
+      { type: "text", value: " about this" },
+    ]);
+  });
+
+  it("finds active mention query at cursor", () => {
+    const text = "Hello @ja";
+    const query = findActiveMentionQuery(text, text.length);
+
+    expect(query).toEqual({ start: 6, query: "ja" });
+    expect(findActiveMentionQuery("email@test.com", 13)).toBeNull();
+  });
+
+  it("filters mention candidates by query", () => {
+    const candidates = [
+      { id: "1", name: "Jane Doe" },
+      { id: "2", name: "John Smith" },
+    ];
+
+    expect(filterMentionCandidates(candidates, "jo")).toEqual([{ id: "2", name: "John Smith" }]);
+  });
+
+  it("inserts encoded mention token replacing active query", () => {
+    const text = "Hello @ja";
+    const activeQuery = findActiveMentionQuery(text, text.length);
+
+    expect(activeQuery).not.toBeNull();
+    if (!activeQuery) {
+      return;
+    }
+
+    const { nextText, nextCursor } = insertMentionToken(text, activeQuery.start, text.length, {
+      id: "1",
+      name: "Jane Doe",
+    });
+
+    expect(nextText).toBe("Hello @[1:Jane Doe] ");
+    expect(nextCursor).toBe(nextText.length);
+  });
+});
diff --git a/tmp/pr-descriptions/pr9-comment-mentions.md b/tmp/pr-descriptions/pr9-comment-mentions.md
new file mode 100644
index 00000000..e2f10cbd
--- /dev/null
+++ b/tmp/pr-descriptions/pr9-comment-mentions.md
@@ -0,0 +1,32 @@
+# PR9 — Work order comment @mentions
+
+## Summary
+
+- Adds `@` autocomplete to the internal comments composer on work order detail (`/workorders/:id`).
+- Encodes selected users as `@[userId:Display Name]` tokens in comment text so mentions stay readable when the backend ignores the optional payload field.
+- Sends `mentions: string[]` on `POST workorders/{id}/comments` when the composer contains encoded tokens.
+- Highlights mentions in the comment thread using encoded tokens and/or `mentions` returned by the API.
+
+## Out of scope
+
+- Notification Center deep-linking for mention events.
+- Backend notification triggers beyond the FE payload.
+
+## BE contract
+
+See `docs/work-orders/pending-be-contract.md` (Comments section):
+
+| Field                                    | Status   |
+| ---------------------------------------- | -------- |
+| POST `{ text, mentions?: string[] }`     | FE ready |
+| Response includes mentions for highlight | FE ready |
+
+Until BE confirms, encoded tokens in `text` preserve highlight behavior client-side.
+
+## Test plan
+
+- [ ] Open a work order detail → Internal tab → type `@` and pick a dispatcher from the list.
+- [ ] Submit comment; verify POST body includes `text` with encoded token and `mentions` array.
+- [ ] Reload detail; verify mention is highlighted in the thread (token and/or API `mentions`).
+- [ ] Type `@` mid-word (e.g. email) — autocomplete should not open.
+- [ ] Run `npm run verify`.