diff --git a/AgentCompany-New/src/main/services/chat-service.ts b/AgentCompany-New/src/main/services/chat-service.ts
index 160a7301..b1be169a 100644
--- a/AgentCompany-New/src/main/services/chat-service.ts
+++ b/AgentCompany-New/src/main/services/chat-service.ts
@@ -2,6 +2,7 @@ import type { DatabaseSync } from "node:sqlite";
 import type { CreateChatSpaceInput, MarkChatSpaceReadInput, SendMessageInput } from "../../shared/commands";
 import { createId } from "../../shared/ids";
 import { AuditService } from "./audit-service";
+import { canonicalMentionHandle } from "./mention-handles";
 
 const SPACE_TYPES = new Set<CreateChatSpaceInput["spaceType"]>(["company", "department", "project", "direct"]);
 const SPACE_VISIBILITIES = new Set<CreateChatSpaceInput["visibility"]>(["workspace", "restricted"]);
@@ -23,6 +24,21 @@ interface PrincipalRef {
   id: string;
 }
 
+interface MentionTarget {
+  type: "employee" | "agent" | "board" | "org_group";
+  id: string;
+}
+
+interface MentionCandidate extends MentionTarget {
+  handle: string;
+}
+
+interface ResolvedMention {
+  target: MentionTarget;
+  offsetStart: number;
+  offsetEnd: number;
+}
+
 export class ChatService {
   private readonly audit: AuditService;
 
@@ -73,6 +89,7 @@ export class ChatService {
     const slash = parseSlashInvocation(body);
     if (slash && !ALLOWED_SLASH_COMMANDS.has(slash.command)) throw new Error(`Slash command /${slash.command} is unavailable.`);
     const attachments = this.requireAttachments(input.orgId, input.attachmentFileIds ?? []);
+    const mentions = this.resolveMentions(input.orgId, input.spaceId, body);
 
     const id = createId("msg");
     const threadId = input.threadId ?? createId("thread");
@@ -101,7 +118,7 @@ export class ChatService {
     } else {
       this.db.prepare("update chat_threads set updated_at = ? where id = ? and org_id = ?").run(now, input.threadId, input.orgId);
     }
-    this.recordMentions(id, body);
+    this.recordMentions(id, mentions);
     if (slash) this.recordSlashInvocation(id, slash, now);
     this.recordAttachments(id, attachments);
     if (input.senderId) {
@@ -147,21 +164,42 @@ export class ChatService {
     `).run(input.orgId, input.employeeId, input.spaceId, latest?.id ?? null, now);
   }
 
-  private recordMentions(messageId: string, body: string): void {
+  private resolveMentions(orgId: string, spaceId: string, body: string): ResolvedMention[] {
+    const mentions: ResolvedMention[] = [];
     const seen = new Set<string>();
     for (const match of body.matchAll(/(^|\s)@([A-Za-z][A-Za-z0-9_-]{1,63})/g)) {
-      const target = match[2];
+      const token = match[2];
+      const target = this.resolveMention(orgId, spaceId, token);
       const offsetStart = match.index + match[1].length;
-      const key = `${target}:${offsetStart}`;
+      const key = `${target.type}:${target.id}:${offsetStart}`;
       if (seen.has(key)) continue;
       seen.add(key);
+      mentions.push({ target, offsetStart, offsetEnd: offsetStart + token.length + 1 });
+    }
+    return mentions;
+  }
+
+  private recordMentions(messageId: string, mentions: ResolvedMention[]): void {
+    for (const mention of mentions) {
       this.db.prepare(`
         insert into chat_mentions(message_id, target_type, target_id, offset_start, offset_end)
         values (?, ?, ?, ?, ?)
-      `).run(messageId, "alias", target, offsetStart, offsetStart + target.length + 1);
+      `).run(messageId, mention.target.type, mention.target.id, mention.offsetStart, mention.offsetEnd);
     }
   }
 
+  private resolveMention(orgId: string, spaceId: string, token: string): MentionTarget {
+    const handles = mentionLookupHandles(token);
+    if (handles.has("board")) return { type: "board", id: orgId };
+    if (handles.has("oncall")) return { type: "org_group", id: `${orgId}:oncall` };
+    const candidates = mentionCandidates(this.db, orgId, spaceId).filter((candidate) => handles.has(candidate.handle));
+    const unique = new Map(candidates.map((candidate) => [`${candidate.type}:${candidate.id}`, candidate]));
+    if (unique.size === 0) throw new Error(`Mention @${token} could not be resolved.`);
+    if (unique.size > 1) throw new Error(`Mention @${token} is ambiguous.`);
+    const target = [...unique.values()][0];
+    return { type: target.type, id: target.id };
+  }
+
   private recordSlashInvocation(messageId: string, slash: SlashInvocation, now: string): void {
     this.db.prepare(`
       insert into chat_slash_invocations(id, message_id, command, args_json, result_ref, created_at)
@@ -284,3 +322,37 @@ function createThreadTitle(body: string): string {
   const firstLine = body.split(/\r?\n/, 1)[0].trim();
   return firstLine.length > 80 ? `${firstLine.slice(0, 77)}...` : firstLine;
 }
+
+function mentionCandidates(db: DatabaseSync, orgId: string, spaceId: string): MentionCandidate[] {
+  const employees = db.prepare(`
+    select employees.id, employees.display_name
+    from employees
+    join chat_memberships memberships
+      on memberships.principal_type = 'employee'
+      and memberships.principal_id = employees.id
+      and memberships.space_id = ?
+    where employees.org_id = ?
+  `).all(spaceId, orgId) as Array<{ id: string; display_name: string }>;
+  const agents = db.prepare(`
+    select agents.id, agents.name
+    from agents
+    join chat_memberships memberships
+      on memberships.principal_type = 'agent'
+      and memberships.principal_id = agents.id
+      and memberships.space_id = ?
+    where agents.org_id = ?
+  `).all(spaceId, orgId) as Array<{ id: string; name: string }>;
+  return [
+    ...employees.flatMap((employee) => principalMentionHandles("employee", employee.id, employee.display_name)),
+    ...agents.flatMap((agent) => principalMentionHandles("agent", agent.id, agent.name)),
+  ];
+}
+
+function principalMentionHandles(type: "employee" | "agent", id: string, name: string): MentionCandidate[] {
+  const handles = new Set([canonicalMentionHandle(name), id.toLowerCase()].filter((handle) => handle.length > 0));
+  return [...handles].map((handle) => ({ type, id, handle }));
+}
+
+function mentionLookupHandles(token: string): Set<string> {
+  return new Set([token.toLowerCase(), canonicalMentionHandle(token)].filter((handle) => handle.length > 0));
+}
diff --git a/AgentCompany-New/src/main/services/mention-handles.ts b/AgentCompany-New/src/main/services/mention-handles.ts
new file mode 100644
index 00000000..2629c359
--- /dev/null
+++ b/AgentCompany-New/src/main/services/mention-handles.ts
@@ -0,0 +1,11 @@
+export const RESERVED_MENTION_HANDLES = new Set(["board", "oncall"]);
+
+export function canonicalMentionHandle(value: string): string {
+  return value.toLowerCase().replace(/[^a-z0-9]/g, "");
+}
+
+export function assertUsableMentionName(value: string): void {
+  if (RESERVED_MENTION_HANDLES.has(canonicalMentionHandle(value))) {
+    throw new Error("Mention handle is reserved.");
+  }
+}
diff --git a/AgentCompany-New/src/main/services/organization-service.ts b/AgentCompany-New/src/main/services/organization-service.ts
index 68c49eaf..358aa327 100644
--- a/AgentCompany-New/src/main/services/organization-service.ts
+++ b/AgentCompany-New/src/main/services/organization-service.ts
@@ -5,6 +5,7 @@ import { createId } from "../../shared/ids";
 import type { CreateAgentInput, CreateOrganizationInput, CreateTaskInput } from "../../shared/commands";
 import { AuditService } from "./audit-service";
 import { PolicyService } from "./policy-service";
+import { assertUsableMentionName } from "./mention-handles";
 
 export class OrganizationService {
   private readonly audit: AuditService;
@@ -16,6 +17,7 @@ export class OrganizationService {
   }
 
   createOrganization(input: CreateOrganizationInput): string {
+    assertUsableMentionName(input.employeeName);
     const orgId = createId("org");
     const employeeId = createId("emp");
     const now = new Date().toISOString();
@@ -127,6 +129,7 @@ export class OrganizationService {
   }
 
   createAgent(input: CreateAgentInput): string {
+    assertUsableMentionName(input.name);
     const id = createId("agt");
     const now = new Date().toISOString();
     this.db.prepare(`
diff --git a/AgentCompany-New/tests/unit/domain-services.test.ts b/AgentCompany-New/tests/unit/domain-services.test.ts
index dac7f107..226714f1 100644
--- a/AgentCompany-New/tests/unit/domain-services.test.ts
+++ b/AgentCompany-New/tests/unit/domain-services.test.ts
@@ -237,9 +237,10 @@ describe("domain services", () => {
     expect(state.chatAttachments).toHaveLength(1);
     expect(state.chatPresence).toHaveLength(1);
     const slash = connection.db.prepare("select command from chat_slash_invocations").get() as { command: string };
-    const mention = connection.db.prepare("select target_id from chat_mentions").get() as { target_id: string };
+    const mention = connection.db.prepare("select target_type, target_id from chat_mentions").get() as { target_type: string; target_id: string };
     expect(slash.command).toBe("handoff");
-    expect(mention.target_id).toBe("Board");
+    expect(mention.target_type).toBe("board");
+    expect(mention.target_id).toBe(orgId);
     connection.close();
   });
 
@@ -297,6 +298,15 @@ describe("domain services", () => {
       bodyMd: "I should not be here.",
       attachmentFileIds: [],
     }))).toThrow("Chat membership is required.");
+    expect(() => connection.transaction(() => chat.sendMessage({
+      orgId,
+      spaceId: restrictedSpaceId,
+      threadId: null,
+      senderType: "employee",
+      senderId: employeeId,
+      bodyMd: "Restricted ping @Ada",
+      attachmentFileIds: [],
+    }))).toThrow("Mention @Ada could not be resolved.");
     expect(() => connection.transaction(() => chat.sendMessage({
       orgId,
       spaceId: workspaceSpaceId,
@@ -315,12 +325,143 @@ describe("domain services", () => {
       bodyMd: "Missing file",
       attachmentFileIds: ["file_missing"],
     }))).toThrow("Attachment file was not found.");
+    expect(() => connection.transaction(() => chat.sendMessage({
+      orgId,
+      spaceId: workspaceSpaceId,
+      threadId: null,
+      senderType: "employee",
+      senderId: employeeId,
+      bodyMd: "Unknown @Nobody",
+      attachmentFileIds: [],
+    }))).toThrow("Mention @Nobody could not be resolved.");
 
     const count = connection.db.prepare("select count(*) as count from chat_messages").get() as { count: number };
     expect(count.count).toBe(0);
     connection.close();
   });
 
+  test("rejects reserved mention handles for employees and agents", () => {
+    const connection = createConnection();
+    const organization = new OrganizationService(connection.db);
+    let orgId = "";
+
+    expect(() => connection.transaction(() => organization.createOrganization({
+      organizationName: "Acme Operations",
+      employeeName: "Board",
+      mission: "Coordinate agents with auditable approvals.",
+      goal: "Ship a verified control plane.",
+    }))).toThrow("Mention handle is reserved.");
+
+    connection.transaction(() => {
+      orgId = organization.createOrganization({
+        organizationName: "Acme Operations",
+        employeeName: "Dana Lee",
+        mission: "Coordinate agents with auditable approvals.",
+        goal: "Ship a verified control plane.",
+      });
+    });
+    expect(() => connection.transaction(() => organization.createAgent({
+      orgId,
+      name: "On Call",
+      role: "Escalation lead",
+      department: "Operations",
+      modelProviderId: null,
+      modelId: null,
+      budgetCents: 10000,
+      managerAgentId: null,
+    }))).toThrow("Mention handle is reserved.");
+    connection.close();
+  });
+
+  test("rejects ambiguous chat mentions", () => {
+    const connection = createConnection();
+    const organization = new OrganizationService(connection.db);
+    const chat = new ChatService(connection.db);
+    let orgId = "";
+    let employeeId = "";
+    let spaceId = "";
+
+    connection.transaction(() => {
+      orgId = organization.createOrganization({
+        organizationName: "Acme Operations",
+        employeeName: "Dana Lee",
+        mission: "Coordinate agents with auditable approvals.",
+        goal: "Ship a verified control plane.",
+      });
+      employeeId = (connection.db.prepare("select id from employees where org_id = ?").get(orgId) as { id: string }).id;
+      organization.createAgent({ orgId, name: "Ada", role: "Reviewer", department: "Engineering", modelProviderId: null, modelId: null, budgetCents: 10000, managerAgentId: null });
+      organization.createAgent({ orgId, name: "Ada", role: "Release lead", department: "Engineering", modelProviderId: null, modelId: null, budgetCents: 10000, managerAgentId: null });
+      spaceId = chat.createSpace({ orgId, spaceType: "project", name: "release", topic: "Release coordination", visibility: "workspace" });
+    });
+
+    expect(() => connection.transaction(() => chat.sendMessage({
+      orgId,
+      spaceId,
+      threadId: null,
+      senderType: "employee",
+      senderId: employeeId,
+      bodyMd: "Please review @Ada",
+      attachmentFileIds: [],
+    }))).toThrow("Mention @Ada is ambiguous.");
+    const count = connection.db.prepare("select count(*) as count from chat_messages").get() as { count: number };
+    expect(count.count).toBe(0);
+    connection.close();
+  });
+
+  test("resolves chat mentions by display handle and principal id", () => {
+    const connection = createConnection();
+    const organization = new OrganizationService(connection.db);
+    const chat = new ChatService(connection.db);
+    let orgId = "";
+    let employeeId = "";
+    let agentId = "";
+    let spaceId = "";
+
+    connection.transaction(() => {
+      orgId = organization.createOrganization({
+        organizationName: "Acme Operations",
+        employeeName: "Dana Lee",
+        mission: "Coordinate agents with auditable approvals.",
+        goal: "Ship a verified control plane.",
+      });
+      employeeId = (connection.db.prepare("select id from employees where org_id = ?").get(orgId) as { id: string }).id;
+      agentId = organization.createAgent({
+        orgId,
+        name: "Ada Lovelace",
+        role: "Reviewer",
+        department: "Engineering",
+        modelProviderId: null,
+        modelId: null,
+        budgetCents: 10000,
+        managerAgentId: null,
+      });
+      spaceId = chat.createSpace({ orgId, spaceType: "project", name: "release", topic: "Release coordination", visibility: "workspace" });
+    });
+
+    connection.transaction(() => {
+      chat.sendMessage({
+        orgId,
+        spaceId,
+        threadId: null,
+        senderType: "employee",
+        senderId: employeeId,
+        bodyMd: `Review @Ada-Lovelace and @${agentId}`,
+        attachmentFileIds: [],
+      });
+    });
+
+    const mentions = connection.db.prepare(`
+      select target_type, target_id
+      from chat_mentions
+      order by offset_start asc
+    `).all() as Array<{ target_type: string; target_id: string }>;
+    expect(mentions).toEqual([
+      { target_type: "agent", target_id: agentId },
+      { target_type: "agent", target_id: agentId },
+    ]);
+    connection.close();
+  });
+
   test("rejects replies to threads from another chat space", () => {
     const connection = createConnection();
     const organization = new OrganizationService(connection.db);