diff --git a/server/src/__tests__/agent-hire-auth-inheritance-routes.test.ts b/server/src/__tests__/agent-hire-auth-inheritance-routes.test.ts
index fd80ddf876..ef03ac91eb 100644
--- a/server/src/__tests__/agent-hire-auth-inheritance-routes.test.ts
+++ b/server/src/__tests__/agent-hire-auth-inheritance-routes.test.ts
@@ -333,6 +333,66 @@ describeEmbeddedPostgres("hired agent provider credential inheritance", () => {
     expect(Object.keys(childEnvOf(res))).toHaveLength(0);
   });
 
+  it("does not inherit a codex_local credential from a hiring agent in another company", async () => {
+    const parentCompanyId = await seedCompany();
+    const targetCompanyId = await seedCompany();
+    const secret = await createCompanySecret(parentCompanyId, "sk-openai-other-company");
+    const parent = await seedParentAgent(parentCompanyId, "codex_local", {
+      OPENAI_API_KEY: secretRef(secret.id),
+    });
+
+    // The actor claims the target company, but the named hiring agent belongs
+    // to a different company. The route must reject the request and must
+    // never copy the other company's credential reference.
+    const res = await hire(agentActor(targetCompanyId, parent.id), targetCompanyId, {
+      name: "Codex Cross-Company Child",
+      role: "engineer",
+      adapterType: "codex_local",
+    });
+
+    expect(res.status).toBe(403);
+    const children = await db.select().from(agents).where(eq(agents.companyId, targetCompanyId));
+    expect(children).toHaveLength(0);
+  });
+
+  it("does not inherit a grok_local credential from a hiring agent in another company", async () => {
+    const parentCompanyId = await seedCompany();
+    const targetCompanyId = await seedCompany();
+    const secret = await createCompanySecret(parentCompanyId, "xai-other-company");
+    const parent = await seedParentAgent(parentCompanyId, "grok_local", {
+      XAI_API_KEY: secretRef(secret.id),
+    });
+
+    const res = await hire(agentActor(targetCompanyId, parent.id), targetCompanyId, {
+      name: "Grok Cross-Company Child",
+      role: "engineer",
+      adapterType: "grok_local",
+    });
+
+    expect(res.status).toBe(403);
+    const children = await db.select().from(agents).where(eq(agents.companyId, targetCompanyId));
+    expect(children).toHaveLength(0);
+  });
+
+  it("does not inherit a claude_local credential, including the fixed OAuth binding, from a hiring agent in another company", async () => {
+    const parentCompanyId = await seedCompany();
+    const targetCompanyId = await seedCompany();
+    const parent = await seedParentAgent(parentCompanyId, "claude_local", {
+      ANTHROPIC_API_KEY: secretRef((await createCompanySecret(parentCompanyId, "ant-other-company")).id),
+      CLAUDE_CODE_OAUTH_TOKEN: { ...FIXED_CLAUDE_OAUTH_BINDING, version: 1 },
+    });
+
+    const res = await hire(agentActor(targetCompanyId, parent.id), targetCompanyId, {
+      name: "Claude Cross-Company Child",
+      role: "engineer",
+      adapterType: "claude_local",
+    });
+
+    expect(res.status).toBe(403);
+    const children = await db.select().from(agents).where(eq(agents.companyId, targetCompanyId));
+    expect(children).toHaveLength(0);
+  });
+
   it("carves out a per-agent CODEX_HOME when the child inherits OPENAI_API_KEY", async () => {
     const companyId = await seedCompany();
     const secret = await createCompanySecret(companyId, "sk-openai-isolated");
diff --git a/server/src/routes/agents.ts b/server/src/routes/agents.ts
index b739ee7356..baa8a39388 100644
--- a/server/src/routes/agents.ts
+++ b/server/src/routes/agents.ts
@@ -2472,8 +2472,13 @@ export function agentRoutes(
   // key inherits no Claude credential key at all. That keeps child-wins
   // precedence and rules out the forbidden pairing of the fixed OAuth binding
   // with an ANTHROPIC_API_KEY.
+  //
+  // The hiring agent must belong to the target company. Without that check, an
+  // agent that can create agents in another company could copy its own
+  // company's credential reference into that other company.
   async function applyHiringAgentAuthInheritance(
     req: Request,
+    companyId: string,
     adapterType: string | null | undefined,
     adapterConfig: Record<string, unknown>,
   ): Promise<{ adapterConfig: Record<string, unknown>; inheritedFixedClaudeOAuthBinding: boolean }> {
@@ -2483,7 +2488,7 @@ export function agentRoutes(
     if (!credentialKeys) return noInheritance;
 
     const parent = await svc.getById(req.actor.agentId);
-    if (!parent || parent.adapterType !== adapterType) return noInheritance;
+    if (!parent || parent.companyId !== companyId || parent.adapterType !== adapterType) return noInheritance;
     const parentEnv = asRecord(asRecord(parent.adapterConfig)?.env);
     if (!parentEnv) return noInheritance;
 
@@ -4263,6 +4268,7 @@ export function agentRoutes(
     const hiredAgentId = randomUUID();
     const authInheritance = await applyHiringAgentAuthInheritance(
       req,
+      companyId,
       hireInput.adapterType,
       applyCreateDefaultsByAdapterType(
         hireInput.adapterType,