diff --git a/static/commands.js b/static/commands.js
index 49b484cd..df0266a0 100644
--- a/static/commands.js
+++ b/static/commands.js
@@ -48,6 +48,127 @@ function parseCommand(text){
   return {name,args};
 }
 
+const DESKTOP_COMPANION_EXTENSION_ID='desktop-companion';
+const DESKTOP_COMPANION_NAME='Desktop Companion';
+const DESKTOP_COMPANION_INSTALL_PATH='Settings -> Extensions -> Gallery -> Desktop Companion';
+const DESKTOP_COMPANION_SETUP_GUIDE_URL='https://github.com/franksong2702/hermes-webui-desktop-companion#after-gallery-install';
+const DESKTOP_COMPANION_LOCAL_APP_LABEL='Desktop Companion app';
+
+function _getDesktopCompanionStatusGlobal(){
+  if(typeof window==='undefined') return null;
+  return window.__HERMES_WEBUI_DESKTOP_COMPANION_STATUS__||null;
+}
+
+function _getDesktopCompanionExtensionStatus(status){
+  return Array.isArray(status&&status.extensions)
+    ? status.extensions.find(ext=>String(ext&&ext.id||'')===DESKTOP_COMPANION_EXTENSION_ID)||null
+    : null;
+}
+
+function _petSlashCommandArgs(rawCommandText){
+  const parsed=parseCommand(String(rawCommandText||'').trim());
+  return parsed&&parsed.name==='pet' ? parsed.args : String(rawCommandText||'').trim().replace(/^\/pet\b\s*/i,'').trim();
+}
+
+function _desktopCompanionMissingMessage(){
+  return `${DESKTOP_COMPANION_NAME} is not installed yet.
+
+Install it from ${DESKTOP_COMPANION_INSTALL_PATH}, then follow the setup guide: ${DESKTOP_COMPANION_SETUP_GUIDE_URL}.
+
+The guide also shows how to start the ${DESKTOP_COMPANION_LOCAL_APP_LABEL}.`;
+}
+
+function _desktopCompanionDisabledMessage(){
+  return `${DESKTOP_COMPANION_NAME} is installed but disabled.
+
+Enable it in Settings -> Extensions, then reload WebUI if you just changed that and start the ${DESKTOP_COMPANION_LOCAL_APP_LABEL}.
+
+Setup guide: ${DESKTOP_COMPANION_SETUP_GUIDE_URL}`;
+}
+
+function _desktopCompanionReloadMessage(){
+  return `${DESKTOP_COMPANION_NAME} is enabled, but the adapter status is not loaded yet.
+
+Reload WebUI if you just enabled it, then start the ${DESKTOP_COMPANION_LOCAL_APP_LABEL}.`;
+}
+
+function _desktopCompanionConnectMessage(){
+  return `${DESKTOP_COMPANION_NAME} is enabled, but the local app is not connected yet.
+
+Start or connect the ${DESKTOP_COMPANION_LOCAL_APP_LABEL}, then retry /pet.
+
+Setup guide: ${DESKTOP_COMPANION_SETUP_GUIDE_URL}`;
+}
+
+function _desktopCompanionStatusUnavailableMessage(){
+  return `${DESKTOP_COMPANION_NAME} status is unavailable right now.
+
+Reload WebUI or check your connection, then retry /pet.`;
+}
+
+function _desktopCompanionUnavailableMessage(){
+  return `${DESKTOP_COMPANION_NAME} is installed and connected, but /pet is not available yet in this Desktop Companion version.
+
+Update the ${DESKTOP_COMPANION_LOCAL_APP_LABEL}, then follow the setup guide: ${DESKTOP_COMPANION_SETUP_GUIDE_URL}.`;
+}
+
+function _desktopCompanionHookErrorMessage(){
+  return `${DESKTOP_COMPANION_NAME} is installed and connected, but it hit an error while handling /pet.
+
+Check the browser console and the ${DESKTOP_COMPANION_LOCAL_APP_LABEL}, then retry /pet.`;
+}
+
+async function handlePetSlashCommand(rawCommandText,meta){
+  const command=String(rawCommandText||'');
+  const commandName=String((meta&&meta.name)||'pet').trim()||'pet';
+  const args=_petSlashCommandArgs(command);
+  let status;
+  try{
+    status=await api('/api/extensions/status');
+  }catch(_e){
+    return {handled:false,message:_desktopCompanionStatusUnavailableMessage()};
+  }
+  const companion=_getDesktopCompanionExtensionStatus(status);
+  if(!companion){
+    return {handled:false,message:_desktopCompanionMissingMessage()};
+  }
+  if(companion.effective_enabled!==true){
+    return {handled:false,message:_desktopCompanionDisabledMessage()};
+  }
+  const companionStatus=_getDesktopCompanionStatusGlobal();
+  if(!companionStatus){
+    return {handled:false,message:_desktopCompanionReloadMessage()};
+  }
+  if(companionStatus.connected!==true){
+    return {handled:false,message:_desktopCompanionConnectMessage()};
+  }
+  const hook=typeof window!=='undefined'&&window.__hermesHandlePetSlashCommand;
+  if(typeof hook==='function'){
+    try{
+      const result=await hook({
+        command,
+        args,
+        source:'webui-slash-command',
+        metadata:{name:commandName},
+      });
+      if(result){
+        return {
+          handled:true,
+          message:result&&typeof result==='object'&&'message' in result
+            ? String(result.message??'')
+            : '',
+        };
+      }
+    }catch(_e){
+      if(typeof console!=='undefined'&&console.error){
+        console.error('[hermes] Desktop Companion /pet hook error:',_e);
+      }
+      return {handled:false,message:_desktopCompanionHookErrorMessage()};
+    }
+  }
+  return {handled:false,message:_desktopCompanionUnavailableMessage()};
+}
+
 function executeCommand(text){
   const parsed=parseCommand(text);
   if(!parsed)return null;
@@ -76,11 +197,22 @@ function getMatchingCommands(prefix){
     });
     seen.add(name);
   }
+  if('pet'.startsWith(q)&&!seen.has('pet')){
+    const petMeta=Array.isArray(_agentCommandCache)
+      ? _agentCommandCache.find(cmd=>String(cmd&&cmd.name||'').toLowerCase()==='pet')
+      : null;
+    matches.push({
+      name:'pet',
+      desc:String((petMeta&&petMeta.description)||'Desktop Companion command').trim()||'Desktop Companion command',
+      source:'agent',
+    });
+    seen.add('pet');
+  }
   // Include agent/plugin commands from /api/commands metadata
   for(const cmd of (_agentCommandCache||[])){
     const name=String(cmd&&cmd.name||'').toLowerCase();
     if(!name.startsWith(q)||seen.has(name))continue;
-    if(cmd.cli_only)continue;
+    if(cmd.cli_only&&name!=='pet')continue;
     matches.push({
       name,
       desc:String(cmd&&cmd.description||'').trim()||'Agent command',
diff --git a/static/messages.js b/static/messages.js
index 73b5d6fe..722ade32 100644
--- a/static/messages.js
+++ b/static/messages.js
@@ -1351,6 +1351,23 @@ async function send(){
       }
     }
     if(_parsedCmd&&!_cmd){
+      if(_parsedCmd.name==='pet'){
+        if(!S.session){await newSession();await renderSessionList();}
+        S.messages.push({role:'user',content:text,_ts:Date.now()/1000});
+        let _petOutput=null;
+        try{
+          _petOutput=typeof handlePetSlashCommand==='function'
+            ? await handlePetSlashCommand(text,{name:'pet'})
+            : {handled:false,message:'Desktop Companion is unavailable in WebUI.'};
+        }catch(e){
+          _petOutput={handled:false,message:`Desktop Companion command error: ${e&&e.message||e}`};
+        }
+        if(_petOutput&&_petOutput.message){
+          S.messages.push({role:'assistant',content:String(_petOutput.message),_ts:Date.now()/1000});
+        }
+        renderMessages();
+        $('msg').value='';autoResize();hideCmdDropdown();return;
+      }
       const _agentCmd=typeof getAgentCommandMetadata==='function'
         ? await getAgentCommandMetadata(_parsedCmd.name)
         : null;
diff --git a/tests/test_cli_only_slash_commands.py b/tests/test_cli_only_slash_commands.py
index c8da5c7e..4f1d9fd4 100644
--- a/tests/test_cli_only_slash_commands.py
+++ b/tests/test_cli_only_slash_commands.py
@@ -100,6 +100,14 @@ def _run_commands_js(script_body: str) -> dict:
           api: async (path) => {{
             if (path === '/api/commands') return {{
               commands: [
+                {{
+                  name: 'pet',
+                  description: 'Desktop Companion command',
+                  category: 'Tools',
+                  aliases: [],
+                  cli_only: true,
+                  gateway_only: false
+                }},
                 {{
                   name: 'browser',
                   description: 'Attach browser tools',
@@ -300,6 +308,8 @@ def test_cli_only_slugs_reserve_skill_autocomplete_namespace():
         await loadAgentCommandMetadata(true);
         await loadBundleCommands(true);
         await loadSkillCommands(true);
+        const pet = await getSlashAutocompleteMatches('/pet');
+        const browser = await getSlashAutocompleteMatches('/bro');
         const handoff = await getSlashAutocompleteMatches('/handoff');
         const delegate = await getSlashAutocompleteMatches('/delegate');
         const incident = await getSlashAutocompleteMatches('/incident');
@@ -308,6 +318,10 @@ def test_cli_only_slugs_reserve_skill_autocomplete_namespace():
         const skills = await getSlashAutocompleteMatches('/skills');
         const use = await getSlashAutocompleteMatches('/use');
         return {
+          pet_names: pet.map(item => item.name),
+          pet_sources: pet.map(item => item.source),
+          pet_descs: pet.map(item => item.desc),
+          browser_names: browser.map(item => item.name),
           handoff_names: handoff.map(item => item.name),
           delegate_names: delegate.map(item => item.name),
           incident_names: incident.map(item => item.name),
@@ -322,6 +336,10 @@ def test_cli_only_slugs_reserve_skill_autocomplete_namespace():
         """
     )
 
+    assert result["pet_names"] == ["pet"]
+    assert result["pet_sources"] == ["agent"]
+    assert result["pet_descs"] == ["Desktop Companion command"]
+    assert result["browser_names"] == []
     assert result["handoff_names"] == []
     assert result["delegate_names"] == []
     assert result["incident_names"] == ["incident-review"]
diff --git a/tests/test_issue4843_pet_webui_command.py b/tests/test_issue4843_pet_webui_command.py
new file mode 100644
index 00000000..112a50ab
--- /dev/null
+++ b/tests/test_issue4843_pet_webui_command.py
@@ -0,0 +1,558 @@
+"""Regression tests for the WebUI /pet handoff."""
+
+import json
+from pathlib import Path
+import subprocess
+import tempfile
+import textwrap
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+COMMANDS_JS = (REPO_ROOT / "static" / "commands.js").read_text(encoding="utf-8")
+MESSAGES_JS = (REPO_ROOT / "static" / "messages.js").read_text(encoding="utf-8")
+
+
+def _run_pet_js(
+    *,
+    status,
+    adapter_status=None,
+    status_throws=False,
+    hook_result=None,
+    hook_throws=False,
+    command="/pet feed tuna",
+):
+    hook_setup = ""
+    if hook_throws:
+        hook_setup += textwrap.dedent(
+            """
+            ctx.window.__hermesHandlePetSlashCommand = async payload => {
+              hookCalls.push(payload);
+              throw new Error('hook failed');
+            };
+            """
+        )
+    elif hook_result is not None:
+        hook_setup += textwrap.dedent(
+            f"""
+            ctx.window.__hermesHandlePetSlashCommand = async payload => {{
+              hookCalls.push(payload);
+              return {json.dumps(hook_result)};
+            }};
+            """
+        )
+
+    script = textwrap.dedent(
+        f"""
+        const vm = require('vm');
+        const hookCalls = [];
+        const consoleErrors = [];
+        const captureConsole = {{
+          ...console,
+          error: (...args) => {{
+            consoleErrors.push(args.map(arg => String(arg && arg.message ? arg.message : arg)).join(' '));
+          }},
+        }};
+        const window = {{
+          __HERMES_WEBUI_DESKTOP_COMPANION_STATUS__: {json.dumps(adapter_status)},
+        }};
+        window.window = window;
+        const ctx = {{
+          console: captureConsole,
+          window,
+          localStorage: {{ getItem(){{return null;}}, setItem(){{}}, removeItem(){{}} }},
+          t: key => key,
+          api: async path => {{
+            if (path === '/api/extensions/status') {{
+              if ({json.dumps(status_throws)}) throw new Error('extensions api failed');
+              return {json.dumps(status)};
+            }}
+            throw new Error('unexpected api path: ' + path);
+          }},
+        }};
+        {hook_setup}
+        vm.createContext(ctx);
+        vm.runInContext({json.dumps(COMMANDS_JS)}, ctx);
+        (async () => {{
+          const result = await vm.runInContext(`(async () => {{ return await handlePetSlashCommand({json.dumps(command)}, {{name:'pet'}}); }})()`, ctx);
+          process.stdout.write(JSON.stringify({{result, hookCalls, consoleErrors}}));
+        }})().catch(err => {{
+          console.error(err && err.stack || err);
+          process.exit(1);
+        }});
+        """
+    )
+    with tempfile.NamedTemporaryFile("w", suffix=".js", encoding="utf-8", delete=False) as handle:
+        handle.write(script)
+        script_path = Path(handle.name)
+    try:
+        proc = subprocess.run(["node", str(script_path)], check=True, capture_output=True, text=True)
+    finally:
+        script_path.unlink(missing_ok=True)
+    return json.loads(proc.stdout)
+
+
+def _run_send_js(*, command, status, adapter_status=None, hook_result=None, hook_throws=False):
+    hook_setup = ""
+    if hook_throws:
+        hook_setup += textwrap.dedent(
+            """
+            ctx.window.__hermesHandlePetSlashCommand = async payload => {
+              throw new Error('hook failed');
+            };
+            """
+        )
+    elif hook_result is not None:
+        hook_setup += textwrap.dedent(
+            f"""
+            ctx.window.__hermesHandlePetSlashCommand = async payload => {{
+              return {json.dumps(hook_result)};
+            }};
+            """
+        )
+    script = textwrap.dedent(
+        f"""
+        const vm = require('vm');
+        const msgInput = {{
+          value: {json.dumps(command)},
+          style: {{}},
+          scrollHeight: 0,
+          addEventListener(){{}},
+          removeEventListener(){{}},
+          focus(){{}},
+          blur(){{}},
+          setSelectionRange(){{}},
+        }};
+        const commandExecCalls = [];
+        const genericEl = {{
+          addEventListener(){{}},
+          removeEventListener(){{}},
+          classList: {{ add(){{}}, remove(){{}} }},
+          style: {{}},
+          dataset: {{}},
+          value: '',
+          textContent: '',
+          innerHTML: '',
+        }};
+        const ctx = {{
+          console,
+          window: {{
+            __HERMES_WEBUI_DESKTOP_COMPANION_STATUS__: {json.dumps(adapter_status)},
+            addEventListener(){{}},
+            requestAnimationFrame(cb){{ return 1; }},
+          }},
+          document: {{
+            addEventListener(){{}},
+            getElementById(id){{ return id === 'msg' ? msgInput : genericEl; }},
+            querySelector(){{ return null; }},
+          }},
+          localStorage: {{ getItem(){{return null;}}, setItem(){{}}, removeItem(){{}} }},
+          t: key => key,
+          S: {{
+            busy: false,
+            session: null,
+            pendingFiles: [],
+            messages: [],
+            activeProfile: 'default',
+            activeStreamId: null,
+          }},
+          INFLIGHT: {{}},
+          _pendingSelections: [],
+          _sendInProgress: false,
+          _sendInProgressSid: null,
+          _composerTextWithPendingSelections(){{ return msgInput.value; }},
+          _flushSelectionBlocksToComposer(){{}},
+          _dismissHandoffHint(){{}},
+          _clearStaleBusyStateBeforeSend(){{ return false; }},
+          _clearComposerAfterQueuedSelectionSend(){{}},
+          _chatPayloadModelState(){{ return {{ model: '', model_provider: '' }}; }},
+          queueSessionMessage(){{}},
+          updateQueueBadge(){{}},
+          renderTray(){{}},
+          showToast(){{}},
+          renderMessages(){{}},
+          renderSessionList(){{}},
+          autoResize(){{}},
+          hideCmdDropdown(){{}},
+          syncTopbar(){{}},
+          setBusy(){{}},
+          setComposerStatus(){{}},
+          setStatus(){{}},
+          updateSendBtn(){{}},
+          clearOptimisticSessionStreaming(){{}},
+          newSession: async () => {{
+            ctx.S.session = {{ session_id: 'sid-1', title: 'New Chat' }};
+          }},
+          $: id => {{
+            if (id === 'msg') return msgInput;
+            return genericEl;
+          }},
+          api: async (path, options) => {{
+            if (path === '/api/commands') return {{
+              commands: [
+                {{
+                  name: 'pet',
+                  description: 'Desktop Companion command',
+                  category: 'Tools',
+                  aliases: [],
+                  cli_only: true,
+                  gateway_only: false
+                }},
+                {{
+                  name: 'browser',
+                  description: 'Attach browser tools',
+                  category: 'Tools',
+                  aliases: ['browse'],
+                  cli_only: true,
+                  gateway_only: false
+                }}
+              ]
+            }};
+            if (path === '/api/extensions/status') return {json.dumps(status)};
+            if (path === '/api/commands/exec') {{
+              commandExecCalls.push(JSON.parse(options.body).command);
+              return {{ output: 'unexpected exec' }};
+            }}
+            throw new Error('unexpected api path: ' + path);
+          }},
+        }};
+        ctx.window.window = ctx.window;
+        vm.createContext(ctx);
+        vm.runInContext({json.dumps(COMMANDS_JS)}, ctx);
+        {hook_setup}
+        vm.runInContext({json.dumps(MESSAGES_JS)}, ctx);
+        (async () => {{
+          await vm.runInContext('send()', ctx);
+          process.stdout.write(JSON.stringify({{
+            messages: ctx.S.messages,
+            commandExecCalls,
+            remainingInput: msgInput.value,
+          }}));
+        }})().catch(err => {{
+          console.error(err && err.stack || err);
+          process.exit(1);
+        }});
+        """
+    )
+    with tempfile.NamedTemporaryFile("w", suffix=".js", encoding="utf-8", delete=False) as handle:
+        handle.write(script)
+        script_path = Path(handle.name)
+    try:
+        proc = subprocess.run(["node", str(script_path)], check=True, capture_output=True, text=True)
+    finally:
+        script_path.unlink(missing_ok=True)
+    return json.loads(proc.stdout)
+
+
+def test_pet_help_routes_to_install_guidance_when_companion_is_missing():
+    result = _run_pet_js(
+        status={"enabled": False, "extensions": [], "gallery_installed": {}},
+        adapter_status=None,
+    )
+
+    assert result["result"]["handled"] is False
+    message = result["result"]["message"]
+    assert "Desktop Companion is not installed yet." in message
+    assert "Settings -> Extensions -> Gallery -> Desktop Companion" in message
+    assert "https://github.com/franksong2702/hermes-webui-desktop-companion#after-gallery-install" in message
+    assert "Desktop Companion app" in message
+
+
+def test_pet_help_routes_to_enable_guidance_when_companion_is_disabled():
+    result = _run_pet_js(
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": False,
+                    "user_disabled": True,
+                    "status": "user_disabled",
+                }
+            ],
+        },
+        adapter_status=None,
+    )
+
+    assert result["result"]["handled"] is False
+    message = result["result"]["message"]
+    assert "Desktop Companion is installed but disabled." in message
+    assert "Enable it in Settings -> Extensions" in message
+    assert "Desktop Companion app" in message
+    assert "https://github.com/franksong2702/hermes-webui-desktop-companion#after-gallery-install" in message
+
+
+def test_pet_help_routes_to_reload_and_start_guidance_when_adapter_status_is_missing():
+    result = _run_pet_js(
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status=None,
+    )
+
+    assert result["result"]["handled"] is False
+    message = result["result"]["message"]
+    assert "adapter status is not loaded yet" in message
+    assert "Reload WebUI if you just enabled it" in message
+    assert "Desktop Companion app" in message
+
+
+def test_pet_help_routes_to_connect_guidance_when_adapter_is_not_connected():
+    result = _run_pet_js(
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status={"connected": False},
+    )
+
+    assert result["result"]["handled"] is False
+    message = result["result"]["message"]
+    assert "local app is not connected yet" in message
+    assert "Start or connect the Desktop Companion app" in message
+    assert "Setup guide:" in message
+
+
+def test_pet_help_hands_off_to_desktop_companion_hook_when_connected():
+    result = _run_pet_js(
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status={"connected": True},
+        hook_result={"handled": True, "message": "mascot handled"},
+        command="/pet   feed  tuna  ",
+    )
+
+    assert result["result"] == {"handled": True, "message": "mascot handled"}
+    assert result["hookCalls"] == [
+        {
+            "command": "/pet   feed  tuna  ",
+            "args": "feed tuna",
+            "source": "webui-slash-command",
+            "metadata": {"name": "pet"},
+        }
+    ]
+
+
+def test_pet_help_preserves_explicit_falsy_hook_message_values():
+    result = _run_pet_js(
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status={"connected": True},
+        hook_result={"handled": True, "message": 0},
+        command="/pet count snacks",
+    )
+
+    assert result["result"] == {"handled": True, "message": "0"}
+    assert result["hookCalls"] == [
+        {
+            "command": "/pet count snacks",
+            "args": "count snacks",
+            "source": "webui-slash-command",
+            "metadata": {"name": "pet"},
+        }
+    ]
+
+
+def test_pet_help_treats_truthy_hook_result_as_handled():
+    result = _run_pet_js(
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status={"connected": True},
+        hook_result="mascot handled",
+        command="/pet wave",
+    )
+
+    assert result["result"] == {"handled": True, "message": ""}
+    assert result["hookCalls"] == [
+        {
+            "command": "/pet wave",
+            "args": "wave",
+            "source": "webui-slash-command",
+            "metadata": {"name": "pet"},
+        }
+    ]
+
+
+def test_pet_help_routes_to_status_error_when_extension_status_api_fails():
+    result = _run_pet_js(
+        status={"enabled": False, "extensions": []},
+        status_throws=True,
+        adapter_status=None,
+    )
+
+    assert result["result"]["handled"] is False
+    assert result["result"]["message"] == (
+        "Desktop Companion status is unavailable right now.\n\n"
+        "Reload WebUI or check your connection, then retry /pet."
+    )
+
+
+def test_pet_help_falls_back_to_unavailable_guidance_when_hook_is_missing():
+    result = _run_pet_js(
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status={"connected": True},
+    )
+
+    message = result["result"]["message"]
+    assert result["result"]["handled"] is False
+    assert "Desktop Companion is installed and connected" in message
+    assert "/pet is not available yet in this Desktop Companion version" in message
+    assert "Update the Desktop Companion app" in message
+    assert "https://github.com/franksong2702/hermes-webui-desktop-companion#after-gallery-install" in message
+
+
+def test_pet_help_routes_to_hook_error_guidance_when_hook_throws():
+    result = _run_pet_js(
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status={"connected": True},
+        hook_throws=True,
+    )
+
+    assert result["result"]["handled"] is False
+    assert result["result"]["message"] == (
+        "Desktop Companion is installed and connected, but it hit an error while handling /pet.\n\n"
+        "Check the browser console and the Desktop Companion app, then retry /pet."
+    )
+    assert any("Desktop Companion /pet hook error:" in entry for entry in result["consoleErrors"])
+    assert any("hook failed" in entry for entry in result["consoleErrors"])
+
+
+def test_pet_slash_intercept_bypasses_generic_agent_execution():
+    pet = _run_send_js(
+        command="/pet feed tuna",
+        status={"enabled": False, "extensions": []},
+        adapter_status=None,
+    )
+    browser = _run_send_js(
+        command="/browser open",
+        status={"enabled": False, "extensions": []},
+        adapter_status=None,
+    )
+
+    assert [item["role"] for item in pet["messages"]] == ["user", "assistant"]
+    assert "Desktop Companion is not installed yet." in pet["messages"][1]["content"]
+    assert "Hermes CLI-only command" not in pet["messages"][1]["content"]
+    assert pet["commandExecCalls"] == []
+    assert pet["remainingInput"] == ""
+
+    assert [item["role"] for item in browser["messages"]] == ["user", "assistant"]
+    assert "`/browser` is a Hermes CLI-only command" in browser["messages"][1]["content"]
+    assert browser["commandExecCalls"] == []
+
+
+def test_pet_send_uses_extension_message_when_hook_returns_one():
+    result = _run_send_js(
+        command="/pet feed tuna",
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status={"connected": True},
+        hook_result={"handled": True, "message": "mascot handled"},
+    )
+
+    assert [item["role"] for item in result["messages"]] == ["user", "assistant"]
+    assert result["messages"][1]["content"] == "mascot handled"
+    assert result["commandExecCalls"] == []
+    assert result["remainingInput"] == ""
+
+
+def test_pet_send_leaves_chat_reply_to_extension_when_hook_handles_silently():
+    result = _run_send_js(
+        command="/pet wave",
+        status={
+            "enabled": True,
+            "extensions": [
+                {
+                    "id": "desktop-companion",
+                    "name": "Desktop Companion",
+                    "effective_enabled": True,
+                    "user_disabled": False,
+                    "status": "enabled",
+                }
+            ],
+        },
+        adapter_status={"connected": True},
+        hook_result=True,
+    )
+
+    assert [item["role"] for item in result["messages"]] == ["user"]
+    assert result["commandExecCalls"] == []
+    assert result["remainingInput"] == ""