add error formatting

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/cache](https://redirect.github.com/actions/cache)
([changelog](8b402f58fb..cdf6c1fa76))
| action | digest | `8b402f5` → `cdf6c1f` |
| [actions/checkout](https://redirect.github.com/actions/checkout)
([changelog](8e8c483db8..de0fac2e45))
| action | digest | `8e8c483` → `de0fac2` |

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This PR was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/googleapis/genai-toolbox).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0Mi45Mi4xIiwidXBkYXRlZEluVmVyIjoiNDIuOTUuMiIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOltdfQ==-->

Co-authored-by: Averi Kitsch <akitsch@google.com>

.github/workflows/deploy_dev_docs.yaml

@@ -40,7 +40,7 @@ jobs:
       group: docs-deployment
       cancel-in-progress: false
     steps:
-      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
           fetch-depth: 0 # Fetch all history for .GitInfo and .Lastmod
 
@@ -56,7 +56,7 @@ jobs:
           node-version: "22"
 
       - name: Cache dependencies
-        uses: actions/cache@8b402f58fbc84540c8b491a91e594a4576fec3d7 # v5
+        uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5
         with:
           path: ~/.npm
           key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

.github/workflows/deploy_previous_version_docs.yaml

@@ -30,14 +30,14 @@ jobs:
 
     steps:
       - name: Checkout main branch (for latest templates and theme)
-        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
           ref: 'main'
           submodules: 'recursive'
           fetch-depth: 0
 
       - name: Checkout old content from tag into a temporary directory
-        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
           ref: ${{ github.event.inputs.version_tag }}
           path: 'old_version_source' # Checkout into a temp subdir

.github/workflows/deploy_versioned_docs.yaml

@@ -30,7 +30,7 @@ jobs:
       cancel-in-progress: false
     steps:
       - name: Checkout Code at Tag
-        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
           ref: ${{ github.event.release.tag_name }}
 

.github/workflows/docs_preview_clean.yaml

@@ -34,7 +34,7 @@ jobs:
       group: "preview-${{ github.event.number }}"
       cancel-in-progress: true
     steps:
-      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
           ref: versioned-gh-pages
 

.github/workflows/docs_preview_deploy.yaml

@@ -49,7 +49,7 @@ jobs:
       group: "preview-${{ github.event.number }}"
       cancel-in-progress: true
     steps:
-      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
           # Checkout the PR's HEAD commit (supports forks).
           ref: ${{ github.event.pull_request.head.sha }}
@@ -67,7 +67,7 @@ jobs:
           node-version: "22"
 
       - name: Cache dependencies
-        uses: actions/cache@8b402f58fbc84540c8b491a91e594a4576fec3d7 # v5
+        uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5
         with:
           path: ~/.npm
           key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

.github/workflows/link_checker_workflow.yaml

@@ -22,10 +22,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
 
       - name: Restore lychee cache
-        uses: actions/cache@8b402f58fbc84540c8b491a91e594a4576fec3d7 # v5
+        uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5
         with:
           path: .lycheecache
           key: cache-lychee-${{ github.sha }}

.github/workflows/publish-mcp.yml

@@ -29,7 +29,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
 
       - name: Wait for image in Artifact Registry
         shell: bash

docs/en/getting-started/local_quickstart_go.md

@@ -46,11 +46,6 @@ from Toolbox.
     go get github.com/googleapis/mcp-toolbox-sdk-go
     ```
 
-1. Set your API key (If you don't have an API key yet, you can get one from [Google AI Studio](https://aistudio.google.com/app/apikey).)
-   ```bash
-   export GOOGLE_API_KEY="YOUR_ACTUAL_GEMINI_API_KEY"
-   ```
-
 1. Create a new file named `hotelagent.go` and copy the following code to create
    an agent:
 

internal/util/errors.go

@@ -0,0 +1,77 @@
+// Copyright 2026 Google LLC
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package util
+
+import "fmt"
+
+type ErrorCategory string
+
+const (
+	CategoryAgent  ErrorCategory = "AGENT_ERROR"
+	CategoryServer ErrorCategory = "SERVER_ERROR"
+)
+
+// ToolboxError is the interface all custom errors must satisfy
+type ToolboxError interface {
+	error
+	Category() ErrorCategory
+	Error() string
+	Unwrap() error
+}
+
+// Agent Errors return 200 to the sender
+type AgentError struct {
+	Msg   string
+	Cause error
+}
+
+var _ ToolboxError = &AgentError{}
+
+func (e *AgentError) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("%s: %v", e.Msg, e.Cause)
+	}
+	return e.Msg
+}
+
+func (e *AgentError) Category() ErrorCategory { return CategoryAgent }
+
+func (e *AgentError) Unwrap() error { return e.Cause }
+
+func NewAgentError(msg string, cause error) *AgentError {
+	return &AgentError{Msg: msg, Cause: cause}
+}
+
+// ClientServerError returns 4XX/5XX error code
+type ClientServerError struct {
+	Msg   string
+	Code  int
+	Cause error
+}
+
+var _ ToolboxError = &ClientServerError{}
+
+func (e *ClientServerError) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("%s: %v", e.Msg, e.Cause)
+	}
+	return e.Msg
+}
+
+func (e *ClientServerError) Category() ErrorCategory { return CategoryServer }
+
+func (e *ClientServerError) Unwrap() error { return e.Cause }
+
+func NewClientServerError(msg string, code int, cause error) *ClientServerError {
+	return &ClientServerError{Msg: msg, Code: code, Cause: cause}
+}