Support removing issue types (#2999)

* Render union types in generated docs Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ea8faa5c-7f26-4e2d-bf9c-6f0b5f173e8c * Support clearing issue types with issue_write Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ea8faa5c-7f26-4e2d-bf9c-6f0b5f173e8c * Support clearing issue types with granular tool Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ea8faa5c-7f26-4e2d-bf9c-6f0b5f173e8c * Validate duplicate closures before updates Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ea8faa5c-7f26-4e2d-bf9c-6f0b5f173e8c --------- Copilot-Session: ea8faa5c-7f26-4e2d-bf9c-6f0b5f173e8c
2026-08-06 20:25:58 -04:00
parent f3cb662c25
commit e7f7bb8b31
14 changed files with 388 additions and 51 deletions
@@ -926,7 +926,7 @@ The following sets of tools are available:
  - **Required OAuth Scopes**: `repo`
  - `assignees`: Usernames to assign to this issue (string[], optional)
  - `body`: Issue body content (string, optional)
-  - `duplicate_of`: Issue number that this issue is a duplicate of. Only used when state_reason is 'duplicate'. (number, optional)
+  - `duplicate_of`: Issue number that this issue is a duplicate of. Required when state_reason is 'duplicate'. (number, optional)
  - `issue_fields`: Issue field values to set or clear. Each item requires 'field_name' and exactly one of 'value', 'field_option_name', or 'delete: true'. (object[], optional)
  - `issue_number`: Issue number to update (number, optional)
  - `labels`: Labels to apply to this issue (string[], optional)
@@ -941,7 +941,7 @@ The following sets of tools are available:
  - `state`: New state (string, optional)
  - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
  - `title`: Issue title (string, optional)
-  - `type`: Type of this issue. Only use if issue types are enabled for this repository. Use list_issue_types tool to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string, optional)
+  - `type`: Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string | null, optional)

 - **list_issue_fields** - List issue fields
  - **Required OAuth Scopes (any of)**: `repo`, `read:org`
@@ -273,19 +273,7 @@ func writeToolDoc(buf *strings.Builder, tool inventory.ServerTool) {
 				requiredStr = "required"
 			}

-			var typeStr string
-
-			// Get the type and description
-			switch prop.Type {
-			case "array":
-				if prop.Items != nil {
-					typeStr = prop.Items.Type + "[]"
-				} else {
-					typeStr = "array"
-				}
-			default:
-				typeStr = prop.Type
-			}
+			typeStr := schemaTypeString(prop)

 			// Indent any continuation lines in the description to maintain markdown formatting
 			description := indentMultilineDescription(prop.Description, "    ")
@@ -300,6 +288,40 @@ func writeToolDoc(buf *strings.Builder, tool inventory.ServerTool) {
 	}
 }

+func schemaTypeString(schema *jsonschema.Schema) string {
+	switch {
+	case schema.Type == "array":
+		if schema.Items != nil {
+			return schema.Items.Type + "[]"
+		}
+		return "array"
+	case schema.Type != "":
+		return schema.Type
+	case len(schema.Types) > 0:
+		return strings.Join(schema.Types, " | ")
+	}
+
+	var union []*jsonschema.Schema
+	switch {
+	case len(schema.AnyOf) > 0:
+		union = schema.AnyOf
+	case len(schema.OneOf) > 0:
+		union = schema.OneOf
+	default:
+		// A schema without type constraints accepts any value.
+		return "any"
+	}
+
+	types := make([]string, 0, len(union))
+	for _, member := range union {
+		memberType := schemaTypeString(member)
+		if !slices.Contains(types, memberType) {
+			types = append(types, memberType)
+		}
+	}
+	return strings.Join(types, " | ")
+}
+
 // scopesEqual checks if two scope slices contain the same elements (order-independent)
 func scopesEqual(a, b []string) bool {
 	if len(a) != len(b) {
@@ -5,6 +5,7 @@ import (
 	"path/filepath"
 	"testing"

+	"github.com/google/jsonschema-go/jsonschema"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -36,3 +37,29 @@ func TestGitHubAppFlagsAreStdioOnly(t *testing.T) {
 	assert.NotNil(t, stdioCmd.Flags().Lookup("app-id"))
 	assert.Nil(t, httpCmd.Flags().Lookup("app-id"))
 }
+
+func TestSchemaTypeString(t *testing.T) {
+	tests := []struct {
+		name   string
+		schema *jsonschema.Schema
+		want   string
+	}{
+		{name: "type", schema: &jsonschema.Schema{Type: "string"}, want: "string"},
+		{name: "types", schema: &jsonschema.Schema{Types: []string{"string", "number"}}, want: "string | number"},
+		{name: "unconstrained", schema: &jsonschema.Schema{}, want: "any"},
+		{name: "anyOf", schema: &jsonschema.Schema{AnyOf: []*jsonschema.Schema{{Type: "string"}, {Type: "null"}}}, want: "string | null"},
+		{name: "oneOf", schema: &jsonschema.Schema{OneOf: []*jsonschema.Schema{{Type: "number"}, {Type: "string"}}}, want: "number | string"},
+		{
+			name:   "array",
+			schema: &jsonschema.Schema{Type: "array", Items: &jsonschema.Schema{Type: "string"}},
+			want:   "string[]",
+		},
+		{name: "untyped array", schema: &jsonschema.Schema{Type: "array"}, want: "array"},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			assert.Equal(t, tc.want, schemaTypeString(tc.schema))
+		})
+	}
+}
@@ -56,7 +56,7 @@ runtime behavior (such as output formatting) won't appear here.
  - **MCP App UI**: `ui://github-mcp-server/issue-write`
  - `assignees`: Usernames to assign to this issue (string[], optional)
  - `body`: Issue body content (string, optional)
-  - `duplicate_of`: Issue number that this issue is a duplicate of. Only used when state_reason is 'duplicate'. (number, optional)
+  - `duplicate_of`: Issue number that this issue is a duplicate of. Required when state_reason is 'duplicate'. (number, optional)
  - `issue_fields`: Issue field values to set or clear. Each item requires 'field_name' and exactly one of 'value', 'field_option_name', or 'delete: true'. (object[], optional)
  - `issue_number`: Issue number to update (number, optional)
  - `labels`: Labels to apply to this issue (string[], optional)
@@ -71,7 +71,7 @@ runtime behavior (such as output formatting) won't appear here.
  - `state`: New state (string, optional)
  - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
  - `title`: Issue title (string, optional)
-  - `type`: Type of this issue. Only use if issue types are enabled for this repository. Use list_issue_types tool to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string, optional)
+  - `type`: Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string | null, optional)

 - **ui_get** - Get UI data
  - **Required OAuth Scopes (any of)**: `repo`, `read:org`
@@ -200,7 +200,7 @@ runtime behavior (such as output formatting) won't appear here.
  - `confidence`: How confident you are in this choice. Use 'HIGH' for clear signal or explicit user request, 'MEDIUM' for reasonable inference with some ambiguity, 'LOW' for best guess with limited signal. (string, optional)
  - `is_suggestion`: If true, this issue type change is sent to the API as a suggestion (suggest:true) rather than an applied value. Whether the type is applied or recorded as a proposal is determined by the API. (boolean, optional)
  - `issue_number`: The issue number to update (number, required)
-  - `issue_type`: The issue type to set (string, required)
+  - `issue_type`: The issue type to set, or null to remove the current type (string | null, required)
  - `owner`: Repository owner (username or organization) (string, required)
  - `rationale`: One concise sentence explaining what specifically about the issue led you to choose this type. State the concrete signal (e.g. 'Reports a crash when saving' → bug, 'Asks for dark mode support' → feature). (string, optional)
  - `repo`: Repository name (string, required)
@@ -50,7 +50,7 @@ The list below is generated from the Go source. It covers tool **inventory and s
  - **MCP App UI**: `ui://github-mcp-server/issue-write`
  - `assignees`: Usernames to assign to this issue (string[], optional)
  - `body`: Issue body content (string, optional)
-  - `duplicate_of`: Issue number that this issue is a duplicate of. Only used when state_reason is 'duplicate'. (number, optional)
+  - `duplicate_of`: Issue number that this issue is a duplicate of. Required when state_reason is 'duplicate'. (number, optional)
  - `issue_fields`: Issue field values to set or clear. Each item requires 'field_name' and exactly one of 'value', 'field_option_name', or 'delete: true'. (object[], optional)
  - `issue_number`: Issue number to update (number, optional)
  - `labels`: Labels to apply to this issue (string[], optional)
@@ -65,7 +65,7 @@ The list below is generated from the Go source. It covers tool **inventory and s
  - `state`: New state (string, optional)
  - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
  - `title`: Issue title (string, optional)
-  - `type`: Type of this issue. Only use if issue types are enabled for this repository. Use list_issue_types tool to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string, optional)
+  - `type`: Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter. (string | null, optional)

 - **ui_get** - Get UI data
  - **Required OAuth Scopes (any of)**: `repo`, `read:org`
@@ -28,7 +28,7 @@
        "type": "string"
      },
      "duplicate_of": {
-        "description": "Issue number that this issue is a duplicate of. Only used when state_reason is 'duplicate'.",
+        "description": "Issue number that this issue is a duplicate of. Required when state_reason is 'duplicate'.",
        "type": "number"
      },
      "issue_fields": {
@@ -120,8 +120,16 @@
        "type": "string"
      },
      "type": {
-        "description": "Type of this issue. Only use if issue types are enabled for this repository. Use list_issue_types tool to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter.",
-        "type": "string"
+        "anyOf": [
+          {
+            "minLength": 1,
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "description": "Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter."
      }
    },
    "required": [
@@ -6,7 +6,7 @@
    "readOnlyHint": false,
    "title": "Update Issue Type"
  },
-  "description": "Update the type of an existing issue (e.g. 'bug', 'feature'). When setting values, include a confidence level (LOW, MEDIUM, or HIGH) reflecting how certain you are about the choice.",
+  "description": "Set or remove the type of an existing issue. Pass null to remove the current type. When setting a value, include a confidence level (LOW, MEDIUM, or HIGH) reflecting how certain you are about the choice.",
  "inputSchema": {
    "properties": {
      "confidence": {
@@ -28,8 +28,16 @@
        "type": "number"
      },
      "issue_type": {
-        "description": "The issue type to set",
-        "type": "string"
+        "anyOf": [
+          {
+            "minLength": 1,
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ],
+        "description": "The issue type to set, or null to remove the current type"
      },
      "owner": {
        "description": "Repository owner (username or organization)",
@@ -3,6 +3,7 @@ package github
 import (
 	"context"
 	"encoding/json"
+	"maps"
 	"net/http"
 	"strings"
 	"testing"
@@ -787,6 +788,18 @@ func TestGranularUpdateIssueType(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "remove type with null",
+			requestArgs: map[string]any{
+				"owner":        "owner",
+				"repo":         "repo",
+				"issue_number": float64(1),
+				"issue_type":   nil,
+			},
+			expectedReq: map[string]any{
+				"type": nil,
+			},
+		},
 	}

 	for _, tc := range tests {
@@ -807,6 +820,45 @@ func TestGranularUpdateIssueType(t *testing.T) {
 	}
 }

+func TestGranularUpdateIssueTypeRejectsInvalidInput(t *testing.T) {
+	tests := []struct {
+		name      string
+		args      map[string]any
+		omitType  bool
+		wantError string
+	}{
+		{name: "missing type", omitType: true, wantError: "missing required parameter: issue_type"},
+		{name: "empty type", args: map[string]any{"issue_type": ""}, wantError: "parameter issue_type must not be empty"},
+		{name: "null with rationale", args: map[string]any{"rationale": "live validation"}, wantError: "suggestion metadata is not supported"},
+		{name: "null with confidence", args: map[string]any{"confidence": "HIGH"}, wantError: "suggestion metadata is not supported"},
+		{name: "null suggestion", args: map[string]any{"is_suggestion": true}, wantError: "suggestion metadata is not supported"},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			deps := BaseDeps{}
+			serverTool := GranularUpdateIssueType(translations.NullTranslationHelper)
+			handler := serverTool.Handler(deps)
+			args := map[string]any{
+				"owner":        "owner",
+				"repo":         "repo",
+				"issue_number": float64(1),
+				"issue_type":   nil,
+			}
+			if tc.omitType {
+				delete(args, "issue_type")
+			}
+			maps.Copy(args, tc.args)
+			request := createMCPRequest(args)
+
+			result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+			require.NoError(t, err)
+			errorContent := getErrorResult(t, result)
+			assert.Contains(t, errorContent.Text, tc.wantError)
+		})
+	}
+}
+
 func TestGranularUpdateIssueTypeSuggest(t *testing.T) {
 	tests := []struct {
 		name        string
@@ -2240,8 +2240,11 @@ Options are:
 						Description: "Milestone number",
 					},
 					"type": {
-						Type:        "string",
-						Description: "Type of this issue. Only use if issue types are enabled for this repository. Use list_issue_types tool to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter.",
+						AnyOf: []*jsonschema.Schema{
+							{Type: "string", MinLength: jsonschema.Ptr(1)},
+							{Type: "null"},
+						},
+						Description: "Type of this issue. For updates, pass null to remove the current type. Only use if issue types are enabled for this repository. Use list_issue_types to get valid type values for this repository or its owner organization. If the repository doesn't support issue types, omit this parameter.",
 					},
 					"state": {
 						Type:        "string",
@@ -2255,7 +2258,7 @@ Options are:
 					},
 					"duplicate_of": {
 						Type:        "number",
-						Description: "Issue number that this issue is a duplicate of. Only used when state_reason is 'duplicate'.",
+						Description: "Issue number that this issue is a duplicate of. Required when state_reason is 'duplicate'.",
 					},
 					"issue_fields": {
 						Type:        "array",
@@ -2365,10 +2368,14 @@ Options are:
 			}

 			// Get optional type
-			issueType, err := OptionalParam[string](args, "type")
+			issueTypeParam, issueTypeProvided, err := OptionalNullableStringParam(args, "type")
 			if err != nil {
 				return utils.NewToolResultError(err.Error()), nil, nil
 			}
+			issueType := ""
+			if issueTypeParam != nil {
+				issueType = *issueTypeParam
+			}

 			// Handle state, state_reason and duplicateOf parameters
 			state, err := OptionalParam[string](args, "state")
@@ -2388,6 +2395,9 @@ Options are:
 			if duplicateOf != 0 && stateReason != "duplicate" {
 				return utils.NewToolResultError("duplicate_of can only be used when state_reason is 'duplicate'"), nil, nil
 			}
+			if err := validateDuplicateState(state, stateReason, duplicateOf); err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}

 			var issueFields []issueWriteFieldInput
 			issueFields, err = optionalIssueWriteFields(args)
@@ -2426,6 +2436,7 @@ Options are:
 				result, err := UpdateIssue(ctx, client, gqlClient, owner, repo, issueNumber, title, body, assignees, labels, milestoneNum, issueType, issueFieldValues, fieldIDsToDelete, state, stateReason, duplicateOf, UpdateIssueOptions{
 					AssigneesProvided: assigneesProvided,
 					LabelsProvided:    labelsProvided,
+					IssueTypeProvided: issueTypeProvided,
 				})
 				return result, nil, err
 			default:
@@ -2496,9 +2507,16 @@ type UpdateIssueOptions struct {
 	AssigneesProvided bool
 	// LabelsProvided sends the labels field even when the slice is empty.
 	LabelsProvided bool
+	// IssueTypeProvided sends the type field, including an explicit clear.
+	IssueTypeProvided bool
 }

 func UpdateIssue(ctx context.Context, client *github.Client, gqlClient *githubv4.Client, owner string, repo string, issueNumber int, title string, body string, assignees []string, labels []string, milestoneNum int, issueType string, issueFieldValues []*github.IssueRequestFieldValue, fieldIDsToDelete []int64, state string, stateReason string, duplicateOf int, opts ...UpdateIssueOptions) (*mcp.CallToolResult, error) {
+	// UpdateIssue is exported and may be called without the tool handler.
+	if err := validateDuplicateState(state, stateReason, duplicateOf); err != nil {
+		return utils.NewToolResultError(err.Error()), nil
+	}
+
 	updateOptions := UpdateIssueOptions{
 		AssigneesProvided: len(assignees) > 0,
 		LabelsProvided:    len(labels) > 0,
@@ -2506,6 +2524,7 @@ func UpdateIssue(ctx context.Context, client *github.Client, gqlClient *githubv4
 	for _, opt := range opts {
 		updateOptions.AssigneesProvided = updateOptions.AssigneesProvided || opt.AssigneesProvided
 		updateOptions.LabelsProvided = updateOptions.LabelsProvided || opt.LabelsProvided
+		updateOptions.IssueTypeProvided = updateOptions.IssueTypeProvided || opt.IssueTypeProvided
 	}

 	// Create the issue request with only provided fields
@@ -2579,7 +2598,7 @@ func UpdateIssue(ctx context.Context, client *github.Client, gqlClient *githubv4
 		}
 	}

-	updatedIssue, resp, err := client.Issues.Update(ctx, owner, repo, issueNumber, issueRequest)
+	updatedIssue, resp, err := patchIssue(ctx, client, owner, repo, issueNumber, issueRequest, issueType, updateOptions.IssueTypeProvided)
 	if err != nil {
 		return ghErrors.NewGitHubAPIErrorResponse(ctx,
 			"failed to update issue",
@@ -2636,11 +2655,6 @@ func UpdateIssue(ctx context.Context, client *github.Client, gqlClient *githubv4

 	// Use GraphQL API for state updates
 	if state != "" {
-		// Mandate specifying duplicateOf when trying to close as duplicate
-		if state == "closed" && stateReason == "duplicate" && duplicateOf == 0 {
-			return utils.NewToolResultError("duplicate_of must be provided when state_reason is 'duplicate'"), nil
-		}
-
 		// Get target issue ID (and duplicate issue ID if needed)
 		issueID, duplicateIssueID, err := fetchIssueIDs(ctx, gqlClient, owner, repo, issueNumber, duplicateOf)
 		if err != nil {
@@ -2712,6 +2726,35 @@ func UpdateIssue(ctx context.Context, client *github.Client, gqlClient *githubv4
 	return utils.NewToolResultText(string(r)), nil
 }

+func validateDuplicateState(state, stateReason string, duplicateOf int) error {
+	if state == "closed" && stateReason == "duplicate" && duplicateOf == 0 {
+		return fmt.Errorf("duplicate_of must be provided when state_reason is 'duplicate'")
+	}
+	return nil
+}
+
+type updateIssueRequestWithNullableType struct {
+	github.UpdateIssueRequest
+	Type *string `json:"type"`
+}
+
+func patchIssue(ctx context.Context, client *github.Client, owner, repo string, issueNumber int, issueRequest github.UpdateIssueRequest, issueType string, issueTypeProvided bool) (*github.Issue, *github.Response, error) {
+	if !issueTypeProvided || issueType != "" {
+		return client.Issues.Update(ctx, owner, repo, issueNumber, issueRequest)
+	}
+
+	apiURL := fmt.Sprintf("repos/%s/%s/issues/%d", owner, repo, issueNumber)
+	body := &updateIssueRequestWithNullableType{UpdateIssueRequest: issueRequest}
+	req, err := client.NewRequest(ctx, http.MethodPatch, apiURL, body)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	issue := &github.Issue{}
+	resp, err := client.Do(req, issue)
+	return issue, resp, err
+}
+
 // ListIssues creates a tool to list issues in a GitHub repository.
 func ListIssues(t translations.TranslationHelperFunc) inventory.ServerTool {
 	schema := &jsonschema.Schema{
@@ -679,13 +679,13 @@ type issueTypeUpdateRequest struct {
 	Type issueTypeWithIntent `json:"type"`
 }

-// GranularUpdateIssueType creates a tool to update an issue's type.
+// GranularUpdateIssueType creates a tool to set or clear an issue's type.
 func GranularUpdateIssueType(t translations.TranslationHelperFunc) inventory.ServerTool {
 	st := NewTool(
 		ToolsetMetadataIssues,
 		mcp.Tool{
 			Name:        "update_issue_type",
-			Description: t("TOOL_UPDATE_ISSUE_TYPE_DESCRIPTION", "Update the type of an existing issue (e.g. 'bug', 'feature'). When setting values, include a confidence level (LOW, MEDIUM, or HIGH) reflecting how certain you are about the choice."),
+			Description: t("TOOL_UPDATE_ISSUE_TYPE_DESCRIPTION", "Set or remove the type of an existing issue. Pass null to remove the current type. When setting a value, include a confidence level (LOW, MEDIUM, or HIGH) reflecting how certain you are about the choice."),
 			Annotations: &mcp.ToolAnnotations{
 				Title:           t("TOOL_UPDATE_ISSUE_TYPE_USER_TITLE", "Update Issue Type"),
 				ReadOnlyHint:    false,
@@ -709,8 +709,11 @@ func GranularUpdateIssueType(t translations.TranslationHelperFunc) inventory.Ser
 						Minimum:     jsonschema.Ptr(1.0),
 					},
 					"issue_type": {
-						Type:        "string",
-						Description: "The issue type to set",
+						AnyOf: []*jsonschema.Schema{
+							{Type: "string", MinLength: jsonschema.Ptr(1)},
+							{Type: "null"},
+						},
+						Description: "The issue type to set, or null to remove the current type",
 					},
 					"rationale": {
 						Type: "string",
@@ -746,10 +749,13 @@ func GranularUpdateIssueType(t translations.TranslationHelperFunc) inventory.Ser
 			if err != nil {
 				return utils.NewToolResultError(err.Error()), nil, nil
 			}
-			issueType, err := RequiredParam[string](args, "issue_type")
+			issueType, issueTypeProvided, err := OptionalNullableStringParam(args, "issue_type")
 			if err != nil {
 				return utils.NewToolResultError(err.Error()), nil, nil
 			}
+			if !issueTypeProvided {
+				return utils.NewToolResultError("missing required parameter: issue_type"), nil, nil
+			}
 			rationale, err := OptionalParam[string](args, "rationale")
 			if err != nil {
 				return utils.NewToolResultError(err.Error()), nil, nil
@@ -770,24 +776,29 @@ func GranularUpdateIssueType(t translations.TranslationHelperFunc) inventory.Ser
 			if err != nil {
 				return utils.NewToolResultError(err.Error()), nil, nil
 			}
-
+			if issueType == nil && (rationale != "" || confidence != "" || isSuggestion) {
+				return utils.NewToolResultError("suggestion metadata is not supported when removing an issue type; omit rationale, confidence, and is_suggestion"), nil, nil
+			}
 			client, err := deps.GetClient(ctx)
 			if err != nil {
 				return utils.NewToolResultErrorFromErr("failed to get GitHub client", err), nil, nil
 			}

 			var body any
-			if rationale != "" || isSuggestion || confidence != "" {
+			switch {
+			case issueType == nil:
+				body = map[string]any{"type": nil}
+			case rationale != "" || isSuggestion || confidence != "":
 				body = &issueTypeUpdateRequest{
 					Type: issueTypeWithIntent{
-						Value:      issueType,
+						Value:      *issueType,
 						Rationale:  rationale,
 						Confidence: confidence,
 						Suggest:    isSuggestion,
 					},
 				}
-			} else {
-				body = &github.UpdateIssueRequest{Type: &issueType}
+			default:
+				body = &github.UpdateIssueRequest{Type: issueType}
 			}

 			apiURL := fmt.Sprintf("repos/%s/%s/issues/%d", owner, repo, issueNumber)
@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"maps"
 	"net/http"
 	"strings"
 	"sync/atomic"
@@ -3062,6 +3063,70 @@ func Test_ListIssues_IFC_InsidersMode(t *testing.T) {
 	})
 }

+func TestIssueWriteUpdatesIssueType(t *testing.T) {
+	tests := []struct {
+		name            string
+		args            map[string]any
+		wantRequestBody string
+	}{
+		{
+			name: "omit issue type",
+			args: map[string]any{
+				"title": "Updated title",
+			},
+			wantRequestBody: `{"title":"Updated title"}`,
+		},
+		{
+			name: "set issue type",
+			args: map[string]any{
+				"type": "Bug",
+			},
+			wantRequestBody: `{"type":"Bug"}`,
+		},
+		{
+			name: "clear issue type",
+			args: map[string]any{
+				"type": nil,
+			},
+			wantRequestBody: `{"type":null}`,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			var gotRequestBody []byte
+			var readErr error
+			client := mustNewGHClient(t, MockHTTPClientWithHandlers(map[string]http.HandlerFunc{
+				PatchReposIssuesByOwnerByRepoByIssueNumber: func(w http.ResponseWriter, r *http.Request) {
+					gotRequestBody, readErr = io.ReadAll(r.Body)
+					w.WriteHeader(http.StatusOK)
+					_, _ = w.Write([]byte(`{"number":123,"html_url":"https://github.com/owner/repo/issues/123"}`))
+				},
+			}))
+			deps := BaseDeps{
+				Client:    client,
+				GQLClient: githubv4.NewClient(githubv4mock.NewMockedHTTPClient()),
+			}
+			serverTool := IssueWrite(translations.NullTranslationHelper)
+			handler := serverTool.Handler(deps)
+			requestArgs := map[string]any{
+				"method":       "update",
+				"owner":        "owner",
+				"repo":         "repo",
+				"issue_number": float64(123),
+			}
+			maps.Copy(requestArgs, tc.args)
+			request := createMCPRequest(requestArgs)
+
+			result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+			require.NoError(t, err)
+			require.False(t, result.IsError)
+			require.NoError(t, readErr)
+			require.JSONEq(t, tc.wantRequestBody, string(gotRequestBody))
+		})
+	}
+}
+
 func Test_UpdateIssue(t *testing.T) {
 	// Verify tool definition
 	serverTool := IssueWrite(translations.NullTranslationHelper)
@@ -3172,6 +3237,7 @@ func Test_UpdateIssue(t *testing.T) {
 		expectError      bool
 		expectedIssue    *github.Issue
 		expectedErrMsg   string
+		expectNoRequests bool
 	}{
 		{
 			name: "partial update of non-state fields only",
@@ -3591,11 +3657,35 @@ func Test_UpdateIssue(t *testing.T) {
 			expectError:    true,
 			expectedErrMsg: "duplicate_of can only be used when state_reason is 'duplicate'",
 		},
+		{
+			name:             "duplicate state reason without duplicate_of should fail before updates",
+			mockedRESTClient: MockHTTPClientWithHandlers(map[string]http.HandlerFunc{}),
+			mockedGQLClient:  githubv4mock.NewMockedHTTPClient(),
+			requestArgs: map[string]any{
+				"method":       "update",
+				"owner":        "owner",
+				"repo":         "repo",
+				"issue_number": float64(123),
+				"type":         nil,
+				"state":        "closed",
+				"state_reason": "duplicate",
+			},
+			expectError:      true,
+			expectedErrMsg:   "duplicate_of must be provided when state_reason is 'duplicate'",
+			expectNoRequests: true,
+		},
 	}

 	for _, tc := range tests {
 		t.Run(tc.name, func(t *testing.T) {
 			// Setup clients with mocks
+			var restRequests, gqlRequests *requestCountingTransport
+			if tc.expectNoRequests {
+				restRequests = &requestCountingTransport{inner: tc.mockedRESTClient.Transport}
+				tc.mockedRESTClient.Transport = restRequests
+				gqlRequests = &requestCountingTransport{inner: tc.mockedGQLClient.Transport}
+				tc.mockedGQLClient.Transport = gqlRequests
+			}
 			restClient := mustNewGHClient(t, tc.mockedRESTClient)
 			gqlClient := githubv4.NewClient(tc.mockedGQLClient)
 			deps := BaseDeps{
@@ -3609,6 +3699,10 @@ func Test_UpdateIssue(t *testing.T) {

 			// Call handler
 			result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+			if tc.expectNoRequests {
+				assert.Zero(t, restRequests.count)
+				assert.Zero(t, gqlRequests.count)
+			}

 			// Verify results
 			if tc.expectError || tc.expectedErrMsg != "" {
@@ -34,6 +34,26 @@ func OptionalParamOK[T any, A map[string]any](args A, p string) (value T, ok boo
 	return
 }

+// OptionalNullableStringParam preserves omitted, null, and non-empty string values.
+func OptionalNullableStringParam(args map[string]any, p string) (*string, bool, error) {
+	value, ok := args[p]
+	if !ok {
+		return nil, false, nil
+	}
+	if value == nil {
+		return nil, true, nil
+	}
+
+	stringValue, ok := value.(string)
+	if !ok {
+		return nil, true, fmt.Errorf("parameter %s is not of type string or null, is %T", p, value)
+	}
+	if stringValue == "" {
+		return nil, true, fmt.Errorf("parameter %s must not be empty", p)
+	}
+	return &stringValue, true, nil
+}
+
 // isAcceptedError checks if the error is an accepted error.
 func isAcceptedError(err error) bool {
 	var acceptedError *github.AcceptedError
@@ -7,6 +7,7 @@ import (

 	"github.com/google/go-github/v89/github"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )

 func Test_IsAcceptedError(t *testing.T) {
@@ -149,6 +150,40 @@ func Test_OptionalStringParam(t *testing.T) {
 	}
 }

+func TestOptionalNullableStringParam(t *testing.T) {
+	tests := []struct {
+		name         string
+		params       map[string]any
+		want         string
+		wantProvided bool
+		wantError    string
+	}{
+		{name: "omitted", params: map[string]any{}},
+		{name: "null", params: map[string]any{"type": nil}, wantProvided: true},
+		{name: "string", params: map[string]any{"type": "Bug"}, want: "Bug", wantProvided: true},
+		{name: "empty", params: map[string]any{"type": ""}, wantProvided: true, wantError: "parameter type must not be empty"},
+		{name: "wrong type", params: map[string]any{"type": float64(1)}, wantProvided: true, wantError: "parameter type is not of type string or null, is float64"},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got, provided, err := OptionalNullableStringParam(tc.params, "type")
+
+			assert.Equal(t, tc.wantProvided, provided)
+			if tc.wantError != "" {
+				require.EqualError(t, err, tc.wantError)
+				return
+			}
+			require.NoError(t, err)
+			if tc.want == "" {
+				assert.Nil(t, got)
+			} else {
+				assert.Equal(t, tc.want, *got)
+			}
+		})
+	}
+}
+
 func Test_RequiredInt(t *testing.T) {
 	tests := []struct {
 		name        string
@@ -418,6 +418,7 @@ function CreateIssueApp() {
  // Issue types state
  const [availableIssueTypes, setAvailableIssueTypes] = useState<IssueTypeItem[]>([]);
  const [selectedIssueType, setSelectedIssueType] = useState<IssueTypeItem | null>(null);
+  const [issueTypeCleared, setIssueTypeCleared] = useState(false);
  const [issueTypesLoading, setIssueTypesLoading] = useState(false);

  // State transition state
@@ -721,7 +722,11 @@ function CreateIssueApp() {
    setSelectedLabels([]);
    setSelectedAssignees([]);
    setSelectedMilestone(null);
-    setSelectedIssueType(null);
+    const inputIssueType = toolInput?.type;
+    setSelectedIssueType(
+      typeof inputIssueType === "string" ? { id: inputIssueType, text: inputIssueType } : null
+    );
+    setIssueTypeCleared(inputIssueType === null);
    setCurrentState("open");
    setStateReason("completed");
    setDuplicateOf("");
@@ -800,7 +805,7 @@ function CreateIssueApp() {

            // Pre-fill issue type immediately from issue data
            const issueTypeName = issueData.type?.name || (typeof issueData.type === 'string' ? issueData.type : null);
-            if (issueTypeName && !prefillApplied.current.type) {
+            if (issueTypeName && toolInput?.type === undefined && !prefillApplied.current.type) {
              setSelectedIssueType({ id: issueTypeName, text: issueTypeName });
              prefillApplied.current.type = true;
            }
@@ -829,7 +834,7 @@ function CreateIssueApp() {
    };

    loadExistingIssue();
-  }, [isUpdateMode, owner, repo, issueNumber, app, callTool, existingIssueData]);
+  }, [isUpdateMode, owner, repo, issueNumber, app, callTool, existingIssueData, toolInput]);

  // Apply existing labels when available labels load
  useEffect(() => {
@@ -1016,6 +1021,7 @@ function CreateIssueApp() {
      delete params.state_reason;
      delete params.duplicate_of;
      delete params.issue_fields;
+      delete params.type;

      if (isUpdateMode && issueNumber) {
        params.issue_number = issueNumber;
@@ -1032,6 +1038,8 @@ function CreateIssueApp() {
      }
      if (selectedIssueType) {
        params.type = selectedIssueType.text;
+      } else if (issueTypeCleared) {
+        params.type = null;
      }

      if (requestedState) {
@@ -1115,6 +1123,7 @@ function CreateIssueApp() {
    selectedAssignees,
    selectedMilestone,
    selectedIssueType,
+    issueTypeCleared,
    isUpdateMode,
    issueNumber,
    stateReason,
@@ -1533,7 +1542,11 @@ function CreateIssueApp() {
                <>
                  {selectedIssueType && (
                    <ActionList.Item
-                      onSelect={() => setSelectedIssueType(null)}
+                      onSelect={() => {
+                        setSelectedIssueType(null);
+                        setIssueTypeCleared(true);
+                        prefillApplied.current.type = true;
+                      }}
                    >
                      Clear selection
                    </ActionList.Item>
@@ -1542,7 +1555,11 @@ function CreateIssueApp() {
                    <ActionList.Item
                      key={type.id}
                      selected={selectedIssueType?.id === type.id}
-                      onSelect={() => setSelectedIssueType(type)}
+                      onSelect={() => {
+                        setSelectedIssueType(type);
+                        setIssueTypeCleared(false);
+                        prefillApplied.current.type = true;
+                      }}
                    >
                      {type.text}
                    </ActionList.Item>