fix(issues): preserve delete field semantics

Clarify that delete:false is ignored, retain mutual exclusion for delete:true, and reject invalid delete types. Add focused schema and handler regressions.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: SamMorrowDrums

pkg/github/__toolsnaps__/issue_write.snap

@@ -37,19 +37,19 @@
           "additionalProperties": false,
           "properties": {
             "delete": {
-              "description": "Set to true to clear this field's current value on the issue. Cannot be combined with 'value' or 'field_option_name'. Omit this property, or set it to false, to leave the field's current value unchanged.",
+              "description": "Set to true to clear this field's current value on the issue. When false or omitted, this property is ignored. Cannot be true when 'value' or 'field_option_name' is provided.",
               "type": "boolean"
             },
             "field_name": {
               "description": "Issue field name (case-insensitive). Must match a field returned by list_issue_fields for this repository or its organization.",
               "type": "string"
             },
             "field_option_name": {
-              "description": "Option name for single-select fields. Validated against the field's options before the API call. Cannot be combined with 'value' or 'delete'.",
+              "description": "Option name for single-select fields. Validated against the field's options before the API call. Cannot be combined with 'value' or 'delete: true'.",
               "type": "string"
             },
             "value": {
-              "description": "Value to set. Use for text, number, and date fields (date as YYYY-MM-DD). For single-select fields, prefer 'field_option_name' so the option is validated before the API call. Cannot be combined with 'field_option_name' or 'delete'.",
+              "description": "Value to set. Use for text, number, and date fields (date as YYYY-MM-DD). For single-select fields, prefer 'field_option_name' so the option is validated before the API call. Cannot be combined with 'field_option_name' or 'delete: true'.",
               "type": [
                 "string",
                 "number",

pkg/github/issues.go

@@ -265,7 +265,10 @@ func optionalIssueWriteFields(args map[string]any) ([]issueWriteFieldInput, erro
 			return nil, err
 		}
 
-		deleteField, _ := OptionalParam[bool](itemMap, "delete")
+		deleteField, err := OptionalParam[bool](itemMap, "delete")
+		if err != nil {
+			return nil, err
+		}
 		value, hasValue := itemMap["value"]
 		if hasValue && value == nil {
 			return nil, fmt.Errorf("value cannot be null for field %q", fieldName)
@@ -2277,20 +2280,19 @@ Options are:
 									Description: "Value to set. Use for text, number, and date fields " +
 										"(date as YYYY-MM-DD). For single-select fields, prefer " +
 										"'field_option_name' so the option is validated before the API " +
-										"call. Cannot be combined with 'field_option_name' or 'delete'.",
+										"call. Cannot be combined with 'field_option_name' or 'delete: true'.",
 								},
 								"field_option_name": {
 									Type: "string",
 									Description: "Option name for single-select fields. Validated against " +
 										"the field's options before the API call. Cannot be combined with " +
-										"'value' or 'delete'.",
+										"'value' or 'delete: true'.",
 								},
 								"delete": {
 									Type: "boolean",
 									Description: "Set to true to clear this field's current value on the " +
-										"issue. Cannot be combined with 'value' or 'field_option_name'. " +
-										"Omit this property, or set it to false, to leave the field's " +
-										"current value unchanged.",
+										"issue. When false or omitted, this property is ignored. Cannot " +
+										"be true when 'value' or 'field_option_name' is provided.",
 								},
 							},
 							Required: []string{"field_name"},

pkg/github/issues_test.go

@@ -1823,8 +1823,8 @@ func Test_CreateIssue(t *testing.T) {
 				"repo":   "repo",
 				"title":  "Issue with fields",
 				"issue_fields": []any{
-					map[string]any{"field_name": "Priority", "field_option_name": "P1"},
-					map[string]any{"field_name": "Customer", "value": "Acme"},
+					map[string]any{"field_name": "Priority", "field_option_name": "P1", "delete": false},
+					map[string]any{"field_name": "Customer", "value": "Acme", "delete": false},
 				},
 			},
 			expectError: false,
@@ -1867,6 +1867,21 @@ func Test_CreateIssue(t *testing.T) {
 			expectError:    false,
 			expectedErrMsg: "cannot specify both value and field_option_name",
 		},
+		{
+			name:         "issue_fields rejects delete true with value",
+			mockedClient: MockHTTPClientWithHandlers(map[string]http.HandlerFunc{}),
+			requestArgs: map[string]any{
+				"method": "create",
+				"owner":  "owner",
+				"repo":   "repo",
+				"title":  "Invalid fields",
+				"issue_fields": []any{
+					map[string]any{"field_name": "Start date", "value": "2026-08-14", "delete": true},
+				},
+			},
+			expectError:    false,
+			expectedErrMsg: "cannot specify 'delete' together with 'value' or 'field_option_name'",
+		},
 	}
 
 	for _, tc := range tests {
@@ -2098,11 +2113,17 @@ func Test_issueWriteHasNonFormParams(t *testing.T) {
 	}
 }
 
-// Test_optionalIssueWriteFields covers parsing of issue_write's issue_fields
-// items. The delete:false cases matter because the schema deliberately does not
-// constrain 'delete' to a single value: clients that populate every property of
-// a schema need a way to say "not deleting", and false must be a no-op that
-// falls through to the normal value path.
+func Test_IssueWriteIssueFieldsDeleteSchema(t *testing.T) {
+	t.Parallel()
+
+	inputSchema := IssueWrite(translations.NullTranslationHelper).Tool.InputSchema.(*jsonschema.Schema)
+	deleteSchema := inputSchema.Properties["issue_fields"].Items.Properties["delete"]
+
+	assert.Equal(t, "boolean", deleteSchema.Type)
+	assert.Empty(t, deleteSchema.Enum)
+	assert.Contains(t, deleteSchema.Description, "When false or omitted, this property is ignored")
+}
+
 func Test_optionalIssueWriteFields(t *testing.T) {
 	t.Parallel()
 
@@ -2113,10 +2134,15 @@ func Test_optionalIssueWriteFields(t *testing.T) {
 		wantErr string
 	}{
 		{
-			name: "delete false alongside a value sets the value",
+			name: "delete false alongside a value is ignored",
 			item: map[string]any{"field_name": "Start date", "value": "2026-08-14", "delete": false, "field_option_name": ""},
 			want: issueWriteFieldInput{FieldName: "Start date", Value: "2026-08-14"},
 		},
+		{
+			name: "delete false alongside field_option_name is ignored",
+			item: map[string]any{"field_name": "Priority", "field_option_name": "High", "delete": false},
+			want: issueWriteFieldInput{FieldName: "Priority", FieldOptionName: "High"},
+		},
 		{
 			name: "delete true alone clears the field",
 			item: map[string]any{"field_name": "Start date", "delete": true},
@@ -2132,11 +2158,21 @@ func Test_optionalIssueWriteFields(t *testing.T) {
 			item:    map[string]any{"field_name": "Start date", "value": "2026-08-14", "delete": true},
 			wantErr: "cannot specify 'delete' together with 'value' or 'field_option_name'",
 		},
+		{
+			name:    "delete true with field_option_name is rejected",
+			item:    map[string]any{"field_name": "Priority", "field_option_name": "High", "delete": true},
+			wantErr: "cannot specify 'delete' together with 'value' or 'field_option_name'",
+		},
 		{
 			name:    "delete false with nothing to set is rejected",
 			item:    map[string]any{"field_name": "Start date", "delete": false},
 			wantErr: "must specify either value or field_option_name",
 		},
+		{
+			name:    "delete with invalid type is rejected",
+			item:    map[string]any{"field_name": "Start date", "delete": "false"},
+			wantErr: "parameter delete is not of type bool",
+		},
 	}
 
 	for _, tc := range tests {