fix(issue_write): make issue_fields schema OpenAI strict-mode safe

Set additionalProperties: false on the issue_fields items object and
give the 'value' property an explicit type union, matching the fix
applied to push_files (see #2011). Without these, OpenAI Responses
API strict-mode callers reject the tool schema with HTTP 400.

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

Author: SamMorrowDrums

pkg/github/__toolsnaps__/issue_write.snap

@@ -32,6 +32,7 @@
       "issue_fields": {
         "description": "Issue field values to set. Each item requires field_name and either value or field_option_name. field_option_name is for single-select fields and is resolved to the corresponding option ID automatically.",
         "items": {
+          "additionalProperties": false,
           "properties": {
             "field_name": {
               "description": "Issue field name",
@@ -42,7 +43,12 @@
               "type": "string"
             },
             "value": {
-              "description": "Value for text/number/date/single-select fields. For single-select, you can use field_option_name instead."
+              "description": "Value for text/number/date/single-select fields. For single-select, you can use field_option_name instead.",
+              "type": [
+                "string",
+                "number",
+                "boolean"
+              ]
             }
           },
           "required": [

pkg/github/issues.go

@@ -1547,13 +1547,15 @@ Options are:
 						Type:        "array",
 						Description: "Issue field values to set. Each item requires field_name and either value or field_option_name. field_option_name is for single-select fields and is resolved to the corresponding option ID automatically.",
 						Items: &jsonschema.Schema{
-							Type: "object",
+							Type:                 "object",
+							AdditionalProperties: &jsonschema.Schema{Not: &jsonschema.Schema{}},
 							Properties: map[string]*jsonschema.Schema{
 								"field_name": {
 									Type:        "string",
 									Description: "Issue field name",
 								},
 								"value": {
+									Types:       []string{"string", "number", "boolean"},
 									Description: "Value for text/number/date/single-select fields. For single-select, you can use field_option_name instead.",
 								},
 								"field_option_name": {