diff --git a/README.md b/README.md
index 9527478a0f..2e6d94b84b 100644
--- a/README.md
+++ b/README.md
@@ -937,6 +937,9 @@ The following sets of tools are available:
      (string, required)
   - `milestone`: Milestone number (number, optional)
   - `owner`: Repository owner (string, required)
+  - `parent_issue_number`: Issue number of the parent issue. Only used when method is 'create' and cannot be combined with issue_fields. The new issue is created and attached to this parent in the same operation. (number, optional)
+  - `parent_owner`: Repository owner of the parent issue. Must be provided with parent_repo. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided. (string, optional)
+  - `parent_repo`: Repository name of the parent issue. Must be provided with parent_owner. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided. (string, optional)
   - `repo`: Repository name (string, required)
   - `state`: New state (string, optional)
   - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
diff --git a/docs/feature-flags.md b/docs/feature-flags.md
index 0de5bdd722..0535631481 100644
--- a/docs/feature-flags.md
+++ b/docs/feature-flags.md
@@ -67,6 +67,9 @@ runtime behavior (such as output formatting) won't appear here.
      (string, required)
   - `milestone`: Milestone number (number, optional)
   - `owner`: Repository owner (string, required)
+  - `parent_issue_number`: Issue number of the parent issue. Only used when method is 'create' and cannot be combined with issue_fields. The new issue is created and attached to this parent in the same operation. (number, optional)
+  - `parent_owner`: Repository owner of the parent issue. Must be provided with parent_repo. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided. (string, optional)
+  - `parent_repo`: Repository name of the parent issue. Must be provided with parent_owner. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided. (string, optional)
   - `repo`: Repository name (string, required)
   - `state`: New state (string, optional)
   - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
@@ -122,6 +125,9 @@ runtime behavior (such as output formatting) won't appear here.
   - **Required OAuth Scopes**: `repo`
   - `body`: Issue body content (optional) (string, optional)
   - `owner`: Repository owner (username or organization) (string, required)
+  - `parent_issue_number`: Issue number of the parent issue. The new issue is created and attached to this parent in the same operation. (number, optional)
+  - `parent_owner`: Repository owner of the parent issue. Must be provided with parent_repo. Omit both to use owner and repo. Only used when parent_issue_number is provided. (string, optional)
+  - `parent_repo`: Repository name of the parent issue. Must be provided with parent_owner. Omit both to use owner and repo. Only used when parent_issue_number is provided. (string, optional)
   - `repo`: Repository name (string, required)
   - `title`: Issue title (string, required)
 
diff --git a/docs/insiders-features.md b/docs/insiders-features.md
index 350522bf5e..c6b1844045 100644
--- a/docs/insiders-features.md
+++ b/docs/insiders-features.md
@@ -61,6 +61,9 @@ The list below is generated from the Go source. It covers tool **inventory and s
      (string, required)
   - `milestone`: Milestone number (number, optional)
   - `owner`: Repository owner (string, required)
+  - `parent_issue_number`: Issue number of the parent issue. Only used when method is 'create' and cannot be combined with issue_fields. The new issue is created and attached to this parent in the same operation. (number, optional)
+  - `parent_owner`: Repository owner of the parent issue. Must be provided with parent_repo. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided. (string, optional)
+  - `parent_repo`: Repository name of the parent issue. Must be provided with parent_owner. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided. (string, optional)
   - `repo`: Repository name (string, required)
   - `state`: New state (string, optional)
   - `state_reason`: Reason for the state change. Ignored unless state is changed. (string, optional)
diff --git a/pkg/github/__toolsnaps__/create_issue.snap b/pkg/github/__toolsnaps__/create_issue.snap
index e0963741ac..d7de241265 100644
--- a/pkg/github/__toolsnaps__/create_issue.snap
+++ b/pkg/github/__toolsnaps__/create_issue.snap
@@ -17,6 +17,19 @@
         "description": "Repository owner (username or organization)",
         "type": "string"
       },
+      "parent_issue_number": {
+        "description": "Issue number of the parent issue. The new issue is created and attached to this parent in the same operation.",
+        "minimum": 1,
+        "type": "number"
+      },
+      "parent_owner": {
+        "description": "Repository owner of the parent issue. Must be provided with parent_repo. Omit both to use owner and repo. Only used when parent_issue_number is provided.",
+        "type": "string"
+      },
+      "parent_repo": {
+        "description": "Repository name of the parent issue. Must be provided with parent_owner. Omit both to use owner and repo. Only used when parent_issue_number is provided.",
+        "type": "string"
+      },
       "repo": {
         "description": "Repository name",
         "type": "string"
diff --git a/pkg/github/__toolsnaps__/issue_write.snap b/pkg/github/__toolsnaps__/issue_write.snap
index d4968c4f2f..20cc730f51 100644
--- a/pkg/github/__toolsnaps__/issue_write.snap
+++ b/pkg/github/__toolsnaps__/issue_write.snap
@@ -91,6 +91,19 @@
         "description": "Repository owner",
         "type": "string"
       },
+      "parent_issue_number": {
+        "description": "Issue number of the parent issue. Only used when method is 'create' and cannot be combined with issue_fields. The new issue is created and attached to this parent in the same operation.",
+        "minimum": 1,
+        "type": "number"
+      },
+      "parent_owner": {
+        "description": "Repository owner of the parent issue. Must be provided with parent_repo. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided.",
+        "type": "string"
+      },
+      "parent_repo": {
+        "description": "Repository name of the parent issue. Must be provided with parent_owner. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided.",
+        "type": "string"
+      },
       "repo": {
         "description": "Repository name",
         "type": "string"
diff --git a/pkg/github/issues.go b/pkg/github/issues.go
index d6cc55e1ed..5767d2ec96 100644
--- a/pkg/github/issues.go
+++ b/pkg/github/issues.go
@@ -3,6 +3,7 @@ package github
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -2326,11 +2327,9 @@ const IssueWriteUIResourceURI = "ui://github-mcp-server/issue-write"
 
 // issueWriteFormParams are the parameters the issue_write MCP App form collects
 // and re-sends on submit. Any other parameter present on a call cannot be
-// represented by the form. The form collects (and prefills) every parameter in
-// the tool's current input schema, so hasNonFormParams against this set is a
-// forward-compatibility safety net: a parameter added to the schema in the
-// future but not yet wired into the form trips the check and bypasses the form
-// so the supplied value isn't silently dropped.
+// represented by the form, so hasNonFormParams bypasses the form rather than
+// silently dropping it. Parent issue parameters are intentionally omitted
+// because the current form cannot represent them.
 var issueWriteFormParams = map[string]struct{}{
 	"method":        {},
 	"owner":         {},
@@ -2425,6 +2424,19 @@ Options are:
 						Type:        "number",
 						Description: "Issue number to update",
 					},
+					"parent_issue_number": {
+						Type:        "number",
+						Description: "Issue number of the parent issue. Only used when method is 'create' and cannot be combined with issue_fields. The new issue is created and attached to this parent in the same operation.",
+						Minimum:     jsonschema.Ptr(1.0),
+					},
+					"parent_owner": {
+						Type:        "string",
+						Description: "Repository owner of the parent issue. Must be provided with parent_repo. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided.",
+					},
+					"parent_repo": {
+						Type:        "string",
+						Description: "Repository name of the parent issue. Must be provided with parent_owner. Omit both to use owner and repo. Only used when method is 'create' and parent_issue_number is provided.",
+					},
 					"title": {
 						Type:        "string",
 						Description: "Issue title",
@@ -2611,11 +2623,38 @@ Options are:
 				return utils.NewToolResultError(err.Error()), nil, nil
 			}
 
+			parentIssueNumber, err := OptionalIntParam(args, "parent_issue_number")
+			if err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}
+			parentValue, parentProvided := args["parent_issue_number"]
+			parentProvided = parentProvided && parentValue != nil
+			if parentProvided && parentIssueNumber < 1 {
+				return utils.NewToolResultError("parent_issue_number must be greater than 0"), nil, nil
+			}
+			if parentProvided && method != "create" {
+				return utils.NewToolResultError("parent_issue_number can only be used with the create method"), nil, nil
+			}
+			parentOwner, err := OptionalParam[string](args, "parent_owner")
+			if err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}
+			parentRepo, err := OptionalParam[string](args, "parent_repo")
+			if err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}
+			if err := validateParentRepository(parentProvided, parentOwner, parentRepo); err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}
+
 			var issueFields []issueWriteFieldInput
 			issueFields, err = optionalIssueWriteFields(args)
 			if err != nil {
 				return utils.NewToolResultError(err.Error()), nil, nil
 			}
+			if parentProvided && len(issueFields) > 0 {
+				return utils.NewToolResultError("issue_fields cannot be used with parent_issue_number"), nil, nil
+			}
 
 			client, err := deps.GetClient(ctx)
 			if err != nil {
@@ -2638,6 +2677,11 @@ Options are:
 
 			switch method {
 			case "create":
+				if parentProvided {
+					result, err := createIssueWithParent(ctx, client, gqlClient, owner, repo, title, body, assignees, labels, milestoneNum, issueType, parentIssueNumber, parentOwner, parentRepo)
+					return result, nil, err
+				}
+
 				result, err := CreateIssue(ctx, client, owner, repo, title, body, assignees, labels, milestoneNum, issueType, issueFieldValues)
 				return result, nil, err
 			case "update":
@@ -2659,6 +2703,242 @@ Options are:
 	return st
 }
 
+type CreateIssueInput struct {
+	RepositoryID githubv4.ID     `json:"repositoryId"`
+	Title        githubv4.String `json:"title"`
+
+	Body          *githubv4.String `json:"body,omitempty"`
+	AssigneeIDs   *[]githubv4.ID   `json:"assigneeIds,omitempty"`
+	MilestoneID   *githubv4.ID     `json:"milestoneId,omitempty"`
+	LabelIDs      *[]githubv4.ID   `json:"labelIds,omitempty"`
+	IssueTypeID   *githubv4.ID     `json:"issueTypeId,omitempty"`
+	ParentIssueID *githubv4.ID     `json:"parentIssueId,omitempty"`
+}
+
+type createIssueMutation struct {
+	CreateIssue struct {
+		Issue struct {
+			FullDatabaseID githubv4.String `graphql:"fullDatabaseId"`
+			URL            githubv4.URI
+		}
+	} `graphql:"createIssue(input: $input)"`
+}
+
+type createIssueParentMetadataQuery struct {
+	ChildRepository struct {
+		ID            githubv4.ID
+		NameWithOwner githubv4.String
+	} `graphql:"childRepository: repository(owner: $owner, name: $repo)"`
+	ParentRepository struct {
+		Issue struct {
+			ID     githubv4.ID
+			Number githubv4.Int
+		} `graphql:"issue(number: $parentIssueNumber)"`
+	} `graphql:"parentRepository: repository(owner: $parentOwner, name: $parentRepo)"`
+}
+
+func createIssueWithParent(
+	ctx context.Context,
+	client *github.Client,
+	gqlClient *githubv4.Client,
+	owner string,
+	repo string,
+	title string,
+	body string,
+	assignees []string,
+	labels []string,
+	milestoneNumber int,
+	issueType string,
+	parentIssueNumber int,
+	parentOwner string,
+	parentRepo string,
+) (*mcp.CallToolResult, error) {
+	if title == "" {
+		return utils.NewToolResultError("missing required parameter: title"), nil
+	}
+	if parentIssueNumber < 1 {
+		return utils.NewToolResultError("parent_issue_number must be greater than 0"), nil
+	}
+
+	parentOwner, parentRepo = parentRepository(owner, repo, parentOwner, parentRepo)
+	repositoryID, parentIssueID, err := resolveCreateIssueParent(ctx, gqlClient, owner, repo, parentOwner, parentRepo, parentIssueNumber)
+	if err != nil {
+		return ghErrors.NewGitHubGraphQLErrorResponse(ctx, "failed to resolve parent issue", err), nil
+	}
+
+	input := CreateIssueInput{
+		RepositoryID:  repositoryID,
+		Title:         githubv4.String(title),
+		ParentIssueID: &parentIssueID,
+	}
+	if body != "" {
+		input.Body = githubv4.NewString(githubv4.String(body))
+	}
+
+	if len(labels) > 0 {
+		labelIDs := make([]githubv4.ID, 0, len(labels))
+		for _, label := range labels {
+			labelID, err := getLabelID(ctx, gqlClient, owner, repo, label)
+			if err != nil {
+				return ghErrors.NewGitHubGraphQLErrorResponse(ctx, fmt.Sprintf("failed to resolve label %q", label), err), nil
+			}
+			labelIDs = append(labelIDs, labelID)
+		}
+		input.LabelIDs = &labelIDs
+	}
+
+	if len(assignees) > 0 {
+		assigneeIDs := make([]githubv4.ID, 0, len(assignees))
+		for _, assignee := range assignees {
+			assigneeID, err := resolveUserID(ctx, gqlClient, assignee)
+			if err != nil {
+				return ghErrors.NewGitHubGraphQLErrorResponse(ctx, fmt.Sprintf("failed to resolve assignee %q", assignee), err), nil
+			}
+			assigneeIDs = append(assigneeIDs, assigneeID)
+		}
+		input.AssigneeIDs = &assigneeIDs
+	}
+
+	if milestoneNumber != 0 {
+		milestoneID, err := resolveMilestoneID(ctx, gqlClient, owner, repo, milestoneNumber)
+		if err != nil {
+			return ghErrors.NewGitHubGraphQLErrorResponse(ctx, "failed to resolve milestone", err), nil
+		}
+		input.MilestoneID = &milestoneID
+	}
+
+	if issueType != "" {
+		issueTypeID, resp, err := resolveIssueTypeID(ctx, client, owner, repo, issueType)
+		if err != nil {
+			return ghErrors.NewGitHubAPIErrorResponse(ctx, fmt.Sprintf("failed to resolve issue type %q", issueType), resp, err), nil
+		}
+		input.IssueTypeID = &issueTypeID
+	}
+
+	var mutation createIssueMutation
+	if err := gqlClient.Mutate(ctx, &mutation, input, nil); err != nil {
+		return ghErrors.NewGitHubGraphQLErrorResponse(ctx, "failed to create issue", err), nil
+	}
+	if mutation.CreateIssue.Issue.FullDatabaseID == "" || mutation.CreateIssue.Issue.URL.URL == nil {
+		return utils.NewToolResultError("failed to create issue: response did not include the created issue"), nil
+	}
+
+	response := MinimalResponse{
+		ID:  string(mutation.CreateIssue.Issue.FullDatabaseID),
+		URL: mutation.CreateIssue.Issue.URL.String(),
+	}
+	encoded, err := json.Marshal(response)
+	if err != nil {
+		return utils.NewToolResultErrorFromErr("failed to marshal response", err), nil
+	}
+	return utils.NewToolResultText(string(encoded)), nil
+}
+
+func parentRepository(owner, repo, parentOwner, parentRepo string) (string, string) {
+	if parentOwner == "" && parentRepo == "" {
+		return owner, repo
+	}
+	return parentOwner, parentRepo
+}
+
+func validateParentRepository(parentProvided bool, parentOwner, parentRepo string) error {
+	if !parentProvided {
+		if parentOwner != "" || parentRepo != "" {
+			return errors.New("parent_owner and parent_repo can only be used when parent_issue_number is provided")
+		}
+		return nil
+	}
+	if (parentOwner == "") != (parentRepo == "") {
+		return errors.New("parent_owner and parent_repo must be provided together")
+	}
+	return nil
+}
+
+func resolveCreateIssueParent(ctx context.Context, gqlClient *githubv4.Client, owner, repo, parentOwner, parentRepo string, parentIssueNumber int) (githubv4.ID, githubv4.ID, error) {
+	var query createIssueParentMetadataQuery
+	variables := map[string]any{
+		"owner":             githubv4.String(owner),
+		"repo":              githubv4.String(repo),
+		"parentOwner":       githubv4.String(parentOwner),
+		"parentRepo":        githubv4.String(parentRepo),
+		"parentIssueNumber": githubv4.Int(parentIssueNumber), // #nosec G115 - issue numbers are small positive integers
+	}
+	if err := gqlClient.Query(ctx, &query, variables); err != nil {
+		return "", "", err
+	}
+	if query.ChildRepository.NameWithOwner == "" {
+		return "", "", fmt.Errorf("repository %s/%s was not found", owner, repo)
+	}
+	if query.ParentRepository.Issue.Number == 0 {
+		return "", "", fmt.Errorf("parent issue #%d was not found in %s/%s", parentIssueNumber, parentOwner, parentRepo)
+	}
+	return query.ChildRepository.ID, query.ParentRepository.Issue.ID, nil
+}
+
+func resolveUserID(ctx context.Context, gqlClient *githubv4.Client, login string) (githubv4.ID, error) {
+	var query struct {
+		User struct {
+			ID    githubv4.ID
+			Login githubv4.String
+		} `graphql:"user(login: $login)"`
+	}
+	if err := gqlClient.Query(ctx, &query, map[string]any{"login": githubv4.String(login)}); err != nil {
+		return "", err
+	}
+	if query.User.Login == "" {
+		return "", fmt.Errorf("user %q was not found", login)
+	}
+	return query.User.ID, nil
+}
+
+func resolveMilestoneID(ctx context.Context, gqlClient *githubv4.Client, owner, repo string, milestoneNumber int) (githubv4.ID, error) {
+	var query struct {
+		Repository struct {
+			Milestone struct {
+				ID     githubv4.ID
+				Number githubv4.Int
+			} `graphql:"milestone(number: $milestoneNumber)"`
+		} `graphql:"repository(owner: $owner, name: $repo)"`
+	}
+	variables := map[string]any{
+		"owner":           githubv4.String(owner),
+		"repo":            githubv4.String(repo),
+		"milestoneNumber": githubv4.Int(milestoneNumber), // #nosec G115 - milestone numbers are small positive integers
+	}
+	if err := gqlClient.Query(ctx, &query, variables); err != nil {
+		return "", err
+	}
+	if query.Repository.Milestone.Number == 0 {
+		return "", fmt.Errorf("milestone #%d was not found in %s/%s", milestoneNumber, owner, repo)
+	}
+	return query.Repository.Milestone.ID, nil
+}
+
+func resolveIssueTypeID(ctx context.Context, client *github.Client, owner, repo, issueTypeName string) (githubv4.ID, *github.Response, error) {
+	req, err := client.NewRequest(ctx, "GET", fmt.Sprintf("repos/%s/%s/issue-types", owner, repo), nil)
+	if err != nil {
+		return "", nil, err
+	}
+
+	var issueTypes []*github.IssueType
+	resp, err := client.Do(req, &issueTypes)
+	if resp != nil && resp.Body != nil {
+		defer func() { _ = resp.Body.Close() }()
+	}
+	if err != nil {
+		return "", resp, err
+	}
+	for _, issueType := range issueTypes {
+		if issueType != nil && strings.EqualFold(strings.TrimSpace(issueType.GetName()), strings.TrimSpace(issueTypeName)) {
+			if issueType.GetNodeID() == "" {
+				return "", resp, fmt.Errorf("issue type %q is missing a node ID", issueTypeName)
+			}
+			return githubv4.ID(issueType.GetNodeID()), resp, nil
+		}
+	}
+	return "", resp, fmt.Errorf("issue type %q was not found in %s/%s", issueTypeName, owner, repo)
+}
+
 func CreateIssue(ctx context.Context, client *github.Client, owner string, repo string, title string, body string, assignees []string, labels []string, milestoneNum int, issueType string, issueFieldValues []*github.IssueRequestFieldValue) (*mcp.CallToolResult, error) {
 	if title == "" {
 		return utils.NewToolResultError("missing required parameter: title"), nil
diff --git a/pkg/github/issues_granular.go b/pkg/github/issues_granular.go
index fb5ff32242..863ad89ab1 100644
--- a/pkg/github/issues_granular.go
+++ b/pkg/github/issues_granular.go
@@ -144,6 +144,19 @@ func GranularCreateIssue(t translations.TranslationHelperFunc) inventory.ServerT
 						Type:        "string",
 						Description: "Issue body content (optional)",
 					},
+					"parent_issue_number": {
+						Type:        "number",
+						Description: "Issue number of the parent issue. The new issue is created and attached to this parent in the same operation.",
+						Minimum:     jsonschema.Ptr(1.0),
+					},
+					"parent_owner": {
+						Type:        "string",
+						Description: "Repository owner of the parent issue. Must be provided with parent_repo. Omit both to use owner and repo. Only used when parent_issue_number is provided.",
+					},
+					"parent_repo": {
+						Type:        "string",
+						Description: "Repository name of the parent issue. Must be provided with parent_owner. Omit both to use owner and repo. Only used when parent_issue_number is provided.",
+					},
 				},
 				Required: []string{"owner", "repo", "title"},
 			},
@@ -163,6 +176,26 @@ func GranularCreateIssue(t translations.TranslationHelperFunc) inventory.ServerT
 				return utils.NewToolResultError(err.Error()), nil, nil
 			}
 			body, _ := OptionalParam[string](args, "body")
+			parentIssueNumber, err := OptionalIntParam(args, "parent_issue_number")
+			if err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}
+			parentValue, parentProvided := args["parent_issue_number"]
+			parentProvided = parentProvided && parentValue != nil
+			if parentProvided && parentIssueNumber < 1 {
+				return utils.NewToolResultError("parent_issue_number must be greater than 0"), nil, nil
+			}
+			parentOwner, err := OptionalParam[string](args, "parent_owner")
+			if err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}
+			parentRepo, err := OptionalParam[string](args, "parent_repo")
+			if err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}
+			if err := validateParentRepository(parentProvided, parentOwner, parentRepo); err != nil {
+				return utils.NewToolResultError(err.Error()), nil, nil
+			}
 
 			issueReq := github.CreateIssueRequest{
 				Title: title,
@@ -176,6 +209,15 @@ func GranularCreateIssue(t translations.TranslationHelperFunc) inventory.ServerT
 				return utils.NewToolResultErrorFromErr("failed to get GitHub client", err), nil, nil
 			}
 
+			if parentProvided {
+				gqlClient, err := deps.GetGQLClient(ctx)
+				if err != nil {
+					return utils.NewToolResultErrorFromErr("failed to get GitHub GraphQL client", err), nil, nil
+				}
+				result, err := createIssueWithParent(ctx, client, gqlClient, owner, repo, title, body, nil, nil, 0, "", parentIssueNumber, parentOwner, parentRepo)
+				return result, nil, err
+			}
+
 			issue, resp, err := client.Issues.Create(ctx, owner, repo, issueReq)
 			if err != nil {
 				return ghErrors.NewGitHubAPIErrorResponse(ctx, "failed to create issue", resp, err), nil, nil
diff --git a/pkg/github/issues_test.go b/pkg/github/issues_test.go
index 7e9fb2ee8e..bf024b545a 100644
--- a/pkg/github/issues_test.go
+++ b/pkg/github/issues_test.go
@@ -22,6 +22,7 @@ import (
 	"github.com/github/github-mcp-server/pkg/translations"
 	"github.com/google/go-github/v89/github"
 	"github.com/google/jsonschema-go/jsonschema"
+	"github.com/modelcontextprotocol/go-sdk/mcp"
 	"github.com/shurcooL/githubv4"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -2240,6 +2241,713 @@ func Test_IssueWrite_MCPAppsFeature_UIGate(t *testing.T) {
 	})
 }
 
+func TestIssueWriteCreateWithParentAndLabelsUsesSingleMutation(t *testing.T) {
+	serverTool := IssueWrite(translations.NullTranslationHelper)
+	schema := serverTool.Tool.InputSchema
+	issueWriteSchema := schema.(*jsonschema.Schema)
+	assert.Contains(t, issueWriteSchema.Properties, "parent_issue_number")
+	assert.Contains(t, issueWriteSchema.Properties, "parent_owner")
+	assert.Contains(t, issueWriteSchema.Properties, "parent_repo")
+	assert.NotContains(t, issueWriteSchema.Required, "parent_issue_number")
+	assert.NotContains(t, issueWriteSchema.Required, "parent_owner")
+	assert.NotContains(t, issueWriteSchema.Required, "parent_repo")
+
+	labelIDs := []githubv4.ID{"LABEL_backlog"}
+	parentID := githubv4.ID("ISSUE_parent")
+	expectedInput := CreateIssueInput{
+		RepositoryID:  githubv4.ID("REPO_1"),
+		Title:         githubv4.String("Atomic child"),
+		Body:          githubv4.NewString(githubv4.String("Created under its parent")),
+		LabelIDs:      &labelIDs,
+		ParentIssueID: &parentID,
+	}
+	createMatcher := githubv4mock.NewMutationMatcher(
+		createIssueMutation{},
+		expectedInput,
+		nil,
+		githubv4mock.DataResponse(map[string]any{
+			"createIssue": map[string]any{
+				"issue": map[string]any{
+					"fullDatabaseId": "12345",
+					"url":            "https://github.com/owner/repo/issues/2",
+				},
+			},
+		}),
+	)
+	assert.Contains(t, createMatcher.Request, "$input:CreateIssueInput!")
+
+	gqlHTTPClient, gqlCalls := countingGraphQLClient(
+		createIssueParentMatcher(1, "parent-owner", "parent-repo", "REPO_1", "ISSUE_parent"),
+		createIssueLabelMatcher("status:backlog", "LABEL_backlog"),
+		createMatcher,
+	)
+	restHTTPClient := MockHTTPClientWithHandlers(nil)
+	restCounter := &countingRoundTripper{next: restHTTPClient.Transport}
+	restHTTPClient.Transport = restCounter
+
+	deps := BaseDeps{
+		Client:    mustNewGHClient(t, restHTTPClient),
+		GQLClient: githubv4.NewClient(gqlHTTPClient),
+	}
+	handler := serverTool.Handler(deps)
+	request := createMCPRequest(map[string]any{
+		"method":              "create",
+		"owner":               "owner",
+		"repo":                "repo",
+		"title":               "Atomic child",
+		"body":                "Created under its parent",
+		"labels":              []any{"status:backlog"},
+		"parent_issue_number": float64(1),
+		"parent_owner":        "parent-owner",
+		"parent_repo":         "parent-repo",
+	})
+
+	result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+	require.NoError(t, err)
+	require.False(t, result.IsError, getTextResult(t, result).Text)
+	assert.Equal(t, 3, gqlCalls(), "metadata lookups and exactly one create mutation are expected")
+	assert.Zero(t, restCounter.count.Load(), "parent creation must not use REST create or attachment requests")
+
+	var response MinimalResponse
+	require.NoError(t, json.Unmarshal([]byte(getTextResult(t, result).Text), &response))
+	assert.Equal(t, "12345", response.ID)
+	assert.Equal(t, "https://github.com/owner/repo/issues/2", response.URL)
+}
+
+func TestIssueWriteCreateWithParentDoesNotFallbackAfterMutationFailure(t *testing.T) {
+	gqlHTTPClient, gqlCalls := countingGraphQLClient(
+		createIssueParentMatcher(7, "owner", "repo", "REPO_1", "ISSUE_parent"),
+		githubv4mock.NewMutationMatcher(
+			createIssueMutation{},
+			CreateIssueInput{
+				RepositoryID:  githubv4.ID("REPO_1"),
+				Title:         githubv4.String("Atomic child"),
+				ParentIssueID: githubv4mock.Ptr[githubv4.ID]("ISSUE_parent"),
+			},
+			nil,
+			githubv4mock.ErrorResponse("parent cannot accept sub-issues"),
+		),
+	)
+	restHTTPClient := MockHTTPClientWithHandlers(nil)
+	restCounter := &countingRoundTripper{next: restHTTPClient.Transport}
+	restHTTPClient.Transport = restCounter
+
+	deps := BaseDeps{
+		Client:    mustNewGHClient(t, restHTTPClient),
+		GQLClient: githubv4.NewClient(gqlHTTPClient),
+	}
+	serverTool := IssueWrite(translations.NullTranslationHelper)
+	handler := serverTool.Handler(deps)
+	request := createMCPRequest(map[string]any{
+		"method":              "create",
+		"owner":               "owner",
+		"repo":                "repo",
+		"title":               "Atomic child",
+		"parent_issue_number": float64(7),
+	})
+
+	result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+	require.NoError(t, err)
+	require.True(t, result.IsError)
+	assert.Contains(t, getTextResult(t, result).Text, "failed to create issue")
+	assert.Equal(t, 2, gqlCalls(), "a failed create mutation must not trigger an attachment mutation")
+	assert.Zero(t, restCounter.count.Load(), "a failed create mutation must not fall back to REST create or attachment requests")
+}
+
+func TestIssueWriteCreateWithParentRejectsIncompleteMutationResponse(t *testing.T) {
+	tests := []struct {
+		name string
+		data map[string]any
+	}{
+		{
+			name: "missing issue",
+			data: map[string]any{"createIssue": map[string]any{"issue": nil}},
+		},
+		{
+			name: "missing database ID",
+			data: map[string]any{
+				"createIssue": map[string]any{
+					"issue": map[string]any{"url": "https://github.com/owner/repo/issues/8"},
+				},
+			},
+		},
+		{
+			name: "missing URL",
+			data: map[string]any{
+				"createIssue": map[string]any{
+					"issue": map[string]any{"fullDatabaseId": "34567"},
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			gqlHTTPClient, gqlCalls := countingGraphQLClient(
+				createIssueParentMatcher(7, "owner", "repo", "REPO_1", "ISSUE_parent"),
+				githubv4mock.NewMutationMatcher(
+					createIssueMutation{},
+					CreateIssueInput{
+						RepositoryID:  githubv4.ID("REPO_1"),
+						Title:         githubv4.String("Atomic child"),
+						ParentIssueID: githubv4mock.Ptr[githubv4.ID]("ISSUE_parent"),
+					},
+					nil,
+					githubv4mock.DataResponse(test.data),
+				),
+			)
+			restHTTPClient := MockHTTPClientWithHandlers(nil)
+			restCounter := &countingRoundTripper{next: restHTTPClient.Transport}
+			restHTTPClient.Transport = restCounter
+			deps := BaseDeps{
+				Client:    mustNewGHClient(t, restHTTPClient),
+				GQLClient: githubv4.NewClient(gqlHTTPClient),
+			}
+			request := createMCPRequest(map[string]any{
+				"method":              "create",
+				"owner":               "owner",
+				"repo":                "repo",
+				"title":               "Atomic child",
+				"parent_issue_number": float64(7),
+			})
+
+			serverTool := IssueWrite(translations.NullTranslationHelper)
+			result, err := serverTool.Handler(deps)(
+				ContextWithDeps(context.Background(), deps),
+				&request,
+			)
+			require.NoError(t, err)
+			require.True(t, result.IsError)
+			assert.Contains(t, getTextResult(t, result).Text, "response did not include the created issue")
+			assert.Equal(t, 2, gqlCalls())
+			assert.Zero(t, restCounter.count.Load())
+		})
+	}
+}
+
+func TestIssueWriteCreateWithParentPreservesSupportedFields(t *testing.T) {
+	labelIDs := []githubv4.ID{"LABEL_bug"}
+	assigneeIDs := []githubv4.ID{"USER_octocat"}
+	milestoneID := githubv4.ID("MILESTONE_1")
+	issueTypeID := githubv4.ID("ISSUE_TYPE_bug")
+	parentID := githubv4.ID("ISSUE_parent")
+	expectedInput := CreateIssueInput{
+		RepositoryID:  githubv4.ID("REPO_1"),
+		Title:         githubv4.String("Fully specified child"),
+		Body:          githubv4.NewString(githubv4.String("Body")),
+		AssigneeIDs:   &assigneeIDs,
+		MilestoneID:   &milestoneID,
+		LabelIDs:      &labelIDs,
+		IssueTypeID:   &issueTypeID,
+		ParentIssueID: &parentID,
+	}
+	gqlHTTPClient, gqlCalls := countingGraphQLClient(
+		createIssueParentMatcher(7, "owner", "repo", "REPO_1", "ISSUE_parent"),
+		createIssueLabelMatcher("bug", "LABEL_bug"),
+		createIssueUserMatcher("octocat", "USER_octocat"),
+		createIssueMilestoneMatcher(1, "MILESTONE_1"),
+		githubv4mock.NewMutationMatcher(
+			createIssueMutation{},
+			expectedInput,
+			nil,
+			githubv4mock.DataResponse(map[string]any{
+				"createIssue": map[string]any{
+					"issue": map[string]any{
+						"fullDatabaseId": "34567",
+						"url":            "https://github.com/owner/repo/issues/8",
+					},
+				},
+			}),
+		),
+	)
+	restHTTPClient := MockHTTPClientWithHandlers(map[string]http.HandlerFunc{
+		"GET /repos/{owner}/{repo}/issue-types": mockResponse(t, http.StatusOK, []*github.IssueType{
+			{Name: github.Ptr("Bug"), NodeID: github.Ptr("ISSUE_TYPE_bug")},
+		}),
+	})
+	restCounter := &countingRoundTripper{next: restHTTPClient.Transport}
+	restHTTPClient.Transport = restCounter
+	deps := BaseDeps{
+		Client:    mustNewGHClient(t, restHTTPClient),
+		GQLClient: githubv4.NewClient(gqlHTTPClient),
+	}
+	request := createMCPRequest(map[string]any{
+		"method":              "create",
+		"owner":               "owner",
+		"repo":                "repo",
+		"title":               "Fully specified child",
+		"body":                "Body",
+		"assignees":           []any{"octocat"},
+		"labels":              []any{"bug"},
+		"milestone":           float64(1),
+		"type":                "Bug",
+		"parent_issue_number": float64(7),
+	})
+
+	serverTool := IssueWrite(translations.NullTranslationHelper)
+	result, err := serverTool.Handler(deps)(
+		ContextWithDeps(context.Background(), deps),
+		&request,
+	)
+	require.NoError(t, err)
+	require.False(t, result.IsError, getTextResult(t, result).Text)
+	assert.Equal(t, 5, gqlCalls(), "four metadata lookups and exactly one create mutation are expected")
+	assert.Equal(t, int64(1), restCounter.count.Load(), "issue type resolution is the only expected REST call")
+}
+
+func TestIssueWriteCreateWithParentRejectsMissingMetadata(t *testing.T) {
+	tests := []struct {
+		name          string
+		args          map[string]any
+		gqlMatchers   []githubv4mock.Matcher
+		restHandlers  map[string]http.HandlerFunc
+		want          string
+		wantGQLCalls  int
+		wantRESTCalls int64
+	}{
+		{
+			name: "child repository",
+			gqlMatchers: []githubv4mock.Matcher{
+				createIssueMissingChildRepositoryMatcher(7),
+			},
+			want:         "failed to resolve parent issue",
+			wantGQLCalls: 1,
+		},
+		{
+			name: "parent issue",
+			gqlMatchers: []githubv4mock.Matcher{
+				createIssueMissingParentMatcher(7),
+			},
+			want:         "failed to resolve parent issue",
+			wantGQLCalls: 1,
+		},
+		{
+			name: "milestone",
+			args: map[string]any{"milestone": float64(99)},
+			gqlMatchers: []githubv4mock.Matcher{
+				createIssueParentMatcher(7, "owner", "repo", "REPO_1", "ISSUE_parent"),
+				createIssueMissingMilestoneMatcher(99),
+			},
+			want:         "failed to resolve milestone",
+			wantGQLCalls: 2,
+		},
+		{
+			name: "assignee",
+			args: map[string]any{"assignees": []any{"missing-user"}},
+			gqlMatchers: []githubv4mock.Matcher{
+				createIssueParentMatcher(7, "owner", "repo", "REPO_1", "ISSUE_parent"),
+				createIssueMissingUserMatcher("missing-user"),
+			},
+			want:         `failed to resolve assignee "missing-user"`,
+			wantGQLCalls: 2,
+		},
+		{
+			name:        "issue type",
+			args:        map[string]any{"type": "Missing"},
+			gqlMatchers: []githubv4mock.Matcher{createIssueParentMatcher(7, "owner", "repo", "REPO_1", "ISSUE_parent")},
+			restHandlers: map[string]http.HandlerFunc{
+				"GET /repos/{owner}/{repo}/issue-types": mockResponse(t, http.StatusOK, []*github.IssueType{}),
+			},
+			want:          `failed to resolve issue type "Missing"`,
+			wantGQLCalls:  1,
+			wantRESTCalls: 1,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			gqlHTTPClient, gqlCalls := countingGraphQLClient(test.gqlMatchers...)
+			restHTTPClient := MockHTTPClientWithHandlers(test.restHandlers)
+			restCounter := &countingRoundTripper{next: restHTTPClient.Transport}
+			restHTTPClient.Transport = restCounter
+			deps := BaseDeps{
+				Client:    mustNewGHClient(t, restHTTPClient),
+				GQLClient: githubv4.NewClient(gqlHTTPClient),
+			}
+			args := map[string]any{
+				"method":              "create",
+				"owner":               "owner",
+				"repo":                "repo",
+				"title":               "Atomic child",
+				"parent_issue_number": float64(7),
+			}
+			maps.Copy(args, test.args)
+			request := createMCPRequest(args)
+
+			serverTool := IssueWrite(translations.NullTranslationHelper)
+			result, err := serverTool.Handler(deps)(
+				ContextWithDeps(context.Background(), deps),
+				&request,
+			)
+			require.NoError(t, err)
+			require.True(t, result.IsError)
+			assert.Contains(t, getTextResult(t, result).Text, test.want)
+			assert.Equal(t, test.wantGQLCalls, gqlCalls())
+			assert.Equal(t, test.wantRESTCalls, restCounter.count.Load())
+		})
+	}
+}
+
+func TestGranularCreateIssueWithParentUsesAtomicMutation(t *testing.T) {
+	serverTool := GranularCreateIssue(translations.NullTranslationHelper)
+	schema := serverTool.Tool.InputSchema.(*jsonschema.Schema)
+	assert.Contains(t, schema.Properties, "parent_issue_number")
+	assert.Contains(t, schema.Properties, "parent_owner")
+	assert.Contains(t, schema.Properties, "parent_repo")
+
+	parentID := githubv4.ID("ISSUE_parent")
+	gqlHTTPClient := githubv4mock.NewMockedHTTPClient(
+		createIssueParentMatcher(3, "owner", "repo", "REPO_1", "ISSUE_parent"),
+		githubv4mock.NewMutationMatcher(
+			createIssueMutation{},
+			CreateIssueInput{
+				RepositoryID:  githubv4.ID("REPO_1"),
+				Title:         githubv4.String("Granular child"),
+				ParentIssueID: &parentID,
+			},
+			nil,
+			githubv4mock.DataResponse(map[string]any{
+				"createIssue": map[string]any{
+					"issue": map[string]any{
+						"fullDatabaseId": "23456",
+						"url":            "https://github.com/owner/repo/issues/4",
+					},
+				},
+			}),
+		),
+	)
+	restHTTPClient := MockHTTPClientWithHandlers(nil)
+
+	deps := BaseDeps{
+		Client:    mustNewGHClient(t, restHTTPClient),
+		GQLClient: githubv4.NewClient(gqlHTTPClient),
+	}
+	handler := serverTool.Handler(deps)
+	request := createMCPRequest(map[string]any{
+		"owner":               "owner",
+		"repo":                "repo",
+		"title":               "Granular child",
+		"parent_issue_number": float64(3),
+	})
+
+	result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+	require.NoError(t, err)
+	assert.False(t, result.IsError)
+}
+
+func TestCreateIssueParentRepositoryValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		handler func(context.Context, *mcp.CallToolRequest) (*mcp.CallToolResult, error)
+		args    map[string]any
+		want    string
+	}{
+		{
+			name: "issue_write",
+			handler: func(ctx context.Context, request *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+				serverTool := IssueWrite(translations.NullTranslationHelper)
+				return serverTool.Handler(BaseDeps{})(ctx, request)
+			},
+			args: map[string]any{
+				"method":       "create",
+				"owner":        "owner",
+				"repo":         "repo",
+				"title":        "Child",
+				"parent_owner": "parent-owner",
+			},
+			want: "can only be used when parent_issue_number is provided",
+		},
+		{
+			name: "create_issue",
+			handler: func(ctx context.Context, request *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+				serverTool := GranularCreateIssue(translations.NullTranslationHelper)
+				return serverTool.Handler(BaseDeps{})(ctx, request)
+			},
+			args: map[string]any{
+				"owner":       "owner",
+				"repo":        "repo",
+				"title":       "Child",
+				"parent_repo": "parent-repo",
+			},
+			want: "can only be used when parent_issue_number is provided",
+		},
+		{
+			name: "issue_write requires parent repo with parent owner",
+			handler: func(ctx context.Context, request *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+				serverTool := IssueWrite(translations.NullTranslationHelper)
+				return serverTool.Handler(BaseDeps{})(ctx, request)
+			},
+			args: map[string]any{
+				"method":              "create",
+				"owner":               "owner",
+				"repo":                "repo",
+				"title":               "Child",
+				"parent_issue_number": float64(1),
+				"parent_owner":        "parent-owner",
+			},
+			want: "parent_owner and parent_repo must be provided together",
+		},
+		{
+			name: "create_issue requires parent owner with parent repo",
+			handler: func(ctx context.Context, request *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+				serverTool := GranularCreateIssue(translations.NullTranslationHelper)
+				return serverTool.Handler(BaseDeps{})(ctx, request)
+			},
+			args: map[string]any{
+				"owner":               "owner",
+				"repo":                "repo",
+				"title":               "Child",
+				"parent_issue_number": float64(1),
+				"parent_repo":         "parent-repo",
+			},
+			want: "parent_owner and parent_repo must be provided together",
+		},
+		{
+			name: "issue fields",
+			handler: func(ctx context.Context, request *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+				serverTool := IssueWrite(translations.NullTranslationHelper)
+				return serverTool.Handler(BaseDeps{})(ctx, request)
+			},
+			args: map[string]any{
+				"method":              "create",
+				"owner":               "owner",
+				"repo":                "repo",
+				"title":               "Child",
+				"parent_issue_number": float64(1),
+				"issue_fields": []any{
+					map[string]any{"field_name": "Priority", "field_option_name": "High"},
+				},
+			},
+			want: "issue_fields cannot be used with parent_issue_number",
+		},
+		{
+			name: "issue_write rejects parent during update",
+			handler: func(ctx context.Context, request *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+				serverTool := IssueWrite(translations.NullTranslationHelper)
+				return serverTool.Handler(BaseDeps{})(ctx, request)
+			},
+			args: map[string]any{
+				"method":              "update",
+				"owner":               "owner",
+				"repo":                "repo",
+				"issue_number":        float64(2),
+				"parent_issue_number": float64(1),
+			},
+			want: "parent_issue_number can only be used with the create method",
+		},
+		{
+			name: "issue_write rejects zero parent number",
+			handler: func(ctx context.Context, request *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+				serverTool := IssueWrite(translations.NullTranslationHelper)
+				return serverTool.Handler(BaseDeps{})(ctx, request)
+			},
+			args: map[string]any{
+				"method":              "create",
+				"owner":               "owner",
+				"repo":                "repo",
+				"title":               "Child",
+				"parent_issue_number": float64(0),
+			},
+			want: "parent_issue_number must be greater than 0",
+		},
+		{
+			name: "create_issue rejects zero parent number",
+			handler: func(ctx context.Context, request *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+				serverTool := GranularCreateIssue(translations.NullTranslationHelper)
+				return serverTool.Handler(BaseDeps{})(ctx, request)
+			},
+			args: map[string]any{
+				"owner":               "owner",
+				"repo":                "repo",
+				"title":               "Child",
+				"parent_issue_number": float64(0),
+			},
+			want: "parent_issue_number must be greater than 0",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			request := createMCPRequest(test.args)
+			result, err := test.handler(ContextWithDeps(context.Background(), BaseDeps{}), &request)
+			require.NoError(t, err)
+			require.True(t, result.IsError)
+			assert.Contains(t, getTextResult(t, result).Text, test.want)
+		})
+	}
+}
+
+func createIssueParentMatcher(parentIssueNumber int, parentOwner, parentRepo string, repositoryID, parentIssueID githubv4.ID) githubv4mock.Matcher {
+	return githubv4mock.NewQueryMatcher(
+		createIssueParentMetadataQuery{},
+		map[string]any{
+			"owner":             githubv4.String("owner"),
+			"repo":              githubv4.String("repo"),
+			"parentOwner":       githubv4.String(parentOwner),
+			"parentRepo":        githubv4.String(parentRepo),
+			"parentIssueNumber": githubv4.Int(parentIssueNumber), // #nosec G115 - test issue numbers are small
+		},
+		githubv4mock.DataResponse(map[string]any{
+			"childRepository": map[string]any{
+				"id":            repositoryID,
+				"nameWithOwner": "owner/repo",
+			},
+			"parentRepository": map[string]any{
+				"issue": map[string]any{
+					"id":     parentIssueID,
+					"number": parentIssueNumber,
+				},
+			},
+		}),
+	)
+}
+
+func createIssueLabelMatcher(name string, id githubv4.ID) githubv4mock.Matcher {
+	return githubv4mock.NewQueryMatcher(
+		struct {
+			Repository struct {
+				Label struct {
+					ID   githubv4.ID
+					Name githubv4.String
+				} `graphql:"label(name: $name)"`
+			} `graphql:"repository(owner: $owner, name: $repo)"`
+		}{},
+		map[string]any{
+			"owner": githubv4.String("owner"),
+			"repo":  githubv4.String("repo"),
+			"name":  githubv4.String(name),
+		},
+		githubv4mock.DataResponse(map[string]any{
+			"repository": map[string]any{
+				"label": map[string]any{
+					"id":   id,
+					"name": name,
+				},
+			},
+		}),
+	)
+}
+
+func createIssueMissingChildRepositoryMatcher(parentIssueNumber int) githubv4mock.Matcher {
+	return githubv4mock.NewQueryMatcher(
+		createIssueParentMetadataQuery{},
+		map[string]any{
+			"owner":             githubv4.String("owner"),
+			"repo":              githubv4.String("repo"),
+			"parentOwner":       githubv4.String("owner"),
+			"parentRepo":        githubv4.String("repo"),
+			"parentIssueNumber": githubv4.Int(parentIssueNumber), // #nosec G115 - test issue numbers are small
+		},
+		githubv4mock.DataResponse(map[string]any{
+			"childRepository": nil,
+			"parentRepository": map[string]any{
+				"issue": map[string]any{
+					"id":     "ISSUE_parent",
+					"number": parentIssueNumber,
+				},
+			},
+		}),
+	)
+}
+
+func createIssueMissingParentMatcher(parentIssueNumber int) githubv4mock.Matcher {
+	return githubv4mock.NewQueryMatcher(
+		createIssueParentMetadataQuery{},
+		map[string]any{
+			"owner":             githubv4.String("owner"),
+			"repo":              githubv4.String("repo"),
+			"parentOwner":       githubv4.String("owner"),
+			"parentRepo":        githubv4.String("repo"),
+			"parentIssueNumber": githubv4.Int(parentIssueNumber), // #nosec G115 - test issue numbers are small
+		},
+		githubv4mock.DataResponse(map[string]any{
+			"childRepository": map[string]any{
+				"id":            "REPO_1",
+				"nameWithOwner": "owner/repo",
+			},
+			"parentRepository": map[string]any{"issue": nil},
+		}),
+	)
+}
+
+func createIssueUserMatcher(login string, id githubv4.ID) githubv4mock.Matcher {
+	return githubv4mock.NewQueryMatcher(
+		struct {
+			User struct {
+				ID    githubv4.ID
+				Login githubv4.String
+			} `graphql:"user(login: $login)"`
+		}{},
+		map[string]any{"login": githubv4.String(login)},
+		githubv4mock.DataResponse(map[string]any{
+			"user": map[string]any{
+				"id":    id,
+				"login": login,
+			},
+		}),
+	)
+}
+
+func createIssueMissingUserMatcher(login string) githubv4mock.Matcher {
+	return githubv4mock.NewQueryMatcher(
+		struct {
+			User struct {
+				ID    githubv4.ID
+				Login githubv4.String
+			} `graphql:"user(login: $login)"`
+		}{},
+		map[string]any{"login": githubv4.String(login)},
+		githubv4mock.DataResponse(map[string]any{"user": nil}),
+	)
+}
+
+func createIssueMilestoneMatcher(number int, id githubv4.ID) githubv4mock.Matcher {
+	return githubv4mock.NewQueryMatcher(
+		struct {
+			Repository struct {
+				Milestone struct {
+					ID     githubv4.ID
+					Number githubv4.Int
+				} `graphql:"milestone(number: $milestoneNumber)"`
+			} `graphql:"repository(owner: $owner, name: $repo)"`
+		}{},
+		map[string]any{
+			"owner":           githubv4.String("owner"),
+			"repo":            githubv4.String("repo"),
+			"milestoneNumber": githubv4.Int(number), // #nosec G115 - test milestone numbers are small
+		},
+		githubv4mock.DataResponse(map[string]any{
+			"repository": map[string]any{
+				"milestone": map[string]any{
+					"id":     id,
+					"number": number,
+				},
+			},
+		}),
+	)
+}
+
+func createIssueMissingMilestoneMatcher(number int) githubv4mock.Matcher {
+	return githubv4mock.NewQueryMatcher(
+		struct {
+			Repository struct {
+				Milestone struct {
+					ID     githubv4.ID
+					Number githubv4.Int
+				} `graphql:"milestone(number: $milestoneNumber)"`
+			} `graphql:"repository(owner: $owner, name: $repo)"`
+		}{},
+		map[string]any{
+			"owner":           githubv4.String("owner"),
+			"repo":            githubv4.String("repo"),
+			"milestoneNumber": githubv4.Int(number), // #nosec G115 - test milestone numbers are small
+		},
+		githubv4mock.DataResponse(map[string]any{
+			"repository": map[string]any{"milestone": nil},
+		}),
+	)
+}
+
 func Test_issueWriteHasNonFormParams(t *testing.T) {
 	t.Parallel()
 
@@ -2258,6 +2966,9 @@ func Test_issueWriteHasNonFormParams(t *testing.T) {
 		{name: "state present", args: map[string]any{"state": "closed"}, want: false},
 		{name: "state_reason present", args: map[string]any{"state_reason": "completed"}, want: false},
 		{name: "duplicate_of present", args: map[string]any{"duplicate_of": float64(7)}, want: false},
+		{name: "parent issue present", args: map[string]any{"parent_issue_number": float64(7)}, want: true},
+		{name: "parent owner present", args: map[string]any{"parent_owner": "octo-org"}, want: true},
+		{name: "parent repo present", args: map[string]any{"parent_repo": "parent-repo"}, want: true},
 		{name: "unknown non-schema param present", args: map[string]any{"title": "t", "not_a_real_param": "x"}, want: true},
 		{name: "nil value is ignored", args: map[string]any{"issue_fields": nil}, want: false},
 	}
@@ -2357,11 +3068,14 @@ func Test_issueWriteSchemaClassification(t *testing.T) {
 	t.Parallel()
 
 	// Schema properties the MCP App form cannot represent — their presence
-	// must trigger the safety-net bypass via hasNonFormParams. The
-	// form currently collects every schema property, so this allowlist is
-	// empty; add a property here only if it is added to the schema without
+	// must trigger the safety-net bypass via hasNonFormParams. Add a
+	// property here only if it is added to the schema without
 	// corresponding form support.
-	knownNonForm := map[string]struct{}{}
+	knownNonForm := map[string]struct{}{
+		"parent_issue_number": {},
+		"parent_owner":        {},
+		"parent_repo":         {},
+	}
 
 	cases := []struct {
 		name string