feat(mcp): accept array issue list filters

docs/tools.md

@@ -41,11 +41,13 @@ GET `/projects/{project_id}/issues/`.
 Required: `project_id`.
 Optional: `per_page` (number), `cursor` (string), `archived` (boolean),
 `state_group` (one of `backlog`, `unstarted`, `started`, `completed`,
-`cancelled`), `assignees`, `labels`, `priority`, `created_at`, `target_date`,
-`completed_at`, `name`, `order_by`, `expand`, `parent` (all strings).
+`cancelled`), `assignees` (array of plane user ids), `labels` (array of label
+ids), `priority`, `created_at`, `target_date`, `completed_at`, `name`,
+`order_by`, `expand`, `parent` (strings).
 
 Date filters use plane's `<value>;<op>` syntax — e.g.
 `"2026-04-01;after,2026-04-30;before"`.
+Comma-separated strings are also accepted for `assignees` and `labels`.
 
 Returns `{ "results": [...], "count": n, "next_cursor": "..." }`.
 

internal/mcpserver/jsonutil.go

@@ -2,6 +2,7 @@ package mcpserver
 
 import (
 	"encoding/json"
+	"strings"
 
 	"github.com/mark3labs/mcp-go/mcp"
 )
@@ -29,17 +30,21 @@ func argStringPtr(args map[string]any, key string) *string {
 // stored under key. Non-string items are skipped. Returns nil if key is
 // missing or not an array.
 func argStringSlicePtr(args map[string]any, key string) *[]string {
-	raw, ok := args[key].([]any)
-	if !ok {
-		return nil
-	}
-	out := make([]string, 0, len(raw))
-	for _, item := range raw {
-		if s, ok := item.(string); ok {
-			out = append(out, s)
+	switch raw := args[key].(type) {
+	case []any:
+		out := make([]string, 0, len(raw))
+		for _, item := range raw {
+			if s, ok := item.(string); ok {
+				out = append(out, s)
+			}
 		}
+		return &out
+	case []string:
+		out := append([]string(nil), raw...)
+		return &out
+	default:
+		return nil
 	}
-	return &out
 }
 
 // argStringSlice returns []string from args[key], or nil. Useful when the
@@ -51,6 +56,20 @@ func argStringSlice(args map[string]any, key string) []string {
 	return nil
 }
 
+// argStringOrStringSliceCSVPtr accepts either a comma-separated string or an
+// array of strings and returns the query-string form expected by Plane.
+func argStringOrStringSliceCSVPtr(args map[string]any, key string) *string {
+	if v, ok := args[key].(string); ok {
+		return &v
+	}
+	values := argStringSlice(args, key)
+	if len(values) == 0 {
+		return nil
+	}
+	joined := strings.Join(values, ",")
+	return &joined
+}
+
 // argIntPtr coerces args[key] from float64 (JSON's number) into *int.
 func argIntPtr(args map[string]any, key string) *int {
 	switch v := args[key].(type) {

internal/mcpserver/server_test.go

@@ -112,6 +112,66 @@ func TestStateListRoundTripsThroughInProcessClient(t *testing.T) {
 	require.Len(t, results, 1)
 }
 
+func TestIssueListFilterSchemaAcceptsArraysAndStrings(t *testing.T) {
+	srv := newTestServer(t, func(w http.ResponseWriter, _ *http.Request) {
+		_, _ = w.Write([]byte(`{}`))
+	})
+	c, err := client.NewInProcessClient(srv.MCPServer())
+	require.NoError(t, err)
+	require.NoError(t, c.Start(context.Background()))
+	t.Cleanup(func() { _ = c.Close() })
+
+	_, err = c.Initialize(context.Background(), mcp.InitializeRequest{})
+	require.NoError(t, err)
+	list, err := c.ListTools(context.Background(), mcp.ListToolsRequest{})
+	require.NoError(t, err)
+
+	for _, tool := range list.Tools {
+		if tool.Name == "plane_issue_list" {
+			requireArrayOrStringFilterSchema(t, tool.InputSchema.Properties, "assignees")
+			requireArrayOrStringFilterSchema(t, tool.InputSchema.Properties, "labels")
+			return
+		}
+	}
+	require.Fail(t, "plane_issue_list should be registered")
+}
+
+func TestIssueListAcceptsArrayAndStringFilters(t *testing.T) {
+	for _, tt := range []struct {
+		name string
+		args map[string]any
+	}{
+		{
+			name: "arrays",
+			args: map[string]any{
+				"project_id": "P",
+				"assignees":  []any{"u1", "u2"},
+				"labels":     []any{"l1", "l2"},
+			},
+		},
+		{
+			name: "strings",
+			args: map[string]any{
+				"project_id": "P",
+				"assignees":  "u1,u2",
+				"labels":     "l1,l2",
+			},
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			srv := newTestServer(t, func(w http.ResponseWriter, r *http.Request) {
+				require.Equal(t, "/api/v1/workspaces/ws/projects/P/issues/", r.URL.Path)
+				require.Equal(t, "u1,u2", r.URL.Query().Get("assignees"))
+				require.Equal(t, "l1,l2", r.URL.Query().Get("labels"))
+				_, _ = w.Write([]byte(`{"results":[],"count":0}`))
+			})
+
+			payload := callToolPayload(t, srv, "plane_issue_list", tt.args)
+			require.Equal(t, float64(0), payload["count"])
+		})
+	}
+}
+
 func TestNotFoundMapsToToolError(t *testing.T) {
 	srv := newTestServer(t, func(w http.ResponseWriter, _ *http.Request) {
 		http.Error(w, `{"detail":"missing"}`, http.StatusNotFound)
@@ -156,6 +216,24 @@ func TestWorkspaceInfoDoesNotEchoToken(t *testing.T) {
 	require.Contains(t, text.Text, "ws")
 }
 
+func requireArrayOrStringFilterSchema(t *testing.T, props map[string]any, name string) {
+	t.Helper()
+	prop, ok := props[name].(map[string]any)
+	require.True(t, ok)
+	oneOf, ok := prop["oneOf"].([]any)
+	require.True(t, ok)
+	require.Len(t, oneOf, 2)
+	arraySchema, ok := oneOf[0].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "array", arraySchema["type"])
+	items, ok := arraySchema["items"].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "string", items["type"])
+	stringSchema, ok := oneOf[1].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "string", stringSchema["type"])
+}
+
 func TestProjectListReturnsCompactResults(t *testing.T) {
 	srv := newTestServer(t, func(w http.ResponseWriter, r *http.Request) {
 		require.Equal(t, "/api/v1/workspaces/ws/projects/", r.URL.Path)

internal/mcpserver/tools_issues.go

@@ -27,8 +27,8 @@ func (s *Server) registerIssueTools() {
 		mcp.WithString("cursor"),
 		mcp.WithBoolean("archived"),
 		mcp.WithString("state_group", mcp.Description(`Plane state group: "backlog", "unstarted", "started", "completed", "cancelled".`)),
-		mcp.WithString("assignees", mcp.Description("Comma-separated assignee UUIDs.")),
-		mcp.WithString("labels", mcp.Description("Comma-separated label UUIDs.")),
+		mcp.WithAny("assignees", issueListIDsFilter("Assignee Plane user UUIDs. Use an array; comma-separated string is accepted.")),
+		mcp.WithAny("labels", issueListIDsFilter("Label UUIDs. Use an array; comma-separated string is accepted.")),
 		mcp.WithString("priority"),
 		mcp.WithString("created_at", mcp.Description(`Range string, e.g. "2026-04-01;after,2026-04-30;before".`)),
 		mcp.WithString("target_date"),
@@ -99,8 +99,8 @@ func (s *Server) handleIssueList(ctx context.Context, req mcp.CallToolRequest) (
 		Cursor:      argStringPtr(args, "cursor"),
 		Archived:    argBoolPtr(args, "archived"),
 		StateGroup:  argStringPtr(args, "state_group"),
-		Assignees:   argStringPtr(args, "assignees"),
-		Labels:      argStringPtr(args, "labels"),
+		Assignees:   argStringOrStringSliceCSVPtr(args, "assignees"),
+		Labels:      argStringOrStringSliceCSVPtr(args, "labels"),
 		Priority:    argStringPtr(args, "priority"),
 		CreatedAt:   argStringPtr(args, "created_at"),
 		TargetDate:  argStringPtr(args, "target_date"),
@@ -189,3 +189,16 @@ func issueOptionsFromArgs(args map[string]any) plane.IssueOptions {
 		Parent:          argStringPtr(args, "parent"),
 	}
 }
+
+func issueListIDsFilter(description string) mcp.PropertyOption {
+	return func(schema map[string]any) {
+		schema["description"] = description
+		schema["oneOf"] = []any{
+			map[string]any{
+				"type":  "array",
+				"items": map[string]any{"type": "string"},
+			},
+			map[string]any{"type": "string"},
+		}
+	}
+}