P3: store group — kv_* + file_* tools (agent memory)

RegisterStore(reg, StoreDeps) registers the persistent-memory tools over the
host's KV and/or File backends:
- kv_get/set/list/delete (KVStorage seam)
- file_save/get/get_text/get_metadata/list/delete (FileStorage seam), plus
  file_search (FileSearcher) and create_file_url (FileTokenMinter) when wired.

Near-zero-config: Quota defaults to a generous static cap (staticQuota), the
per-value/per-file caps default, and the kv vs file groups register
independently (a host can take just one). Seams moved clean (interface-only):
kv_storage.go, quota_provider.go, file_descendant_grant.go. The default
in-memory KV/File backends come with contrib/store at P4.

Core go.sum still free of gorm/redis/discordgo/sqlite.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/file_list.go

@@ -0,0 +1,74 @@
+// file_list returns metadata for files in a scope. Blob bytes are NOT
+// loaded — listing is a hot path that must stay light, and the LLM
+// would burn tokens for no benefit.
+package tools
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+	"time"
+
+	"gitea.stevedudenhoeffer.com/steve/executus/tool"
+)
+
+type fileListArgs struct {
+	Scope string `json:"scope" description:"Storage scope: 'skill', 'user:<your_id>', or 'run:<run_id>'."`
+}
+
+type fileListEntry struct {
+	FileID    string `json:"file_id"`
+	Name      string `json:"name"`
+	Mime      string `json:"mime"`
+	SizeBytes int64  `json:"size_bytes"`
+	CreatedAt string `json:"created_at"`
+}
+
+// NewFileList constructs the file_list tool. storage nil → "not
+// configured" at execute time.
+func NewFileList(storage FileStorage) tool.Tool {
+	return tool.NewGatedTool[fileListArgs](
+		"file_list",
+		"List files in a scope. Returns a JSON array of {file_id, name, mime, size_bytes, created_at}. Does NOT include bytes — call file_get with a file_id to fetch content.",
+		tool.Permission{
+			AuthoringRequirement: tool.RequirementAnyone,
+			OperatesOn:           tool.ScopeCaller,
+			SafeForShare:         true,
+			Categories:           []string{"storage", "read"},
+		},
+		func(ctx context.Context, inv tool.Invocation, args fileListArgs) (string, error) {
+			if storage == nil {
+				return "", fmt.Errorf("file_list: not configured")
+			}
+			if err := ValidateScope(inv, args.Scope, false); err != nil {
+				return "", fmt.Errorf("file_list: %w", err)
+			}
+			// root_run is a KV-only scope (v1) — see file_save's guard.
+			if strings.HasPrefix(args.Scope, "root_run:") {
+				return "", fmt.Errorf("file_list: root_run scope is KV-only")
+			}
+
+			rows, err := storage.FileList(ctx, inv.SkillID, args.Scope)
+			if err != nil {
+				return "", fmt.Errorf("file_list: %w", err)
+			}
+
+			out := make([]fileListEntry, 0, len(rows))
+			for _, r := range rows {
+				out = append(out, fileListEntry{
+					FileID:    r.ID,
+					Name:      r.Name,
+					Mime:      r.MimeType,
+					SizeBytes: r.SizeBytes,
+					CreatedAt: r.CreatedAt.UTC().Format(time.RFC3339),
+				})
+			}
+			b, err := json.Marshal(out)
+			if err != nil {
+				return "", fmt.Errorf("file_list: marshal: %w", err)
+			}
+			return string(b), nil
+		},
+	)
+}