Feat v0.8.1 workspace module

Managed disk directories for extensions needing real filesystem access
(git, compilers, media tools). Five builtins: create, path, list,
delete, usage. Extension-scoped to {WORKSPACE_ROOT}/{packageID}/{name}/.

- New sandbox/workspace_module.go with path traversal + symlink protection
- Permission: workspace.manage; config: WORKSPACE_ROOT, WORKSPACE_QUOTA_MB
- Runner wiring with graceful degradation (module absent if root unwritable)
- 16 new tests, all passing with -race

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/sandbox/runner.go

@@ -79,6 +79,8 @@ type Runner struct {
 	allowPrivateIPs bool
 	bus             *events.Bus
 	objectStore     storage.ObjectStore  // nil = files module unavailable
+	workspaceRoot   string               // empty = workspace module unavailable
+	workspaceQuota  int                  // MB, 0 = unlimited
 }
 
 // NewRunner creates a runner with the given sandbox and dependencies.
@@ -123,6 +125,13 @@ func (r *Runner) SetObjectStore(s storage.ObjectStore) {
 	r.objectStore = s
 }
 
+// SetWorkspaceRoot sets the base directory for extension workspaces.
+// quotaMB is the per-extension quota in MB (0 = unlimited).
+func (r *Runner) SetWorkspaceRoot(root string, quotaMB int) {
+	r.workspaceRoot = root
+	r.workspaceQuota = quotaMB
+}
+
 // SetAllowPrivateIPs disables the SSRF check that blocks connections to
 // private/loopback IPs. For self-hosted environments where extensions
 // reach internal services. Controlled by EXT_ALLOW_PRIVATE_IPS env var.
@@ -392,6 +401,15 @@ func (r *Runner) buildModulesWithLibCtx(ctx context.Context, packageID string, m
 				modules["realtime"] = BuildRealtimeModule(ctx, r.bus, packageID)
 			}
 
+		case models.ExtPermWorkspaceManage:
+			if r.workspaceRoot != "" {
+				modules["workspace"] = BuildWorkspaceModule(ctx, WorkspaceModuleConfig{
+					PackageID:     packageID,
+					WorkspaceRoot: r.workspaceRoot,
+					QuotaMB:       r.workspaceQuota,
+				})
+			}
+
 		case models.ExtPermBatchExec:
 			hasBatchExec = true
 		}