feat: self-service worker enrollment bound to a user account

Let a signed-in user turn their own machine into a worker without the
shared token. The coordinator already binds a JWT-authenticated
registration to owner_id as untrusted; this adds the missing pieces.

userservice: long-lived worker keys (scimesh_wk_live_*, hash-at-rest)
with create/list/revoke and a public /worker-tokens/exchange that trades
a key for a short-lived JWT carrying the owner current role/verified.

python worker: SCIMESH_WORKER_KEY + SCIMESH_USERSERVICE_URL; a token
provider exchanges the key and refreshes the JWT proactively and on 401,
so a long-running worker survives token expiry. Static bearer token path
is unchanged.

coordinator UI: an "add your machine" page that mints a key and shows a
ready-to-run command, proxying key management to the userservice; the
dashboard gains an owner-scoped "my machines" section.

docs: how to run a worker from your account, plus the untrusted/quorum/
verified trust model.

users/internal/transport/http/handlers.go

@@ -13,12 +13,16 @@ import (
 
 // Handlers holds the use cases each endpoint drives.
 type Handlers struct {
-	register    *usecase.Register
-	login       *usecase.Login
-	setVerified *usecase.SetVerified
-	setRole     *usecase.SetRole
-	users       usecase.UserRepository
-	log         *slog.Logger
+	register          *usecase.Register
+	login             *usecase.Login
+	setVerified       *usecase.SetVerified
+	setRole           *usecase.SetRole
+	createWorkerKey   *usecase.CreateWorkerKey
+	listWorkerKeys    *usecase.ListWorkerKeys
+	revokeWorkerKey   *usecase.RevokeWorkerKey
+	exchangeWorkerKey *usecase.ExchangeWorkerKey
+	users             usecase.UserRepository
+	log               *slog.Logger
 }
 
 // handleHealth is an unauthenticated liveness probe for the container and load
@@ -113,6 +117,90 @@ func (h *Handlers) handleSetRole(role domain.Role) http.HandlerFunc {
 	}
 }
 
+// handleCreateWorkerKey mints a long-lived worker key for the authenticated
+// caller and returns it once, plaintext included. The user copies it into their
+// worker's SCIMESH_WORKER_KEY; it is never retrievable again.
+func (h *Handlers) handleCreateWorkerKey(w http.ResponseWriter, r *http.Request) {
+	id, ok := userIDFrom(r.Context())
+	if !ok {
+		unauthorized(w, r)
+		return
+	}
+	var req createWorkerKeyRequest
+	if !decodeJSON(w, r, &req) {
+		return
+	}
+	key, raw, err := h.createWorkerKey.Execute(r.Context(), id, req.Name)
+	if err != nil {
+		writeError(w, r, h.log, err)
+		return
+	}
+	writeJSON(w, http.StatusCreated, createdWorkerKeyResponse{
+		workerKeyResponse: toWorkerKeyResponse(key),
+		Key:               raw,
+	})
+}
+
+// handleListWorkerKeys returns the caller's live keys (no secrets) for display
+// and revocation.
+func (h *Handlers) handleListWorkerKeys(w http.ResponseWriter, r *http.Request) {
+	id, ok := userIDFrom(r.Context())
+	if !ok {
+		unauthorized(w, r)
+		return
+	}
+	keys, err := h.listWorkerKeys.Execute(r.Context(), id)
+	if err != nil {
+		writeError(w, r, h.log, err)
+		return
+	}
+	out := make([]workerKeyResponse, 0, len(keys))
+	for _, k := range keys {
+		out = append(out, toWorkerKeyResponse(k))
+	}
+	writeJSON(w, http.StatusOK, workerKeysResponse{WorkerKeys: out})
+}
+
+// handleRevokeWorkerKey retires one of the caller's keys. The repository scopes
+// the delete to the owner, so a mismatched id is a clean 404, not another user's
+// key.
+func (h *Handlers) handleRevokeWorkerKey(w http.ResponseWriter, r *http.Request) {
+	userID, ok := userIDFrom(r.Context())
+	if !ok {
+		unauthorized(w, r)
+		return
+	}
+	keyID, err := uuid.Parse(r.PathValue("id"))
+	if err != nil {
+		writeJSON(w, http.StatusBadRequest, errorResponse{
+			Error:     "invalid worker key id",
+			RequestID: requestIDFrom(r.Context()),
+		})
+		return
+	}
+	if err := h.revokeWorkerKey.Execute(r.Context(), userID, keyID); err != nil {
+		writeError(w, r, h.log, err)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// handleExchangeWorkerKey trades a worker key for a short-lived JWT. It is
+// unauthenticated: the key itself is the credential. A worker calls this on
+// startup and again to refresh before the JWT expires.
+func (h *Handlers) handleExchangeWorkerKey(w http.ResponseWriter, r *http.Request) {
+	var req exchangeWorkerKeyRequest
+	if !decodeJSON(w, r, &req) {
+		return
+	}
+	token, expiresIn, err := h.exchangeWorkerKey.Execute(r.Context(), req.Key)
+	if err != nil {
+		writeError(w, r, h.log, err)
+		return
+	}
+	writeJSON(w, http.StatusOK, exchangeWorkerKeyResponse{Token: token, ExpiresIn: expiresIn})
+}
+
 // decodeJSON reads a size-capped JSON body into dst, rejecting unknown fields.
 // It writes a 400 and returns false on any problem, so callers can `if
 // !decodeJSON(...) { return }`.