improvement on user management

internal/api/handlers_identity.go

@@ -50,6 +50,26 @@ type identityImportResponse struct {
 	UID       string `json:"uid"`
 	Curve     string `json:"curve"`
 	CreatedAt int64  `json:"createdAt"`
+	// Created distinguishes "this key was new here" (201) from "this key was
+	// already in the keystore" (200). Import is the sign-in primitive for
+	// clients: presenting the secret key is the proof of ownership, so a
+	// re-import must succeed rather than conflict. Clients use the flag only
+	// to word the confirmation ("new profile" vs "welcome back").
+	Created bool `json:"created"`
+}
+
+// identityRevealRequest asks for an existing account's private key back. The
+// key was shown once at generate; without a way to see it again, a client with
+// a real sign-out has no recovery path for a user who never saved it.
+type identityRevealRequest struct {
+	Confirm bool   `json:"confirm"`
+	UID     string `json:"uid"`
+}
+
+type identityRevealResponse struct {
+	UID           string `json:"uid"`
+	Curve         string `json:"curve"`
+	PrivateKeyHex string `json:"privateKeyHex"`
 }
 
 type identityDeleteRequest struct {
@@ -172,9 +192,17 @@ func (s *Server) handleIdentityImport(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	dir := s.config.IdentityAccountsDir()
-	if identity.ExistsByUID(dir, id.UID) {
+	// Idempotent: importing a key that is already in the keystore is how a
-		writeErrorSlug(w, http.StatusConflict, "identity_exists",
+	// second device signs in to an existing account. Answer 200 with the
-			"an account with this key already exists", false)
+	// stored account (preserving its original createdAt) instead of 409 —
+	// the caller proved ownership by presenting the key.
+	if existing, err := identity.LoadByUID(dir, id.UID); err == nil && existing != nil {
+		writeJSON(w, http.StatusOK, identityImportResponse{
+			UID:       existing.UID,
+			Curve:     existing.Curve,
+			CreatedAt: existing.CreatedAt,
+			Created:   false,
+		})
 		return
 	}
 	if err := identity.SaveAccount(dir, id); err != nil {
@@ -185,6 +213,35 @@ func (s *Server) handleIdentityImport(w http.ResponseWriter, r *http.Request) {
 		UID:       id.UID,
 		Curve:     id.Curve,
 		CreatedAt: id.CreatedAt,
+		Created:   true,
+	})
+}
+
+// handleIdentityReveal returns an existing account's private key. Deliberately
+// POST + explicit confirm (never a bare GET) so it cannot be triggered by a
+// link or an image tag, and so it reads as the deliberate act it is. The
+// endpoint is auth-gated at the perimeter like the rest of /api/identity/*.
+func (s *Server) handleIdentityReveal(w http.ResponseWriter, r *http.Request) {
+	var body identityRevealRequest
+	_ = json.NewDecoder(r.Body).Decode(&body)
+	if !body.Confirm && r.URL.Query().Get("confirm") != "true" {
+		writeErrorSlug(w, http.StatusBadRequest, "confirm_required",
+			"revealing a private key requires {\"confirm\": true} or ?confirm=true", false)
+		return
+	}
+	uid := strings.TrimSpace(body.UID)
+	if uid == "" {
+		uid = strings.TrimSpace(r.URL.Query().Get("uid"))
+	}
+	id, status, slug, msg := s.resolveAccount(uid)
+	if status != 0 {
+		writeErrorSlug(w, status, slug, msg, false)
+		return
+	}
+	writeJSON(w, http.StatusOK, identityRevealResponse{
+		UID:           id.UID,
+		Curve:         id.Curve,
+		PrivateKeyHex: id.PrivateKeyHex,
 	})
 }
 

internal/api/server.go

@@ -172,6 +172,7 @@ func (s *Server) setupRoutes() {
 	s.router.HandleFunc("/api/identity/accounts", s.handleIdentityAccounts).Methods("GET")
 	s.router.HandleFunc("/api/identity/generate", s.handleIdentityGenerate).Methods("POST")
 	s.router.HandleFunc("/api/identity/import", s.handleIdentityImport).Methods("POST")
+	s.router.HandleFunc("/api/identity/reveal", s.handleIdentityReveal).Methods("POST")
 	s.router.HandleFunc("/api/identity", s.handleIdentityDelete).Methods("DELETE")
 	s.router.HandleFunc("/api/identity/sign", s.handleIdentitySign).Methods("POST")
 	s.router.HandleFunc("/api/identity/aead-key", s.handleIdentityAEADKey).Methods("GET")

internal/api/udl.go

@@ -27,6 +27,14 @@ type UDLPutRequest struct {
 	Ts      int64            `json:"ts"`
 	Record  string           `json:"record"` // base64 CBOR, opaque + signed
 	Value   *json.RawMessage `json:"value,omitempty"`
+	// Tombstone marks this write as a deletion of (uid, cid, key). The record
+	// itself is opaque here — meta-core never decodes the CBOR, and a private-
+	// tier value and a tombstone are equally "no plaintext value" — so the
+	// writer has to say. Without it the cid is never removed from
+	// udl:idx:user:<uid>:key:<key>, which then grows for the life of the
+	// account and is returned in full on every My List / Continue Watching
+	// read. Omitted by older writers, which keeps the previous behaviour.
+	Tombstone bool `json:"tombstone,omitempty"`
 }
 
 // UDLPutResponse is the response of PUT /api/udl/record.
@@ -104,7 +112,7 @@ func (s *Server) handleUDLRecordPut(w http.ResponseWriter, r *http.Request) {
 		hasValue = true
 	}
 
-	accepted, err := s.storage.UDLUpsertIfNewer(req.Uid, req.Cid, req.Key, req.Version, req.Ts, req.Record, publicValue, hasValue)
+	accepted, err := s.storage.UDLUpsertIfNewer(req.Uid, req.Cid, req.Key, req.Version, req.Ts, req.Record, publicValue, hasValue, req.Tombstone)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, err.Error())
 		return

internal/storage/udl.go

@@ -72,7 +72,15 @@ func udlIdxCidUsers(cid string) string      { return fmt.Sprintf("udl:idx:cid:%s
 //
 //	KEYS: 1=cell 2=idx:user:key 3=idx:user:cid 4=idx:cid:key 5=idx:cid:users
 //	ARGV: 1=version 2=ts 3=record 4=value 5=hasValue("1"/"0")
-//	      6=cid 7=key 8=uid
+//	      6=cid 7=key 8=uid 9=tombstone("1"/"0")
+//
+// A tombstone still writes the cell — that is the CRDT state, and dropping it
+// would let an older write resurrect the value — but it SREMs the cid from the
+// user+key index. That index is what `active_for_user_key` returns, so leaving
+// deleted cids in it means every My List / Continue Watching read carries every
+// title ever un-liked or finished, forever. The other three indexes are left
+// alone: they answer "who has an opinion about this cid", where a tombstone is
+// still an answer.
 var udlUpsertScript = redis.NewScript(`
 local stored = redis.call('HGET', KEYS[1], 'version')
 if stored and tonumber(stored) >= tonumber(ARGV[1]) then
@@ -84,7 +92,11 @@ if ARGV[5] == '1' then
 else
   redis.call('HDEL', KEYS[1], 'value')
 end
+if ARGV[9] == '1' then
+  redis.call('SREM', KEYS[2], ARGV[6])
+else
   redis.call('SADD', KEYS[2], ARGV[6])
+end
 redis.call('SADD', KEYS[3], ARGV[7])
 redis.call('SADD', KEYS[4], ARGV[8])
 redis.call('SADD', KEYS[5], ARGV[8])
@@ -94,8 +106,10 @@ return 1
 // UDLUpsertIfNewer stores a record cell iff version strictly exceeds the stored
 // one. publicValue/hasValue carry the plaintext JSON scalar for public keys
 // (used by aggregation); pass hasValue=false for private-tier keys and
-// tombstones. Returns accepted=false when the write is stale.
+// tombstones. Set tombstone=true when the record deletes the cell, which also
-func (c *Client) UDLUpsertIfNewer(uid, cid, key string, version, ts int64, record, publicValue string, hasValue bool) (bool, error) {
+// prunes the cid from the user+key index. Returns accepted=false when the write
+// is stale.
+func (c *Client) UDLUpsertIfNewer(uid, cid, key string, version, ts int64, record, publicValue string, hasValue, tombstone bool) (bool, error) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
@@ -117,7 +131,11 @@ func (c *Client) UDLUpsertIfNewer(uid, cid, key string, version, ts int64, recor
 	if hasValue {
 		hv = "1"
 	}
-	res, err := udlUpsertScript.Run(ctx, c.client, keys, version, ts, record, publicValue, hv, cid, key, uid).Result()
+	tomb := "0"
+	if tombstone {
+		tomb = "1"
+	}
+	res, err := udlUpsertScript.Run(ctx, c.client, keys, version, ts, record, publicValue, hv, cid, key, uid, tomb).Result()
 	if err != nil {
 		return false, fmt.Errorf("udl upsert failed: %w", err)
 	}

internal/storage/udl_test.go

@@ -0,0 +1,79 @@
+package storage
+
+import (
+	"testing"
+)
+
+// A tombstone must leave the cell in place but drop the cid from the user+key
+// index.
+//
+// The cell has to stay: it *is* the CRDT state, and deleting it would let an
+// older write resurrect the value the tombstone retracted. The index entry has
+// to go: `active_for_user_key` returns every member of that set, so a set that
+// only ever grows means each My List / Continue Watching read carries every
+// title the user has ever un-liked or finished — with its full record blob —
+// forever. The reader filters them out again, so the cost is invisible until
+// the account is old.
+func TestUDLUpsert_TombstonePrunesUserKeyIndexButKeepsCell(t *testing.T) {
+	c, _ := newTestClient(t, "")
+
+	const (
+		uid = "zAlice"
+		cid = "bagcsaaalocator"
+		key = "seek"
+	)
+
+	// A live position: indexed, readable.
+	if ok, err := c.UDLUpsertIfNewer(uid, cid, key, 1, 100, "rec-v1", "", false, false); err != nil || !ok {
+		t.Fatalf("live upsert: ok=%v err=%v", ok, err)
+	}
+	entries, err := c.UDLListUserKey(uid, key)
+	if err != nil {
+		t.Fatalf("active_for_user_key: %v", err)
+	}
+	if len(entries) != 1 || entries[0].Cid != cid {
+		t.Fatalf("live position should be indexed, got %+v", entries)
+	}
+
+	// Finishing it tombstones the seek.
+	if ok, err := c.UDLUpsertIfNewer(uid, cid, key, 2, 200, "rec-v2-tombstone", "", false, true); err != nil || !ok {
+		t.Fatalf("tombstone upsert: ok=%v err=%v", ok, err)
+	}
+
+	entries, err = c.UDLListUserKey(uid, key)
+	if err != nil {
+		t.Fatalf("active_for_user_key after tombstone: %v", err)
+	}
+	if len(entries) != 0 {
+		t.Fatalf("tombstoned cid must leave the user+key index, got %+v", entries)
+	}
+
+	// ...but the cell itself survives, at the tombstone's version.
+	cell, exists, err := c.UDLGetCell(uid, cid, key)
+	if err != nil {
+		t.Fatalf("get cell: %v", err)
+	}
+	if !exists {
+		t.Fatal("tombstone must not delete the cell — an older write could then resurrect the value")
+	}
+	if cell.Version != 2 || cell.Record != "rec-v2-tombstone" {
+		t.Fatalf("cell should hold the tombstone record at v2, got %+v", cell)
+	}
+
+	// And the high-water mark still rejects the superseded write.
+	if ok, err := c.UDLUpsertIfNewer(uid, cid, key, 1, 300, "rec-v1-replay", "", false, false); err != nil || ok {
+		t.Fatalf("stale replay must be rejected: ok=%v err=%v", ok, err)
+	}
+
+	// Re-watching re-establishes the cell and puts it back in the index.
+	if ok, err := c.UDLUpsertIfNewer(uid, cid, key, 3, 400, "rec-v3", "", false, false); err != nil || !ok {
+		t.Fatalf("re-establish upsert: ok=%v err=%v", ok, err)
+	}
+	entries, err = c.UDLListUserKey(uid, key)
+	if err != nil {
+		t.Fatalf("active_for_user_key after re-establish: %v", err)
+	}
+	if len(entries) != 1 || entries[0].Cid != cid {
+		t.Fatalf("re-established cid must return to the index, got %+v", entries)
+	}
+}