improve identity handling

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) {
-		writeErrorSlug(w, http.StatusConflict, "identity_exists",
-			"an account with this key already exists", false)
+	// Idempotent: importing a key that is already in the keystore is how a
+	// second device signs in to an existing account. Answer 200 with the
+	// 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/cid/cid-rank-vectors.json

@@ -22,7 +22,7 @@
     "25": "nzb-posting - content-derived (Message-ID set digest), but not itself fetchable",
     "20": "BitTorrent infohashes - swarm interop",
     "10": "midhash256 - the record address",
-    "5": "opaque locators (nzb-release, url) - never outrank a real digest",
+    "5": "opaque locators (nzb-release, url, card) - never outrank a real digest",
     "0": "weak/unknown digests, unparseable input"
   },
   "tieBreak": "lexicographically smaller cid wins",
@@ -110,6 +110,12 @@
       "rank": 5,
       "note": "codec 0x1006 + IDENTITY multihash 0x00. Same tier/reasoning as nzb-release."
     },
+    {
+      "name": "card-locator",
+      "cid": "bagdsaaanar2g2zdcor3duojvgq3ts",
+      "rank": 5,
+      "note": "codec 0x1007 + IDENTITY multihash 0x00, digest = varint(len(source)) || source || id — here (\"tmdb\",\"tv:95479\"). Same codec-slot rule as nzb-release/url: match on the CODEC, never the mh. The limit case of the family — the only CID in MetaMesh with NO bytes behind it anywhere, ever: it addresses a *work* (a series, a film), not a file, so the byte path 404s by design and bitswap never offers it (seeding is gated on sha2-256). Tier 5 is load-bearing for the planned cross-source merge: one card record may carry BOTH a TMDB and a MyAnimeList locator, and if a real card body is ever added (see card-tier-search.md §4.3) its sha2-256 must win the canonical election over both locators without any addressing change. Ranking it 0 instead would still lose to a digest, but would put the implementations back out of agreement — which is the exact failure this fixture exists to prevent."
+    },
     {
       "name": "sha1",
       "cid": "baeircff3eqvxxaqqot2lt242stkdtk3gq4c2vra",

internal/cid/rank.go

@@ -49,6 +49,14 @@ const (
 	// these — matching on mh would see 0x00 and rank them 0.
 	CodeNzbRelease = 0x1005 // custom — self-describing Newznab release locator
 	CodeURL        = 0x1006 // custom — identity-multihash CID wrapping an http(s) URL
+	// CodeCard is the limit case of the family: the only CID with NO bytes
+	// behind it anywhere, ever. It addresses a *work* (a series, a film) via
+	// varint(len(source))‖source‖id — ("tmdb","tv:95479") — so `/api/file/{cid}`
+	// correctly 404s and bitswap never offers it. Ranking it here (rather than
+	// letting it fall to RankUnknown) is what makes the planned "one card, two
+	// CIDs" cross-source merge safe: a TMDB and a MyAnimeList locator can sit on
+	// one record, and a real digest added later still wins the election.
+	CodeCard = 0x1007 // custom — identity-multihash CID wrapping a card (work) id
 
 	// CodeNzbPosting is the INVERSE trap of the two above: its multihash is a
 	// REAL sha2-256 digest (over the normalised, sorted article Message-ID
@@ -134,7 +142,7 @@ func Decode(cidStr string) (codec uint64, mhCode uint64, err error) {
 //     swarm interop, not strength.
 //   - midhash256 is the floor among real *digests*: internally meaningful,
 //     externally invisible.
-//   - opaque locators (nzb-release, url) sit BELOW midhash. They are not
+//   - opaque locators (nzb-release, url, card) sit BELOW midhash. They are not
 //     content-derived — two URLs to the same bytes yield two different locator
 //     CIDs — so a locator must never displace a real digest as the identity a
 //     record is advertised under. Tier 5 means a locator wins the election only
@@ -157,7 +165,7 @@ func Rank(cidStr string) int {
 	}
 	// Opaque locators. Codec-only: their multihash is identity (0x00), so
 	// there is nothing to match on the mh side.
-	if codec == CodeNzbRelease || codec == CodeURL {
+	if codec == CodeNzbRelease || codec == CodeURL || codec == CodeCard {
 		return RankLocator
 	}
 	// nzb-posting: codec-only, checked BEFORE the mh switch below — its