diff --git a/sidecar/handlers_ppproxy.go b/sidecar/handlers_ppproxy.go
new file mode 100644
index 0000000..6ef3dfb
--- /dev/null
+++ b/sidecar/handlers_ppproxy.go
@@ -0,0 +1,270 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"log/slog"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"regexp"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+// Scoped PhotoPrism-compatible API proxy.
+//
+// PhotoPrism CE does not enforce auth_users.base_path on API reads — any
+// authenticated user can search the whole library (`q=path:"other/*"`),
+// verified empirically against this deployment. The web client compensates
+// by post-filtering inside /api/sidecar/*, but third-party PhotoPrism apps
+// (Gallery for PhotoPrism, Photo Uploader, …) speak to /api/v1 directly.
+//
+// This proxy is the public face for those apps. It forwards /api/v1/* to
+// PhotoPrism with these rules for sessions that carry a BasePath:
+//
+//   - search endpoints (photos, geo) get their `path` filter rewritten so
+//     results stay inside the caller's BasePath subtree;
+//   - single-photo reads and like/unlike are ownership-checked per UID;
+//   - hash-addressed media (t/, dl/, videos/) and session/config pass
+//     through — media URLs embed per-instance preview/download tokens and
+//     unguessable content hashes, the same protection PhotoPrism's own
+//     share links rely on;
+//   - album/label/subject reads pass through (names are visible across
+//     users; the photos inside stay path-scoped);
+//   - everything else (settings, users, index, import, batch, uploads,
+//     any mutation) answers 403.
+//
+// Sessions with an empty BasePath (unscoped admins) pass through fully.
+
+// ppQPathTerm matches a `path:` filter inside PhotoPrism's q-DSL — either
+// quoted (path:"a b/*") or bare (path:a/*).
+var ppQPathTerm = regexp.MustCompile(`(?i)\bpath:("[^"]*"|\S+)`)
+
+// pathValueAllowed reports whether one path-filter value stays inside base.
+// PhotoPrism ORs `|`-separated alternatives inside a single value, so every
+// alternative must pass. A bare `base*` (no slash) is rejected because the
+// wildcard would also match sibling folders like `base2/…`.
+func pathValueAllowed(val, base string) bool {
+	val = strings.Trim(val, `"`)
+	for _, alt := range strings.Split(val, "|") {
+		v := strings.Trim(strings.TrimSpace(alt), "/")
+		if v == base {
+			continue
+		}
+		if strings.HasPrefix(v, base+"/") {
+			continue
+		}
+		return false
+	}
+	return true
+}
+
+// scopeQ rewrites a q-DSL string so its path filter cannot leave base.
+// User-supplied path terms that already stay inside base are kept (the web
+// client and gallery apps use them for folder drills); any term that
+// escapes — or the absence of one — collapses to `path:"base/*"`.
+func scopeQ(q, base string) string {
+	terms := ppQPathTerm.FindAllStringSubmatch(q, -1)
+	if len(terms) > 0 {
+		ok := true
+		for _, m := range terms {
+			if !pathValueAllowed(m[1], base) {
+				ok = false
+				break
+			}
+		}
+		if ok {
+			return q
+		}
+		q = strings.TrimSpace(ppQPathTerm.ReplaceAllString(q, ""))
+	}
+	scope := ` path:"` + strings.ReplaceAll(base, `"`, "") + `/*"`
+	return strings.TrimSpace(q + scope)
+}
+
+// scopeSearchValues enforces the BasePath on a search request's query
+// string. The q-DSL `path:` term overrides the `path` form parameter in
+// PhotoPrism's parser (verified empirically), so the guarantee lives in q;
+// the standalone param is validated too so it can't disagree.
+func scopeSearchValues(v url.Values, base string) url.Values {
+	v.Set("q", scopeQ(v.Get("q"), base))
+	if p := v.Get("path"); p != "" && !pathValueAllowed(p, base) {
+		v.Del("path")
+	}
+	return v
+}
+
+// ppProxyPhoto is the projection needed for per-UID ownership checks.
+type ppProxyPhoto struct {
+	Path  string   `json:"Path"`
+	Files []ppFile `json:"Files"`
+}
+
+// photoWithinBase fetches one photo with the caller's own token and checks
+// that it lives inside base. Fails closed on any error.
+func photoWithinBase(ctx context.Context, pp *ppClient, token, uid, base string) bool {
+	resp, err := pp.call(ctx, http.MethodGet, "/api/v1/photos/"+url.PathEscape(uid), token, nil)
+	if err != nil || !resp.OK {
+		return false
+	}
+	var p ppProxyPhoto
+	if err := json.Unmarshal(resp.Body, &p); err != nil {
+		return false
+	}
+	if p.Path != "" {
+		return p.Path == base || strings.HasPrefix(p.Path, base+"/")
+	}
+	for _, f := range p.Files {
+		if f.Root == "/" && strings.HasPrefix(f.Name, base+"/") {
+			return true
+		}
+	}
+	return false
+}
+
+// cachedSession is a short-lived token→user cache so a burst of gallery
+// requests doesn't double every call with a /session probe. 60s matches
+// the BasePath reconciler cadence; a revoked token lives at most that long.
+type cachedSession struct {
+	user   *ppSessionUser
+	expiry time.Time
+}
+
+type sessionCache struct {
+	mu sync.Mutex
+	m  map[string]cachedSession
+}
+
+func (sc *sessionCache) resolve(ctx context.Context, pp *ppClient, token string) *ppSessionUser {
+	if token == "" {
+		return nil
+	}
+	now := time.Now()
+	sc.mu.Lock()
+	if e, ok := sc.m[token]; ok && now.Before(e.expiry) {
+		sc.mu.Unlock()
+		return e.user
+	}
+	sc.mu.Unlock()
+	user := pp.resolveSession(ctx, token)
+	if user == nil {
+		return nil
+	}
+	sc.mu.Lock()
+	if len(sc.m) > 1024 { // hard cap; sessions are few, tokens churn rarely
+		sc.m = map[string]cachedSession{}
+	}
+	sc.m[token] = cachedSession{user: user, expiry: now.Add(60 * time.Second)}
+	sc.mu.Unlock()
+	return user
+}
+
+// proxyToken pulls the session token from any header form PhotoPrism
+// clients use: X-Auth-Token (canonical), Authorization: Bearer, or the
+// legacy X-Session-ID.
+func proxyToken(r *http.Request) string {
+	if t := r.Header.Get("X-Auth-Token"); t != "" {
+		return t
+	}
+	if a := r.Header.Get("Authorization"); strings.HasPrefix(a, "Bearer ") {
+		return strings.TrimPrefix(a, "Bearer ")
+	}
+	return r.Header.Get("X-Session-ID")
+}
+
+// handlePPProxy returns the gin handler mounted at /api/v1/*rest.
+func handlePPProxy(cfg *Config) gin.HandlerFunc {
+	target, err := url.Parse(cfg.PhotoprismBaseURL)
+	if err != nil {
+		slog.Error("pp-proxy: bad PHOTOPRISM_BASE_URL", "err", err)
+		return func(c *gin.Context) { c.AbortWithStatus(http.StatusBadGateway) }
+	}
+	proxy := httputil.NewSingleHostReverseProxy(target)
+	proxy.ErrorHandler = func(w http.ResponseWriter, r *http.Request, err error) {
+		slog.Warn("pp-proxy: upstream error", "path", r.URL.Path, "err", err)
+		w.WriteHeader(http.StatusBadGateway)
+	}
+	// Ownership checks reuse the normal client; a dedicated instance would
+	// gain nothing.
+	pp := newPPClient(cfg.PhotoprismBaseURL)
+	cache := &sessionCache{m: map[string]cachedSession{}}
+
+	forbid := func(c *gin.Context) {
+		c.AbortWithStatusJSON(http.StatusForbidden,
+			gin.H{"error": "not available through this proxy"})
+	}
+
+	return func(c *gin.Context) {
+		rest := strings.TrimPrefix(strings.TrimPrefix(c.Param("rest"), "/"), "")
+		method := c.Request.Method
+
+		// Unauthenticated / token-in-URL surface: login+logout, client
+		// config, hash-addressed media, websocket.
+		passUnscoped := rest == "session" || strings.HasPrefix(rest, "session/") ||
+			strings.HasPrefix(rest, "oauth/") ||
+			rest == "config" || rest == "ws" ||
+			strings.HasPrefix(rest, "t/") ||
+			strings.HasPrefix(rest, "dl/") ||
+			strings.HasPrefix(rest, "videos/") ||
+			strings.HasPrefix(rest, "svg/")
+		if passUnscoped {
+			proxy.ServeHTTP(c.Writer, c.Request)
+			return
+		}
+
+		user := cache.resolve(c.Request.Context(), pp, proxyToken(c.Request))
+		if user == nil {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "invalid session"})
+			return
+		}
+		base := strings.Trim(user.BasePath, "/")
+		if base == "" {
+			// Unscoped admin — full pass-through.
+			proxy.ServeHTTP(c.Writer, c.Request)
+			return
+		}
+
+		isGet := method == http.MethodGet || method == http.MethodHead
+		switch {
+		// Search endpoints: enforce the path scope inside the query.
+		case isGet && (rest == "photos" || rest == "photos/view" || rest == "geo"):
+			q := c.Request.URL.Query()
+			c.Request.URL.RawQuery = scopeSearchValues(q, base).Encode()
+			proxy.ServeHTTP(c.Writer, c.Request)
+
+		// Single-photo reads + like/unlike: ownership-checked per UID.
+		case strings.HasPrefix(rest, "photos/"):
+			parts := strings.Split(rest, "/")
+			uid := parts[1]
+			allowed := (isGet && len(parts) == 2) || // GET photos/:uid
+				(isGet && len(parts) == 3 && parts[2] == "dl") ||
+				(len(parts) == 3 && parts[2] == "like" &&
+					(method == http.MethodPost || method == http.MethodDelete))
+			if !allowed {
+				forbid(c)
+				return
+			}
+			if !photoWithinBase(c.Request.Context(), pp, proxyToken(c.Request), uid, base) {
+				c.AbortWithStatusJSON(http.StatusNotFound, gin.H{"error": "photo not found"})
+				return
+			}
+			proxy.ServeHTTP(c.Writer, c.Request)
+
+		// Collection reads: names are shared across users by design (CE has
+		// no per-user albums); their photo contents stay path-scoped above.
+		case isGet && (rest == "albums" || strings.HasPrefix(rest, "albums/") ||
+			rest == "labels" || strings.HasPrefix(rest, "labels/") ||
+			rest == "subjects" || strings.HasPrefix(rest, "subjects/") ||
+			rest == "faces" || strings.HasPrefix(rest, "faces/")):
+			proxy.ServeHTTP(c.Writer, c.Request)
+
+		default:
+			slog.Info("pp-proxy: blocked", "user", user.UserName, "method", method, "path", rest)
+			forbid(c)
+		}
+	}
+}
diff --git a/sidecar/handlers_ppproxy_test.go b/sidecar/handlers_ppproxy_test.go
new file mode 100644
index 0000000..c60b077
--- /dev/null
+++ b/sidecar/handlers_ppproxy_test.go
@@ -0,0 +1,72 @@
+package main
+
+import (
+	"net/url"
+	"testing"
+)
+
+func TestScopeQ(t *testing.T) {
+	cases := []struct {
+		name string
+		q    string
+		base string
+		want string
+	}{
+		{"empty q gains scope", "", "dtoro", `path:"dtoro/*"`},
+		{"plain search gains scope", "label:dog", "dtoro", `label:dog path:"dtoro/*"`},
+		{"inside path kept", `path:"dtoro/2024/*" label:dog`, "dtoro", `path:"dtoro/2024/*" label:dog`},
+		{"exact base kept", `path:"dtoro"`, "dtoro", `path:"dtoro"`},
+		{"outside path replaced", `path:"muli/*"`, "dtoro", `path:"dtoro/*"`},
+		{"bare term outside replaced", `path:muli/x label:dog`, "dtoro", `label:dog path:"dtoro/*"`},
+		{"pipe alternative escaping", `path:"dtoro/*|muli/*"`, "dtoro", `path:"dtoro/*"`},
+		{"pipe all inside kept", `path:"dtoro/a|dtoro/b/*"`, "dtoro", `path:"dtoro/a|dtoro/b/*"`},
+		{"sibling prefix rejected", `path:"dtoro2/*"`, "dtoro", `path:"dtoro/*"`},
+		{"bare wildcard on base rejected", `path:dtoro*`, "dtoro", `path:"dtoro/*"`},
+		{"mixed valid+invalid terms collapse", `path:"dtoro/a" path:"muli/b"`, "dtoro", `path:"dtoro/*"`},
+		{"case-insensitive filter name", `PATH:"muli/*"`, "dtoro", `path:"dtoro/*"`},
+		{"nested base", `path:"family/alice/x"`, "family/alice", `path:"family/alice/x"`},
+		{"nested base parent escape", `path:"family/*"`, "family/alice", `path:"family/alice/*"`},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := scopeQ(tc.q, tc.base); got != tc.want {
+				t.Errorf("scopeQ(%q, %q) = %q, want %q", tc.q, tc.base, got, tc.want)
+			}
+		})
+	}
+}
+
+func TestScopeSearchValues(t *testing.T) {
+	v := url.Values{}
+	v.Set("count", "60")
+	v.Set("path", "muli/*")
+	got := scopeSearchValues(v, "dtoro")
+	if got.Get("path") != "" {
+		t.Errorf("outside path param should be dropped, got %q", got.Get("path"))
+	}
+	if got.Get("q") != `path:"dtoro/*"` {
+		t.Errorf("q should carry the scope, got %q", got.Get("q"))
+	}
+	if got.Get("count") != "60" {
+		t.Errorf("unrelated params must survive, got count=%q", got.Get("count"))
+	}
+
+	v2 := url.Values{}
+	v2.Set("path", "dtoro/2024")
+	got2 := scopeSearchValues(v2, "dtoro")
+	if got2.Get("path") != "dtoro/2024" {
+		t.Errorf("inside path param should be kept, got %q", got2.Get("path"))
+	}
+}
+
+func TestPathValueAllowed(t *testing.T) {
+	if pathValueAllowed(`"muli/*"`, "dtoro") {
+		t.Error("outside value must be rejected")
+	}
+	if !pathValueAllowed(`"dtoro/Photos/2024"`, "dtoro") {
+		t.Error("inside value must be allowed")
+	}
+	if pathValueAllowed("dtoro/a|muli/b", "dtoro") {
+		t.Error("any escaping pipe alternative must reject the whole value")
+	}
+}
diff --git a/sidecar/main.go b/sidecar/main.go
index 4c3a0b3..7bc50f2 100644
--- a/sidecar/main.go
+++ b/sidecar/main.go
@@ -123,6 +123,11 @@ func main() {
 									auth.GET("/folders", handleFoldersProxy(pp))
 					}
 
+	// PhotoPrism-compatible scoped proxy — the public surface for third-
+	// party PhotoPrism apps (prism.hubris.network routes here instead of
+	// straight to PhotoPrism). See handlers_ppproxy.go for the rules.
+	r.Any("/api/v1/*rest", handlePPProxy(cfg))
+
 	addr := cfg.ListenAddr + ":" + itoa(cfg.Port)
 	srv := &http.Server{
 		Addr:              addr,