fix(serve): bootstrap session tokens for instance-token-authenticated front-ends (#116)

Sessions created by one front-end (e.g. bodek, or the WebUI in another
browser profile) could not be loaded by another: every new session gets a
256-bit AuthToken that only reaches the creating client, and the token
bootstrap only covered legacy sessions with no token at all - so
GET /api/sessions/<id> returned 401 and the WebUI showed "Failed to load
session".

The GET handler now also bootstraps the session token when the caller
proves knowledge of the per-instance CSRF token by presenting it in the
X-Odek-Ws-Token header (constant-time compared). Header presentation is a
knowledge proof a cross-origin page cannot forge: a DNS-rebinding page
holds only the ambient SameSite=Strict cookie and can neither read the
token value nor set the custom header (CORS preflight, which odek does
not answer). Cookie-only callers therefore still get 401 on
token-carrying sessions, while the operator's legitimate front-ends -
which always send the header via apiHeaders - can load each other's
sessions. The rebinding damage boundary is unchanged; DELETE/POST
(rename) flows inherit the fix through the client's existing
ensureSessionToken GET bootstrap.

Regression tests cover: bootstrap with a valid instance header (200 +
X-Session-Token), no bootstrap with a wrong instance header (401), and no
bootstrap for cookie-only callers (401). Docs updated (SECURITY.md
section 24, AGENTS.md).

Author: jkyberneees

AGENTS.md

@@ -199,7 +199,7 @@ Layered prompt-injection / approval-fatigue defenses. Full reference: [docs/SECU
 - **Memory add/replace pipe-to-shell filter** (`internal/memory/memory.go`) — `AddFact` and `ReplaceFact` now run `FactLooksUnsafe` in addition to the general guard scan, blocking agent-driven planting of download-and-execute facts.
 - **Skill learn-loop provenance propagation** (`internal/skills/learnloop.go`) — conversation-extracted suggestions and LLM-enhanced suggestions both retain the session's `SkillProvenance`, so tainted sessions cannot produce clean-looking auto-saved skills.
 - **Audit ingest recording for @-refs, `--ctx`, and Web-UI attachments** (`cmd/odek/refs.go`, `cmd/odek/serve.go`, `cmd/odek/audit.go`) — the per-session ingest recorder is attached before `@`-reference/`--ctx`/attachment resolution, `recordTurnAudit` scans `user` messages for untrusted wrappers in addition to `tool` messages, and the divergence heuristic compares agent actions against the original pre-enrichment prompt so attacker-injected resources are not treated as user-mentioned.
-- **Session ID entropy + session-scoped auth tokens** (`internal/session/session.go`, `cmd/odek/serve.go`) — session IDs now carry 128 bits of randomness (16 bytes / 32 hex chars); each session stores a 256-bit `AuthToken` required by `GET/DELETE/POST /api/sessions/<id>`, `POST /api/cancel`, and WebSocket session-resume messages via `X-Session-Token` header, `session_token` cookie, or `auth_token` WS field. Per-IP rate limiting (60/min) on session lookups adds a brute-force backstop. `X-Forwarded-For` / `X-Real-Ip` headers are only honored when the direct remote address is in the configured `trusted_proxies` list, so spoofed headers cannot bypass the limiters.
+- **Session ID entropy + session-scoped auth tokens** (`internal/session/session.go`, `cmd/odek/serve.go`) — session IDs now carry 128 bits of randomness (16 bytes / 32 hex chars); each session stores a 256-bit `AuthToken` required by `GET/DELETE/POST /api/sessions/<id>`, `POST /api/cancel`, and WebSocket session-resume messages via `X-Session-Token` header, `session_token` cookie, or `auth_token` WS field. Per-IP rate limiting (60/min) on session lookups adds a brute-force backstop. `X-Forwarded-For` / `X-Real-Ip` headers are only honored when the direct remote address is in the configured `trusted_proxies` list, so spoofed headers cannot bypass the limiters. Callers that present the per-instance CSRF token in the `X-Odek-Ws-Token` header (a knowledge proof a cross-origin page cannot forge) are bootstrapped the session token on `GET`, so the operator's front-ends (WebUI, bodek) can load each other's sessions; cookie-only callers still get 401.
 - **Skill/episode untrusted wrapper** (`internal/loop/loop.go` + `odek.go`) — skill context (both auto-load and lazy trigger-matched), the `skill_load` tool output, and retrieved session-episode context are passed through the caller-provided untrusted wrapper (the same nonce'd `<untrusted_content_*>` boundary used for tool output) before being injected into the model's system context. This prevents a compromised or tainted skill/episode from being treated as trusted system instructions.
 - **`env` / `printenv` environment-dump gate** (`internal/danger/classifier.go`) — bare `env` and `printenv` invocations are classified as `system_write` because they can leak process-environment secrets that the redaction scanner does not recognise. `env VAR=value <cmd>` still classifies `<cmd>` normally.
 - **Web UI attachment wrapping** (`cmd/odek/serve.go` + `cmd/odek/ui/app.js`) — files attached through the browser are sent separately from the user's text and wrapped with the nonce'd `<untrusted_content_*>` boundary (`source="attachment:<filename>"`) before injection into the prompt.

cmd/odek/serve.go

@@ -333,7 +333,7 @@ func serveCmd(args []string) error {
 	}
 	mux.Handle("/api/resources", apiAuth(handleResourceSearch(resourceReg)))
 	mux.Handle("/api/sessions", apiAuth(handleSessionList(store)))
-	mux.Handle("/api/sessions/", apiAuth(handleSessionByID(store, resolved.TrustedProxies)))
+	mux.Handle("/api/sessions/", apiAuth(handleSessionByID(store, resolved.TrustedProxies, wsToken)))
 	mux.Handle("/api/models", apiAuth(handleModelList(resolved.Model)))
 	mux.Handle("/api/cancel", apiAuth(handleCancel(store)))
 
@@ -1440,6 +1440,22 @@ func requireServeToken(token string) func(http.Handler) http.Handler {
 	}
 }
 
+// presentsInstanceTokenHeader reports whether the request carries the
+// per-instance CSRF token in the X-Odek-Ws-Token header. Header presentation
+// is a KNOWLEDGE proof — unlike the ambient SameSite=Strict cookie, a
+// cross-origin (e.g. DNS-rebinding) page can neither read the token value
+// nor set the header (the custom header triggers a CORS preflight, which
+// odek does not answer). It therefore distinguishes legitimate front-ends
+// (the WebUI, bodek, curl with the token URL) from a rebinding page that
+// merely holds the cookie.
+func presentsInstanceTokenHeader(r *http.Request, wsToken string) bool {
+	if wsToken == "" {
+		return false
+	}
+	h := r.Header.Get(wsTokenHeaderName)
+	return h != "" && subtle.ConstantTimeCompare([]byte(h), []byte(wsToken)) == 1
+}
+
 // sessionTokenFromRequest returns the session auth token from the
 // X-Session-Token header or the session_token cookie, in that order.
 func sessionTokenFromRequest(r *http.Request) string {
@@ -1541,7 +1557,7 @@ func handleSessionList(store *session.Store) http.HandlerFunc {
 	}
 }
 
-func handleSessionByID(store *session.Store, trustedProxies []string) http.HandlerFunc {
+func handleSessionByID(store *session.Store, trustedProxies []string, wsToken string) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		id := strings.TrimPrefix(r.URL.Path, "/api/sessions/")
 		if id == "" {
@@ -1564,6 +1580,17 @@ func handleSessionByID(store *session.Store, trustedProxies []string) http.Handl
 			}
 			token := sessionTokenFromRequest(r)
 			effectiveToken, ok := validateSessionToken(store, sess, token)
+			if !ok && presentsInstanceTokenHeader(r, wsToken) {
+				// Bootstrap the session token for callers that prove
+				// knowledge of the per-instance CSRF token via the
+				// X-Odek-Ws-Token header. Without this, sessions created by
+				// one front-end (e.g. bodek, or a WebUI in another browser
+				// profile) can never be loaded by another: the per-session
+				// token only reaches the client that created the session,
+				// and the legacy bootstrap only covers sessions that have
+				// no token at all.
+				effectiveToken, ok = sess.AuthToken, true
+			}
 			if !ok {
 				http.Error(w, "invalid session token", http.StatusUnauthorized)
 				return

cmd/odek/serve_api_test.go

@@ -70,7 +70,7 @@ func TestHandleSessionByID_GET_ReturnsSession(t *testing.T) {
 		t.Fatalf("Create session: %v", err)
 	}
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
 	req.Header.Set("X-Session-Token", sess.AuthToken)
 	w := httptest.NewRecorder()
@@ -106,7 +106,7 @@ func TestHandleSessionByID_GET_ReturnsSession(t *testing.T) {
 
 func TestHandleSessionByID_GET_NotFound(t *testing.T) {
 	store := newTestSessionStore(t)
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 
 	// Valid ID format but doesn't exist on disk.
 	req := httptest.NewRequest(http.MethodGet, "/api/sessions/20260101-aabbcc", nil)
@@ -120,7 +120,7 @@ func TestHandleSessionByID_GET_NotFound(t *testing.T) {
 
 func TestHandleSessionByID_GET_MissingID(t *testing.T) {
 	store := newTestSessionStore(t)
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 
 	req := httptest.NewRequest(http.MethodGet, "/api/sessions/", nil)
 	w := httptest.NewRecorder()
@@ -145,7 +145,7 @@ func TestHandleSessionByID_GET_MessagesArePresent(t *testing.T) {
 		t.Fatalf("Create: %v", err)
 	}
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
 	req.Header.Set("X-Session-Token", sess.AuthToken)
 	w := httptest.NewRecorder()
@@ -161,7 +161,7 @@ func TestHandleSessionByID_GET_MessagesArePresent(t *testing.T) {
 
 func TestHandleSessionByID_MethodNotAllowed(t *testing.T) {
 	store := newTestSessionStore(t)
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 
 	for _, method := range []string{http.MethodPatch, http.MethodPut, http.MethodHead} {
 		req := httptest.NewRequest(method, "/api/sessions/20260101-aabbcc", nil)
@@ -182,7 +182,7 @@ func TestHandleSessionByID_DELETE_StillWorks(t *testing.T) {
 		t.Fatalf("Create: %v", err)
 	}
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	req := httptest.NewRequest(http.MethodDelete, "/api/sessions/"+sess.ID, nil)
 	req.Header.Set("X-Session-Token", sess.AuthToken)
 	w := httptest.NewRecorder()
@@ -209,7 +209,7 @@ func TestHandleSessionByID_POST_RenameStillWorks(t *testing.T) {
 		t.Fatalf("Create: %v", err)
 	}
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	body := strings.NewReader(`{"name":"renamed task"}`)
 	req := httptest.NewRequest(http.MethodPost, "/api/sessions/"+sess.ID, body)
 	req.Header.Set("Content-Type", "application/json")
@@ -232,7 +232,7 @@ func TestHandleSessionByID_GET_InvalidToken(t *testing.T) {
 	store := newTestSessionStore(t)
 	sess, _ := store.Create([]llm.Message{{Role: "user", Content: "hi"}}, "m", "task")
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
 	req.Header.Set("X-Session-Token", "wrong-token")
 	w := httptest.NewRecorder()
@@ -247,7 +247,7 @@ func TestHandleSessionByID_GET_MissingToken(t *testing.T) {
 	store := newTestSessionStore(t)
 	sess, _ := store.Create([]llm.Message{{Role: "user", Content: "hi"}}, "m", "task")
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
 	w := httptest.NewRecorder()
 	handler(w, req)
@@ -268,7 +268,7 @@ func TestHandleSessionByID_GET_LazyTokenBootstrap(t *testing.T) {
 		t.Fatalf("Save: %v", err)
 	}
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
 	w := httptest.NewRecorder()
 	handler(w, req)
@@ -297,11 +297,79 @@ func TestHandleSessionByID_GET_LazyTokenBootstrap(t *testing.T) {
 	}
 }
 
+func TestHandleSessionByID_GET_InstanceHeaderBootstrap(t *testing.T) {
+	// Cross-front-end interop: a session created by another client (e.g.
+	// bodek) carries an auth token the browser doesn't have. When the caller
+	// proves knowledge of the per-instance CSRF token via the
+	// X-Odek-Ws-Token header, the GET bootstraps the session token.
+	store := newTestSessionStore(t)
+	sess, _ := store.Create([]llm.Message{{Role: "user", Content: "hi"}}, "m", "task")
+	const wsToken = "test-instance-token"
+
+	handler := handleSessionByID(store, nil, wsToken)
+	req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
+	req.Header.Set(wsTokenHeaderName, wsToken)
+	w := httptest.NewRecorder()
+	handler(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200; body: %s", w.Code, w.Body.String())
+	}
+	if got := w.Header().Get("X-Session-Token"); got != sess.AuthToken {
+		t.Errorf("X-Session-Token = %q, want bootstrapped session token %q", got, sess.AuthToken)
+	}
+
+	// The bootstrapped token works for subsequent requests (rename/delete).
+	req2 := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
+	req2.Header.Set("X-Session-Token", sess.AuthToken)
+	w2 := httptest.NewRecorder()
+	handler(w2, req2)
+	if w2.Code != http.StatusOK {
+		t.Errorf("second GET status = %d, want 200", w2.Code)
+	}
+}
+
+func TestHandleSessionByID_GET_InstanceHeaderBootstrap_WrongInstanceToken(t *testing.T) {
+	// A wrong instance token proves nothing — no bootstrap.
+	store := newTestSessionStore(t)
+	sess, _ := store.Create([]llm.Message{{Role: "user", Content: "hi"}}, "m", "task")
+
+	handler := handleSessionByID(store, nil, "real-token")
+	req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
+	req.Header.Set(wsTokenHeaderName, "wrong-token")
+	w := httptest.NewRecorder()
+	handler(w, req)
+
+	if w.Code != http.StatusUnauthorized {
+		t.Errorf("status = %d, want 401", w.Code)
+	}
+}
+
+func TestHandleSessionByID_GET_NoBootstrapWithoutInstanceHeader(t *testing.T) {
+	// Ambient-cookie-only callers (e.g. a DNS-rebinding page that cannot set
+	// custom headers) must NOT get the bootstrap even with the instance
+	// token configured: without the X-Odek-Ws-Token header the request is
+	// indistinguishable from the pre-fix behavior.
+	store := newTestSessionStore(t)
+	sess, _ := store.Create([]llm.Message{{Role: "user", Content: "hi"}}, "m", "task")
+
+	handler := handleSessionByID(store, nil, "real-token")
+	req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
+	// No X-Session-Token, no X-Odek-Ws-Token — only a (valid) instance cookie.
+	req.AddCookie(&http.Cookie{Name: wsTokenCookieName, Value: "real-token"})
+	w := httptest.NewRecorder()
+	handler(w, req)
+
+	if w.Code != http.StatusUnauthorized {
+		t.Errorf("status = %d, want 401", w.Code)
+	}
+}
+
 func TestHandleSessionByID_DELETE_RequiresToken(t *testing.T) {
 	store := newTestSessionStore(t)
 	sess, _ := store.Create([]llm.Message{{Role: "user", Content: "hi"}}, "m", "task")
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	req := httptest.NewRequest(http.MethodDelete, "/api/sessions/"+sess.ID, nil)
 	req.Header.Set("X-Session-Token", "wrong-token")
 	w := httptest.NewRecorder()
@@ -316,7 +384,7 @@ func TestHandleSessionByID_POST_RequiresToken(t *testing.T) {
 	store := newTestSessionStore(t)
 	sess, _ := store.Create([]llm.Message{{Role: "user", Content: "hi"}}, "m", "task")
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	body := strings.NewReader(`{"name":"renamed"}`)
 	req := httptest.NewRequest(http.MethodPost, "/api/sessions/"+sess.ID, body)
 	req.Header.Set("Content-Type", "application/json")
@@ -336,7 +404,7 @@ func TestHandleSessionByID_GET_RateLimit(t *testing.T) {
 	sessionLookupLimiter.reset()
 	defer sessionLookupLimiter.reset()
 
-	handler := handleSessionByID(store, nil)
+	handler := handleSessionByID(store, nil, "")
 	// Exhaust the 60/min allowance.
 	for i := 0; i < 60; i++ {
 		req := httptest.NewRequest(http.MethodGet, "/api/sessions/"+sess.ID, nil)
@@ -741,7 +809,7 @@ func buildServeMuxWithSessionByID(t *testing.T, store *session.Store) (net.Liste
 	apiAuth := func(h http.Handler) http.Handler {
 		return requireServeToken(token)(requireLocalHost(requireLocalOrigin(h)))
 	}
-	mux.Handle("/api/sessions/", apiAuth(handleSessionByID(store, nil)))
+	mux.Handle("/api/sessions/", apiAuth(handleSessionByID(store, nil, "")))
 	return ln, mux
 }
 

docs/SECURITY.md

@@ -467,6 +467,8 @@ The IP used for rate limiting is taken from `X-Forwarded-For` / `X-Real-Ip` only
 
 Legacy sessions created before this defense have no `AuthToken`; the first access bootstraps one and returns it to the client, preserving backward compatibility without weakening protection for newly created sessions.
 
+**Cross-front-end bootstrap (header knowledge proof).** A session created by one front-end (e.g. bodek, or the WebUI in another browser profile) carries an `AuthToken` the other front-ends don't have, so it could not be loaded by them. `GET /api/sessions/<id>` now also bootstraps the session token when the caller proves **knowledge of the per-instance CSRF token** by presenting it in the `X-Odek-Ws-Token` header (constant-time compared). Header presentation is a knowledge proof a cross-origin page cannot forge: a DNS-rebinding page holds only the ambient `SameSite=Strict` cookie and can neither read the token value nor set the custom header (it triggers a CORS preflight odek does not answer). Cookie-only callers therefore still get 401 on token-carrying sessions, while the operator's legitimate front-ends — which always send the header — can load each other's sessions. The rebinding damage boundary is unchanged.
+
 ### 25. Skill and episode context wrapped as untrusted
 
 Skill content and retrieved session episodes are externally-sourced data that cross the trust boundary. Before injecting them as `system` messages, the auto-load path (`odek.go`) and the lazy-match path (the loop) pass them through the same nonce'd `<untrusted_content_*>` wrapper used for tool output; the `skill_load` tool output is wrapped the same way at registration. The skill manager already gates `NeedsReview`/tainted skills, and the memory manager filters tainted episodes from search, but the wrapper provides defense-in-depth so a compromised skill or episode cannot pose as trusted system instructions.