diff --git a/internal/gateway/fallback.go b/internal/gateway/fallback.go
index c600b7e2..c6b18402 100644
--- a/internal/gateway/fallback.go
+++ b/internal/gateway/fallback.go
@@ -596,6 +596,61 @@ func retryable(status int, body []byte) bool {
 	return false
 }
 
+// unsaidMargin is how far past a model's window a request's estimate
+// must go to be taken as too long for it: estimate counts a token as four
+// bytes, which most text runs under (Devin counted 173,954 tokens of one
+// estimated at 151,851), so one past it by a fifth hardly fits.
+const unsaidMargin = 1.2
+
+// tooLongUnsaid says a failure that doesn't say why was the request being too
+// long for the model, as some vendors put it: Devin's 502 "capacity
+// issues", WorkBuddy's 400 "Invalid request parameters", Qoder's 400
+// "Error in upstream response" — each for a conversation well past the
+// model's window, and answered at a size it holds. Retried, or asked of
+// another account of the model, it fails the same, and the agent, told it
+// as a vendor's error, never compacts. The message it is told instead
+// says the prompt is too long. Not for a rate limit, an account's
+// trouble, a model it doesn't serve, or one already saying it overflowed.
+func tooLongUnsaid(p provider.Provider, model string, tokens, status int, body []byte) (string, bool) {
+	switch status {
+	case 400, 413, 422, 500, 502, 503, 504:
+	default:
+		return "", false
+	}
+	if overflowed(status, body) || failure(status, body) != failOther || quotaWords.Match(body) ||
+		unservedWords.Match(body) || refusedWords.Match(body) || provider.EdgeBlocked(body) {
+		return "", false
+	}
+	window := windowOf(p, model)
+	if window <= 0 || float64(tokens) < float64(window)*unsaidMargin {
+		return "", false
+	}
+	msg := fmt.Sprintf("prompt is too long: about %d tokens, more than %s's context window of %d", tokens, model, window)
+	said := strings.TrimSpace(vendorMessage(body))
+	if len(said) > 200 {
+		said = said[:200] + "…"
+	}
+	// the vendor's words, unless they'd read as a limit of another kind
+	if full := fmt.Sprintf("%s (%s answered %d: %s)", msg, p.Name, status, said); said != "" && tooLong(400, full) {
+		return full, true
+	}
+	return fmt.Sprintf("%s (%s answered %d)", msg, p.Name, status), true
+}
+
+// windowOf is the tokens a provider's model takes, where known: the
+// user's (Provider.ContextOf), else its catalog entry's.
+func windowOf(p provider.Provider, model string) int {
+	if n := p.ContextOf(model); n > 0 {
+		return n
+	}
+	for _, e := range provider.Served() {
+		if e.Group == "" && e.Provider.ID == p.ID && (e.Model == model || e.ID == model) && e.Context > 0 {
+			return e.Context
+		}
+	}
+	return 0
+}
+
 const (
 	// lastRetries is how many times the last one left is tried again after
 	// a failure that passes — a busy vendor, a dropped connection.
diff --git a/internal/gateway/gateway.go b/internal/gateway/gateway.go
index cb880950..433b48b8 100644
--- a/internal/gateway/gateway.go
+++ b/internal/gateway/gateway.go
@@ -1443,6 +1443,16 @@ func (s *Server) serve(w http.ResponseWriter, r *http.Request, from provider.Pro
 			stop()
 		}
 		hw.settle()
+		outgrew := false // a failure that didn't say so was the request's length
+		if !hw.passing && !hw.refused && hw.code() >= 400 {
+			if req, err := parse(from, attemptBody); err == nil {
+				if msg, ok := tooLongUnsaid(c.p, c.model, estimate(req), hw.code(), hw.errBody()); ok {
+					// told as an overflow: not asked again, of this one or
+					// another, and nobody rests
+					hw.failure, hw.failMsg, outgrew = http.StatusBadRequest, msg, true
+				}
+			}
+		}
 		if hw.failure != 0 { // the stream failed before any of it was sent
 			call.Status, call.Error = hw.failure, c.p.Name+": "+hw.failMsg
 		}
@@ -1496,7 +1506,7 @@ func (s *Server) serve(w http.ResponseWriter, r *http.Request, from provider.Pro
 				continue
 			}
 		}
-		if updated && !hw.passing && hw.code() == 400 {
+		if updated && !outgrew && !hw.passing && hw.code() == 400 {
 			// the upstream turned the update items away: asked again as
 			// the agent sent it, and if that goes, never sent them again
 			plainFor = c.who() + "|" + c.model
@@ -1667,6 +1677,9 @@ func (s *Server) serve(w http.ResponseWriter, r *http.Request, from provider.Pro
 			call.Status, call.Error = other.Status, other.Error
 			writeError(w, from, call.Status, call.Error)
 			break
+		} else if outgrew {
+			// in the agent's own words for it, for it to compact
+			writeError(w, from, call.Status, hw.failMsg)
 		} else {
 			hw.release()
 		}
diff --git a/internal/gateway/toolong_unsaid_test.go b/internal/gateway/toolong_unsaid_test.go
new file mode 100644
index 00000000..e679c12e
--- /dev/null
+++ b/internal/gateway/toolong_unsaid_test.go
@@ -0,0 +1,66 @@
+package gateway
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/yetone/magpie/internal/provider"
+)
+
+// Some vendors don't say a conversation is too long for the model: Devin
+// answered one of about 225k tokens for swe-1.7-lightning (a 202,752
+// window) with a 502 "capacity issues", WorkBuddy one for glm-5.1 with a
+// 400 "Invalid request parameters", Qoder one of 2M for qmodel with a 400
+// "Error in upstream response" — each answered at a size the model holds.
+// Asked again in place three times, the agent was then handed a 502 and
+// never compacted. A request well past the model's window that fails so
+// is told as one too long, at once.
+func TestOverflowTheVendorDidntSay(t *testing.T) {
+	big := strings.Repeat("word ", 2400)  // about 3000 tokens as estimated
+	small := strings.Repeat("word ", 100) // about 125
+	near := strings.Repeat("word ", 1760) // about 2200, which may yet fit
+	for _, tc := range []struct {
+		name, path, body string
+		code             int
+		reply            string
+		wantCode, calls  int
+		want             string
+	}{
+		{"502 anthropic", "/v1/messages", big, 502, `{"error":{"message":"We are experiencing capacity issues"}}`, 400, 1, "prompt is too long"},
+		{"400 chat", "/v1/chat/completions", big, 400, `{"error":{"message":"Invalid request parameters"}}`, 400, 1, "context_length_exceeded"},
+		// not the conversation's length
+		{"small 502", "/v1/messages", small, 502, `{"error":{"message":"We are experiencing capacity issues"}}`, 502, 1 + lastRetries, "capacity issues"},
+		{"near the window", "/v1/messages", near, 502, `{"error":{"message":"We are experiencing capacity issues"}}`, 502, 1 + lastRetries, "capacity issues"},
+		{"429", "/v1/messages", big, 429, `{"error":{"message":"Rate limit reached"}}`, 429, 1 + rateRetries, "Rate limit"},
+		{"401", "/v1/messages", big, 401, `{"error":{"message":"invalid token"}}`, 401, 1, "invalid token"},
+		{"quota", "/v1/messages", big, 400, `{"error":{"message":"insufficient balance"}}`, 400, 1, "insufficient balance"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			proto := provider.Anthropic
+			if strings.Contains(tc.path, "chat") {
+				proto = provider.Chat
+			}
+			f := &fake{code: tc.code, ctype: "application/json", reply: tc.reply}
+			up := setup(t, proto, f)
+			p := provider.Provider{ID: "fake", Name: "Fake", Key: "k", Models: []string{"m1"}, Contexts: map[string]int{"m1": 2000}}
+			if proto == provider.Chat {
+				p.Chat = up.URL + "/v1"
+			} else {
+				p.Anthropic = up.URL
+			}
+			if err := provider.Save(p); err != nil {
+				t.Fatal(err)
+			}
+			req := `{"model":"fake/m1","max_tokens":10,"messages":[{"role":"user","content":"` + tc.body + `"}]}`
+			code, body := post(t, tc.path, req)
+			if code != tc.wantCode || !strings.Contains(body, tc.want) || f.calls != tc.calls {
+				t.Fatalf("status %d after %d calls (want %d after %d): %s", code, f.calls, tc.wantCode, tc.calls, body)
+			}
+			if tc.wantCode != 400 || tc.name == "quota" {
+				if strings.Contains(body, "prompt is too long") || strings.Contains(body, "context_length_exceeded") {
+					t.Fatalf("told as an overflow: %s", body)
+				}
+			}
+		})
+	}
+}
diff --git a/internal/provider/migrate_qoder.go b/internal/provider/migrate_qoder.go
index 311301e9..439f824c 100644
--- a/internal/provider/migrate_qoder.go
+++ b/internal/provider/migrate_qoder.go
@@ -24,7 +24,7 @@ func init() {
 func qoderMover(id string) *mover {
 	return &mover{
 		pkg:    "@magpie-community/opencode-qoder-auth",
-		min:    "0.2.3", // Qoder CN as "qoder-cn", its device-token chat as the built-in's; each model's credit rate; the sign-in renewed ahead of time through auth.refresh
+		min:    "0.2.4", // Qoder CN as "qoder-cn", its device-token chat as the built-in's; each model's credit rate; the sign-in renewed ahead of time through auth.refresh; token usage read
 		agents: []string{id},
 		out: func() ([]Moving, error) {
 			// no refresh of the built-in's runs while the pairs are read