Preserve authentication cancellation at the response limit

bundled_smoke_contract_test.go

@@ -3,6 +3,7 @@ package promptkit_test
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"io"
 	"net/http"
 	"reflect"
@@ -13,6 +14,45 @@ import (
 	"go.maximumdirect.net/promptkit"
 )
 
+type cancelingAuthenticationBody struct {
+	remaining int
+	cancel    context.CancelFunc
+	closed    bool
+}
+
+func (b *cancelingAuthenticationBody) Read(p []byte) (int, error) {
+	n := min(len(p), b.remaining)
+	for i := range p[:n] {
+		p[i] = 'x'
+	}
+	b.remaining -= n
+	if b.remaining == 0 {
+		b.cancel()
+		return n, context.Canceled
+	}
+	return n, nil
+}
+func (b *cancelingAuthenticationBody) Close() error { b.closed = true; return nil }
+
+func TestAuthenticationReadCancellationWinsOverOverflow(t *testing.T) {
+	for _, size := range []int{1024, (1 << 20) + 1} {
+		ctx, cancel := context.WithCancel(context.Background())
+		body := &cancelingAuthenticationBody{remaining: size, cancel: cancel}
+		engine, err := promptkit.NewEngine(promptkit.Config{HTTPClient: &http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) {
+			return &http.Response{StatusCode: 200, Header: make(http.Header), Body: body}, nil
+		})}})
+		if err != nil {
+			cancel()
+			t.Fatal(err)
+		}
+		report, err := engine.SmokeTest(ctx, promptkit.SmokeTestRequest{Kind: promptkit.SmokeTestAuthentication, BackendID: "openrouter"})
+		cancel()
+		if !errors.Is(err, context.Canceled) || report == nil || report.Completed || report.Failure != promptkit.ExecutionFailureCanceled || report.Facts.CredentialsAccepted != nil || report.Facts.ResponseReceived == nil || !*report.Facts.ResponseReceived || !body.closed {
+			t.Fatalf("size %d: report=%+v error=%v closed=%v", size, report, err, body.closed)
+		}
+	}
+}
+
 func TestBundledSmokeHTTPDefaults(t *testing.T) {
 	t.Setenv("OPENROUTER_API_KEY", "synthetic-key")
 	var urls []string

docs/roadmap/remediation.md

@@ -27,7 +27,11 @@ contracts.
 
 ### 1. Preserve Caller Cancellation When Authentication Also Overflows [P2]
 
-**Status:** Open. **Stages:** 7, 21–22.
+**Status:** Complete. **Stages:** 7, 21–22.
+
+Completion: interrupted body reads preserve caller cancellation before overflow
+classification. Public below-limit and overflow-boundary regressions retain HTTP
+facts, unknown acceptance, incomplete cancellation reports, and body closure.
 
 **Locations:** [authentication adapter](../../internal/llm/openrouter_authentication.go),
 `ProbeOpenRouterKey`, lines 61–67;

internal/llm/openrouter_authentication.go

@@ -59,6 +59,9 @@ func (c *OpenAICompatibleClient) ProbeOpenRouterKey(ctx context.Context, endpoin
 			return result, nil
 		}
 		contents, err := io.ReadAll(io.LimitReader(response.Body, maxAuthenticationResponseBytes+1))
+		if err != nil && ctx.Err() != nil {
+			return result, ctx.Err()
+		}
 		if len(contents) > maxAuthenticationResponseBytes {
 			result.Overflow = true
 			return result, nil