Defer guest commands after incomplete HTTP error responses

The HTTP error wrapper hid truncated response bodies from guest admission. Preserve the bounded read failure as a private wrapping type so error statuses also cool down the whole guest. Cover both 200 and 500 truncation, and retain complete permission refusals plus subsequent healthy reads.

Contract-Neutral: Completes the existing full-response/incomplete-body guest safety contract; error text and ordinary API errors retain compatibility, with no new interface or surface.
Change-source: pulse-maintainer

pkg/proxmox/client.go

@@ -52,13 +52,20 @@ func classifyAPIErrorLog(status int, path string) (apiErrorLogLevel, string) {
 	return apiErrorLogNone, ""
 }
 
+// Preserve an incomplete body through the HTTP error-response wrapper too.
+// An error status alone is not a completed refusal if its body was truncated.
+type responseBodyReadError struct{ cause error }
+
+func (e *responseBodyReadError) Error() string { return e.cause.Error() }
+func (e *responseBodyReadError) Unwrap() error { return e.cause }
+
 func readResponseBodyLimited(r io.Reader) ([]byte, error) {
 	body, err := io.ReadAll(io.LimitReader(r, maxResponseBodyBytes+1))
 	if err != nil {
-		return nil, err
+		return nil, &responseBodyReadError{cause: err}
 	}
 	if int64(len(body)) > maxResponseBodyBytes {
-		return nil, fmt.Errorf("response body exceeds %d bytes", maxResponseBodyBytes)
+		return nil, &responseBodyReadError{cause: fmt.Errorf("response body exceeds %d bytes", maxResponseBodyBytes)}
 	}
 	return body, nil
 }

pkg/proxmox/guest_agent_guard.go

@@ -176,6 +176,11 @@ func (c *Client) getGuestAgent(ctx context.Context, path, node string, vmid int)
 	// own their usual session recovery; this guest admission is single-attempt.
 	resp, err := c.requestWithRetry(ctx, http.MethodGet, path, nil, true)
 	if err != nil {
+		var incomplete *responseBodyReadError
+		if errors.As(err, &incomplete) {
+			uncertain = true
+			return nil, &guestAgentDeferredError{reason: "agent-response-incomplete", cause: err}
+		}
 		// Explicit refusals/unsupported commands remain ordinary errors. An
 		// uncertain completion blocks every command, not just this method.
 		lower := strings.ToLower(err.Error())

pkg/proxmox/guest_agent_guard_test.go

@@ -101,6 +101,14 @@ func TestGuestAgentLockAppearingInFlightDiscardsPayload(t *testing.T) {
 }
 
 func TestGuestAgentIncompleteBodyBlocksWholeVM(t *testing.T) {
+	for _, status := range []int{http.StatusOK, http.StatusInternalServerError} {
+		t.Run(fmt.Sprintf("status-%d", status), func(t *testing.T) {
+			testGuestAgentIncompleteBodyBlocksWholeVM(t, status)
+		})
+	}
+}
+
+func testGuestAgentIncompleteBodyBlocksWholeVM(t *testing.T, status int) {
 	var calls atomic.Int32
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if strings.HasSuffix(r.URL.Path, "/config") {
@@ -109,12 +117,13 @@ func TestGuestAgentIncompleteBodyBlocksWholeVM(t *testing.T) {
 		}
 		calls.Add(1)
 		w.Header().Set("Content-Length", "1000")
+		w.WriteHeader(status)
 		fmt.Fprint(w, `{"data":{"result":[]}}`)
 	}))
 	defer server.Close()
 	c := backupTestClient(t, server.URL)
 	if _, err := c.GetVMFSInfo(context.Background(), "node", 105); GuestAgentDeferredReason(err) != "agent-response-incomplete" {
-		t.Fatalf("incomplete body not deferred: %v", err)
+		t.Errorf("incomplete body not deferred: %v", err)
 	}
 	for name, read := range backupAgentReads() {
 		t.Run(name, func(t *testing.T) {
@@ -128,6 +137,33 @@ func TestGuestAgentIncompleteBodyBlocksWholeVM(t *testing.T) {
 	}
 }
 
+func TestGuestAgentDeferralDoesNotHideCompletedRefusal(t *testing.T) {
+	var calls atomic.Int32
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if strings.HasSuffix(r.URL.Path, "/config") {
+			fmt.Fprint(w, `{"data":{}}`)
+			return
+		}
+		calls.Add(1)
+		if strings.HasSuffix(r.URL.Path, "/get-fsinfo") {
+			http.Error(w, "permission denied", http.StatusForbidden)
+			return
+		}
+		backupAgentPayload(w, r)
+	}))
+	defer server.Close()
+	c := backupTestClient(t, server.URL)
+	if _, err := c.GetVMFSInfo(context.Background(), "node", 105); err == nil || errors.Is(err, ErrGuestAgentDeferred) || !strings.Contains(err.Error(), "403") {
+		t.Fatalf("completed refusal hidden or lost: %v", err)
+	}
+	if _, err := c.GetVMAgentInfo(context.Background(), "node", 105); err != nil {
+		t.Fatalf("completed refusal poisoned other healthy reads: %v", err)
+	}
+	if calls.Load() != 2 {
+		t.Fatalf("refused/healthy command count = %d", calls.Load())
+	}
+}
+
 func TestGuestAgentClusterDoesNotReplayUncertainCall(t *testing.T) {
 	var calls atomic.Int32
 	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {