From aeb86f55b96462435f3e90d7ea10d12239efb2a3 Mon Sep 17 00:00:00 2001
From: yurii <author8132@gmail.com>
Date: Tue, 22 Sep 2026 18:27:57 +0100
Subject: [PATCH] fix(dispenser): retry on transient prepare failure

---
 cmd/hardlink/main.go                       |  2 +-
 internal/dispenser/dispenserclient.go      | 32 ++++++++++++++++++++
 internal/dispenser/dispenserclient_test.go | 34 ++++++++++++++++++++++
 release notes.md                           |  3 ++
 4 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/cmd/hardlink/main.go b/cmd/hardlink/main.go
index abe2b48..c931330 100644
--- a/cmd/hardlink/main.go
+++ b/cmd/hardlink/main.go
@@ -33,7 +33,7 @@ import (
 )
 
 const (
-	buildVersion     = "v2.0.1"
+	buildVersion     = "v2.0.2"
 	serviceName      = "hardlink"
 	pollingFrequency = 8 * time.Second
 )
diff --git a/internal/dispenser/dispenserclient.go b/internal/dispenser/dispenserclient.go
index d1473f1..02bc35f 100644
--- a/internal/dispenser/dispenserclient.go
+++ b/internal/dispenser/dispenserclient.go
@@ -201,10 +201,14 @@ func (c *Client) handle(req cmdReq) {
 
 	case cmdToEncoder:
 		err := cardToEncoderPosition(c.port)
+		// A movement command makes any previously cached position unreliable.
+		c.invalidateStatusCache()
 		req.respCh <- cmdResp{err: err}
 
 	case cmdOutOfMouth:
 		err := cardOutOfMouth(c.port)
+		// A movement command makes any previously cached position unreliable.
+		c.invalidateStatusCache()
 		req.respCh <- cmdResp{err: err}
 
 	default:
@@ -246,6 +250,13 @@ func (c *Client) CheckStatus(ctx context.Context) ([]byte, error) {
 	return c.do(ctx, cmdStatus)
 }
 
+func (c *Client) invalidateStatusCache() {
+	c.mu.Lock()
+	c.lastStatus = nil
+	c.lastStatusT = time.Time{}
+	c.mu.Unlock()
+}
+
 func (c *Client) ToEncoder(ctx context.Context) error {
 	_, err := c.do(ctx, cmdToEncoder)
 	return err
@@ -339,6 +350,27 @@ func preparationStatus(operation string, status []byte) (bool, error) {
 	if isPreparationMoving(status) {
 		return false, nil
 	}
+
+	// Some dispenser firmware briefly reports 0x32 ("Preparing card fails")
+	// while the card is still travelling to the encoder. Treat that one
+	// diagnostic as transient during an active preparation sequence and let
+	// pollForEncoderPosition decide success (0x33) or timeout. Do not mask
+	// independent hard errors reported in the other status bytes.
+	if status[0] == 0x32 {
+		statusWithoutPrepareFailure := append([]byte(nil), status...)
+		statusWithoutPrepareFailure[0] = 0x30
+		if err := dispenserStatusError(statusWithoutPrepareFailure); err != nil {
+			return false, fmt.Errorf("[%s] %w", operation, err)
+		}
+
+		log.Warnf(
+			"[%s] transient Preparing card fails; waiting for encoder position, raw status: % X",
+			operation,
+			status,
+		)
+		return false, nil
+	}
+
 	if err := dispenserStatusError(status); err != nil {
 		return false, fmt.Errorf("[%s] %w", operation, err)
 	}
diff --git a/internal/dispenser/dispenserclient_test.go b/internal/dispenser/dispenserclient_test.go
index cb3c019..0a4cdd0 100644
--- a/internal/dispenser/dispenserclient_test.go
+++ b/internal/dispenser/dispenserclient_test.go
@@ -147,6 +147,40 @@ func TestPrepareCurrentCardAcceptsEncoderPositionWithStaleDiagnostics(t *testing
 	}
 }
 
+func TestPrepareCurrentCardToleratesTransientPrepareFailureUntilEncoder(t *testing.T) {
+	client, device := newSequenceTestClient(t,
+		cmdResp{status: []byte{0x32, 0x30, 0x30, 0x30}},
+		cmdResp{status: []byte{0x32, 0x30, 0x30, 0x30}},
+		cmdResp{status: []byte{0x32, 0x30, 0x30, 0x30}},
+		cmdResp{status: []byte{0x32, 0x30, 0x30, 0x33}},
+	)
+
+	stock, err := client.PrepareCurrentCard(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stock != "Preparing card fails" {
+		t.Fatalf("stock status = %q, want Preparing card fails", stock)
+	}
+	if got := commandCount(device.commands, cmdToEncoder); got != 1 {
+		t.Fatalf("to-encoder commands = %d, want 1", got)
+	}
+	if got := commandCount(device.commands, cmdStatus); got != 4 {
+		t.Fatalf("status reads = %d, want 4", got)
+	}
+}
+
+func TestPrepareCurrentCardDoesNotMaskHardErrorAlongsideTransientPrepareFailure(t *testing.T) {
+	client, _ := newSequenceTestClient(t,
+		cmdResp{status: []byte{0x32, 0x30, 0x32, 0x30}},
+	)
+
+	_, err := client.PrepareCurrentCard(context.Background())
+	if err == nil || !strings.Contains(err.Error(), "Card jammed") {
+		t.Fatalf("error = %v, want Card jammed", err)
+	}
+}
+
 func TestPrepareCurrentCardPollingAllowsTransientMovementWithStaleErrors(t *testing.T) {
 	client, device := newSequenceTestClient(t,
 		cmdResp{status: status(0x34)},
diff --git a/release notes.md b/release notes.md
index 2d67969..8a98e68 100644
--- a/release notes.md	
+++ b/release notes.md	
@@ -2,6 +2,9 @@
 
 builtVersion is a const in main.go
 
+#### v2.0.2 - 22 September 2026
+fix(dispenser): retry on transient prepare failure
+
 #### v2.0.1 - 10 September 2026
 feat: add CreditCall preauth streaming