From b0a011f6b41e0b6bead5741fee09bac5c243a4f6 Mon Sep 17 00:00:00 2001
From: clawbot <clawbot@noreply.example.org>
Date: Mon, 24 Aug 2026 17:52:25 +0200
Subject: [PATCH] Render unknown for a zero CreatedAt in Slack/Mattermost
 messages (closes #298)

---
 internal/delivery/event_timestamp_test.go | 35 +++++++++++++++++++++++
 internal/delivery/target_slack.go         |  7 ++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/internal/delivery/event_timestamp_test.go b/internal/delivery/event_timestamp_test.go
index 87bd07f..09e70cf 100644
--- a/internal/delivery/event_timestamp_test.go
+++ b/internal/delivery/event_timestamp_test.go
@@ -365,6 +365,41 @@ func TestFormatSlackMessageOverTaskReconstructedEvent(
 	)
 }
 
+// TestFormatSlackMessageZeroTimestamp asserts the rendering choice
+// directly, without going through the engine: a zero CreatedAt (the
+// shape a reaped-row fallback produces) renders as "unknown" rather
+// than the year-1 zero time, while a real CreatedAt still renders as
+// RFC3339.
+func TestFormatSlackMessageZeroTimestamp(t *testing.T) {
+	t.Parallel()
+
+	zeroEvent := database.Event{
+		Method:      http.MethodPost,
+		ContentType: testContentType,
+		Body:        tsEventBody,
+	}
+
+	zeroText := delivery.FormatSlackMessage(&zeroEvent)
+
+	assert.NotContains(t, zeroText, "0001-01-01",
+		"slack message carries the zero-time year",
+	)
+	assert.Contains(t, zeroText, "*Timestamp:* `unknown`",
+		"slack message does not mark an unset receipt time as unknown",
+	)
+
+	nonZeroEvent := zeroEvent
+	nonZeroEvent.CreatedAt = tsEventCreatedAt()
+
+	nonZeroText := delivery.FormatSlackMessage(&nonZeroEvent)
+
+	assert.Contains(t, nonZeroText,
+		"*Timestamp:* `"+
+			tsEventCreatedAt().UTC().Format(time.RFC3339)+"`",
+		"slack message does not render a real receipt time as RFC3339",
+	)
+}
+
 // TestEventReconstructionSurvivesAReapedRow pins the fallback: an
 // event row reaped by retention while its delivery still holds the
 // body inline is still delivered, with the receipt time unset,
diff --git a/internal/delivery/target_slack.go b/internal/delivery/target_slack.go
index f10cc15..c2f7ff7 100644
--- a/internal/delivery/target_slack.go
+++ b/internal/delivery/target_slack.go
@@ -231,10 +231,15 @@ func FormatSlackMessage(
 		event.ContentType,
 	)
 
+	timestamp := "unknown"
+	if !event.CreatedAt.IsZero() {
+		timestamp = event.CreatedAt.UTC().Format(time.RFC3339)
+	}
+
 	fmt.Fprintf(
 		&b,
 		"*Timestamp:* `%s`\n",
-		event.CreatedAt.UTC().Format(time.RFC3339),
+		timestamp,
 	)
 
 	fmt.Fprintf(