Preserve civil daypart clocks across DST

docs/internal/report-registry.md

@@ -13,7 +13,12 @@ Each `Definition` declares a stable ID and display name, prompt ID and version,
 | `tomorrow` | `2.0.0` | `weather-balanced` | Next local civil day | Evening | `tomorrow.md` |
 | `hourly` | `2.0.0` | `weather-light` | Rolling six-hour interval | — | `hourly.md` |
 
-Daily derives its filename from the resolved valid-period start in the effective timezone, so multiple Daily items have distinct destinations. Exact template fields and schema assets belong to [report templates](../templates.md) and [generated-text internals](generatedtext.md). Prompt assets own default profile selection; the registry stores no provider setting.
+Daily derives its filename and run identity from the resolved valid-period start
+in the effective timezone, so multiple Daily items have distinct destinations
+and identifiers. Exact template fields and schema assets belong to [report
+templates](../templates.md) and [generated-text internals](generatedtext.md).
+Prompt assets own default profile selection; the registry stores no provider
+setting.
 
 ## Collaborators And Boundaries
 

internal/report/period_test.go

@@ -43,6 +43,37 @@ func TestResolveDailyRequiresDate(t *testing.T) {
 	}
 }
 
+func TestDailyRunIDsDistinguishResolvedDates(t *testing.T) {
+	location := loadTestLocation(t)
+	now := parseTestTime("2026-05-29T17:45:00-05:00")
+	tests := []struct {
+		date     time.Time
+		wantDate string
+	}{
+		{date: time.Date(2026, time.May, 30, 12, 0, 0, 0, location), wantDate: "2026-05-30"},
+		{date: time.Date(2026, time.May, 31, 12, 0, 0, 0, location), wantDate: "2026-05-31"},
+	}
+
+	runIDs := make(map[string]struct{}, len(tests))
+	for _, tt := range tests {
+		resolved, err := Resolve(Daily, ResolveRequest{Now: now, Location: location, Date: tt.date})
+		if err != nil {
+			t.Fatalf("Resolve(Daily) error = %v", err)
+		}
+		runID := resolved.Metadata().RunID
+		if runID == "" {
+			t.Fatal("Daily RunID is empty")
+		}
+		if !strings.HasSuffix(runID, "_"+tt.wantDate) {
+			t.Fatalf("Daily RunID = %q, want resolved date %q", runID, tt.wantDate)
+		}
+		if _, exists := runIDs[runID]; exists {
+			t.Fatalf("duplicate Daily RunID %q", runID)
+		}
+		runIDs[runID] = struct{}{}
+	}
+}
+
 func TestRegistryContainsOnlyPromptBackedReports(t *testing.T) {
 	registry := DefaultRegistry()
 	definitions := registry.All()

internal/timeutil/periods.go

@@ -72,10 +72,17 @@ func CivilDay(date time.Time, location *time.Location) Period {
 
 func ClockWindow(date time.Time, location *time.Location, startClock time.Duration, endClock time.Duration) Period {
 	day := CivilDay(date, location)
-	start := day.Start.Add(startClock)
-	end := day.Start.Add(endClock)
+	start := civilClock(day.Start, location, startClock)
+	end := civilClock(day.Start, location, endClock)
 	if !end.After(start) {
-		end = end.AddDate(0, 0, 1)
+		end = civilClock(day.Start.AddDate(0, 0, 1), location, endClock)
 	}
 	return Period{Start: start, End: end}
 }
+
+func civilClock(date time.Time, location *time.Location, clock time.Duration) time.Time {
+	local := date.In(location)
+	hour := int(clock / time.Hour)
+	minute := int(clock%time.Hour) / int(time.Minute)
+	return time.Date(local.Year(), local.Month(), local.Day(), hour, minute, 0, 0, location)
+}

internal/timeutil/periods_test.go

@@ -33,3 +33,72 @@ func TestClockWindowHandlesOvernight(t *testing.T) {
 		t.Fatalf("End = %s, want 2026-05-30T06:00", got)
 	}
 }
+
+func TestClockWindowUsesCivilTimeAcrossDSTTransitions(t *testing.T) {
+	location, err := LoadLocation("America/Chicago")
+	if err != nil {
+		t.Fatalf("LoadLocation() error = %v", err)
+	}
+	tests := []struct {
+		name      string
+		date      time.Time
+		start     string
+		end       string
+		wantStart string
+		wantEnd   string
+	}{
+		{
+			name:      "spring-forward daytime",
+			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
+			start:     "00:00",
+			end:       "06:00",
+			wantStart: "2026-03-08T00:00:00-06:00",
+			wantEnd:   "2026-03-08T06:00:00-05:00",
+		},
+		{
+			name:      "fall-back daytime",
+			date:      time.Date(2026, time.November, 1, 12, 0, 0, 0, location),
+			start:     "00:00",
+			end:       "06:00",
+			wantStart: "2026-11-01T00:00:00-05:00",
+			wantEnd:   "2026-11-01T06:00:00-06:00",
+		},
+		{
+			name:      "spring-forward overnight",
+			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
+			start:     "22:00",
+			end:       "06:00",
+			wantStart: "2026-03-08T22:00:00-05:00",
+			wantEnd:   "2026-03-09T06:00:00-05:00",
+		},
+		{
+			name:      "spring-forward end of day",
+			date:      time.Date(2026, time.March, 8, 12, 0, 0, 0, location),
+			start:     "18:00",
+			end:       "24:00",
+			wantStart: "2026-03-08T18:00:00-05:00",
+			wantEnd:   "2026-03-09T00:00:00-05:00",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			start, err := ParseClock(tt.start)
+			if err != nil {
+				t.Fatalf("ParseClock(%q) error = %v", tt.start, err)
+			}
+			end, err := ParseClock(tt.end)
+			if err != nil {
+				t.Fatalf("ParseClock(%q) error = %v", tt.end, err)
+			}
+
+			window := ClockWindow(tt.date, location, start, end)
+			if got := window.Start.Format(time.RFC3339); got != tt.wantStart {
+				t.Fatalf("Start = %s, want %s", got, tt.wantStart)
+			}
+			if got := window.End.Format(time.RFC3339); got != tt.wantEnd {
+				t.Fatalf("End = %s, want %s", got, tt.wantEnd)
+			}
+		})
+	}
+}