Compare recent changes from module snapshots

2026-06-09 21:20:53 +00:00
parent 479d144592
commit 816cfb24aa
17 changed files with 508 additions and 346 deletions
--- a/docs/config.md
+++ b/docs/config.md
@@ -171,7 +171,7 @@ midday, afternoon, and evening.
 - `wind_gust_miles_per_hour`: wind gust change threshold. Default: `10`.
 - `precip_timing_shift_minutes`: precipitation timing shift threshold. Default: `120`.

-Recent Changes are added to prompt input when a prior comparable briefing
+Recent Changes are added to prompt input when a prior comparable module
 snapshot exists and a threshold is crossed.

 ### `reports`
--- a/docs/internal/app-orchestration.md
+++ b/docs/internal/app-orchestration.md
@@ -70,19 +70,20 @@ Single-report generation follows this order:
 2. Create or use a filesystem store.
 3. Locate any prior compatible snapshot through `internal/state`.
 4. Fetch a Weather API bundle.
-5. Build a report-specific briefing package.
-6. Save the briefing snapshot.
-7. Compute Recent Changes from structured prior and current briefings.
-8. Build and save the Scriptorium `data_package`.
-9. Run Scriptorium render preflight.
-10. Save preflight JSON when a render result is available.
-11. Save metadata for inspection.
-12. Run Scriptorium report generation to the managed report path.
-13. Copy the managed report to the requested `--out` path when provided.
-14. Save metadata with the managed report path.
-15. If distributor notification is enabled, notify using the managed report
+5. Build collected and derived facts once.
+6. Execute configured modules and save the module snapshot.
+7. Build and save the compatibility briefing snapshot.
+8. Compute Recent Changes from structured prior and current module snapshots.
+9. Build and save the YAML Scriptorium `data_package`.
+10. Run Scriptorium render preflight.
+11. Save preflight JSON when a render result is available.
+12. Save metadata for inspection.
+13. Run Scriptorium report generation to the managed report path.
+14. Copy the managed report to the requested `--out` path when provided.
+15. Save metadata with the managed report path.
+16. If distributor notification is enabled, notify using the managed report
    path as the source file.
-16. Save a distributor notification debug artifact and update metadata with its
+17. Save a distributor notification debug artifact and update metadata with its
    path.

 If render preflight returns both a result and an error, preflight JSON and
@@ -141,7 +142,7 @@ Inspect:
 - Generated reports use the same app request and result types regardless of
  report ID.
 - Render preflight precedes Scriptorium report generation.
- Recent Changes are computed from structured briefing snapshots.
+- Recent Changes are computed from structured module snapshots.
 - Metadata links artifacts produced for a run.
 - Distributor notification maps the managed Markdown report path to configured
  bundle paths; extra output copies are not upload sources.
--- a/docs/internal/changes.md
+++ b/docs/internal/changes.md
@@ -4,15 +4,15 @@ This document describes structured Recent Changes comparison.

 ## Purpose

-`internal/changes` compares current and prior briefing packages and emits
+`internal/changes` compares current and prior module snapshots and emits
 compact change records for prompt input data packages.

 ## Inputs And Outputs

 Inputs:

- prior briefing package
- current briefing package
+- prior module snapshot
+- current module snapshot
 - comparison thresholds from configuration

 Outputs:
@@ -22,7 +22,7 @@ Outputs:

 ## Boundaries

- This package compares structured briefing data only.
+- This package compares structured module snapshot data only.
 - It does not read filesystem state, find prior snapshots, render Markdown,
  invoke Scriptorium, or compare generated report text.

@@ -41,7 +41,7 @@ None.

 ## State Or Manifest Behavior

-None directly. The app loads prior briefing snapshots through `internal/state`
+None directly. The app loads prior module snapshots through `internal/state`
 before calling comparison functions.

 ## Skip And Resume Behavior
@@ -51,9 +51,11 @@ empty Recent Changes list without calling a comparison function.

 ## Failure Behavior

- Daily comparison requires both inputs to contain Daily briefing content.
- 3-Day comparison requires both inputs to contain 3-Day briefing content.
- Weekend comparison requires both inputs to contain Weekend briefing content.
+- Daily comparison requires `derived_daily_summary` and
+  `derived_daypart_summaries` stanzas. It also uses `alert_digest` and
+  `precip_timing` when present.
+- 3-Day comparison requires `derived_daypart_summaries`.
+- Weekend comparison requires `derived_daypart_summaries`.
 - Storm Report currently has no comparison implementation, so the app leaves
  Recent Changes empty for Storm reports.

--- a/docs/internal/prompt-input.md
+++ b/docs/internal/prompt-input.md
@@ -4,26 +4,24 @@ This document describes prompt input data package construction.

 ## Purpose

-`internal/promptinput` converts a structured briefing package and optional
-Recent Changes into the `data_package` JSON passed to Scriptorium prompts.
+`internal/promptinput` converts report metadata, module snapshots, and optional
+Recent Changes into the YAML `data_package` passed to Scriptorium prompts.

 ## Inputs And Outputs

 Inputs:

- `briefing.Package`
+- report metadata
+- `module.Snapshot`
 - optional `[]changes.Change`

 Outputs:

 - `promptinput.Package` containing schema version, RunID, report metadata,
-  briefing content, Recent Changes, and source warnings. Briefing content
-  includes configured location context, current conditions when available,
-  structured weather story context when available, discussion key messages, and
-  short/long-term AFD narratives when the Weather API provides them.
+  named briefing stanzas, Recent Changes, and source warnings.
 - report metadata includes `currentLocalDate`, the generation date formatted as
  `YYYY-MM-DD` in the effective report timezone.
- optional JSON file written by `promptinput.Save`
+- optional YAML file written by `promptinput.Save`

 ## Boundaries

@@ -34,7 +32,8 @@ Outputs:
 ## Config Fields Used

 None directly. Config-derived values, including timezone and prompt location
-context, are already present in briefing metadata before this package runs.
+context, are already present in report metadata and module stanzas before this
+package runs.

 ## External Adapters Used

@@ -42,7 +41,7 @@ None.

 ## State Or Manifest Behavior

-`promptinput.Save` writes JSON atomically. Managed workspace paths are owned by
+`promptinput.Save` writes YAML atomically. Managed workspace paths are owned by
 `internal/state`.

 ## Skip And Resume Behavior
@@ -51,9 +50,9 @@ None. Recent Changes is always present as an `items` list and may be empty.

 ## Failure Behavior

-Validation fails before render preflight when required top-level or briefing
-metadata fields are missing or inconsistent, or when no report content is
-present. Save failures include filesystem operation and path context.
+Validation fails before render preflight when required top-level fields are
+missing or inconsistent, or when no named briefing stanzas are present. Save
+failures include filesystem operation and path context.

 ## Tests

@@ -64,6 +63,6 @@ Inspect:

 ## Invariants

- Scriptorium receives structured `data_package` JSON.
- Briefing metadata and top-level report metadata must agree.
+- Scriptorium receives structured `data_package` YAML.
+- Module stanza order is deterministic for generated snapshots.
 - Recent Changes are not inferred from rendered report text.
--- a/docs/operations.md
+++ b/docs/operations.md
@@ -216,8 +216,8 @@ source provenance and warnings without dumping full weather payloads.

 ## Recent Changes

-Recent Changes are computed from structured briefing snapshots, not rendered
-Markdown text.
+Recent Changes are computed from structured module snapshots, not rendered
+Markdown or YAML text.

 Daily Today and Daily Tomorrow can compare with each other when they cover the
 same valid local date. 3-Day Outlook compares with prior compatible 3-Day
--- a/docs/policy/architecture.md
+++ b/docs/policy/architecture.md
@@ -3,7 +3,7 @@
 This document defines the development principles for this Go project. It is inward-facing: developers and LLM coding agents should use it to preserve the project’s shape, boundaries, and invariants as the code evolves.

 ## weatherreporter
-`weatherreporter` is a deterministic weather briefing and report-preparation application. It consumes normalized weather data from the internal weatherfeeder-backed API, derives report-specific briefing packages, compares those packages against prior snapshots, and invokes an external prompt runner to produce human-facing reports.
+`weatherreporter` is a deterministic weather briefing and report-preparation application. It consumes normalized weather data from the internal weatherfeeder-backed API, derives report-specific module snapshots and prompt packages, compares module snapshots against prior runs, and invokes an external prompt runner to produce human-facing reports.

 The application should keep meteorological data selection, daypart grouping, threshold detection, forecast-period resolution, and recent-change comparison inside Go domain packages. LLM prompts should receive curated briefing packages rather than raw unbounded source payloads wherever practical.

--- a/internal/app/app.go
+++ b/internal/app/app.go
@@ -530,7 +530,7 @@ func GenerateReport(ctx context.Context, req ReportRequest) (*ReportResult, erro
 		return nil, err
 	}

-	recentChanges, err := recentChanges(ctx, store, priorSnapshot, briefingPackage, req.Config.RecentChange)
+	recentChanges, err := recentChanges(ctx, store, priorSnapshot, req.Resolved.Definition.ID, moduleSnapshot, req.Config.RecentChange)
 	if err != nil {
 		return nil, err
 	}
@@ -988,11 +988,11 @@ func defaultStore(cfg config.Config) (*state.FilesystemStore, error) {
 	return state.NewFilesystemStore(cfg.Workspace)
 }

-func recentChanges(ctx context.Context, store state.Store, priorSnapshot *state.PriorSnapshot, current briefing.Package, cfg config.RecentChangeConfig) ([]changes.Change, error) {
+func recentChanges(ctx context.Context, store state.Store, priorSnapshot *state.PriorSnapshot, reportID report.ID, current module.Snapshot, cfg config.RecentChangeConfig) ([]changes.Change, error) {
 	if priorSnapshot == nil {
 		return nil, nil
 	}
-	previous, err := store.LoadBriefing(ctx, priorSnapshot.BriefingPath)
+	previous, err := store.LoadModuleSnapshot(ctx, priorSnapshot.ModuleSnapshotPath)
 	if err != nil {
 		return nil, err
 	}
@@ -1002,7 +1002,7 @@ func recentChanges(ctx context.Context, store state.Store, priorSnapshot *state.
 		WindGustMilesPerHour:     cfg.WindGustMilesPerHour,
 		PrecipTimingShiftMinutes: cfg.PrecipTimingShiftMinutes,
 	}
-	switch current.Metadata.ReportID {
+	switch reportID {
 	case report.DailyToday, report.DailyTomorrow:
 		return changes.CompareDaily(previous, current, thresholds)
 	case report.ThreeDay:
--- a/internal/app/app_test.go
+++ b/internal/app/app_test.go
@@ -20,6 +20,7 @@ import (
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/promptinput"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/state"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
 )

 func TestFetchAndSaveBundle(t *testing.T) {
@@ -655,25 +656,7 @@ func TestGenerateReportIncludesRecentChangesFromPriorSnapshot(t *testing.T) {
 		t.Fatalf("ResolveGenerate(prior) error = %v", err)
 	}
 	priorBriefing := priorDailyBriefing(priorResolved)
-	priorBriefingPath, err := store.SaveBriefing(context.Background(), priorResolved, priorBriefing)
-	if err != nil {
-		t.Fatalf("SaveBriefing() error = %v", err)
-	}
-	priorPaths, err := store.Paths(priorResolved)
-	if err != nil {
-		t.Fatalf("Paths() error = %v", err)
-	}
-	_, err = store.SaveMetadata(context.Background(), state.BuildMetadata(priorResolved, priorBriefing, state.ArtifactPaths{
-		Briefing:       priorBriefingPath,
-		ModuleSnapshot: priorPaths.ModuleSnapshot,
-		Metadata:       priorPaths.Metadata,
-		DataPackage:    priorPaths.DataPackage,
-		Preflight:      priorPaths.Preflight,
-		RenderedReport: priorPaths.RenderedReport,
-	}))
-	if err != nil {
-		t.Fatalf("SaveMetadata() error = %v", err)
-	}
+	savePriorRun(t, store, priorResolved, priorBriefing, priorDailyModuleSnapshot(t, priorResolved))

 	currentResolved, err := ResolveGenerate(GenerateRequest{
 		Config: cfg,
@@ -771,25 +754,7 @@ func TestTomorrowReportCanCompareAgainstPriorDailySnapshot(t *testing.T) {
 		t.Fatalf("ResolveGenerate(prior) error = %v", err)
 	}
 	priorBriefing := priorDailyBriefing(priorResolved)
-	priorBriefingPath, err := store.SaveBriefing(context.Background(), priorResolved, priorBriefing)
-	if err != nil {
-		t.Fatalf("SaveBriefing() error = %v", err)
-	}
-	priorPaths, err := store.Paths(priorResolved)
-	if err != nil {
-		t.Fatalf("Paths() error = %v", err)
-	}
-	_, err = store.SaveMetadata(context.Background(), state.BuildMetadata(priorResolved, priorBriefing, state.ArtifactPaths{
-		Briefing:       priorBriefingPath,
-		ModuleSnapshot: priorPaths.ModuleSnapshot,
-		Metadata:       priorPaths.Metadata,
-		DataPackage:    priorPaths.DataPackage,
-		Preflight:      priorPaths.Preflight,
-		RenderedReport: priorPaths.RenderedReport,
-	}))
-	if err != nil {
-		t.Fatalf("SaveMetadata() error = %v", err)
-	}
+	savePriorRun(t, store, priorResolved, priorBriefing, priorDailyModuleSnapshot(t, priorResolved))

 	currentResolved, err := ResolveGenerate(GenerateRequest{
 		Config: cfg,
@@ -839,25 +804,7 @@ func TestGenerateThreeDayReportWritesReportAndRecentChanges(t *testing.T) {
 		t.Fatalf("ResolveGenerate(prior) error = %v", err)
 	}
 	priorBriefing := priorThreeDayBriefing(priorResolved)
-	priorBriefingPath, err := store.SaveBriefing(context.Background(), priorResolved, priorBriefing)
-	if err != nil {
-		t.Fatalf("SaveBriefing() error = %v", err)
-	}
-	priorPaths, err := store.Paths(priorResolved)
-	if err != nil {
-		t.Fatalf("Paths() error = %v", err)
-	}
-	_, err = store.SaveMetadata(context.Background(), state.BuildMetadata(priorResolved, priorBriefing, state.ArtifactPaths{
-		Briefing:       priorBriefingPath,
-		ModuleSnapshot: priorPaths.ModuleSnapshot,
-		Metadata:       priorPaths.Metadata,
-		DataPackage:    priorPaths.DataPackage,
-		Preflight:      priorPaths.Preflight,
-		RenderedReport: priorPaths.RenderedReport,
-	}))
-	if err != nil {
-		t.Fatalf("SaveMetadata() error = %v", err)
-	}
+	savePriorRun(t, store, priorResolved, priorBriefing, priorOutlookModuleSnapshot(t, "2026-05-30"))
 	currentResolved, err := ResolveGenerate(GenerateRequest{
 		Config: cfg,
 		Report: ReportThreeDay,
@@ -916,25 +863,7 @@ func TestGenerateWeekendReportWritesReportAndRecentChanges(t *testing.T) {
 		t.Fatalf("ResolveGenerate(prior) error = %v", err)
 	}
 	priorBriefing := priorWeekendBriefing(priorResolved)
-	priorBriefingPath, err := store.SaveBriefing(context.Background(), priorResolved, priorBriefing)
-	if err != nil {
-		t.Fatalf("SaveBriefing() error = %v", err)
-	}
-	priorPaths, err := store.Paths(priorResolved)
-	if err != nil {
-		t.Fatalf("Paths() error = %v", err)
-	}
-	_, err = store.SaveMetadata(context.Background(), state.BuildMetadata(priorResolved, priorBriefing, state.ArtifactPaths{
-		Briefing:       priorBriefingPath,
-		ModuleSnapshot: priorPaths.ModuleSnapshot,
-		Metadata:       priorPaths.Metadata,
-		DataPackage:    priorPaths.DataPackage,
-		Preflight:      priorPaths.Preflight,
-		RenderedReport: priorPaths.RenderedReport,
-	}))
-	if err != nil {
-		t.Fatalf("SaveMetadata() error = %v", err)
-	}
+	savePriorRun(t, store, priorResolved, priorBriefing, priorOutlookModuleSnapshot(t, "2026-05-30"))
 	currentResolved, err := ResolveGenerate(GenerateRequest{
 		Config: cfg,
 		Report: ReportWeekend,
@@ -1475,6 +1404,82 @@ func priorDailyBriefing(resolved report.Resolved) briefing.Package {
 	}
 }

+func savePriorRun(t *testing.T, store state.Store, resolved report.Resolved, briefingPackage briefing.Package, snapshot module.Snapshot) {
+	t.Helper()
+	briefingPath, err := store.SaveBriefing(context.Background(), resolved, briefingPackage)
+	if err != nil {
+		t.Fatalf("SaveBriefing() error = %v", err)
+	}
+	moduleSnapshotPath, err := store.SaveModuleSnapshot(context.Background(), resolved, snapshot)
+	if err != nil {
+		t.Fatalf("SaveModuleSnapshot() error = %v", err)
+	}
+	paths, err := store.Paths(resolved)
+	if err != nil {
+		t.Fatalf("Paths() error = %v", err)
+	}
+	_, err = store.SaveMetadata(context.Background(), state.BuildMetadata(resolved, briefingPackage, state.ArtifactPaths{
+		Briefing:       briefingPath,
+		ModuleSnapshot: moduleSnapshotPath,
+		Metadata:       paths.Metadata,
+		DataPackage:    paths.DataPackage,
+		Preflight:      paths.Preflight,
+		RenderedReport: paths.RenderedReport,
+	}))
+	if err != nil {
+		t.Fatalf("SaveMetadata() error = %v", err)
+	}
+}
+
+func priorDailyModuleSnapshot(t *testing.T, resolved report.Resolved) module.Snapshot {
+	t.Helper()
+	low := 50
+	high := 58
+	precip := 10
+	snapshot, err := module.NewSnapshot([]module.Output{
+		{ID: module.DerivedDailySummary, StanzaName: "derived_daily_summary", Value: map[string]any{
+			"date":            resolved.ValidPeriod.Start.Format(timeutil.DateLayout),
+			"low_temp_f":      low,
+			"high_temp_f":     high,
+			"max_pop_percent": precip,
+		}},
+		{ID: module.DerivedDaypartSummaries, StanzaName: "derived_daypart_summaries", Value: map[string]any{
+			"morning": map[string]any{
+				"period":       timeutil.Period{Start: resolved.ValidPeriod.Start.Add(6 * time.Hour), End: resolved.ValidPeriod.Start.Add(10 * time.Hour)},
+				"temp_range_f": "50-58",
+			},
+		}},
+		{ID: module.PrecipTiming, StanzaName: "precip_timing", Value: map[string]any{
+			"max_pop_percent": precip,
+			"max_pop_time":    "6 AM",
+		}},
+		{ID: module.AlertDigest, StanzaName: "alert_digest", Value: map[string]any{}},
+	})
+	if err != nil {
+		t.Fatalf("NewSnapshot() error = %v", err)
+	}
+	return snapshot
+}
+
+func priorOutlookModuleSnapshot(t *testing.T, date string) module.Snapshot {
+	t.Helper()
+	precip := 10
+	snapshot, err := module.NewSnapshot([]module.Output{
+		{ID: module.DerivedDaypartSummaries, StanzaName: "derived_daypart_summaries", Value: map[string]any{
+			date + "_morning": map[string]any{
+				"period":          timeutil.Period{Start: mustParse(date + "T06:00:00Z"), End: mustParse(date + "T10:00:00Z")},
+				"temp_range_f":    "50-58",
+				"max_pop_percent": precip,
+				"max_pop_time":    "6 AM",
+			},
+		}},
+	})
+	if err != nil {
+		t.Fatalf("NewSnapshot() error = %v", err)
+	}
+	return snapshot
+}
+
 func priorThreeDayBriefing(resolved report.Resolved) briefing.Package {
 	high := 58.0
 	precip := 10.0
--- a/internal/changes/daily.go
+++ b/internal/changes/daily.go
@@ -1,14 +1,16 @@
-// Package changes compares structured briefing snapshots.
+// Package changes compares structured module snapshots.
 package changes

 import (
 	"fmt"
 	"math"
 	"sort"
+	"strconv"
+	"strings"
 	"time"

-	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/forecast"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
 )

 type Thresholds struct {
@@ -25,83 +27,168 @@ type Change struct {
 	Current  string `json:"current,omitempty"`
 }

-func CompareDaily(previous briefing.Package, current briefing.Package, thresholds Thresholds) ([]Change, error) {
-	if previous.Daily == nil {
-		return nil, fmt.Errorf("previous daily briefing is required")
+func CompareDaily(previous module.Snapshot, current module.Snapshot, thresholds Thresholds) ([]Change, error) {
+	previousSummary, err := requiredStanza[dailySummaryStanza](previous, "derived_daily_summary")
+	if err != nil {
+		return nil, fmt.Errorf("previous daily summary: %w", err)
 	}
-	if current.Daily == nil {
-		return nil, fmt.Errorf("current daily briefing is required")
+	currentSummary, err := requiredStanza[dailySummaryStanza](current, "derived_daily_summary")
+	if err != nil {
+		return nil, fmt.Errorf("current daily summary: %w", err)
 	}
+	previousDayparts, err := requiredStanza[map[string]daypartSummaryStanza](previous, "derived_daypart_summaries")
+	if err != nil {
+		return nil, fmt.Errorf("previous daypart summaries: %w", err)
+	}
+	currentDayparts, err := requiredStanza[map[string]daypartSummaryStanza](current, "derived_daypart_summaries")
+	if err != nil {
+		return nil, fmt.Errorf("current daypart summaries: %w", err)
+	}
+	previousAlerts, _, err := module.StanzaValue[alertDigestStanza](previous, "alert_digest")
+	if err != nil {
+		return nil, err
+	}
+	currentAlerts, _, err := module.StanzaValue[alertDigestStanza](current, "alert_digest")
+	if err != nil {
+		return nil, err
+	}
+	previousTiming, previousHasTiming, err := module.StanzaValue[precipTimingStanza](previous, "precip_timing")
+	if err != nil {
+		return nil, err
+	}
+	currentTiming, currentHasTiming, err := module.StanzaValue[precipTimingStanza](current, "precip_timing")
+	if err != nil {
+		return nil, err
+	}
+
 	var changes []Change
-	changes = append(changes, compareTemperature(previous.Daily.BottomLine.Temperature, current.Daily.BottomLine.Temperature, thresholds.TemperatureDegrees)...)
-	changes = append(changes, comparePrecipitation(previous.Daily.BottomLine.MaxPrecipProbability, current.Daily.BottomLine.MaxPrecipProbability, thresholds)...)
-	changes = append(changes, compareWind(previous.Daily.BottomLine.PeakWindGust, current.Daily.BottomLine.PeakWindGust, float64(thresholds.WindGustMilesPerHour))...)
-	changes = append(changes, compareAlerts(previous.Daily.RelevantAlerts, current.Daily.RelevantAlerts)...)
-	changes = append(changes, compareIndicators(aggregateIndicators(previous.Daily.Dayparts), aggregateIndicators(current.Daily.Dayparts))...)
+	changes = append(changes, compareTemperatureValues("Low", previousSummary.LowTempF, currentSummary.LowTempF, thresholds.TemperatureDegrees)...)
+	changes = append(changes, compareTemperatureValues("High", previousSummary.HighTempF, currentSummary.HighTempF, thresholds.TemperatureDegrees)...)
+	changes = append(changes, comparePrecipitationValues(previousSummary.MaxPopPercent, currentSummary.MaxPopPercent, thresholds.PrecipProbabilityPoints, "")...)
+	if previousHasTiming && currentHasTiming {
+		changes = append(changes, comparePrecipTiming(previousTiming.MaxPopTime, currentTiming.MaxPopTime, thresholds.PrecipTimingShiftMinutes, "")...)
+	}
+	changes = append(changes, compareWindValues(previousSummary.MaxWindGustMph, currentSummary.MaxWindGustMph, thresholds.WindGustMilesPerHour, "")...)
+	changes = append(changes, compareAlerts(previousAlerts.Relevant, currentAlerts.Relevant)...)
+	changes = append(changes, compareIndicators(aggregateIndicators(previousDayparts), aggregateIndicators(currentDayparts), "")...)
+	sortChanges(changes)
 	return changes, nil
 }

-func compareTemperature(previous forecast.Range, current forecast.Range, threshold float64) []Change {
-	var changes []Change
-	if previous.Min != nil && current.Min != nil && differenceAtLeast(*previous.Min, *current.Min, threshold) {
-		changes = append(changes, Change{
-			Type:     "temperature_shift",
-			Message:  fmt.Sprintf("Low temperature changed from %.0f to %.0f.", *previous.Min, *current.Min),
-			Previous: fmt.Sprintf("%.0f", *previous.Min),
-			Current:  fmt.Sprintf("%.0f", *current.Min),
-		})
-	}
-	if previous.Max != nil && current.Max != nil && differenceAtLeast(*previous.Max, *current.Max, threshold) {
-		changes = append(changes, Change{
-			Type:     "temperature_shift",
-			Message:  fmt.Sprintf("High temperature changed from %.0f to %.0f.", *previous.Max, *current.Max),
-			Previous: fmt.Sprintf("%.0f", *previous.Max),
-			Current:  fmt.Sprintf("%.0f", *current.Max),
-		})
-	}
-	return changes
+type dailySummaryStanza struct {
+	Date           string `json:"date,omitempty"`
+	HighTempF      *int   `json:"high_temp_f,omitempty"`
+	LowTempF       *int   `json:"low_temp_f,omitempty"`
+	MaxPopPercent  *int   `json:"max_pop_percent,omitempty"`
+	MaxWindGustMph *int   `json:"max_wind_gust_mph,omitempty"`
 }

-func comparePrecipitation(previous *forecast.TimedValue, current *forecast.TimedValue, thresholds Thresholds) []Change {
+type daypartSummaryStanza struct {
+	Period         timeutil.Period `json:"period"`
+	TempRangeF     string          `json:"temp_range_f,omitempty"`
+	MaxPopPercent  *int            `json:"max_pop_percent,omitempty"`
+	MaxPopTime     string          `json:"max_pop_time,omitempty"`
+	MaxWindGustMph *int            `json:"max_wind_gust_mph,omitempty"`
+	Snow           bool            `json:"snow,omitempty"`
+	Ice            bool            `json:"ice,omitempty"`
+}
+
+type precipTimingStanza struct {
+	MaxPopPercent *int   `json:"max_pop_percent,omitempty"`
+	MaxPopTime    string `json:"max_pop_time,omitempty"`
+}
+
+type alertDigestStanza struct {
+	Relevant []alertSummaryStanza `json:"relevant,omitempty"`
+}
+
+type alertSummaryStanza struct {
+	Event    string `json:"event,omitempty"`
+	Headline string `json:"headline,omitempty"`
+}
+
+type indicators struct {
+	Snow bool
+	Ice  bool
+}
+
+func requiredStanza[T any](snapshot module.Snapshot, name string) (T, error) {
+	value, ok, err := module.StanzaValue[T](snapshot, name)
+	if err != nil {
+		return value, err
+	}
+	if !ok {
+		return value, fmt.Errorf("stanza %q is required", name)
+	}
+	return value, nil
+}
+
+func compareTemperatureValues(label string, previous *int, current *int, threshold float64) []Change {
 	if previous == nil || current == nil {
 		return nil
 	}
-	var changes []Change
-	previousCategory := precipitationCategory(previous.Value)
-	currentCategory := precipitationCategory(current.Value)
-	if previousCategory != currentCategory || differenceAtLeast(previous.Value, current.Value, float64(thresholds.PrecipProbabilityPoints)) {
-		changes = append(changes, Change{
-			Type:     "precip_probability_change",
-			Message:  fmt.Sprintf("Peak precipitation chance changed from %.0f%% (%s) to %.0f%% (%s).", previous.Value, previousCategory, current.Value, currentCategory),
-			Previous: fmt.Sprintf("%.0f%% %s", previous.Value, previousCategory),
-			Current:  fmt.Sprintf("%.0f%% %s", current.Value, currentCategory),
-		})
-	}
-	shiftMinutes := int(math.Abs(current.Time.Sub(previous.Time).Minutes()))
-	if thresholds.PrecipTimingShiftMinutes > 0 && shiftMinutes >= thresholds.PrecipTimingShiftMinutes {
-		changes = append(changes, Change{
-			Type:     "precip_timing_shift",
-			Message:  fmt.Sprintf("Peak precipitation timing shifted from %s to %s.", clock(previous.Time), clock(current.Time)),
-			Previous: clock(previous.Time),
-			Current:  clock(current.Time),
-		})
-	}
-	return changes
-}
-
-func compareWind(previous *forecast.TimedValue, current *forecast.TimedValue, threshold float64) []Change {
-	if previous == nil || current == nil || !differenceAtLeast(previous.Value, current.Value, threshold) {
+	if !differenceAtLeast(float64(*previous), float64(*current), threshold) {
 		return nil
 	}
 	return []Change{{
-		Type:     "wind_gust_change",
-		Message:  fmt.Sprintf("Peak wind gust changed from %.0f mph to %.0f mph.", previous.Value, current.Value),
-		Previous: fmt.Sprintf("%.0f mph", previous.Value),
-		Current:  fmt.Sprintf("%.0f mph", current.Value),
+		Type:     "temperature_shift",
+		Message:  fmt.Sprintf("%s temperature changed from %d to %d.", label, *previous, *current),
+		Previous: fmt.Sprintf("%d", *previous),
+		Current:  fmt.Sprintf("%d", *current),
 	}}
 }

-func compareAlerts(previous []forecast.AlertOverlap, current []forecast.AlertOverlap) []Change {
+func comparePrecipitationValues(previous *int, current *int, threshold int, prefix string) []Change {
+	if previous == nil || current == nil {
+		return nil
+	}
+	previousCategory := precipitationCategory(float64(*previous))
+	currentCategory := precipitationCategory(float64(*current))
+	if previousCategory == currentCategory && !differenceAtLeast(float64(*previous), float64(*current), float64(threshold)) {
+		return nil
+	}
+	changeType := prefix + "precip_probability_change"
+	return []Change{{
+		Type:     changeType,
+		Message:  fmt.Sprintf("Peak precipitation chance changed from %d%% (%s) to %d%% (%s).", *previous, previousCategory, *current, currentCategory),
+		Previous: fmt.Sprintf("%d%% %s", *previous, previousCategory),
+		Current:  fmt.Sprintf("%d%% %s", *current, currentCategory),
+	}}
+}
+
+func comparePrecipTiming(previous string, current string, thresholdMinutes int, prefix string) []Change {
+	if thresholdMinutes <= 0 || previous == "" || current == "" || previous == current {
+		return nil
+	}
+	previousTime, previousOK := parseClock(previous)
+	currentTime, currentOK := parseClock(current)
+	if !previousOK || !currentOK {
+		return nil
+	}
+	if int(math.Abs(currentTime.Sub(previousTime).Minutes())) < thresholdMinutes {
+		return nil
+	}
+	return []Change{{
+		Type:     prefix + "precip_timing_shift",
+		Message:  fmt.Sprintf("Peak precipitation timing shifted from %s to %s.", previous, current),
+		Previous: previous,
+		Current:  current,
+	}}
+}
+
+func compareWindValues(previous *int, current *int, threshold int, prefix string) []Change {
+	if previous == nil || current == nil || !differenceAtLeast(float64(*previous), float64(*current), float64(threshold)) {
+		return nil
+	}
+	return []Change{{
+		Type:     prefix + "wind_gust_change",
+		Message:  fmt.Sprintf("Peak wind gust changed from %d mph to %d mph.", *previous, *current),
+		Previous: fmt.Sprintf("%d mph", *previous),
+		Current:  fmt.Sprintf("%d mph", *current),
+	}}
+}
+
+func compareAlerts(previous []alertSummaryStanza, current []alertSummaryStanza) []Change {
 	previousSet := alertSet(previous)
 	currentSet := alertSet(current)
 	var changes []Change
@@ -119,7 +206,7 @@ func compareAlerts(previous []forecast.AlertOverlap, current []forecast.AlertOve
 	return changes
 }

-func compareIndicators(previous forecast.Indicators, current forecast.Indicators) []Change {
+func compareIndicators(previous indicators, current indicators, prefix string) []Change {
 	var changes []Change
 	for _, item := range []struct {
 		name     string
@@ -132,7 +219,7 @@ func compareIndicators(previous forecast.Indicators, current forecast.Indicators
 		if item.previous == item.current {
 			continue
 		}
-		changeType := item.name + "_risk_change"
+		changeType := prefix + item.name + "_risk_change"
 		if item.current {
 			changes = append(changes, Change{Type: changeType, Message: fmt.Sprintf("%s risk is now present.", item.name), Current: "present"})
 		} else {
@@ -142,16 +229,16 @@ func compareIndicators(previous forecast.Indicators, current forecast.Indicators
 	return changes
 }

-func aggregateIndicators(dayparts []forecast.DaypartSummary) forecast.Indicators {
-	out := forecast.Indicators{}
+func aggregateIndicators(dayparts map[string]daypartSummaryStanza) indicators {
+	out := indicators{}
 	for _, daypart := range dayparts {
-		out.Snow = out.Snow || daypart.Indicators.Snow
-		out.Ice = out.Ice || daypart.Indicators.Ice
+		out.Snow = out.Snow || daypart.Snow
+		out.Ice = out.Ice || daypart.Ice
 	}
 	return out
 }

-func alertSet(alerts []forecast.AlertOverlap) map[string]struct{} {
+func alertSet(alerts []alertSummaryStanza) map[string]struct{} {
 	out := map[string]struct{}{}
 	for _, alert := range alerts {
 		event := alert.Event
@@ -185,10 +272,6 @@ func differenceAtLeast(previous float64, current float64, threshold float64) boo
 	return math.Abs(current-previous) >= threshold
 }

-func clock(t time.Time) string {
-	return t.Format("15:04")
-}
-
 func sortChanges(items []Change) {
 	sort.SliceStable(items, func(i, j int) bool {
 		if items[i].Type == items[j].Type {
@@ -197,3 +280,33 @@ func sortChanges(items []Change) {
 		return items[i].Type < items[j].Type
 	})
 }
+
+func parseClock(value string) (time.Time, bool) {
+	value = strings.TrimSpace(value)
+	for _, layout := range []string{"3 PM", "3:04 PM", "15:04"} {
+		if parsed, err := time.Parse(layout, value); err == nil {
+			return parsed, true
+		}
+	}
+	return time.Time{}, false
+}
+
+func parseTempRange(value string) (*int, *int) {
+	value = strings.TrimSpace(value)
+	if value == "" {
+		return nil, nil
+	}
+	parts := strings.Split(value, "-")
+	if len(parts) == 1 {
+		if parsed, err := strconv.Atoi(strings.TrimSpace(parts[0])); err == nil {
+			return &parsed, &parsed
+		}
+		return nil, nil
+	}
+	minValue, minErr := strconv.Atoi(strings.TrimSpace(parts[0]))
+	maxValue, maxErr := strconv.Atoi(strings.TrimSpace(parts[len(parts)-1]))
+	if minErr != nil || maxErr != nil {
+		return nil, nil
+	}
+	return &minValue, &maxValue
+}
--- a/internal/changes/daily_test.go
+++ b/internal/changes/daily_test.go
@@ -1,16 +1,17 @@
 package changes

 import (
+	"strings"
 	"testing"
 	"time"

-	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/forecast"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
 )

 func TestCompareDailyNoMeaningfulChanges(t *testing.T) {
-	previous := dailyBriefing(60, 70, 30, at("2026-05-29T08:00:00Z"), nil, forecast.Indicators{})
-	current := dailyBriefing(61, 71, 35, at("2026-05-29T08:30:00Z"), nil, forecast.Indicators{})
+	previous := dailySnapshot(t, 60, 70, 30, "8 AM", nil, false)
+	current := dailySnapshot(t, 61, 71, 35, "8:30 AM", nil, false)

 	changes, err := CompareDaily(previous, current, testThresholds())
 	if err != nil {
@@ -22,8 +23,8 @@ func TestCompareDailyNoMeaningfulChanges(t *testing.T) {
 }

 func TestCompareDailyTemperatureThreshold(t *testing.T) {
-	previous := dailyBriefing(50, 70, 10, at("2026-05-29T08:00:00Z"), nil, forecast.Indicators{})
-	current := dailyBriefing(58, 79, 10, at("2026-05-29T08:00:00Z"), nil, forecast.Indicators{})
+	previous := dailySnapshot(t, 50, 70, 10, "8 AM", nil, false)
+	current := dailySnapshot(t, 58, 79, 10, "8 AM", nil, false)

 	changes, err := CompareDaily(previous, current, testThresholds())
 	if err != nil {
@@ -35,8 +36,8 @@ func TestCompareDailyTemperatureThreshold(t *testing.T) {
 }

 func TestCompareDailyPrecipTimingShift(t *testing.T) {
-	previous := dailyBriefing(60, 70, 60, at("2026-05-29T08:00:00Z"), nil, forecast.Indicators{})
-	current := dailyBriefing(60, 70, 60, at("2026-05-29T11:00:00Z"), nil, forecast.Indicators{})
+	previous := dailySnapshot(t, 60, 70, 60, "8 AM", nil, false)
+	current := dailySnapshot(t, 60, 70, 60, "11 AM", nil, false)

 	changes, err := CompareDaily(previous, current, testThresholds())
 	if err != nil {
@@ -48,8 +49,8 @@ func TestCompareDailyPrecipTimingShift(t *testing.T) {
 }

 func TestCompareDailyAlertAddedAndRemoved(t *testing.T) {
-	previous := dailyBriefing(60, 70, 10, at("2026-05-29T08:00:00Z"), []string{"Wind Advisory"}, forecast.Indicators{})
-	current := dailyBriefing(60, 70, 10, at("2026-05-29T08:00:00Z"), []string{"Flood Watch"}, forecast.Indicators{})
+	previous := dailySnapshot(t, 60, 70, 10, "8 AM", []string{"Wind Advisory"}, false)
+	current := dailySnapshot(t, 60, 70, 10, "8 AM", []string{"Flood Watch"}, false)

 	changes, err := CompareDaily(previous, current, testThresholds())
 	if err != nil {
@@ -61,8 +62,8 @@ func TestCompareDailyAlertAddedAndRemoved(t *testing.T) {
 }

 func TestCompareDailyIndicatorChange(t *testing.T) {
-	previous := dailyBriefing(60, 70, 10, at("2026-05-29T08:00:00Z"), nil, forecast.Indicators{})
-	current := dailyBriefing(60, 70, 10, at("2026-05-29T08:00:00Z"), nil, forecast.Indicators{Snow: true})
+	previous := dailySnapshot(t, 60, 70, 10, "8 AM", nil, false)
+	current := dailySnapshot(t, 60, 70, 10, "8 AM", nil, true)

 	changes, err := CompareDaily(previous, current, testThresholds())
 	if err != nil {
@@ -73,26 +74,48 @@ func TestCompareDailyIndicatorChange(t *testing.T) {
 	}
 }

-func dailyBriefing(low float64, high float64, precip float64, precipTime time.Time, alerts []string, indicators forecast.Indicators) briefing.Package {
-	alertOverlaps := make([]forecast.AlertOverlap, 0, len(alerts))
+func TestCompareDailyRequiresComparisonStanzas(t *testing.T) {
+	_, err := CompareDaily(snapshot(t), dailySnapshot(t, 60, 70, 10, "8 AM", nil, false), testThresholds())
+	if err == nil {
+		t.Fatal("CompareDaily() error = nil, want missing stanza error")
+	}
+	if !strings.Contains(err.Error(), "derived_daily_summary") {
+		t.Fatalf("error = %q, want derived_daily_summary context", err.Error())
+	}
+}
+
+func dailySnapshot(t *testing.T, low int, high int, precip int, precipTime string, alerts []string, snow bool) module.Snapshot {
+	t.Helper()
+	relevant := make([]alertSummaryStanza, 0, len(alerts))
 	for _, alert := range alerts {
-		alertOverlaps = append(alertOverlaps, forecast.AlertOverlap{Event: alert})
+		relevant = append(relevant, alertSummaryStanza{Event: alert})
 	}
-	return briefing.Package{
-		Daily: &briefing.Daily{
-			BottomLine: briefing.BottomLine{
-				Temperature: forecast.Range{Min: &low, Max: &high},
-				MaxPrecipProbability: &forecast.TimedValue{
-					Value: precip,
-					Time:  precipTime,
-				},
-			},
-			RelevantAlerts: alertOverlaps,
-			Dayparts: []forecast.DaypartSummary{
-				{Name: "morning", Indicators: indicators},
-			},
-		},
+	return snapshot(t,
+		module.Output{ID: module.DerivedDailySummary, StanzaName: "derived_daily_summary", Value: dailySummaryStanza{
+			Date:          "2026-05-29",
+			HighTempF:     &high,
+			LowTempF:      &low,
+			MaxPopPercent: &precip,
+		}},
+		module.Output{ID: module.DerivedDaypartSummaries, StanzaName: "derived_daypart_summaries", Value: map[string]daypartSummaryStanza{
+			"morning": {Period: period("2026-05-29T06:00:00Z", "2026-05-29T10:00:00Z"), TempRangeF: "60-70", Snow: snow},
+		}},
+		module.Output{ID: module.PrecipTiming, StanzaName: "precip_timing", Value: precipTimingStanza{MaxPopPercent: &precip, MaxPopTime: precipTime}},
+		module.Output{ID: module.AlertDigest, StanzaName: "alert_digest", Value: alertDigestStanza{Relevant: relevant}},
+	)
+}
+
+func snapshot(t *testing.T, outputs ...module.Output) module.Snapshot {
+	t.Helper()
+	snapshot, err := module.NewSnapshot(outputs)
+	if err != nil {
+		t.Fatalf("NewSnapshot() error = %v", err)
 	}
+	return snapshot
+}
+
+func period(start string, end string) timeutil.Period {
+	return timeutil.Period{Start: at(start), End: at(end)}
 }

 func testThresholds() Thresholds {
--- a/internal/changes/three_day.go
+++ b/internal/changes/three_day.go
@@ -2,77 +2,147 @@ package changes

 import (
 	"fmt"
-	"time"
+	"sort"

-	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
 )

-func CompareThreeDay(previous briefing.Package, current briefing.Package, thresholds Thresholds) ([]Change, error) {
-	if previous.ThreeDay == nil {
-		return nil, fmt.Errorf("previous 3-day briefing is required")
+func CompareThreeDay(previous module.Snapshot, current module.Snapshot, thresholds Thresholds) ([]Change, error) {
+	previousDayparts, err := requiredStanza[map[string]daypartSummaryStanza](previous, "derived_daypart_summaries")
+	if err != nil {
+		return nil, fmt.Errorf("previous daypart summaries: %w", err)
 	}
-	if current.ThreeDay == nil {
-		return nil, fmt.Errorf("current 3-day briefing is required")
+	currentDayparts, err := requiredStanza[map[string]daypartSummaryStanza](current, "derived_daypart_summaries")
+	if err != nil {
+		return nil, fmt.Errorf("current daypart summaries: %w", err)
 	}
-	previousDays := outlookDaysByDate(previous.ThreeDay.Days)
-	currentDays := outlookDaysByDate(current.ThreeDay.Days)
+	previousDays := outlookDaysFromDayparts(previousDayparts)
+	currentDays := outlookDaysFromDayparts(currentDayparts)
+	return compareOutlookDays(previousDays, currentDays, thresholds, "")
+}
+
+type outlookDay struct {
+	Date           string
+	LowTempF       *int
+	HighTempF      *int
+	MaxPopPercent  *int
+	MaxPopTime     string
+	MaxWindGustMph *int
+	Indicators     indicators
+}
+
+func compareOutlookDays(previousDays map[string]outlookDay, currentDays map[string]outlookDay, thresholds Thresholds, prefix string) ([]Change, error) {
 	var changes []Change
 	for date, currentDay := range currentDays {
 		previousDay, ok := previousDays[date]
 		if !ok {
-			changes = append(changes, Change{Type: "outlook_day_added", Message: fmt.Sprintf("Outlook day added: %s.", date), Current: date})
+			changes = append(changes, Change{Type: prefix + "outlook_day_added", Message: fmt.Sprintf("Outlook day added: %s.", date), Current: date})
 			continue
 		}
-		changes = append(changes, compareOutlookDay(date, previousDay, currentDay, thresholds)...)
+		changes = append(changes, compareOutlookDay(date, previousDay, currentDay, thresholds, prefix)...)
 	}
 	for date := range previousDays {
 		if _, ok := currentDays[date]; !ok {
-			changes = append(changes, Change{Type: "outlook_day_removed", Message: fmt.Sprintf("Outlook day removed: %s.", date), Previous: date})
+			changes = append(changes, Change{Type: prefix + "outlook_day_removed", Message: fmt.Sprintf("Outlook day removed: %s.", date), Previous: date})
 		}
 	}
 	sortChanges(changes)
 	return changes, nil
 }

-func compareOutlookDay(date string, previous briefing.OutlookDay, current briefing.OutlookDay, thresholds Thresholds) []Change {
+func compareOutlookDay(date string, previous outlookDay, current outlookDay, thresholds Thresholds, prefix string) []Change {
 	var changes []Change
-	for _, change := range compareTemperature(previous.Temperature, current.Temperature, thresholds.TemperatureDegrees) {
+	for _, change := range compareTemperatureValues("Low", previous.LowTempF, current.LowTempF, thresholds.TemperatureDegrees) {
+		change.Message = date + ": " + change.Message
+		change.Type = prefix + "outlook_" + change.Type
+		changes = append(changes, change)
+	}
+	for _, change := range compareTemperatureValues("High", previous.HighTempF, current.HighTempF, thresholds.TemperatureDegrees) {
+		change.Message = date + ": " + change.Message
+		change.Type = prefix + "outlook_" + change.Type
+		changes = append(changes, change)
+	}
+	for _, change := range comparePrecipitationValues(previous.MaxPopPercent, current.MaxPopPercent, thresholds.PrecipProbabilityPoints, prefix+"outlook_") {
 		change.Message = date + ": " + change.Message
 		changes = append(changes, change)
 	}
-	for _, change := range comparePrecipitation(previous.MaxPrecipitationProbability, current.MaxPrecipitationProbability, thresholds) {
+	for _, change := range comparePrecipTiming(previous.MaxPopTime, current.MaxPopTime, thresholds.PrecipTimingShiftMinutes, prefix+"outlook_") {
 		change.Message = date + ": " + change.Message
 		changes = append(changes, change)
-		changes[len(changes)-1].Type = "outlook_" + change.Type
 	}
-	for _, change := range compareWind(previous.PeakWindGust, current.PeakWindGust, float64(thresholds.WindGustMilesPerHour)) {
+	for _, change := range compareWindValues(previous.MaxWindGustMph, current.MaxWindGustMph, thresholds.WindGustMilesPerHour, prefix+"outlook_") {
 		change.Message = date + ": " + change.Message
-		change.Type = "outlook_" + change.Type
 		changes = append(changes, change)
 	}
-	for _, change := range compareAlerts(previous.RelevantAlerts, current.RelevantAlerts) {
+	for _, change := range compareIndicators(previous.Indicators, current.Indicators, prefix+"outlook_") {
 		change.Message = date + ": " + change.Message
-		change.Type = "outlook_" + change.Type
-		changes = append(changes, change)
-	}
-	for _, change := range compareIndicators(aggregateIndicators(previous.Dayparts), aggregateIndicators(current.Dayparts)) {
-		change.Message = date + ": " + change.Message
-		change.Type = "outlook_" + change.Type
 		changes = append(changes, change)
 	}
 	return changes
 }

-func outlookDaysByDate(days []briefing.OutlookDay) map[string]briefing.OutlookDay {
-	out := map[string]briefing.OutlookDay{}
-	for _, day := range days {
-		date := day.Date
-		if date == "" && !day.Period.Start.IsZero() {
-			date = day.Period.Start.Format(time.DateOnly)
+func outlookDaysFromDayparts(dayparts map[string]daypartSummaryStanza) map[string]outlookDay {
+	out := map[string]outlookDay{}
+	var keys []string
+	for key := range dayparts {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		daypart := dayparts[key]
+		date := daypartDate(daypart)
+		if date == "" {
+			continue
 		}
-		if date != "" {
-			out[date] = day
+		day := out[date]
+		day.Date = date
+		low, high := parseTempRange(daypart.TempRangeF)
+		day.LowTempF = minInt(day.LowTempF, low)
+		day.HighTempF = maxInt(day.HighTempF, high)
+		day.MaxPopPercent = maxInt(day.MaxPopPercent, daypart.MaxPopPercent)
+		if daypart.MaxPopPercent != nil && day.MaxPopPercent != nil && *daypart.MaxPopPercent == *day.MaxPopPercent {
+			day.MaxPopTime = daypart.MaxPopTime
 		}
+		day.MaxWindGustMph = maxInt(day.MaxWindGustMph, daypart.MaxWindGustMph)
+		day.Indicators.Snow = day.Indicators.Snow || daypart.Snow
+		day.Indicators.Ice = day.Indicators.Ice || daypart.Ice
+		out[date] = day
 	}
 	return out
 }
+
+func daypartDate(daypart daypartSummaryStanza) string {
+	if !daypart.Period.Start.IsZero() {
+		return daypart.Period.Start.Format(timeutil.DateLayout)
+	}
+	return ""
+}
+
+func minInt(a *int, b *int) *int {
+	if a == nil {
+		return copyInt(b)
+	}
+	if b != nil && *b < *a {
+		return copyInt(b)
+	}
+	return a
+}
+
+func maxInt(a *int, b *int) *int {
+	if a == nil {
+		return copyInt(b)
+	}
+	if b != nil && *b > *a {
+		return copyInt(b)
+	}
+	return a
+}
+
+func copyInt(value *int) *int {
+	if value == nil {
+		return nil
+	}
+	copied := *value
+	return &copied
+}
--- a/internal/changes/three_day_test.go
+++ b/internal/changes/three_day_test.go
@@ -2,41 +2,13 @@ package changes

 import (
 	"testing"
-	"time"

-	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/forecast"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
 )

 func TestCompareThreeDayDetectsDayChanges(t *testing.T) {
-	previousTemp := 70.0
-	currentTemp := 78.0
-	previousPrecip := 20.0
-	currentPrecip := 70.0
-	previous := briefing.Package{
-		Metadata: briefing.Metadata{ReportID: report.ThreeDay},
-		ThreeDay: &briefing.ThreeDay{Days: []briefing.OutlookDay{{
-			Date:        "2026-05-29",
-			Temperature: forecast.Range{Max: &previousTemp},
-			MaxPrecipitationProbability: &forecast.TimedValue{
-				Value: previousPrecip,
-				Time:  time.Date(2026, 5, 29, 9, 0, 0, 0, time.UTC),
-			},
-		}}},
-	}
-	current := briefing.Package{
-		Metadata: briefing.Metadata{ReportID: report.ThreeDay},
-		ThreeDay: &briefing.ThreeDay{Days: []briefing.OutlookDay{{
-			Date:        "2026-05-29",
-			Temperature: forecast.Range{Max: &currentTemp},
-			MaxPrecipitationProbability: &forecast.TimedValue{
-				Value: currentPrecip,
-				Time:  time.Date(2026, 5, 29, 12, 0, 0, 0, time.UTC),
-			},
-			Dayparts: []forecast.DaypartSummary{{Indicators: forecast.Indicators{Snow: true}}},
-		}}},
-	}
+	previous := outlookSnapshot(t, "2026-05-29", "70", 20, "9 AM", false)
+	current := outlookSnapshot(t, "2026-05-29", "78", 70, "12 PM", true)

 	changes, err := CompareThreeDay(previous, current, Thresholds{
 		TemperatureDegrees:       5,
@@ -50,17 +22,20 @@ func TestCompareThreeDayDetectsDayChanges(t *testing.T) {
 	if len(changes) == 0 {
 		t.Fatal("changes length = 0, want detected 3-day changes")
 	}
-	var foundPrecip bool
-	var foundSnow bool
-	for _, change := range changes {
-		if change.Type == "outlook_precip_probability_change" {
-			foundPrecip = true
-		}
-		if change.Type == "outlook_snow_risk_change" {
-			foundSnow = true
-		}
-	}
-	if !foundPrecip || !foundSnow {
+	if countType(changes, "outlook_precip_probability_change") == 0 || countType(changes, "outlook_snow_risk_change") == 0 {
 		t.Fatalf("changes = %#v, want precipitation and snow changes", changes)
 	}
 }
+
+func outlookSnapshot(t *testing.T, date string, tempRange string, precip int, precipTime string, snow bool) module.Snapshot {
+	t.Helper()
+	return snapshot(t, module.Output{ID: module.DerivedDaypartSummaries, StanzaName: "derived_daypart_summaries", Value: map[string]daypartSummaryStanza{
+		date + "_morning": {
+			Period:        period(date+"T06:00:00Z", date+"T10:00:00Z"),
+			TempRangeF:    tempRange,
+			MaxPopPercent: &precip,
+			MaxPopTime:    precipTime,
+			Snow:          snow,
+		},
+	}})
+}
--- a/internal/changes/weekend.go
+++ b/internal/changes/weekend.go
@@ -3,24 +3,17 @@ package changes
 import (
 	"fmt"

-	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
 )

-func CompareWeekend(previous briefing.Package, current briefing.Package, thresholds Thresholds) ([]Change, error) {
-	if previous.Weekend == nil {
-		return nil, fmt.Errorf("previous weekend briefing is required")
-	}
-	if current.Weekend == nil {
-		return nil, fmt.Errorf("current weekend briefing is required")
-	}
-	previousOutlook := briefing.Package{ThreeDay: &briefing.ThreeDay{Days: previous.Weekend.Days}}
-	currentOutlook := briefing.Package{ThreeDay: &briefing.ThreeDay{Days: current.Weekend.Days}}
-	changes, err := CompareThreeDay(previousOutlook, currentOutlook, thresholds)
+func CompareWeekend(previous module.Snapshot, current module.Snapshot, thresholds Thresholds) ([]Change, error) {
+	previousDayparts, err := requiredStanza[map[string]daypartSummaryStanza](previous, "derived_daypart_summaries")
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("previous weekend daypart summaries: %w", err)
 	}
-	for i := range changes {
-		changes[i].Type = "weekend_" + changes[i].Type
+	currentDayparts, err := requiredStanza[map[string]daypartSummaryStanza](current, "derived_daypart_summaries")
+	if err != nil {
+		return nil, fmt.Errorf("current weekend daypart summaries: %w", err)
 	}
-	return changes, nil
+	return compareOutlookDays(outlookDaysFromDayparts(previousDayparts), outlookDaysFromDayparts(currentDayparts), thresholds, "weekend_")
 }
--- a/internal/changes/weekend_test.go
+++ b/internal/changes/weekend_test.go
@@ -1,31 +1,10 @@
 package changes

-import (
-	"testing"
-
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/forecast"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
-)
+import "testing"

 func TestCompareWeekendDetectsOutlookChanges(t *testing.T) {
-	previousTemp := 70.0
-	currentTemp := 78.0
-	previous := briefing.Package{
-		Metadata: briefing.Metadata{ReportID: report.Weekend},
-		Weekend: &briefing.Weekend{Days: []briefing.OutlookDay{{
-			Date:        "2026-05-30",
-			Temperature: forecast.Range{Max: &previousTemp},
-		}}},
-	}
-	current := briefing.Package{
-		Metadata: briefing.Metadata{ReportID: report.Weekend},
-		Weekend: &briefing.Weekend{Days: []briefing.OutlookDay{{
-			Date:        "2026-05-30",
-			Temperature: forecast.Range{Max: &currentTemp},
-			Dayparts:    []forecast.DaypartSummary{{Indicators: forecast.Indicators{Snow: true}}},
-		}}},
-	}
+	previous := outlookSnapshot(t, "2026-05-30", "70", 10, "9 AM", false)
+	current := outlookSnapshot(t, "2026-05-30", "78", 10, "9 AM", true)

 	changes, err := CompareWeekend(previous, current, Thresholds{TemperatureDegrees: 5})
 	if err != nil {
@@ -34,10 +13,7 @@ func TestCompareWeekendDetectsOutlookChanges(t *testing.T) {
 	if len(changes) == 0 {
 		t.Fatal("changes length = 0, want weekend changes")
 	}
-	for _, change := range changes {
-		if change.Type == "weekend_outlook_snow_risk_change" {
-			return
-		}
+	if countType(changes, "weekend_outlook_snow_risk_change") == 0 {
+		t.Fatalf("changes = %#v, want snow risk change", changes)
 	}
-	t.Fatalf("changes = %#v, want snow risk change", changes)
 }
--- a/internal/state/filesystem.go
+++ b/internal/state/filesystem.go
@@ -252,8 +252,9 @@ func (s *FilesystemStore) FindPriorSnapshot(_ context.Context, resolved report.R
 		return candidates[i].GeneratedAt.After(candidates[j].GeneratedAt)
 	})
 	return &PriorSnapshot{
-		Metadata:     candidates[0],
-		BriefingPath: candidates[0].BriefingPath,
+		Metadata:           candidates[0],
+		BriefingPath:       candidates[0].BriefingPath,
+		ModuleSnapshotPath: candidates[0].ModuleSnapshotPath,
 	}, nil
 }

--- a/internal/state/filesystem_test.go
+++ b/internal/state/filesystem_test.go
@@ -268,6 +268,9 @@ func TestFindPriorSnapshot(t *testing.T) {
 	if prior.BriefingPath != briefingPath {
 		t.Fatalf("BriefingPath = %q, want %q", prior.BriefingPath, briefingPath)
 	}
+	if prior.ModuleSnapshotPath != paths.ModuleSnapshot {
+		t.Fatalf("ModuleSnapshotPath = %q, want %q", prior.ModuleSnapshotPath, paths.ModuleSnapshot)
+	}
 }

 func TestFindPriorSnapshotUsesValidDate(t *testing.T) {
--- a/internal/state/store.go
+++ b/internal/state/store.go
@@ -27,8 +27,9 @@ type Store interface {
 }

 type PriorSnapshot struct {
-	Metadata     Metadata
-	BriefingPath string
+	Metadata           Metadata
+	BriefingPath       string
+	ModuleSnapshotPath string
 }

 type PreflightArtifact struct {