Implement source-oriented briefing modules

docs/internal/briefing.md

@@ -23,6 +23,8 @@ Outputs:
   object for Daily, 3-Day, Weekend, or Storm Report
 - module registry definitions for known module IDs, stanza names, option
   shapes, fact requirements, report compatibility, and missing-data behavior
+- source-oriented module outputs for `metadata`, `current_conditions`,
+  `alert_digest`, `area_forecast_discussion`, and `weather_story`
 - optional `currentConditions` prompt context from normalized
   `/conditions/current` data when available
 - optional structured `weatherStory` context on report-specific briefing
@@ -73,6 +75,10 @@ None. Builders either return a complete briefing package or an error.
   stanza names.
 - Module composition validation rejects unknown modules, duplicate modules,
   incompatible report/module combinations, and invalid typed options.
+- Source-oriented module builders omit missing optional current conditions,
+  forecast discussion, and weather story stanzas.
+- Alert digest output distinguishes checked empty alert data from missing alert
+  source data.
 - Save failures include path and operation context.
 
 ## Tests
@@ -83,6 +89,7 @@ Inspect:
 - `internal/briefing/three_day_test.go`
 - `internal/briefing/weekend_test.go`
 - `internal/briefing/storm_test.go`
+- `internal/briefing/base_modules_test.go`
 - `internal/briefing/modules_test.go`
 - `internal/app/app_test.go`
 

internal/briefing/base_modules.go

@@ -0,0 +1,236 @@
+package briefing
+
+import (
+	"time"
+
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/facts"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/forecast"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/weatherdata"
+)
+
+type MetadataModule struct {
+	RunID          string                 `json:"run_id"`
+	ReportID       report.ID              `json:"report_id"`
+	Variant        string                 `json:"variant,omitempty"`
+	PromptID       string                 `json:"prompt_id"`
+	GeneratedAt    time.Time              `json:"generated_at"`
+	Units          string                 `json:"units"`
+	Timezone       string                 `json:"timezone"`
+	ValidPeriod    timeutil.Period        `json:"valid_period"`
+	Location       *LocationContext       `json:"location,omitempty"`
+	SourceWarnings []SourceWarningSummary `json:"source_warnings,omitempty"`
+	Alerts         *AlertDigestModule     `json:"alerts,omitempty"`
+}
+
+type SourceWarningSummary struct {
+	Source             string `json:"source"`
+	Code               string `json:"code"`
+	Severity           string `json:"severity"`
+	Message            string `json:"message"`
+	CompletenessImpact string `json:"completeness_impact,omitempty"`
+}
+
+type CurrentConditionsModule struct {
+	ConditionText           string   `json:"condition_text,omitempty"`
+	IsDay                   *bool    `json:"is_day,omitempty"`
+	TemperatureC            *float64 `json:"temperature_c,omitempty"`
+	TemperatureF            *float64 `json:"temperature_f,omitempty"`
+	ApparentTemperatureC    *float64 `json:"apparent_temperature_c,omitempty"`
+	ApparentTemperatureF    *float64 `json:"apparent_temperature_f,omitempty"`
+	DewpointC               *float64 `json:"dewpoint_c,omitempty"`
+	DewpointF               *float64 `json:"dewpoint_f,omitempty"`
+	RelativeHumidityPercent *float64 `json:"relative_humidity_percent,omitempty"`
+	WindSpeedKmh            *float64 `json:"wind_speed_kmh,omitempty"`
+	WindSpeedMph            *float64 `json:"wind_speed_mph,omitempty"`
+	WindDirectionDegrees    *float64 `json:"wind_direction_degrees,omitempty"`
+}
+
+type AlertDigestModule struct {
+	Checked       bool           `json:"checked"`
+	ActiveCount   int            `json:"active_count"`
+	RelevantCount int            `json:"relevant_count"`
+	Missing       bool           `json:"missing,omitempty"`
+	Relevant      []AlertSummary `json:"relevant,omitempty"`
+}
+
+type AlertSummary struct {
+	Event    string `json:"event,omitempty"`
+	Headline string `json:"headline,omitempty"`
+	Severity string `json:"severity,omitempty"`
+}
+
+type AreaForecastDiscussionModule struct {
+	Product     string   `json:"product,omitempty"`
+	KeyMessages []string `json:"key_messages,omitempty"`
+	ShortTerm   string   `json:"short_term,omitempty"`
+	LongTerm    string   `json:"long_term,omitempty"`
+}
+
+type WeatherStoryModule struct {
+	Available   bool       `json:"available"`
+	OfficeID    string     `json:"office_id,omitempty"`
+	StartTime   time.Time  `json:"start_time"`
+	EndTime     time.Time  `json:"end_time"`
+	UpdatedAt   *time.Time `json:"updated_at,omitempty"`
+	Title       string     `json:"title,omitempty"`
+	Description string     `json:"description,omitempty"`
+	AltText     string     `json:"alt_text,omitempty"`
+	Priority    bool       `json:"priority"`
+	Order       int        `json:"order"`
+	DownloadURL string     `json:"download_url,omitempty"`
+}
+
+func buildMetadataModule(ctx ModuleContext, _ any) (*module.Output, error) {
+	metadata := ctx.Resolved.Metadata()
+	value := MetadataModule{
+		RunID:          metadata.RunID,
+		ReportID:       metadata.ReportID,
+		Variant:        variantForReport(metadata.ReportID),
+		PromptID:       metadata.PromptID,
+		GeneratedAt:    metadata.GeneratedAt,
+		Units:          ctx.Units,
+		Timezone:       ctx.Timezone,
+		ValidPeriod:    metadata.ValidPeriod,
+		Location:       copyLocation(ctx.Location),
+		SourceWarnings: sourceWarningSummaries(ctx.Collected.SourceWarnings),
+		Alerts:         alertDigest(ctx.Collected, ctx.Derived.AlertOverlaps),
+	}
+	return &module.Output{ID: module.Metadata, StanzaName: "metadata", Value: value}, nil
+}
+
+func buildCurrentConditionsModule(ctx ModuleContext, _ any) (*module.Output, error) {
+	current := ctx.Collected.Current
+	if current == nil {
+		return nil, nil
+	}
+	value := CurrentConditionsModule{
+		ConditionText:           current.ConditionText,
+		IsDay:                   copyBool(current.IsDay),
+		TemperatureC:            copyFloat(current.TemperatureC),
+		TemperatureF:            copyFloat(current.TemperatureF),
+		ApparentTemperatureC:    copyFloat(current.ApparentTemperatureC),
+		ApparentTemperatureF:    copyFloat(current.ApparentTemperatureF),
+		DewpointC:               copyFloat(current.DewpointC),
+		DewpointF:               copyFloat(current.DewpointF),
+		RelativeHumidityPercent: copyFloat(current.RelativeHumidityPercent),
+		WindSpeedKmh:            copyFloat(current.WindSpeedKmh),
+		WindSpeedMph:            copyFloat(current.WindSpeedMph),
+		WindDirectionDegrees:    copyFloat(current.WindDirectionDegrees),
+	}
+	if value.isEmpty() {
+		return nil, nil
+	}
+	return &module.Output{ID: module.CurrentConditions, StanzaName: "current_conditions", Value: value}, nil
+}
+
+func buildAlertDigestModule(ctx ModuleContext, _ any) (*module.Output, error) {
+	value := alertDigest(ctx.Collected, ctx.Derived.AlertOverlaps)
+	if value == nil {
+		value = &AlertDigestModule{}
+	}
+	return &module.Output{ID: module.AlertDigest, StanzaName: "alert_digest", Value: *value}, nil
+}
+
+func buildAreaForecastDiscussionModule(ctx ModuleContext, _ any) (*module.Output, error) {
+	discussion := ctx.Collected.Discussion
+	if discussion == nil {
+		return nil, nil
+	}
+	value := AreaForecastDiscussionModule{
+		Product:     discussion.Product,
+		KeyMessages: append([]string(nil), discussion.KeyMessages...),
+	}
+	if discussion.ShortTerm != nil {
+		value.ShortTerm = discussion.ShortTerm.Text
+	}
+	if discussion.LongTerm != nil {
+		value.LongTerm = discussion.LongTerm.Text
+	}
+	if value.Product == "" && len(value.KeyMessages) == 0 && value.ShortTerm == "" && value.LongTerm == "" {
+		return nil, nil
+	}
+	return &module.Output{ID: module.AreaForecastDiscussion, StanzaName: "area_forecast_discussion", Value: value}, nil
+}
+
+func buildWeatherStoryModule(ctx ModuleContext, _ any) (*module.Output, error) {
+	story := ctx.Collected.WeatherStory
+	if story == nil {
+		return nil, nil
+	}
+	value := WeatherStoryModule{
+		Available:   true,
+		OfficeID:    story.OfficeID,
+		StartTime:   story.StartTime,
+		EndTime:     story.EndTime,
+		UpdatedAt:   copyTime(story.UpdatedAt),
+		Title:       story.Title,
+		Description: story.Description,
+		AltText:     story.AltText,
+		Priority:    story.Priority,
+		Order:       story.Order,
+		DownloadURL: story.DownloadURL,
+	}
+	return &module.Output{ID: module.WeatherStory, StanzaName: "weather_story", Value: value}, nil
+}
+
+func sourceWarningSummaries(warnings []weatherdata.SourceWarning) []SourceWarningSummary {
+	out := make([]SourceWarningSummary, 0, len(warnings))
+	for _, warning := range warnings {
+		out = append(out, SourceWarningSummary{
+			Source:             warning.Source,
+			Code:               warning.Code,
+			Severity:           warning.Severity,
+			Message:            warning.Message,
+			CompletenessImpact: warning.CompletenessImpact,
+		})
+	}
+	return out
+}
+
+func alertDigest(collected facts.CollectedFacts, overlaps []forecast.AlertOverlap) *AlertDigestModule {
+	missing := sourceMissing(collected.SourceProvenance, "alerts")
+	if collected.Alerts == nil && !missing {
+		return nil
+	}
+	value := &AlertDigestModule{Missing: missing}
+	if collected.Alerts != nil {
+		value.Checked = true
+		value.ActiveCount = len(collected.Alerts.Alerts)
+	}
+	value.RelevantCount = len(overlaps)
+	for _, overlap := range overlaps {
+		value.Relevant = append(value.Relevant, AlertSummary{
+			Event:    overlap.Event,
+			Headline: overlap.Headline,
+			Severity: overlap.Severity,
+		})
+	}
+	return value
+}
+
+func sourceMissing(sources []weatherdata.Source, name string) bool {
+	for _, source := range sources {
+		if source.Name == name && source.Missing {
+			return true
+		}
+	}
+	return false
+}
+
+func (v CurrentConditionsModule) isEmpty() bool {
+	return v.ConditionText == "" &&
+		v.IsDay == nil &&
+		v.TemperatureC == nil &&
+		v.TemperatureF == nil &&
+		v.ApparentTemperatureC == nil &&
+		v.ApparentTemperatureF == nil &&
+		v.DewpointC == nil &&
+		v.DewpointF == nil &&
+		v.RelativeHumidityPercent == nil &&
+		v.WindSpeedKmh == nil &&
+		v.WindSpeedMph == nil &&
+		v.WindDirectionDegrees == nil
+}

internal/briefing/base_modules_test.go

@@ -0,0 +1,276 @@
+package briefing
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/facts"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/forecast"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/timeutil"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/weatherdata"
+)
+
+func TestBaseModulesBuildAvailableSourceOutputs(t *testing.T) {
+	registry := MustDefaultModuleRegistry()
+	ctx := testModuleContext()
+
+	tests := []struct {
+		id     module.ID
+		stanza string
+	}{
+		{id: module.Metadata, stanza: "metadata"},
+		{id: module.CurrentConditions, stanza: "current_conditions"},
+		{id: module.AlertDigest, stanza: "alert_digest"},
+		{id: module.AreaForecastDiscussion, stanza: "area_forecast_discussion"},
+		{id: module.WeatherStory, stanza: "weather_story"},
+	}
+	for _, tt := range tests {
+		t.Run(string(tt.id), func(t *testing.T) {
+			output, err := registry.BuildModule(ctx, module.ConfigItem{ID: tt.id})
+			if err != nil {
+				t.Fatalf("BuildModule() error = %v", err)
+			}
+			if output == nil {
+				t.Fatal("BuildModule() output = nil, want stanza")
+			}
+			if output.ID != tt.id || output.StanzaName != tt.stanza {
+				t.Fatalf("output = %#v, want id %q stanza %q", output, tt.id, tt.stanza)
+			}
+		})
+	}
+}
+
+func TestMetadataModuleUsesPromptSafeSourceWarningSummary(t *testing.T) {
+	registry := MustDefaultModuleRegistry()
+	ctx := testModuleContext()
+
+	output, err := registry.BuildModule(ctx, module.ConfigItem{ID: module.Metadata})
+	if err != nil {
+		t.Fatalf("BuildModule() error = %v", err)
+	}
+	value := moduleValue[MetadataModule](t, output)
+	if value.RunID == "" || value.ReportID != report.DailyToday || value.PromptID != "weather.daily_report" {
+		t.Fatalf("metadata = %#v, want report identity", value)
+	}
+	if value.Location == nil || value.Location.Name != "Brentwood" {
+		t.Fatalf("Location = %#v, want configured location", value.Location)
+	}
+	if len(value.SourceWarnings) != 1 || value.SourceWarnings[0].CompletenessImpact != "source omitted" {
+		t.Fatalf("SourceWarnings = %#v, want warning summary", value.SourceWarnings)
+	}
+	if value.Alerts == nil || !value.Alerts.Checked || value.Alerts.ActiveCount != 1 || value.Alerts.RelevantCount != 1 {
+		t.Fatalf("Alerts = %#v, want checked alert status", value.Alerts)
+	}
+	data, err := json.Marshal(output.Value)
+	if err != nil {
+		t.Fatalf("Marshal metadata: %v", err)
+	}
+	jsonText := string(data)
+	if !strings.Contains(jsonText, "source_warnings") || strings.Contains(jsonText, "endpoint") || strings.Contains(jsonText, "dataSha256") {
+		t.Fatalf("metadata json = %s, want source warning summary without transport provenance", jsonText)
+	}
+}
+
+func TestCurrentConditionsModuleUsesSnakeCaseUnitFields(t *testing.T) {
+	registry := MustDefaultModuleRegistry()
+	ctx := testModuleContext()
+
+	output, err := registry.BuildModule(ctx, module.ConfigItem{ID: module.CurrentConditions})
+	if err != nil {
+		t.Fatalf("BuildModule() error = %v", err)
+	}
+	value := moduleValue[CurrentConditionsModule](t, output)
+	if value.ConditionText != "Partly cloudy" || value.TemperatureF == nil || *value.TemperatureF != 74 {
+		t.Fatalf("CurrentConditions = %#v, want current condition facts", value)
+	}
+	data, err := json.Marshal(output.Value)
+	if err != nil {
+		t.Fatalf("Marshal current conditions: %v", err)
+	}
+	jsonText := string(data)
+	for _, field := range []string{"condition_text", "temperature_f", "apparent_temperature_f", "relative_humidity_percent", "wind_speed_mph"} {
+		if !strings.Contains(jsonText, field) {
+			t.Fatalf("current json = %s, want field %s", jsonText, field)
+		}
+	}
+}
+
+func TestAlertDigestDistinguishesCheckedEmptyAndMissing(t *testing.T) {
+	registry := MustDefaultModuleRegistry()
+	ctx := testModuleContext()
+	ctx.Collected.Alerts = &weatherdata.AlertRun{}
+	ctx.Derived.AlertOverlaps = nil
+
+	output, err := registry.BuildModule(ctx, module.ConfigItem{ID: module.AlertDigest})
+	if err != nil {
+		t.Fatalf("BuildModule(checked empty) error = %v", err)
+	}
+	checked := moduleValue[AlertDigestModule](t, output)
+	if !checked.Checked || checked.ActiveCount != 0 || checked.RelevantCount != 0 || checked.Missing {
+		t.Fatalf("checked empty alert digest = %#v, want checked/no active", checked)
+	}
+
+	ctx.Collected.Alerts = nil
+	ctx.Collected.SourceProvenance = []weatherdata.Source{{Name: "alerts", Missing: true}}
+	output, err = registry.BuildModule(ctx, module.ConfigItem{ID: module.AlertDigest})
+	if err != nil {
+		t.Fatalf("BuildModule(missing) error = %v", err)
+	}
+	missing := moduleValue[AlertDigestModule](t, output)
+	if missing.Checked || !missing.Missing {
+		t.Fatalf("missing alert digest = %#v, want missing unchecked source", missing)
+	}
+}
+
+func TestBaseModulesOmitMissingOptionalOutputs(t *testing.T) {
+	registry := MustDefaultModuleRegistry()
+	ctx := testModuleContext()
+	ctx.Collected.Current = nil
+	ctx.Collected.Discussion = nil
+	ctx.Collected.WeatherStory = nil
+
+	for _, id := range []module.ID{module.CurrentConditions, module.AreaForecastDiscussion, module.WeatherStory} {
+		output, err := registry.BuildModule(ctx, module.ConfigItem{ID: id})
+		if err != nil {
+			t.Fatalf("BuildModule(%s) error = %v", id, err)
+		}
+		if output != nil {
+			t.Fatalf("BuildModule(%s) output = %#v, want omitted", id, output)
+		}
+	}
+}
+
+func TestAreaForecastDiscussionAndWeatherStoryModules(t *testing.T) {
+	registry := MustDefaultModuleRegistry()
+	ctx := testModuleContext()
+
+	afdOutput, err := registry.BuildModule(ctx, module.ConfigItem{ID: module.AreaForecastDiscussion})
+	if err != nil {
+		t.Fatalf("BuildModule(afd) error = %v", err)
+	}
+	afd := moduleValue[AreaForecastDiscussionModule](t, afdOutput)
+	if len(afd.KeyMessages) != 1 || afd.ShortTerm != "Showers increase this afternoon." || afd.LongTerm != "Periodic rain chances continue." {
+		t.Fatalf("AFD = %#v, want discussion sections", afd)
+	}
+
+	storyOutput, err := registry.BuildModule(ctx, module.ConfigItem{ID: module.WeatherStory})
+	if err != nil {
+		t.Fatalf("BuildModule(weather story) error = %v", err)
+	}
+	story := moduleValue[WeatherStoryModule](t, storyOutput)
+	if !story.Available || story.Title != "Rain Chances" || story.Description != "Scattered showers are possible." {
+		t.Fatalf("WeatherStory = %#v, want structured story fields", story)
+	}
+	data, err := json.Marshal(storyOutput.Value)
+	if err != nil {
+		t.Fatalf("Marshal weather story: %v", err)
+	}
+	if !strings.Contains(string(data), "download_url") {
+		t.Fatalf("weather story json = %s, want snake_case download_url", string(data))
+	}
+}
+
+func testModuleContext() ModuleContext {
+	generatedAt := mustParseModuleTime("2026-05-29T08:00:00-05:00")
+	definition := report.DefaultRegistry().MustLookup(report.DailyToday)
+	resolved := report.Resolved{
+		Definition:  definition,
+		GeneratedAt: generatedAt,
+		Timezone:    "America/Chicago",
+		ValidPeriod: timeutil.Period{
+			Start: mustParseModuleTime("2026-05-29T00:00:00-05:00"),
+			End:   mustParseModuleTime("2026-05-30T00:00:00-05:00"),
+		},
+	}
+	isDay := true
+	tempF := 74.0
+	apparentF := 76.0
+	humidity := 71.0
+	windMph := 8.0
+	windDirection := 190.0
+	updatedAt := mustParseModuleTime("2026-05-29T07:30:00-05:00")
+	return ModuleContext{
+		Resolved: resolved,
+		Collected: facts.CollectedFacts{
+			Current: &weatherdata.Current{
+				ConditionText:           "Partly cloudy",
+				IsDay:                   &isDay,
+				TemperatureF:            &tempF,
+				ApparentTemperatureF:    &apparentF,
+				RelativeHumidityPercent: &humidity,
+				WindSpeedMph:            &windMph,
+				WindDirectionDegrees:    &windDirection,
+			},
+			Alerts: &weatherdata.AlertRun{Alerts: []json.RawMessage{
+				json.RawMessage(`{"event":"Flood Watch","headline":"Flooding possible","severity":"Moderate"}`),
+			}},
+			Discussion: &weatherdata.Discussion{
+				Product:     "discussion",
+				KeyMessages: []string{"Scattered showers are possible."},
+				ShortTerm:   &weatherdata.DiscussionSection{Text: "Showers increase this afternoon."},
+				LongTerm:    &weatherdata.DiscussionSection{Text: "Periodic rain chances continue."},
+			},
+			WeatherStory: &weatherdata.WeatherStory{
+				OfficeID:    "LSX",
+				StartTime:   mustParseModuleTime("2026-05-29T06:00:00-05:00"),
+				EndTime:     mustParseModuleTime("2026-05-29T18:00:00-05:00"),
+				UpdatedAt:   &updatedAt,
+				Title:       "Rain Chances",
+				Description: "Scattered showers are possible.",
+				AltText:     "Weather story graphic with rain chances.",
+				Priority:    true,
+				Order:       1,
+				DownloadURL: "https://example.invalid/story.png",
+			},
+			SourceProvenance: []weatherdata.Source{{Name: "alerts", FetchedAt: generatedAt}},
+			SourceWarnings: []weatherdata.SourceWarning{{
+				Source:             "daily",
+				Code:               "missing_source",
+				Severity:           "warning",
+				Message:            "daily source is missing",
+				Endpoint:           "/forecast/daily",
+				CompletenessImpact: "source omitted",
+			}},
+		},
+		Derived: facts.DerivedFacts{
+			AlertOverlaps: []forecast.AlertOverlap{{
+				Event:    "Flood Watch",
+				Headline: "Flooding possible",
+				Severity: "Moderate",
+			}},
+		},
+		Units:    "us",
+		Timezone: "America/Chicago",
+		Location: &LocationContext{
+			ID:       "home",
+			Name:     "Brentwood",
+			Region:   "St. Louis Metro",
+			Timezone: "America/Chicago",
+		},
+	}
+}
+
+func moduleValue[T any](t *testing.T, output *module.Output) T {
+	t.Helper()
+	var value T
+	data, err := json.Marshal(output.Value)
+	if err != nil {
+		t.Fatalf("marshal module value: %v", err)
+	}
+	if err := json.Unmarshal(data, &value); err != nil {
+		t.Fatalf("decode module value: %v", err)
+	}
+	return value
+}
+
+func mustParseModuleTime(value string) time.Time {
+	parsed, err := time.Parse(time.RFC3339, value)
+	if err != nil {
+		panic(err)
+	}
+	return parsed
+}

internal/briefing/modules.go

@@ -4,10 +4,22 @@ import (
 	"fmt"
 	"reflect"
 
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/facts"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
 )
 
+type ModuleContext struct {
+	Resolved  report.Resolved
+	Collected facts.CollectedFacts
+	Derived   facts.DerivedFacts
+	Units     string
+	Timezone  string
+	Location  *LocationContext
+}
+
+type ModuleBuilder func(ModuleContext, any) (*module.Output, error)
+
 type ModuleDefinition struct {
 	ID                module.ID
 	StanzaName        string
@@ -17,6 +29,7 @@ type ModuleDefinition struct {
 	SupportedReports  []report.ID
 	MissingData       module.MissingDataBehavior
 	AllowDuplicate    bool
+	Builder           ModuleBuilder
 }
 
 type ModuleRegistry struct {
@@ -65,6 +78,40 @@ func (r ModuleRegistry) Lookup(id module.ID) (ModuleDefinition, error) {
 	return definition, nil
 }
 
+func (r ModuleRegistry) BuildModule(ctx ModuleContext, item module.ConfigItem) (*module.Output, error) {
+	definition, err := r.Lookup(item.ID)
+	if err != nil {
+		return nil, err
+	}
+	if !definition.SupportsReport(ctx.Resolved.Definition.ID) {
+		return nil, fmt.Errorf("module %q is not compatible with report %q", item.ID, ctx.Resolved.Definition.ID)
+	}
+	if err := definition.ValidateOptions(item.Options); err != nil {
+		return nil, err
+	}
+	if definition.Builder == nil {
+		return nil, fmt.Errorf("module %q has no builder", item.ID)
+	}
+	options := item.Options
+	if options == nil {
+		options = definition.DefaultOptions
+	}
+	output, err := definition.Builder(ctx, options)
+	if err != nil {
+		return nil, err
+	}
+	if output == nil {
+		return nil, nil
+	}
+	if output.ID != definition.ID {
+		return nil, fmt.Errorf("module %q produced output id %q", definition.ID, output.ID)
+	}
+	if output.StanzaName != definition.StanzaName {
+		return nil, fmt.Errorf("module %q produced stanza %q, want %q", definition.ID, output.StanzaName, definition.StanzaName)
+	}
+	return output, nil
+}
+
 func (r ModuleRegistry) ValidateComposition(reportID report.ID, items []module.ConfigItem) error {
 	seenModules := map[module.ID]struct{}{}
 	seenStanzas := map[string]module.ID{}
@@ -132,6 +179,7 @@ func defaultModuleDefinitions() []ModuleDefinition {
 			RequiredCollected: []module.FactRequirement{module.CollectedSourceMetadata},
 			SupportedReports:  allReports,
 			MissingData:       module.MissingDataEmpty,
+			Builder:           buildMetadataModule,
 		},
 		{
 			ID:                module.CurrentConditions,
@@ -140,6 +188,7 @@ func defaultModuleDefinitions() []ModuleDefinition {
 			RequiredCollected: []module.FactRequirement{module.CollectedCurrentConditions},
 			SupportedReports:  allReports,
 			MissingData:       module.MissingDataOmit,
+			Builder:           buildCurrentConditionsModule,
 		},
 		{
 			ID:               module.DerivedDailySummary,
@@ -181,6 +230,7 @@ func defaultModuleDefinitions() []ModuleDefinition {
 			RequiredDerived:   []module.FactRequirement{module.RequiresDerivedAlertOverlaps},
 			SupportedReports:  allReports,
 			MissingData:       module.MissingDataEmpty,
+			Builder:           buildAlertDigestModule,
 		},
 		{
 			ID:                module.AreaForecastDiscussion,
@@ -189,6 +239,7 @@ func defaultModuleDefinitions() []ModuleDefinition {
 			RequiredCollected: []module.FactRequirement{module.CollectedDiscussion},
 			SupportedReports:  allReports,
 			MissingData:       module.MissingDataOmit,
+			Builder:           buildAreaForecastDiscussionModule,
 		},
 		{
 			ID:                module.WeatherStory,
@@ -197,6 +248,7 @@ func defaultModuleDefinitions() []ModuleDefinition {
 			RequiredCollected: []module.FactRequirement{module.CollectedWeatherStory},
 			SupportedReports:  allReports,
 			MissingData:       module.MissingDataOmit,
+			Builder:           buildWeatherStoryModule,
 		},
 		{
 			ID:               module.ForecastDelta,