Extract immutable report preparation

internal/app/generation_test.go

@@ -20,6 +20,7 @@ type generationCollector struct {
 	bundle    *weatherdata.Bundle
 	err       error
 	called    bool
+	calls     int
 	beforeRun func()
 }
 
@@ -28,6 +29,7 @@ func (c *generationCollector) Run(context.Context, collect.Request) (*collect.Re
 		c.beforeRun()
 	}
 	c.called = true
+	c.calls++
 	return &collect.Result{Bundle: c.bundle}, c.err
 }
 
@@ -93,12 +95,13 @@ func TestGenerateDetailedPublishesOnlySelectedOutput(t *testing.T) {
 	cfg.WeatherAPI.Timezone, cfg.Location.ID = "America/Chicago", "home"
 	bundle := generationBundle(t)
 	executor := &generationExecutor{}
+	collector := &generationCollector{bundle: &bundle}
 	workingDir := t.TempDir()
-	result, err := GenerateDetailed(context.Background(), GenerateRequest{Config: cfg, Report: ReportDaily, Date: generationTime("2026-05-29T12:00:00-05:00"), Now: generationTime("2026-05-29T08:30:00-05:00"), WorkingDir: workingDir, Collector: &generationCollector{bundle: &bundle}, Executor: executor})
+	result, err := GenerateDetailed(context.Background(), GenerateRequest{Config: cfg, Report: ReportDaily, Date: generationTime("2026-05-29T12:00:00-05:00"), Now: generationTime("2026-05-29T08:30:00-05:00"), WorkingDir: workingDir, Collector: collector, Executor: executor})
 	if err != nil {
 		t.Fatalf("GenerateDetailed() error = %v", err)
 	}
-	if !executor.called || result.OutputPath != filepath.Join(workingDir, "daily-2026-05-29.md") || result.ValidationStatus != promptexec.ValidationPassed || result.ProfileID == "" || result.BackendID == "" || result.ModelName == "" {
+	if !executor.called || collector.calls != 1 || result.OutputPath != filepath.Join(workingDir, "daily-2026-05-29.md") || result.ValidationStatus != promptexec.ValidationPassed || result.ProfileID == "" || result.BackendID == "" || result.ModelName == "" {
 		t.Fatalf("result = %#v", result)
 	}
 	if result.LLMDebugPath != "" {

internal/app/prepared_report.go

@@ -0,0 +1,150 @@
+package app
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/collect"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/config"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/generatedtext"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/promptinput"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/weatherdata"
+)
+
+// preparedReport contains the immutable deterministic inputs shared by prompt
+// executions for one resolved report.
+type preparedReport struct {
+	resolved         report.Resolved
+	reportFacts      ReportFacts
+	moduleSnapshot   module.Snapshot
+	briefingMetadata briefing.Metadata
+	sourceWarnings   []weatherdata.SourceWarning
+	dataPackage      []byte
+	handler          generatedtext.Handler
+}
+
+type prepareReportRequest struct {
+	Config     config.Config
+	Resolved   report.Resolved
+	Collection collect.Result
+}
+
+type preparationError struct {
+	operation string
+	err       error
+}
+
+func (e *preparationError) Error() string {
+	return e.operation + ": " + e.err.Error()
+}
+
+func (e *preparationError) Unwrap() error {
+	return e.err
+}
+
+func prepareReport(req prepareReportRequest) (preparedReport, error) {
+	if req.Collection.Bundle == nil {
+		return preparedReport{}, &preparationError{operation: "prepare report", err: fmt.Errorf("collected weather bundle is required")}
+	}
+
+	reportFacts, err := BuildReportFacts(ModuleSnapshotRequest{Config: req.Config, Resolved: req.Resolved}, req.Collection.Bundle)
+	if err != nil {
+		return preparedReport{}, &preparationError{operation: "build report facts", err: err}
+	}
+	moduleSnapshot, err := BuildModuleSnapshotFromFacts(ModuleSnapshotRequest{Config: req.Config, Resolved: req.Resolved}, reportFacts)
+	if err != nil {
+		return preparedReport{}, &preparationError{operation: "build module snapshot", err: err}
+	}
+	metadata := briefing.BuildMetadata(briefingBuildContext(req.Config, req.Resolved, reportFacts.Collected))
+	dataPackage, err := promptinput.Build(promptinput.BuildRequest{Metadata: promptMetadata(metadata), Modules: moduleSnapshot})
+	if err != nil {
+		return preparedReport{}, &preparationError{operation: "build data package", err: err}
+	}
+	serializedDataPackage, err := promptinput.MarshalYAML(dataPackage)
+	if err != nil {
+		return preparedReport{}, &preparationError{operation: "marshal data package", err: err}
+	}
+	handler, err := generatedtext.LookupDefinition(req.Resolved.Definition)
+	if err != nil {
+		return preparedReport{}, &preparationError{operation: "lookup generated text catalog", err: err}
+	}
+
+	clonedFacts, err := clonePreparedValue(reportFacts)
+	if err != nil {
+		return preparedReport{}, &preparationError{operation: "copy prepared report facts", err: err}
+	}
+	clonedSnapshot, err := clonePreparedValue(moduleSnapshot)
+	if err != nil {
+		return preparedReport{}, &preparationError{operation: "copy prepared module snapshot", err: err}
+	}
+	clonedMetadata, err := clonePreparedValue(metadata)
+	if err != nil {
+		return preparedReport{}, &preparationError{operation: "copy prepared briefing metadata", err: err}
+	}
+	prepared := preparedReport{
+		resolved:         cloneResolved(req.Resolved),
+		reportFacts:      clonedFacts,
+		moduleSnapshot:   clonedSnapshot,
+		briefingMetadata: clonedMetadata,
+		sourceWarnings:   append([]weatherdata.SourceWarning(nil), clonedMetadata.SourceWarnings...),
+		dataPackage:      append([]byte(nil), serializedDataPackage...),
+		handler:          handler,
+	}
+	return prepared, nil
+}
+
+func cloneResolved(value report.Resolved) report.Resolved {
+	cloned := value
+	cloned.Definition.DistributorPathTemplates = append([]string(nil), value.Definition.DistributorPathTemplates...)
+	cloned.Definition.Modules = make([]module.ConfigItem, len(value.Definition.Modules))
+	for i, item := range value.Definition.Modules {
+		cloned.Definition.Modules[i] = item
+		switch options := item.Options.(type) {
+		case module.AreaForecastDiscussionOptions:
+			options.Sections = append([]string(nil), options.Sections...)
+			cloned.Definition.Modules[i].Options = options
+		}
+	}
+	return cloned
+}
+
+func (p preparedReport) dataPackageCopy() []byte {
+	return append([]byte(nil), p.dataPackage...)
+}
+
+func (p preparedReport) sourceWarningsCopy() []weatherdata.SourceWarning {
+	return append([]weatherdata.SourceWarning(nil), p.sourceWarnings...)
+}
+
+func (p preparedReport) renderInputs() (briefing.Metadata, module.Snapshot, ReportFacts, error) {
+	metadata, err := clonePreparedValue(p.briefingMetadata)
+	if err != nil {
+		return briefing.Metadata{}, module.Snapshot{}, ReportFacts{}, err
+	}
+	snapshot, err := clonePreparedValue(p.moduleSnapshot)
+	if err != nil {
+		return briefing.Metadata{}, module.Snapshot{}, ReportFacts{}, err
+	}
+	reportFacts, err := clonePreparedValue(p.reportFacts)
+	if err != nil {
+		return briefing.Metadata{}, module.Snapshot{}, ReportFacts{}, err
+	}
+	return metadata, snapshot, reportFacts, nil
+}
+
+func clonePreparedValue[T any](value T) (T, error) {
+	encoded, err := json.Marshal(value)
+	if err != nil {
+		var zero T
+		return zero, fmt.Errorf("marshal immutable prepared value: %w", err)
+	}
+	var cloned T
+	if err := json.Unmarshal(encoded, &cloned); err != nil {
+		var zero T
+		return zero, fmt.Errorf("unmarshal immutable prepared value: %w", err)
+	}
+	return cloned, nil
+}

internal/app/prepared_report_test.go

@@ -0,0 +1,64 @@
+package app
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/collect"
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/weatherdata"
+)
+
+func TestPrepareReportBuildsImmutableDeterministicInputs(t *testing.T) {
+	cfg := generationConfig()
+	bundle := generationBundle(t)
+	resolved, err := ResolveGenerate(GenerateRequest{
+		Config: cfg, Report: ReportDaily,
+		Date: generationTime("2026-05-29T12:00:00-05:00"), Now: generationTime("2026-05-29T08:30:00-05:00"),
+	}, generationTime("2026-05-29T08:30:00-05:00"))
+	if err != nil {
+		t.Fatalf("ResolveGenerate() error = %v", err)
+	}
+
+	request := prepareReportRequest{Config: cfg, Resolved: resolved, Collection: collect.Result{Bundle: &bundle}}
+	prepared, err := prepareReport(request)
+	if err != nil {
+		t.Fatalf("prepareReport() error = %v", err)
+	}
+	repeated, err := prepareReport(request)
+	if err != nil {
+		t.Fatalf("second prepareReport() error = %v", err)
+	}
+	if len(prepared.dataPackage) == 0 || !bytes.Equal(prepared.dataPackage, repeated.dataPackage) || !reflect.DeepEqual(prepared.briefingMetadata, repeated.briefingMetadata) {
+		t.Fatalf("prepared package/metadata are not deterministic: %q/%#v", prepared.dataPackage, prepared.briefingMetadata)
+	}
+
+	originalDataPackage := append([]byte(nil), prepared.dataPackage...)
+	originalMetadata := prepared.briefingMetadata
+	originalWarnings := append([]weatherdata.SourceWarning(nil), prepared.sourceWarnings...)
+	metadata, snapshot, reportFacts, err := prepared.renderInputs()
+	if err != nil {
+		t.Fatalf("renderInputs() error = %v", err)
+	}
+	metadata.SourceWarnings = append(metadata.SourceWarnings, weatherdata.SourceWarning{Source: "test", Message: "consumer mutation"})
+	snapshot.Outputs = nil
+	reportFacts.Collected.Hourly.Periods[0].TextDescription = "consumer mutation"
+	bundle.Hourly.Periods[0].TextDescription = "mutated after preparation"
+	bundle.Warnings = append(bundle.Warnings, weatherdata.SourceWarning{Source: "test", Message: "mutated warning"})
+	if len(bundle.Sources) > 0 {
+		if bundle.Sources[0].Query == nil {
+			bundle.Sources[0].Query = map[string]string{}
+		}
+		bundle.Sources[0].Query["mutated"] = "true"
+	}
+
+	if !bytes.Equal(prepared.dataPackage, originalDataPackage) || !reflect.DeepEqual(prepared.briefingMetadata, originalMetadata) || !reflect.DeepEqual(prepared.sourceWarnings, originalWarnings) {
+		t.Fatalf("prepared values changed after caller mutation: %#v", prepared)
+	}
+	if prepared.reportFacts.Collected.Hourly.Periods[0].TextDescription == "mutated after preparation" {
+		t.Fatal("prepared report facts retain caller-owned weather data")
+	}
+	if prepared.reportFacts.Collected.Hourly.Periods[0].TextDescription == "consumer mutation" || len(prepared.moduleSnapshot.Outputs) == 0 {
+		t.Fatal("prepared report values retain consumer mutation")
+	}
+}

internal/app/prompt_generate.go

@@ -5,16 +5,11 @@ import (
 	"errors"
 	"fmt"
 
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/collect"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/fileutil"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/generatedtext"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/module"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/promptdebug"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/promptexec"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/promptinput"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
-	"gitea.maximumdirect.net/eric/weatherreporter/internal/weatherdata"
 )
 
 type promptReportRequest struct {
@@ -31,11 +26,7 @@ type promptReportWorkflow struct {
 	ctx            context.Context
 	req            promptReportRequest
 	result         *ReportResult
-	briefingMetadata briefing.Metadata
+	prepared       preparedReport
-	reportFacts      ReportFacts
-	moduleSnapshot   module.Snapshot
-	dataPackage      []byte
-	handler          generatedtext.Handler
 	debugRef       promptdebug.PromptDebugRef
 	callbackFailed bool
 }
@@ -97,36 +88,23 @@ func initialReportResult(req GenerateRequest, resolved report.Resolved, inspecti
 }
 
 func (w *promptReportWorkflow) buildInputs() error {
-	var err error
+	prepared, err := prepareReport(prepareReportRequest{Config: w.req.Config, Resolved: w.req.Resolved, Collection: w.req.Collection})
-	w.reportFacts, err = BuildReportFacts(ModuleSnapshotRequest{Config: w.req.Config, Resolved: w.req.Resolved}, w.req.Collection.Bundle)
 	if err != nil {
-		return w.reportError("build report facts", err)
+		var preparation *preparationError
+		if errors.As(err, &preparation) {
+			return w.reportError(preparation.operation, preparation.err)
 		}
-	w.moduleSnapshot, err = BuildModuleSnapshotFromFacts(ModuleSnapshotRequest{Config: w.req.Config, Resolved: w.req.Resolved}, w.reportFacts)
+		return w.reportError("prepare report", err)
-	if err != nil {
-		return w.reportError("build module snapshot", err)
 	}
-	w.briefingMetadata = briefing.BuildMetadata(briefingBuildContext(w.req.Config, w.req.Resolved, w.reportFacts.Collected))
+	w.prepared = prepared
-	w.result.SourceWarnings = append([]weatherdata.SourceWarning(nil), w.briefingMetadata.SourceWarnings...)
+	w.result.SourceWarnings = w.prepared.sourceWarningsCopy()
-	dataPackage, err := promptinput.Build(promptinput.BuildRequest{Metadata: promptMetadata(w.briefingMetadata), Modules: w.moduleSnapshot})
+	w.debugRef = promptdebug.PromptDebugRef{ReportID: w.result.ReportID, ValidDate: w.prepared.resolved.ValidPeriod.Start.Format("2006-01-02"), RunID: w.result.RunID}
-	if err != nil {
-		return w.reportError("build data package", err)
-	}
-	w.dataPackage, err = promptinput.MarshalYAML(dataPackage)
-	if err != nil {
-		return w.reportError("marshal data package", err)
-	}
-	w.handler, err = generatedtext.LookupDefinition(w.req.Resolved.Definition)
-	if err != nil {
-		return w.reportError("lookup generated text catalog", err)
-	}
-	w.debugRef = promptdebug.PromptDebugRef{ReportID: w.result.ReportID, ValidDate: w.req.Resolved.ValidPeriod.Start.Format("2006-01-02"), RunID: w.result.RunID}
 	return nil
 }
 
 func (w *promptReportWorkflow) executePrompt() (*promptexec.Execution, error) {
 	captureDebug := w.req.DebugWriter != nil && w.req.DebugWriter.Enabled()
-	return w.req.Executor.Execute(w.ctx, promptexec.ExecuteRequest{PromptID: w.req.Inspection.PromptID, PromptVersion: w.req.Inspection.PromptVersion, ProfileID: w.req.Inspection.ProfileID, DataPackage: w.dataPackage, CaptureDebug: captureDebug}, w.writePreparationDebug)
+	return w.req.Executor.Execute(w.ctx, promptexec.ExecuteRequest{PromptID: w.req.Inspection.PromptID, PromptVersion: w.req.Inspection.PromptVersion, ProfileID: w.req.Inspection.ProfileID, DataPackage: w.prepared.dataPackageCopy(), CaptureDebug: captureDebug}, w.writePreparationDebug)
 }
 
 func (w *promptReportWorkflow) writePreparationDebug(preparation promptexec.Preparation, debug *promptexec.PreparationDebug) error {
@@ -158,15 +136,19 @@ func (w *promptReportWorkflow) writeExecutionDebug(execution promptexec.Executio
 }
 
 func (w *promptReportWorkflow) renderAndPublish(raw []byte) (*ReportResult, error) {
-	generatedText, _, err := w.handler.Validate(raw)
+	generatedText, _, err := w.prepared.handler.Validate(raw)
 	if err != nil {
 		return w.result, w.reportError("validate generated text", err)
 	}
-	renderContext, err := w.handler.BuildRenderContext(w.briefingMetadata, w.moduleSnapshot, w.reportFacts.Collected, w.reportFacts.Derived, generatedText)
+	metadata, snapshot, reportFacts, err := w.prepared.renderInputs()
+	if err != nil {
+		return w.result, w.reportError("copy prepared render inputs", err)
+	}
+	renderContext, err := w.prepared.handler.BuildRenderContext(metadata, snapshot, reportFacts.Collected, reportFacts.Derived, generatedText)
 	if err != nil {
 		return w.result, w.reportError("build render context", err)
 	}
-	rendered, err := w.handler.Render(renderContext)
+	rendered, err := w.prepared.handler.Render(renderContext)
 	if err != nil {
 		return w.result, w.reportError("render template", err)
 	}