feat: dedup and format the output

internal/archive/archive.go

@@ -1,6 +1,6 @@
-// Package archive optionally saves a local copy of each run's fetched data
-// and analysis, for debugging prompt/parsing issues without reproducing a
-// live run.
+// Package archive saves a local copy of each run's fetched data and
+// analysis. It doubles as the source of the previous run's report, which
+// the prompt uses to dedup successive briefings against each other.
 package archive
 
 import (
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 	"time"
 
@@ -31,13 +32,9 @@ type Run struct {
 // path. Callers should treat a non-nil error as non-fatal — archiving is a
 // debugging aid, not part of the report pipeline.
 func Save(cfg config.ArchiveConfig, run Run, now time.Time) (string, error) {
-	base := cfg.Dir
-	if base == "" {
-		base = defaultDir
-	}
-	base, err := expandHome(base)
+	base, err := resolveDir(cfg)
 	if err != nil {
-		return "", fmt.Errorf("archive: %w", err)
+		return "", err
 	}
 
 	dir := filepath.Join(base, now.UTC().Format("20060102T150405Z"))
@@ -70,6 +67,59 @@ func Save(cfg config.ArchiveConfig, run Run, now time.Time) (string, error) {
 	return dir, nil
 }
 
+// LoadLatest reads back the most recent previously-archived run's
+// report.md, for the prompt to dedup the next briefing against. Returns
+// ("", nil) if no prior run exists yet (e.g. first-ever run) — callers
+// should treat that as "no previous report" rather than an error.
+func LoadLatest(cfg config.ArchiveConfig) (string, error) {
+	base, err := resolveDir(cfg)
+	if err != nil {
+		return "", err
+	}
+
+	entries, err := os.ReadDir(base)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return "", nil
+		}
+		return "", fmt.Errorf("archive: list %q: %w", base, err)
+	}
+
+	var runDirs []string
+	for _, e := range entries {
+		if e.IsDir() {
+			runDirs = append(runDirs, e.Name())
+		}
+	}
+	if len(runDirs) == 0 {
+		return "", nil
+	}
+	sort.Strings(runDirs) // timestamp-named dirs sort chronologically
+	latest := runDirs[len(runDirs)-1]
+
+	data, err := os.ReadFile(filepath.Join(base, latest, "report.md"))
+	if err != nil {
+		if os.IsNotExist(err) {
+			return "", nil
+		}
+		return "", fmt.Errorf("archive: read previous report: %w", err)
+	}
+	return string(data), nil
+}
+
+// resolveDir returns cfg.Dir (or defaultDir if empty) with "~" expanded.
+func resolveDir(cfg config.ArchiveConfig) (string, error) {
+	base := cfg.Dir
+	if base == "" {
+		base = defaultDir
+	}
+	base, err := expandHome(base)
+	if err != nil {
+		return "", fmt.Errorf("archive: %w", err)
+	}
+	return base, nil
+}
+
 // expandHome replaces a leading "~" with the current user's home directory.
 func expandHome(path string) (string, error) {
 	if path != "~" && !strings.HasPrefix(path, "~/") {