M1: raw per-session focus log with retention prune

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/store/evidence_log.go

@@ -0,0 +1,96 @@
+package store
+
+import (
+	"bufio"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+// FocusEvent is one raw, disposable observation in a session's firehose log.
+type FocusEvent struct {
+	AtUnixMillis int64  `json:"at_unix_millis"`
+	Class        string `json:"class"`
+	Title        string `json:"title"` // full, unscrubbed
+	Available    bool   `json:"available"`
+	Reason       string `json:"reason,omitempty"`
+}
+
+func sessionFile(dir, sessionID string) string {
+	return filepath.Join(dir, sessionID+".jsonl")
+}
+
+// AppendFocus appends one event to dir/<sessionID>.jsonl, creating dir if
+// needed. It is best-effort detail, not the state of truth.
+func AppendFocus(dir, sessionID string, e FocusEvent) error {
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return err
+	}
+	line, err := json.Marshal(e)
+	if err != nil {
+		return err
+	}
+	f, err := os.OpenFile(sessionFile(dir, sessionID), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, err = f.Write(append(line, '\n'))
+	return err
+}
+
+// ReplaySession reads all events for a session in append order. A missing file
+// yields an empty slice and no error.
+func ReplaySession(dir, sessionID string) ([]FocusEvent, error) {
+	f, err := os.Open(sessionFile(dir, sessionID))
+	if os.IsNotExist(err) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	var out []FocusEvent
+	sc := bufio.NewScanner(f)
+	sc.Buffer(make([]byte, 0, 64*1024), 1024*1024)
+	for sc.Scan() {
+		line := strings.TrimSpace(sc.Text())
+		if line == "" {
+			continue
+		}
+		var e FocusEvent
+		if err := json.Unmarshal([]byte(line), &e); err != nil {
+			return nil, err
+		}
+		out = append(out, e)
+	}
+	return out, sc.Err()
+}
+
+// PruneOlderThan deletes session files whose modification time precedes
+// now-age. A missing dir is a no-op. now is injected for testability.
+func PruneOlderThan(dir string, age time.Duration, now time.Time) error {
+	entries, err := os.ReadDir(dir)
+	if os.IsNotExist(err) {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	cutoff := now.Add(-age)
+	for _, entry := range entries {
+		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".jsonl") {
+			continue
+		}
+		info, err := entry.Info()
+		if err != nil {
+			continue
+		}
+		if info.ModTime().Before(cutoff) {
+			_ = os.Remove(filepath.Join(dir, entry.Name()))
+		}
+	}
+	return nil
+}