chore: import upstream snapshot with attribution

internal/hooks/transcript.go

@@ -0,0 +1,70 @@
+package hooks
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"os"
+	"strings"
+)
+
+// transcriptTailBytes bounds how much of the end of a (potentially large)
+// session transcript we scan for the model — enough to span several
+// recent turns without reading a multi-megabyte file on every tool call.
+const transcriptTailBytes = 256 * 1024
+
+// modelFromTranscript returns the model id of the most recent assistant
+// turn in a Claude Code transcript JSONL file, or "" when it can't be
+// determined. Each transcript line is a JSON record; assistant turns
+// carry the model at message.model. The scan reads only the file's tail
+// and walks lines from the end, so the freshest model — including one
+// chosen by a mid-session /model switch — wins. Best-effort: any I/O or
+// parse failure yields "".
+func modelFromTranscript(path string) string {
+	if path == "" {
+		return ""
+	}
+	f, err := os.Open(path)
+	if err != nil {
+		return ""
+	}
+	defer f.Close()
+
+	fi, err := f.Stat()
+	if err != nil {
+		return ""
+	}
+	start := int64(0)
+	if fi.Size() > transcriptTailBytes {
+		start = fi.Size() - transcriptTailBytes
+	}
+	if _, err := f.Seek(start, io.SeekStart); err != nil {
+		return ""
+	}
+	data, err := io.ReadAll(f)
+	if err != nil {
+		return ""
+	}
+
+	lines := bytes.Split(data, []byte("\n"))
+	for i := len(lines) - 1; i >= 0; i-- {
+		line := bytes.TrimSpace(lines[i])
+		// A tail read may begin mid-line; such a leading partial line
+		// fails to parse and is simply skipped.
+		if len(line) == 0 || line[0] != '{' {
+			continue
+		}
+		var rec struct {
+			Message struct {
+				Model string `json:"model"`
+			} `json:"message"`
+		}
+		if json.Unmarshal(line, &rec) != nil {
+			continue
+		}
+		if m := strings.TrimSpace(rec.Message.Model); m != "" {
+			return m
+		}
+	}
+	return ""
+}