feat(session): add FormatHistory for worker context injection

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/session/history.go

@@ -0,0 +1,38 @@
+// internal/session/history.go
+package session
+
+import (
+	"fmt"
+	"strings"
+)
+
+// FormatHistory formats prior session entries as a structured block for
+// injection into a worker task prompt. Entries matching excludePhase are
+// omitted (pass the current phase to avoid circular injection).
+func FormatHistory(entries []Entry, excludePhase string) string {
+	var filtered []Entry
+	for _, e := range entries {
+		if e.Phase != excludePhase {
+			filtered = append(filtered, e)
+		}
+	}
+	if len(filtered) == 0 {
+		return ""
+	}
+
+	var b strings.Builder
+	b.WriteString("## Session history\n\n")
+	for _, e := range filtered {
+		b.WriteString(fmt.Sprintf("### Phase: %s\n", e.Phase))
+		b.WriteString(fmt.Sprintf("- Skill: %s\n", e.Skill))
+		b.WriteString(fmt.Sprintf("- Status: %s\n", e.FinalStatus))
+		if e.FilePath != "" {
+			b.WriteString(fmt.Sprintf("- File: %s\n", e.FilePath))
+		}
+		if e.Message != "" {
+			b.WriteString(fmt.Sprintf("- Summary: %s\n", e.Message))
+		}
+		b.WriteString("\n")
+	}
+	return b.String()
+}