Add session discovery and template support

internal/app/session_config_path_test.go

@@ -0,0 +1,68 @@
+package app
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestResolveSessionConfigPathWithCandidatesExplicitWins(t *testing.T) {
+	got, err := resolveSessionConfigPathWithCandidates("  ./custom/session.yml  ", []string{"./session.yml", "/a", "/b"})
+	if err != nil {
+		t.Fatalf("resolveSessionConfigPathWithCandidates() error = %v", err)
+	}
+	if got != "./custom/session.yml" {
+		t.Fatalf("resolved path = %q, want explicit path", got)
+	}
+}
+
+func TestResolveSessionConfigPathWithCandidatesUsesFirstExisting(t *testing.T) {
+	dir := t.TempDir()
+	first := filepath.Join(dir, "first.yml")
+	second := filepath.Join(dir, "second.yml")
+	if err := os.WriteFile(second, []byte("session_id: 2026-05-03\n"), 0o644); err != nil {
+		t.Fatalf("write second default: %v", err)
+	}
+
+	got, err := resolveSessionConfigPathWithCandidates("", []string{first, second})
+	if err != nil {
+		t.Fatalf("resolveSessionConfigPathWithCandidates() error = %v", err)
+	}
+	if got != filepath.Clean(second) {
+		t.Fatalf("resolved path = %q, want %q", got, filepath.Clean(second))
+	}
+}
+
+func TestResolveSessionConfigPathWithCandidatesPrecedence(t *testing.T) {
+	dir := t.TempDir()
+	first := filepath.Join(dir, "first.yml")
+	second := filepath.Join(dir, "second.yml")
+	if err := os.WriteFile(first, []byte("session_id: 2026-05-03\n"), 0o644); err != nil {
+		t.Fatalf("write first default: %v", err)
+	}
+	if err := os.WriteFile(second, []byte("session_id: 2026-05-03\n"), 0o644); err != nil {
+		t.Fatalf("write second default: %v", err)
+	}
+
+	got, err := resolveSessionConfigPathWithCandidates("", []string{first, second})
+	if err != nil {
+		t.Fatalf("resolveSessionConfigPathWithCandidates() error = %v", err)
+	}
+	if got != filepath.Clean(first) {
+		t.Fatalf("resolved path = %q, want first candidate %q", got, filepath.Clean(first))
+	}
+}
+
+func TestResolveSessionConfigPathWithCandidatesMissing(t *testing.T) {
+	_, err := resolveSessionConfigPathWithCandidates("", []string{"/does/not/exist/one.yml", "/does/not/exist/two.yml"})
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), "no default session config found") {
+		t.Fatalf("error = %q, want missing-defaults context", err.Error())
+	}
+	if !strings.Contains(err.Error(), "pass --session") {
+		t.Fatalf("error = %q, want explicit-path guidance", err.Error())
+	}
+}