diff --git a/CLAUDE.md b/CLAUDE.md
index e82d30f..59d2750 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -45,5 +45,6 @@ Coverage target: maintain ≥90.9%.
 - Explicit types on all function signatures and struct fields
 - `go test ./...` and `go vet ./...` must pass before commit
 - SPDX header on all source files: `// SPDX-Licence-Identifier: EUPL-1.2`
+- Error handling: all errors must use `coreerr.E(op, msg, err)` from `forge.lthn.ai/core/go-log`, never `fmt.Errorf` or `errors.New`
 - Conventional commits: `type(scope): description`
 - Co-Author trailer: `Co-Authored-By: Virgil <virgil@lethean.io>`
diff --git a/parser_test.go b/parser_test.go
index 7ec5326..cf8ed2a 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -1311,6 +1311,127 @@ func TestParseTranscript_AllBadLines_Good(t *testing.T) {
 
 // --- ListSessions with truncated files ---
 
+// --- PruneSessions tests ---
+
+func TestPruneSessions_DeletesOldFiles_Good(t *testing.T) {
+	dir := t.TempDir()
+
+	// Create a session file with an old modification time.
+	path := writeJSONL(t, dir, "old-session.jsonl",
+		userTextEntry(ts(0), "old"),
+	)
+	// Backdate the file's mtime by 2 hours.
+	oldTime := time.Now().Add(-2 * time.Hour)
+	require.NoError(t, os.Chtimes(path, oldTime, oldTime))
+
+	// Create a recent session file.
+	writeJSONL(t, dir, "new-session.jsonl",
+		userTextEntry(ts(0), "new"),
+	)
+
+	// Prune sessions older than 1 hour.
+	deleted, err := PruneSessions(dir, 1*time.Hour)
+	require.NoError(t, err)
+	assert.Equal(t, 1, deleted)
+
+	// Verify only the new file remains.
+	sessions, err := ListSessions(dir)
+	require.NoError(t, err)
+	require.Len(t, sessions, 1)
+	assert.Equal(t, "new-session", sessions[0].ID)
+}
+
+func TestPruneSessions_NothingToDelete_Good(t *testing.T) {
+	dir := t.TempDir()
+
+	writeJSONL(t, dir, "recent.jsonl",
+		userTextEntry(ts(0), "fresh"),
+	)
+
+	deleted, err := PruneSessions(dir, 24*time.Hour)
+	require.NoError(t, err)
+	assert.Equal(t, 0, deleted)
+}
+
+func TestPruneSessions_EmptyDir_Good(t *testing.T) {
+	dir := t.TempDir()
+
+	deleted, err := PruneSessions(dir, 1*time.Hour)
+	require.NoError(t, err)
+	assert.Equal(t, 0, deleted)
+}
+
+// --- IsExpired tests ---
+
+func TestIsExpired_RecentSession_Good(t *testing.T) {
+	sess := &Session{
+		EndTime: time.Now().Add(-5 * time.Minute),
+	}
+	assert.False(t, sess.IsExpired(1*time.Hour))
+}
+
+func TestIsExpired_OldSession_Good(t *testing.T) {
+	sess := &Session{
+		EndTime: time.Now().Add(-2 * time.Hour),
+	}
+	assert.True(t, sess.IsExpired(1*time.Hour))
+}
+
+func TestIsExpired_ZeroEndTime_Bad(t *testing.T) {
+	sess := &Session{}
+	assert.False(t, sess.IsExpired(1*time.Hour))
+}
+
+// --- FetchSession tests ---
+
+func TestFetchSession_ValidID_Good(t *testing.T) {
+	dir := t.TempDir()
+	writeJSONL(t, dir, "abc123.jsonl",
+		userTextEntry(ts(0), "hello"),
+	)
+
+	sess, stats, err := FetchSession(dir, "abc123")
+	require.NoError(t, err)
+	require.NotNil(t, sess)
+	require.NotNil(t, stats)
+	assert.Equal(t, "abc123", sess.ID)
+	assert.Len(t, sess.Events, 1)
+}
+
+func TestFetchSession_PathTraversal_Ugly(t *testing.T) {
+	dir := t.TempDir()
+
+	_, _, err := FetchSession(dir, "../etc/passwd")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "invalid session id")
+}
+
+func TestFetchSession_BackslashTraversal_Ugly(t *testing.T) {
+	dir := t.TempDir()
+
+	_, _, err := FetchSession(dir, `foo\bar`)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "invalid session id")
+}
+
+func TestFetchSession_ForwardSlash_Ugly(t *testing.T) {
+	dir := t.TempDir()
+
+	_, _, err := FetchSession(dir, "foo/bar")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "invalid session id")
+}
+
+func TestFetchSession_NotFound_Bad(t *testing.T) {
+	dir := t.TempDir()
+
+	_, _, err := FetchSession(dir, "nonexistent")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "open transcript")
+}
+
+// --- ListSessions with truncated files ---
+
 func TestListSessions_TruncatedFile_Good(t *testing.T) {
 	dir := t.TempDir()
 	// A .jsonl file where some lines are truncated — ListSessions should