diff --git a/tests/unit/test_seasons_helpers.py b/tests/unit/test_seasons_helpers.py
new file mode 100644
index 0000000..c8360d9
--- /dev/null
+++ b/tests/unit/test_seasons_helpers.py
@@ -0,0 +1,285 @@
+"""Unit tests for pure helper functions in contribarena.engine.seasons.
+
+Tests cover:
+- normalize_model_identity: string normalization for model identifiers
+- derive_participant_id: season:identity ID construction
+- parse_duration_seconds: duration string parsing (s/m/h/d)
+- _append_runtime_event: bounded runtime event list management
+- SeasonAdmission: frozen dataclass defaults
+- SeasonStatus literal: accepted/rejected values
+- Module constants: MAX_REPLACEMENT_ATTEMPTS, MAX_LIVE_SUBMISSION_RETRY_ATTEMPTS
+"""
+
+from __future__ import annotations
+
+import unittest
+
+from contribarena.engine.seasons import (
+    MAX_LIVE_SUBMISSION_RETRY_ATTEMPTS,
+    MAX_REPLACEMENT_ATTEMPTS,
+    SeasonAdmission,
+    _append_runtime_event,
+    derive_participant_id,
+    normalize_model_identity,
+    parse_duration_seconds,
+)
+from contribarena.errors import ConfigError
+
+
+class NormalizeModelIdentityTest(unittest.TestCase):
+    """Tests for normalize_model_identity."""
+
+    def test_simple_name(self) -> None:
+        self.assertEqual("gpt-4o", normalize_model_identity("gpt-4o"))
+
+    def test_strip_whitespace(self) -> None:
+        self.assertEqual("gpt-4o", normalize_model_identity("  gpt-4o  "))
+
+    def test_lowercase(self) -> None:
+        self.assertEqual("gpt-4o", normalize_model_identity("GPT-4O"))
+
+    def test_remove_slash_prefix(self) -> None:
+        self.assertEqual("gpt-4o", normalize_model_identity("openai/gpt-4o"))
+
+    def test_remove_colon_prefix(self) -> None:
+        self.assertEqual("gpt-4o", normalize_model_identity("provider:gpt-4o"))
+
+    def test_remove_nested_slash(self) -> None:
+        self.assertEqual("gpt-4o", normalize_model_identity("org/openai/gpt-4o"))
+
+    def test_remove_nested_colon(self) -> None:
+        self.assertEqual("gpt-4o", normalize_model_identity("tier:provider:gpt-4o"))
+
+    def test_special_chars_replaced_with_hyphen(self) -> None:
+        self.assertEqual("my-model", normalize_model_identity("my model"))
+
+    def test_preserve_dots(self) -> None:
+        # Dots in input are preserved, but spaces become hyphens first
+        self.assertEqual("model-v2.0", normalize_model_identity("model v2.0"))
+        # Pure dot-separated values keep their dots
+        self.assertEqual("model.v2.0", normalize_model_identity("model.v2.0"))
+
+    def test_preserve_underscores(self) -> None:
+        self.assertEqual("my_model", normalize_model_identity("my_model"))
+
+    def test_strip_leading_trailing_hyphens(self) -> None:
+        self.assertEqual("model", normalize_model_identity("---model---"))
+
+    def test_empty_string_returns_unknown(self) -> None:
+        self.assertEqual("unknown", normalize_model_identity(""))
+
+    def test_whitespace_only_returns_unknown(self) -> None:
+        self.assertEqual("unknown", normalize_model_identity("   "))
+
+    def test_special_chars_only_returns_unknown(self) -> None:
+        self.assertEqual("unknown", normalize_model_identity("!!!"))
+
+    def test_slash_only_returns_unknown(self) -> None:
+        self.assertEqual("unknown", normalize_model_identity("///"))
+
+    def test_colon_only_returns_unknown(self) -> None:
+        self.assertEqual("unknown", normalize_model_identity(":::"))
+
+    def test_slash_with_empty_suffix(self) -> None:
+        self.assertEqual("unknown", normalize_model_identity("openai/"))
+
+    def test_colon_with_empty_suffix(self) -> None:
+        self.assertEqual("unknown", normalize_model_identity("provider:"))
+
+    def test_mixed_nested_prefixes_slash_and_colon(self) -> None:
+        # Slash is stripped first, then colon from the remaining part
+        self.assertEqual("gpt-4o", normalize_model_identity("org/provider:gpt-4o"))
+
+
+class DeriveParticipantIdTest(unittest.TestCase):
+    """Tests for derive_participant_id."""
+
+    def test_basic_derivation(self) -> None:
+        self.assertEqual("season_0:gpt-4o", derive_participant_id("season_0", "gpt-4o"))
+
+    def test_model_normalization_applied(self) -> None:
+        self.assertEqual("season_0:gpt-4o", derive_participant_id("season_0", "OpenAI/gpt-4o"))
+
+    def test_whitespace_model_normalized(self) -> None:
+        self.assertEqual("season_0:gpt-4o", derive_participant_id("season_0", "  gpt-4o  "))
+
+    def test_empty_model_uses_unknown(self) -> None:
+        self.assertEqual("season_0:unknown", derive_participant_id("season_0", ""))
+
+    def test_season_id_preserved_exact(self) -> None:
+        self.assertEqual("my-season:glm-5.1", derive_participant_id("my-season", "glm-5.1"))
+
+    def test_colon_in_season_id(self) -> None:
+        self.assertEqual("s0:gpt-4o", derive_participant_id("s0", "gpt-4o"))
+
+
+class ParseDurationSecondsTest(unittest.TestCase):
+    """Tests for parse_duration_seconds."""
+
+    def test_seconds(self) -> None:
+        self.assertEqual(30, parse_duration_seconds("30s"))
+
+    def test_seconds_with_space(self) -> None:
+        self.assertEqual(30, parse_duration_seconds("30 s"))
+
+    def test_minutes(self) -> None:
+        self.assertEqual(300, parse_duration_seconds("5m"))
+
+    def test_hours(self) -> None:
+        self.assertEqual(7200, parse_duration_seconds("2h"))
+
+    def test_days(self) -> None:
+        self.assertEqual(86400, parse_duration_seconds("1d"))
+
+    def test_zero_seconds(self) -> None:
+        self.assertEqual(0, parse_duration_seconds("0s"))
+
+    def test_whitespace_stripped(self) -> None:
+        self.assertEqual(60, parse_duration_seconds("  1m  "))
+
+    def test_case_insensitive(self) -> None:
+        self.assertEqual(30, parse_duration_seconds("30S"))
+
+    def test_invalid_format_raises(self) -> None:
+        with self.assertRaises(ConfigError):
+            parse_duration_seconds("30")
+
+    def test_invalid_unit_raises(self) -> None:
+        with self.assertRaises(ConfigError):
+            parse_duration_seconds("30x")
+
+    def test_empty_raises(self) -> None:
+        with self.assertRaises(ConfigError):
+            parse_duration_seconds("")
+
+    def test_whitespace_only_raises(self) -> None:
+        with self.assertRaises(ConfigError):
+            parse_duration_seconds("   ")
+
+    def test_no_unit_raises(self) -> None:
+        with self.assertRaises(ConfigError):
+            parse_duration_seconds("100")
+
+    def test_double_unit_raises(self) -> None:
+        with self.assertRaises(ConfigError):
+            parse_duration_seconds("5mm")
+
+    def test_negative_raises_via_regex(self) -> None:
+        with self.assertRaises(ConfigError):
+            parse_duration_seconds("-5m")
+
+
+class AppendRuntimeEventTest(unittest.TestCase):
+    """Tests for _append_runtime_event."""
+
+    def test_appends_event_to_empty_state(self) -> None:
+        state: dict = {}
+        event = {"type": "start", "run_id": "abc"}
+        _append_runtime_event(state, event)
+        self.assertEqual([event], state["runtime_events"])
+
+    def test_appends_event_to_existing_list(self) -> None:
+        state = {"runtime_events": [{"type": "first"}]}
+        event = {"type": "second"}
+        _append_runtime_event(state, event)
+        self.assertEqual(2, len(state["runtime_events"]))
+        self.assertEqual({"type": "second"}, state["runtime_events"][1])
+
+    def test_preserves_order(self) -> None:
+        state: dict = {}
+        for i in range(3):
+            _append_runtime_event(state, {"i": i})
+        events = state["runtime_events"]
+        self.assertEqual([{"i": 0}, {"i": 1}, {"i": 2}], events)
+
+    def test_truncates_at_200(self) -> None:
+        state: dict = {}
+        for i in range(205):
+            _append_runtime_event(state, {"i": i})
+        events = state["runtime_events"]
+        self.assertEqual(200, len(events))
+        # First 5 events should be dropped; last 200 preserved
+        self.assertEqual(5, events[0]["i"])
+        self.assertEqual(204, events[-1]["i"])
+
+    def test_replaces_non_list_runtime_events(self) -> None:
+        state = {"runtime_events": "not a list"}
+        event = {"type": "start"}
+        _append_runtime_event(state, event)
+        self.assertEqual([event], state["runtime_events"])
+
+    def test_handles_missing_runtime_events_key(self) -> None:
+        state: dict = {}
+        event = {"type": "start"}
+        _append_runtime_event(state, event)
+        self.assertIn("runtime_events", state)
+
+
+class SeasonAdmissionTest(unittest.TestCase):
+    """Tests for SeasonAdmission frozen dataclass."""
+
+    def test_defaults(self) -> None:
+        admission = SeasonAdmission()
+        self.assertEqual("", admission.season_id)
+        self.assertEqual("", admission.participant_id)
+        self.assertIsNone(admission.participant)
+        self.assertFalse(admission.ranked)
+        self.assertEqual("unranked", admission.wake_source)
+
+    def test_explicit_values(self) -> None:
+        admission = SeasonAdmission(
+            season_id="season_0",
+            participant_id="season_0:glm-5.1",
+            ranked=True,
+            wake_source="auto",
+        )
+        self.assertEqual("season_0", admission.season_id)
+        self.assertTrue(admission.ranked)
+        self.assertEqual("auto", admission.wake_source)
+
+    def test_frozen_immutability(self) -> None:
+        admission = SeasonAdmission()
+        with self.assertRaises(AttributeError):
+            admission.season_id = "modified"  # type: ignore[misc]
+
+    def test_all_wake_source_literals(self) -> None:
+        for source in ("manual", "auto", "unranked"):
+            admission = SeasonAdmission(wake_source=source)
+            self.assertEqual(source, admission.wake_source)
+
+
+class SeasonStatusLiteralTest(unittest.TestCase):
+    """Tests for the SeasonStatus Literal type alias."""
+
+    def test_all_accepted_values(self) -> None:
+        """Verify the SeasonStatus Literal accepts all four valid strings."""
+        from contribarena.engine.seasons import SeasonStatus
+        from typing import get_args
+        expected = ("draft", "active", "observing", "completed")
+        actual = get_args(SeasonStatus)
+        self.assertEqual(expected, actual)
+
+    def test_literal_type_is_str_subclass(self) -> None:
+        """Verify each SeasonStatus member is a str instance."""
+        from contribarena.engine.seasons import SeasonStatus
+        from typing import get_args
+        for value in get_args(SeasonStatus):
+            self.assertIsInstance(value, str)
+
+
+class ModuleConstantsTest(unittest.TestCase):
+    """Tests for module-level constants."""
+
+    def test_max_replacement_attempts(self) -> None:
+        self.assertEqual(5, MAX_REPLACEMENT_ATTEMPTS)
+
+    def test_max_live_submission_retry_attempts(self) -> None:
+        self.assertEqual(3, MAX_LIVE_SUBMISSION_RETRY_ATTEMPTS)
+
+    def test_constants_are_integers(self) -> None:
+        self.assertIsInstance(MAX_REPLACEMENT_ATTEMPTS, int)
+        self.assertIsInstance(MAX_LIVE_SUBMISSION_RETRY_ATTEMPTS, int)
+
+
+if __name__ == "__main__":
+    unittest.main()