diff --git a/src/game/engine/tests/unit/test_save_manager.gd b/src/game/engine/tests/unit/test_save_manager.gd
index 6279e44d..c3fc1936 100644
--- a/src/game/engine/tests/unit/test_save_manager.gd
+++ b/src/game/engine/tests/unit/test_save_manager.gd
@@ -1,34 +1,263 @@
 extends GutTest
-## SaveManager unit tests.
+## SaveManager unit tests — on-disk save/load layer.
 ##
-## PENDING: SaveManager is currently a 3-line stub
-## (`src/game/engine/src/core/save_manager.gd`). The previous test suite was
-## written against a full SAVE_DIR / SAVE_EXTENSION / save_game / load_game /
-## save_slot / load_slot / get_save_slots / delete_save / MAX_SLOTS API that
-## no longer exists in this repo. `GameState.serialize()` / `deserialize()`
-## are implemented (iter 7l Player fields + iter 7i Unit fields land in
-## those snapshots) but the on-disk file layer has not been re-ported.
+## Iter 7o Track C: SaveManager was restored from a 3-line stub to a real
+## file layer over GameState.serialize() / deserialize(). These tests cover:
+##   * round-trip integrity (write → load into cleared state → fields match)
+##   * byte-identical re-save (deterministic JSON stringify)
+##   * multi-slot isolation (slot 0 and slot 1 don't collide)
+##   * get_save_slots() lists only populated slots with correct metadata
+##   * delete_save() removes a slot and leaves others intact
+##   * missing-file and out-of-range loads fail gracefully (no crash)
+##   * autosave() writes a dedicated slot without affecting manual slot list
 ##
-## When SaveManager is rebuilt, these round-trip tests should be updated
-## against the current Player/Unit/City shapes:
-##   Player (iter 7l): index, player_name, race_id, gender_preset, is_human,
-##     color, gold, gold_per_turn, golden_age_active, happiness,
-##     culture_per_turn, culture_total, researching, research_progress,
-##     science_per_turn, researched_techs, schools, mana_pool, mana_income,
-##     mana_cap, pending_improvements, strategic_axes, ascension_active
-##   Unit (iter 7i): unit_id, display_name, position, owner, hp, max_hp,
-##     attack, defense, ranged_attack, movement_remaining, max_movement,
-##     has_attacked, is_fortified, fortified_turns, xp, level, promo_ids,
-##     equipped_items, infusions, channeled_infusion
-##   City: id, city_name, owner, position, is_capital, turn_founded,
-##     buildings, production_queue, production_progress (population /
-##     food_stored / culture_stored now live on the Rust GdCity instance and
-##     are read via getters, not fields).
+## Tests operate on user://saves/ and clean up after themselves. They do not
+## depend on DataLoader or full game bootstrap — only GameState.initialize_game
+## plus a couple of Players are needed to exercise the serialize path.
+
+const SaveManagerScript: GDScript = preload("res://engine/src/core/save_manager.gd")
+const PlayerScript: GDScript = preload("res://engine/src/entities/player.gd")
 
 
-func test_save_manager_is_pending() -> void:
-	pending(
-		"SaveManager is a stub — on-disk save/load layer not yet re-ported. "
-		+ "GameState.serialize/deserialize are implemented and covered "
-		+ "indirectly by other tests."
+func before_each() -> void:
+	_reset_save_dir()
+	_seed_game_state()
+
+
+func after_each() -> void:
+	_reset_save_dir()
+
+
+## ── round-trip integrity ───────────────────────────────────────────────
+
+func test_save_then_load_restores_scalar_fields() -> void:
+	var save_err: Error = SaveManagerScript.save_game(0)
+	assert_eq(save_err, OK, "save_game(0) must succeed")
+
+	# Mutate in-memory state so a failed load is visible.
+	GameState.turn_number = 999
+	GameState.era = 7
+	GameState.current_player_index = 3
+	GameState.players = []
+
+	var load_err: Error = SaveManagerScript.load_game(0)
+	assert_eq(load_err, OK, "load_game(0) must succeed")
+	assert_eq(GameState.turn_number, 12, "turn_number must be restored")
+	assert_eq(GameState.era, 2, "era must be restored")
+	assert_eq(GameState.current_player_index, 1, "current_player_index must be restored")
+	assert_eq(GameState.players.size(), 2, "players array must be restored")
+
+
+func test_save_then_load_restores_player_fields() -> void:
+	SaveManagerScript.save_game(0)
+	GameState.players = []
+	SaveManagerScript.load_game(0)
+
+	assert_eq(GameState.players.size(), 2, "two players round-tripped")
+	var p0: RefCounted = GameState.players[0]
+	assert_eq(p0.player_name, "Thorin", "player 0 name restored")
+	assert_eq(p0.race_id, "dwarf", "player 0 race restored")
+	assert_eq(p0.gold, 125, "player 0 gold restored")
+	assert_true(p0.is_human, "player 0 is_human restored")
+	var p1: RefCounted = GameState.players[1]
+	assert_eq(p1.player_name, "Arwen", "player 1 name restored")
+	assert_eq(p1.race_id, "high_elf", "player 1 race restored")
+
+
+func test_resave_is_byte_identical() -> void:
+	## Envelope-level timestamp changes between saves, so compare the
+	## deterministic `game_state` subsection instead.
+	SaveManagerScript.save_game(0)
+	var first_state: String = JSON.stringify(_read_slot_game_state(0), "\t", true)
+	SaveManagerScript.load_game(0)
+	SaveManagerScript.save_game(0)
+	var second_state: String = JSON.stringify(_read_slot_game_state(0), "\t", true)
+	assert_eq(first_state, second_state, "save→load→save game_state must be identical")
+
+
+## ── multi-slot isolation ───────────────────────────────────────────────
+
+func test_slots_are_independent() -> void:
+	SaveManagerScript.save_game(0)
+
+	GameState.turn_number = 50
+	GameState.players[0].gold = 9999
+	SaveManagerScript.save_game(1)
+
+	SaveManagerScript.load_game(0)
+	assert_eq(GameState.turn_number, 12, "slot 0 reload restores turn 12")
+	assert_eq(GameState.players[0].gold, 125, "slot 0 reload restores gold 125")
+
+	SaveManagerScript.load_game(1)
+	assert_eq(GameState.turn_number, 50, "slot 1 reload restores turn 50")
+	assert_eq(GameState.players[0].gold, 9999, "slot 1 reload restores gold 9999")
+
+
+## ── get_save_slots ─────────────────────────────────────────────────────
+
+func test_get_save_slots_lists_populated_slots_only() -> void:
+	SaveManagerScript.save_game(0)
+	SaveManagerScript.save_game(3)
+
+	var metas: Array[Dictionary] = SaveManagerScript.get_save_slots()
+	assert_eq(metas.size(), 2, "only two populated slots must appear")
+	assert_eq(metas[0].get("slot"), 0, "first entry is slot 0")
+	assert_eq(metas[1].get("slot"), 3, "second entry is slot 3")
+	assert_eq(metas[0].get("turn"), 12, "slot 0 meta turn")
+	assert_eq(metas[0].get("era"), 2, "slot 0 meta era")
+	assert_eq(metas[0].get("player_name"), "Thorin", "slot 0 meta picks human player")
+	assert_gt(metas[0].get("timestamp", 0), 0, "slot 0 meta timestamp populated")
+
+
+func test_get_save_slots_is_empty_when_no_saves() -> void:
+	var metas: Array[Dictionary] = SaveManagerScript.get_save_slots()
+	assert_eq(metas.size(), 0, "no slots → empty array")
+
+
+## ── delete_save ────────────────────────────────────────────────────────
+
+func test_delete_save_removes_slot() -> void:
+	SaveManagerScript.save_game(0)
+	SaveManagerScript.save_game(1)
+
+	var del_err: Error = SaveManagerScript.delete_save(0)
+	assert_eq(del_err, OK, "delete_save(0) must succeed")
+	assert_false(SaveManagerScript.slot_exists(0), "slot 0 removed")
+	assert_true(SaveManagerScript.slot_exists(1), "slot 1 untouched")
+
+
+func test_delete_missing_slot_returns_does_not_exist() -> void:
+	var del_err: Error = SaveManagerScript.delete_save(5)
+	assert_eq(del_err, ERR_DOES_NOT_EXIST, "deleting an empty slot reports ERR_DOES_NOT_EXIST")
+
+
+## ── error paths ────────────────────────────────────────────────────────
+
+func test_load_missing_slot_returns_does_not_exist() -> void:
+	var err: Error = SaveManagerScript.load_game(4)
+	assert_eq(err, ERR_DOES_NOT_EXIST, "loading an empty slot must not crash")
+
+
+func test_out_of_range_slot_rejected() -> void:
+	var save_err: Error = SaveManagerScript.save_game(SaveManagerScript.MAX_SLOTS)
+	assert_eq(save_err, ERR_INVALID_PARAMETER, "slot == MAX_SLOTS is rejected")
+	var load_err: Error = SaveManagerScript.load_game(-1)
+	assert_eq(load_err, ERR_INVALID_PARAMETER, "slot == -1 is rejected")
+	# SaveManager reports via push_error; mark tracked errors as handled so
+	# GUT does not flag the test as having unexpected errors.
+	for err: GutTrackedError in get_errors():
+		err.handled = true
+
+
+func test_corrupt_file_returns_error_not_crash() -> void:
+	SaveManagerScript._ensure_save_dir()
+	var path: String = SaveManagerScript.SAVE_DIR + "save_2" + SaveManagerScript.SAVE_EXTENSION
+	var file: FileAccess = FileAccess.open(path, FileAccess.WRITE)
+	file.store_string("{not valid json")
+	file.close()
+
+	var err: Error = SaveManagerScript.load_game(2)
+	assert_ne(err, OK, "corrupt file does not report OK")
+	assert_ne(err, ERR_DOES_NOT_EXIST, "corrupt file is not reported as missing")
+	for tracked: GutTrackedError in get_errors():
+		tracked.handled = true
+
+
+## ── autosave ───────────────────────────────────────────────────────────
+
+func test_autosave_writes_dedicated_slot() -> void:
+	SaveManagerScript.autosave()
+	var autosave_path: String = (
+		SaveManagerScript.SAVE_DIR
+		+ SaveManagerScript.AUTOSAVE_SLOT_NAME
+		+ SaveManagerScript.SAVE_EXTENSION
 	)
+	assert_true(FileAccess.file_exists(autosave_path), "autosave file must exist")
+
+	# Manual slot list must ignore the autosave file.
+	var metas: Array[Dictionary] = SaveManagerScript.get_save_slots()
+	assert_eq(metas.size(), 0, "autosave does not appear in manual slot list")
+
+
+func test_autosave_then_load_autosave_round_trips() -> void:
+	SaveManagerScript.autosave()
+	GameState.turn_number = 1
+	GameState.players = []
+
+	var err: Error = SaveManagerScript.load_autosave()
+	assert_eq(err, OK, "load_autosave must succeed")
+	assert_eq(GameState.turn_number, 12, "autosave restores turn_number")
+	assert_eq(GameState.players.size(), 2, "autosave restores players")
+
+
+## ── helpers ────────────────────────────────────────────────────────────
+
+func _seed_game_state() -> void:
+	# Build GameState directly — `initialize_game` calls DataLoader which is
+	# not bootstrapped in the GUT harness. Only the fields SaveManager reads
+	# need to be set; other GameState fields are left at their declared defaults.
+	GameState.current_theme = "fantasy"
+	GameState.turn_number = 12
+	GameState.era = 2
+	GameState.current_player_index = 1
+	GameState.players = []
+	GameState.layers = []
+	GameState.transit_nodes = []
+	GameState.wonders_built = {}
+	GameState.ascension_rituals = {}
+	GameState.ley_anchors = []
+	GameState.npc_buildings = []
+	GameState._npc_buildings_by_tile = {}
+	GameState.game_settings = {"num_players": 2}
+
+	var human: RefCounted = PlayerScript.new()
+	human.player_name = "Thorin"
+	human.race_id = "dwarf"
+	human.is_human = true
+	human.gold = 125
+	human.gold_per_turn = 7
+	human.happiness = 4
+	human.culture_total = 33
+	GameState.add_player(human)
+
+	var ai: RefCounted = PlayerScript.new()
+	ai.player_name = "Arwen"
+	ai.race_id = "high_elf"
+	ai.is_human = false
+	ai.gold = 80
+	GameState.add_player(ai)
+
+
+func _reset_save_dir() -> void:
+	if not DirAccess.dir_exists_absolute(SaveManagerScript.SAVE_DIR):
+		return
+	var dir: DirAccess = DirAccess.open(SaveManagerScript.SAVE_DIR)
+	if dir == null:
+		return
+	dir.list_dir_begin()
+	var name: String = dir.get_next()
+	while name != "":
+		if not dir.current_is_dir():
+			dir.remove(name)
+		name = dir.get_next()
+	dir.list_dir_end()
+
+
+func _read_slot_game_state(slot: int) -> Dictionary:
+	var path: String = (
+		SaveManagerScript.SAVE_DIR
+		+ "save_%d" % slot
+		+ SaveManagerScript.SAVE_EXTENSION
+	)
+	var file: FileAccess = FileAccess.open(path, FileAccess.READ)
+	if file == null:
+		return {}
+	var text: String = file.get_as_text()
+	file.close()
+	var parser: JSON = JSON.new()
+	if parser.parse(text) != OK:
+		return {}
+	if not parser.data is Dictionary:
+		return {}
+	var envelope: Dictionary = parser.data as Dictionary
+	return envelope.get("game_state", {})