diff --git a/tests/test_provider_state_migration.py b/tests/test_provider_state_migration.py
new file mode 100644
index 00000000..f2dc2626
--- /dev/null
+++ b/tests/test_provider_state_migration.py
@@ -0,0 +1,170 @@
+"""Regression-guard tests for src/provider_state.py
+Phase 3 of any_type_componentization_20260621. Verifies the 4-method
+ProviderHistory API is reachable and behaves correctly for all 6
+providers (anthropic/deepseek/minimax/qwen/grok/llama) following the
+migration of _X_history aliases in src/ai_client.py.
+CONVENTION: 1-space indentation. NO COMMENTS.
+"""
+from __future__ import annotations
+
+import threading
+
+import pytest
+from src import provider_state
+
+
+EXPECTED_PROVIDERS: tuple[str, ...] = ("anthropic", "deepseek", "minimax", "qwen", "grok", "llama")
+
+
+def _clear_all() -> None:
+ provider_state.clear_all()
+
+
+def test_each_provider_reachable() -> None:
+ histories = [provider_state.get_history(p) for p in EXPECTED_PROVIDERS]
+ assert all(isinstance(h, provider_state.ProviderHistory) for h in histories)
+ assert len({id(h) for h in histories}) == 6
+ for p in EXPECTED_PROVIDERS:
+  assert provider_state.get_history(p) is provider_state.get_history(p)
+
+
+def test_append_preserves_ordering() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  h = provider_state.get_history(p)
+  h.append({"role": "user", "content": f"{p}-1"})
+  h.append({"role": "assistant", "content": f"{p}-2"})
+  h.append({"role": "user", "content": f"{p}-3"})
+  assert h.get_all() == [
+   {"role": "user", "content": f"{p}-1"},
+   {"role": "assistant", "content": f"{p}-2"},
+   {"role": "user", "content": f"{p}-3"},
+  ]
+
+
+def test_lock_acquisition_no_deadlock() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  h = provider_state.get_history(p)
+  def inner() -> None:
+   with h.lock:
+    h.append({"role": "user", "content": f"{p}-inner"})
+  with h.lock:
+   assert len(h) == 0
+   inner()
+  assert len(h) == 1
+  assert h.get_all() == [{"role": "user", "content": f"{p}-inner"}]
+
+
+def test_concurrent_append_thread_safety() -> None:
+ h = provider_state.get_history("anthropic")
+ h.clear()
+ def worker(start: int) -> None:
+  for i in range(100):
+   role = "user" if (i % 2 == 0) else "assistant"
+   h.append({"role": role, "content": f"t{start}-{i}"})
+ threads = [threading.Thread(target=worker, args=(t,)) for t in range(2)]
+ for t in threads:
+  t.start()
+ for t in threads:
+  t.join()
+ all_msgs = h.get_all()
+ assert len(all_msgs) == 200
+ contents = {m["content"] for m in all_msgs}
+ assert len(contents) == 200
+
+
+def test_get_all_returns_copy() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  h = provider_state.get_history(p)
+  h.append({"role": "user", "content": f"{p}-original"})
+  snapshot = h.get_all()
+  snapshot.append({"role": "user", "content": f"{p}-leaked"})
+  assert h.get_all() == [{"role": "user", "content": f"{p}-original"}]
+
+
+def test_replace_all_replaces_state() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  h = provider_state.get_history(p)
+  h.append({"role": "user", "content": f"{p}-a"})
+  h.append({"role": "assistant", "content": f"{p}-b"})
+  h.append({"role": "user", "content": f"{p}-c"})
+  h.replace_all([{"role": "user", "content": "fresh"}])
+  assert len(h.get_all()) == 1
+  assert h.get_all() == [{"role": "user", "content": "fresh"}]
+
+
+def test_clear_resets_history() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  h = provider_state.get_history(p)
+  h.append({"role": "user", "content": "x"})
+  h.append({"role": "assistant", "content": "y"})
+  h.clear()
+  assert len(h.get_all()) == 0
+  assert bool(h) is False
+
+
+def test_getitem_returns_specific_message() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  h = provider_state.get_history(p)
+  h.append({"role": "user", "content": f"{p}-first"})
+  h.append({"role": "assistant", "content": f"{p}-mid"})
+  h.append({"role": "user", "content": f"{p}-last"})
+  assert h[0] == {"role": "user", "content": f"{p}-first"}
+  assert h[1] == {"role": "assistant", "content": f"{p}-mid"}
+  assert h[-1] == {"role": "user", "content": f"{p}-last"}
+
+
+def test_iter_returns_messages() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  h = provider_state.get_history(p)
+  h.append({"role": "user", "content": f"{p}-1"})
+  h.append({"role": "assistant", "content": f"{p}-2"})
+  h.append({"role": "user", "content": f"{p}-3"})
+  collected = [m for m in h]
+  assert collected == h.get_all()
+
+
+def test_len_returns_count() -> None:
+ _clear_all()
+ for n in (0, 1, 5, 10):
+  for p in EXPECTED_PROVIDERS:
+   h = provider_state.get_history(p)
+   h.clear()
+   for i in range(n):
+    h.append({"role": "user", "content": f"{p}-{i}"})
+   assert len(h) == n
+
+
+def test_bool_empty_vs_populated() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  h = provider_state.get_history(p)
+  assert bool(h) is False
+  h.append({"role": "user", "content": "x"})
+  assert bool(h) is True
+  h.clear()
+  assert bool(h) is False
+
+
+def test_clear_all_resets_all_6() -> None:
+ _clear_all()
+ for p in EXPECTED_PROVIDERS:
+  provider_state.get_history(p).append({"role": "user", "content": f"{p}-msg"})
+ provider_state.clear_all()
+ for p in EXPECTED_PROVIDERS:
+  assert len(provider_state.get_history(p).get_all()) == 0
+
+
+def test_providers_returns_6_tuple() -> None:
+ assert provider_state.providers() == EXPECTED_PROVIDERS
+
+
+def test_unknown_provider_raises() -> None:
+ with pytest.raises(KeyError):
+  provider_state.get_history("nonexistent")