fix(cli): honor env precedence for LLM and run config

Interactive selections and flag defaults overrode TRADINGAGENTS_* env vars.
Rule: an explicit env value or CLI flag wins; otherwise the env-applied
default is kept.

- Research depth: skip the prompt when both round-count env vars are set, and
  stop overwriting them (#977).
- Checkpoint: --checkpoint/--no-checkpoint is tri-state; omitting it keeps
  TRADINGAGENTS_CHECKPOINT_ENABLED (#976).
- Docker ollama: use TRADINGAGENTS_LLM_PROVIDER + OLLAMA_BASE_URL, not a bare
  LLM_PROVIDER the overlay never reads (#975).
- Reasoning/thinking knobs: settable via env; the prompt is skipped when set.
- Effort gating: forward effort only to models that accept it (Anthropic
  Opus 4.5+/Sonnet 4.6+, OpenAI reasoning models); drop it elsewhere.
- Boolean env values: raise a named error on invalid input instead of
  silently becoming False.

tests/test_openai_reasoning_effort.py

@@ -0,0 +1,42 @@
+"""OpenAI ``reasoning_effort`` is gated to reasoning models.
+
+Non-reasoning OpenAI models (gpt-4.1, gpt-4o, ...) 400 with "Unsupported
+parameter: 'reasoning.effort'". The client must drop the kwarg for those rather
+than forward it and crash the run. The GPT-5 family and the o-series accept it.
+"""
+
+import pytest
+
+from tradingagents.llm_clients.openai_client import (
+    OpenAIClient,
+    _supports_reasoning_effort,
+)
+
+
+@pytest.mark.parametrize(
+    "model,expected",
+    [
+        ("gpt-5.5", True), ("gpt-5.4", True), ("gpt-5.4-mini", True),
+        ("gpt-5.5-pro", True), ("o1", True), ("o3-mini", True),
+        ("gpt-4.1", False), ("gpt-4o", False), ("gpt-4o-mini", False),
+        ("gpt-3.5-turbo", False),
+    ],
+)
+def test_supports_reasoning_effort(model, expected):
+    assert _supports_reasoning_effort(model) is expected
+
+
+def _effort_on(model, monkeypatch):
+    # A fake key lets get_llm() construct the client without a network call.
+    monkeypatch.setenv("OPENAI_API_KEY", "test-key")
+    llm = OpenAIClient(model, provider="openai", reasoning_effort="low").get_llm()
+    return getattr(llm, "reasoning_effort", None)
+
+
+def test_reasoning_model_receives_effort(monkeypatch):
+    assert _effort_on("gpt-5.4-mini", monkeypatch) == "low"
+
+
+def test_non_reasoning_model_drops_effort(monkeypatch):
+    # gpt-4.1 would 400 with reasoning_effort — it must be dropped.
+    assert _effort_on("gpt-4.1", monkeypatch) is None