test: 补充知识处理、检索与 Agent 回归用例

覆盖切块、向量检索、工具调用和历史预算；模型相关用例使用桩。

backend/tests/utils/test_model_context.py

@@ -0,0 +1,62 @@
+"""
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+from app.core.config import settings
+from app.utils.model_context import (
+    context_tokens_for,
+    faq_batch_chars_for,
+    output_tokens_for,
+)
+
+
+def test_longest_prefix_wins():
+    assert context_tokens_for("OPENAI", "gpt-4o-mini") == 128_000
+    assert context_tokens_for("OPENAI", "gpt-4") == 8_000  # bare gpt-4, not gpt-4o
+    assert context_tokens_for("MISTRAL", "mistral-large-latest") == 128_000
+    assert context_tokens_for("MISTRAL", "mistral-small") == 32_000
+
+
+def test_unknown_model_falls_back_to_provider_default():
+    assert context_tokens_for("ANTHROPIC", "some-future-model") == 200_000
+    assert context_tokens_for("GROQ", "unknown") == 8_000
+    assert context_tokens_for("", "") == 8_000  # unknown provider → global floor
+
+
+def test_env_override_wins(monkeypatch):
+    monkeypatch.setattr(settings, "FAQ_CONTEXT_TOKENS_OVERRIDE", 42_000)
+    assert context_tokens_for("OPENAI", "gpt-4o") == 42_000
+
+
+def test_small_context_model_keeps_floor_batch():
+    batch_chars, max_faqs = faq_batch_chars_for("GROQ", "llama3-8b-8192")
+    assert batch_chars == settings.FAQ_MAX_BATCH_CHARS
+    assert max_faqs >= 15
+
+
+def test_large_context_model_hits_ceiling():
+    batch_chars, max_faqs = faq_batch_chars_for("ANTHROPIC", "claude-sonnet-5")
+    assert batch_chars == settings.FAQ_MAX_BATCH_CHARS_CEILING
+    assert batch_chars > settings.FAQ_MAX_BATCH_CHARS
+    assert 15 <= max_faqs <= 40
+
+
+def test_mid_context_model_lands_between_floor_and_ceiling():
+    batch_chars, _ = faq_batch_chars_for("OPENAI", "gpt-3.5-turbo")
+    assert settings.FAQ_MAX_BATCH_CHARS <= batch_chars <= settings.FAQ_MAX_BATCH_CHARS_CEILING
+
+
+def test_output_reserve_scales_with_faq_count():
+    assert output_tokens_for(40) > output_tokens_for(15) > 0