feat(ai): add model caching, settings, and commands

- Introduce model caching with persistence to preferences
- Add provider default model and custom settings management
- Implement `/ai switch`, `/ai models`, and improve `/ai start`
- Add model name autocomplete for chat commands
- Update command definitions and help text
- Add unit tests for new functionality

tests/unittests/test_ai_client.c

@@ -461,3 +461,186 @@ test_ai_providers_find_case_insensitive(void** state)
     assert_non_null(result);
     assert_string_equal("openai", result);
 }
+
+/* ========================================================================
+ * AI Autocomplete Integration Tests
+ * ======================================================================== */
+
+void
+test_ai_start_provider_autocomplete_only_on_exact(void** state)
+{
+    auto_gchar gchar* result = ai_providers_find("", FALSE, NULL);
+    assert_non_null(result);
+    assert_string_equal("openai", result);
+}
+
+void
+test_ai_models_find_null_session(void** state)
+{
+    auto_gchar gchar* result = ai_models_find("gpt", FALSE, NULL);
+    assert_null(result);
+}
+
+void
+test_ai_models_find_null_provider(void** state)
+{
+    ai_add_provider("temp", "https://temp.api.com/v1", NULL);
+    AISession* session = ai_session_create("temp", "gpt-4");
+    assert_non_null(session);
+    ai_session_unref(session);
+}
+
+void
+test_ai_providers_find_cycling(void** state)
+{
+    /* NULL search_str should cycle through providers */
+    auto_gchar gchar* result1 = ai_providers_find(NULL, FALSE, NULL);
+    assert_non_null(result1);
+
+    auto_gchar gchar* result2 = ai_providers_find(NULL, FALSE, NULL);
+    assert_non_null(result2);
+
+    /* Cycling: consecutive calls with NULL should return different providers */
+    assert_string_not_equal(result1, result2);
+}
+
+/* ========================================================================
+ * Provider Default Model and Settings Tests
+ * ======================================================================== */
+
+void
+test_ai_set_provider_default_model(void** state)
+{
+    /* Set default model for openai provider */
+    ai_set_provider_default_model("openai", "gpt-5");
+
+    /* Verify the model was set */
+    const gchar* model = ai_get_provider_default_model("openai");
+    assert_non_null(model);
+    assert_string_equal("gpt-5", model);
+
+    /* Update default model */
+    ai_set_provider_default_model("openai", "gpt-4o");
+    model = ai_get_provider_default_model("openai");
+    assert_non_null(model);
+    assert_string_equal("gpt-4o", model);
+
+    /* Set default model for perplexity */
+    ai_set_provider_default_model("perplexity", "sonar-pro");
+    model = ai_get_provider_default_model("perplexity");
+    assert_non_null(model);
+    assert_string_equal("sonar-pro", model);
+}
+
+void
+test_ai_get_provider_default_model(void** state)
+{
+    /* NULL provider returns NULL */
+    assert_null(ai_get_provider_default_model(NULL));
+
+    /* Non-existent provider returns NULL */
+    assert_null(ai_get_provider_default_model("nonexistent"));
+
+    /* Default providers may or may not have default models set initially */
+    /* After setting, they should return the model */
+    ai_set_provider_default_model("openai", "test-model");
+    assert_string_equal("test-model", ai_get_provider_default_model("openai"));
+
+    /* NULL model argument should be ignored (no change) */
+    ai_set_provider_default_model("openai", NULL);
+    /* After setting NULL, the model should still be "test-model" because
+     * ai_set_provider_default_model returns early on NULL model */
+    assert_string_equal("test-model", ai_get_provider_default_model("openai"));
+}
+
+void
+test_ai_set_provider_setting(void** state)
+{
+    /* NULL provider should be ignored */
+    ai_set_provider_setting(NULL, "tools", "enabled");
+
+    /* NULL setting should be ignored */
+    ai_set_provider_setting("openai", NULL, "enabled");
+
+    /* Non-existent provider should log warning but not crash */
+    ai_set_provider_setting("nonexistent", "tools", "enabled");
+
+    /* Set a setting for openai */
+    ai_set_provider_setting("openai", "tools", "enabled");
+    ai_set_provider_setting("openai", "search", "disabled");
+
+    /* Verify settings were set */
+    gchar* tools = ai_get_provider_setting("openai", "tools");
+    assert_non_null(tools);
+    assert_string_equal("enabled", tools);
+    g_free(tools);
+
+    gchar* search = ai_get_provider_setting("openai", "search");
+    assert_non_null(search);
+    assert_string_equal("disabled", search);
+    g_free(search);
+
+    /* NULL value removes the setting */
+    ai_set_provider_setting("openai", "tools", NULL);
+    tools = ai_get_provider_setting("openai", "tools");
+    assert_null(tools);
+
+    /* Setting that was never set returns NULL */
+    assert_null(ai_get_provider_setting("openai", "nonexistent_setting"));
+}
+
+void
+test_ai_get_provider_setting(void** state)
+{
+    /* NULL provider returns NULL */
+    assert_null(ai_get_provider_setting(NULL, "tools"));
+
+    /* NULL setting returns NULL */
+    assert_null(ai_get_provider_setting("openai", NULL));
+
+    /* Non-existent provider returns NULL */
+    assert_null(ai_get_provider_setting("nonexistent", "tools"));
+
+    /* Provider without settings returns NULL */
+    assert_null(ai_get_provider_setting("perplexity", "tools"));
+
+    /* Set and get setting */
+    ai_set_provider_setting("openai", "temperature", "0.7");
+    gchar* temp = ai_get_provider_setting("openai", "temperature");
+    assert_non_null(temp);
+    assert_string_equal("0.7", temp);
+    g_free(temp);
+
+    /* Setting value is a copy (caller must free) */
+    ai_set_provider_setting("openai", "max_tokens", "2048");
+    temp = ai_get_provider_setting("openai", "max_tokens");
+    assert_non_null(temp);
+    assert_string_equal("2048", temp);
+    g_free(temp);
+}
+
+/* ========================================================================
+ * Model Caching Tests
+ * ======================================================================== */
+
+void
+test_ai_models_are_fresh_initial(void** state)
+{
+    /* After init, models should be fresh (or at least not crash) */
+    /* The ai_client_init() loads models from prefs, which may be empty initially */
+    /* So we just verify the function works correctly */
+
+    /* NULL provider returns FALSE */
+    assert_false(ai_models_are_fresh(NULL));
+
+    /* Non-existent provider returns FALSE */
+    assert_false(ai_models_are_fresh("nonexistent"));
+
+    /* Default providers - check that function doesn't crash */
+    /* Freshness depends on whether models were loaded from prefs */
+    gboolean fresh_openai = ai_models_are_fresh("openai");
+    assert_true(fresh_openai == TRUE || fresh_openai == FALSE); /* Just verify no crash */
+
+    gboolean fresh_perplexity = ai_models_are_fresh("perplexity");
+    assert_true(fresh_perplexity == TRUE || fresh_perplexity == FALSE); /* Just verify no crash */
+}

tests/unittests/test_ai_client.h

@@ -40,3 +40,15 @@ void test_ai_providers_find_previous(void** state);
 void test_ai_providers_find_null_search_str(void** state);
 void test_ai_providers_find_empty_search_str(void** state);
 void test_ai_providers_find_case_insensitive(void** state);
+/* Provider default model and settings tests */
+void test_ai_set_provider_default_model(void** state);
+void test_ai_get_provider_default_model(void** state);
+void test_ai_set_provider_setting(void** state);
+void test_ai_get_provider_setting(void** state);
+/* Model caching tests */
+void test_ai_models_are_fresh_initial(void** state);
+/* AI autocomplete integration tests */
+void test_ai_start_provider_autocomplete_only_on_exact(void** state);
+void test_ai_models_find_null_session(void** state);
+void test_ai_models_find_null_provider(void** state);
+void test_ai_providers_find_cycling(void** state);

tests/unittests/unittests.c

@@ -690,6 +690,18 @@ main(int argc, char* argv[])
         cmocka_unit_test_setup_teardown(test_ai_providers_find_null_search_str, ai_client_setup, ai_client_teardown),
         cmocka_unit_test_setup_teardown(test_ai_providers_find_empty_search_str, ai_client_setup, ai_client_teardown),
         cmocka_unit_test_setup_teardown(test_ai_providers_find_case_insensitive, ai_client_setup, ai_client_teardown),
+        /* Provider default model and settings tests */
+        cmocka_unit_test_setup_teardown(test_ai_set_provider_default_model, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_get_provider_default_model, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_set_provider_setting, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_get_provider_setting, ai_client_setup, ai_client_teardown),
+        /* Model caching tests */
+        cmocka_unit_test_setup_teardown(test_ai_models_are_fresh_initial, ai_client_setup, ai_client_teardown),
+        /* AI autocomplete integration tests */
+        cmocka_unit_test_setup_teardown(test_ai_start_provider_autocomplete_only_on_exact, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_models_find_null_session, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_models_find_null_provider, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_providers_find_cycling, ai_client_setup, ai_client_teardown),
         cmocka_unit_test(test_ai_json_escape),
         cmocka_unit_test(test_ai_json_escape_null),
         cmocka_unit_test(test_ai_json_escape_empty),