feat(ai): add AI client with multi-provider support and UI

Add an AI client module that integrates with OpenAI-compatible API
providers (OpenAI, Perplexity, and custom providers) to provide
AI-assisted responses within the profanity client.

The implementation includes:

- src/ai/ai_client.c/h: Core AI client with provider management,
  session handling, and async HTTP request handling via libcurl.
  Supports per-provider API keys stored in preferences, reference-
  counted sessions, and conversation history tracking.

- src/ui/window.c/window_list.c: New AI window type (ProfAiWin) for
  displaying AI conversations, with response streaming and error
  display capabilities.

- Command integration: New `/ai` command (cmd_defs.c, cmd_funcs.c)
  for creating sessions, sending prompts, and managing providers.
  Provider autocomplete support in cmd_ac.c.

- Preferences integration: API keys for providers are persisted in
  the preferences system (config/preferences.c).

- Unit tests: 472 lines of comprehensive tests covering provider
  management, session lifecycle, JSON escaping, and autocomplete
  (tests/unittests/test_ai_client.c).

Architecture decisions:
- Asynchronous design: HTTP requests run on a separate thread to
  avoid blocking the main UI loop. Callbacks are invoked on the main
  thread via direct function call (profanity uses ncurses, not GLib
  main loop).
- Reference counting: Both AIProvider and AISession use ref counting
  for safe shared ownership.
- Response size limit: 10MB cap on HTTP responses to prevent OOM.

tests/unittests/test_ai_client.c

@@ -0,0 +1,472 @@
+#include "prof_cmocka.h"
+#include "common.h"
+#include "ai/ai_client.h"
+#include <stdlib.h>
+
+/* ========================================================================
+ * Setup/Teardown
+ * ======================================================================== */
+
+int
+ai_client_setup(void** state)
+{
+    ai_client_init();
+    return 0;
+}
+
+int
+ai_client_teardown(void** state)
+{
+    ai_client_shutdown();
+    return 0;
+}
+
+/* ========================================================================
+ * Provider Management Tests
+ * ======================================================================== */
+
+void
+test_ai_client_init(void** state)
+{
+    /* After init, default providers should exist */
+    AIProvider* openai = ai_get_provider("openai");
+    assert_non_null(openai);
+    assert_string_equal("openai", openai->name);
+    assert_string_equal("https://api.openai.com/v1/chat/completions", openai->api_url);
+
+    AIProvider* perplexity = ai_get_provider("perplexity");
+    assert_non_null(perplexity);
+    assert_string_equal("perplexity", perplexity->name);
+    assert_string_equal("https://api.perplexity.ai/v1/chat/completions", perplexity->api_url);
+}
+
+void
+test_ai_add_provider(void** state)
+{
+    /* Add a custom provider (hash table owns ref; caller gets non-owning pointer) */
+    AIProvider* provider = ai_add_provider("custom", "https://custom.api.com/v1", "my-org");
+    assert_non_null(provider);
+    assert_string_equal("custom", provider->name);
+    assert_string_equal("https://custom.api.com/v1", provider->api_url);
+    assert_string_equal("my-org", provider->org_id);
+
+    /* Update existing provider (returns ref; caller owns it) */
+    AIProvider* updated = ai_add_provider("custom", "https://new.api.com/v1", NULL);
+    assert_non_null(updated);
+    assert_string_equal("https://new.api.com/v1", updated->api_url);
+    assert_null(updated->org_id);
+
+    ai_provider_unref(updated);
+}
+
+void
+test_ai_remove_provider(void** state)
+{
+    /* Remove default provider should fail */
+    assert_false(ai_remove_provider("nonexistent"));
+
+    /* Add and remove custom provider */
+    ai_add_provider("temp", "https://temp.api.com/v1", NULL);
+    assert_true(ai_remove_provider("temp"));
+    assert_null(ai_get_provider("temp"));
+}
+
+void
+test_ai_list_providers(void** state)
+{
+    GList* providers = ai_list_providers();
+    assert_non_null(providers);
+    assert_int_equal(2, g_list_length(providers)); /* openai and perplexity */
+
+    /* Free list and unref providers (ai_list_providers returns ref'd providers) */
+    for (GList* l = providers; l; l = g_list_next(l)) {
+        ai_provider_unref(l->data);
+    }
+    g_list_free(providers);
+
+    /* Add another provider */
+    ai_add_provider("test", "https://test.api.com/v1", NULL);
+    providers = ai_list_providers();
+    assert_int_equal(3, g_list_length(providers));
+
+    /* Free list and unref providers */
+    for (GList* l = providers; l; l = g_list_next(l)) {
+        ai_provider_unref(l->data);
+    }
+    g_list_free(providers);
+}
+
+/* ========================================================================
+ * API Key Tests
+ * ======================================================================== */
+
+void
+test_ai_set_provider_key(void** state)
+{
+    ai_set_provider_key("openai", "sk-test-key-123");
+    {
+        auto_gchar gchar* key = ai_get_provider_key("openai");
+        assert_non_null(key);
+        assert_string_equal("sk-test-key-123", key);
+    }
+
+    /* Update key */
+    ai_set_provider_key("openai", "sk-new-key-456");
+    {
+        auto_gchar gchar* key = ai_get_provider_key("openai");
+        assert_string_equal("sk-new-key-456", key);
+    }
+
+    /* Remove key */
+    ai_set_provider_key("openai", NULL);
+    {
+        auto_gchar gchar* key = ai_get_provider_key("openai");
+        assert_null(key);
+    }
+}
+
+void
+test_ai_get_provider_key(void** state)
+{
+    /* No key set initially */
+    {
+        auto_gchar gchar* key = ai_get_provider_key("openai");
+        assert_null(key);
+    }
+
+    /* Set and get key */
+    ai_set_provider_key("perplexity", "pplx-abc123");
+    {
+        auto_gchar gchar* key = ai_get_provider_key("perplexity");
+        assert_non_null(key);
+        assert_string_equal("pplx-abc123", key);
+    }
+
+    /* Wrong provider returns null */
+    {
+        auto_gchar gchar* key = ai_get_provider_key("openai");
+        assert_null(key);
+    }
+}
+
+/* ========================================================================
+ * Session Tests
+ * ======================================================================== */
+
+void
+test_ai_session_create(void** state)
+{
+    AISession* session = ai_session_create("openai", "gpt-4");
+    assert_non_null(session);
+    assert_string_equal("openai", session->provider_name);
+    assert_string_equal("gpt-4", session->model);
+    assert_null(session->api_key); /* No key set */
+
+    ai_session_unref(session);
+}
+
+void
+test_ai_session_ref_unref(void** state)
+{
+    AISession* session = ai_session_create("openai", "gpt-4");
+    assert_non_null(session);
+
+    /* Reference */
+    AISession* ref = ai_session_ref(session);
+    assert_true(ref == session);
+
+    /* Unreference twice */
+    ai_session_unref(session);
+    ai_session_unref(ref); /* Should free here */
+}
+
+void
+test_ai_session_add_message(void** state)
+{
+    AISession* session = ai_session_create("openai", "gpt-4");
+    assert_non_null(session);
+
+    ai_session_add_message(session, "user", "Hello");
+    ai_session_add_message(session, "assistant", "Hi there!");
+
+    assert_int_equal(2, g_list_length(session->history));
+
+    AIMessage* first = session->history->data;
+    assert_string_equal("user", first->role);
+    assert_string_equal("Hello", first->content);
+
+    AIMessage* second = g_list_next(session->history)->data;
+    assert_string_equal("assistant", second->role);
+    assert_string_equal("Hi there!", second->content);
+
+    ai_session_unref(session);
+}
+
+void
+test_ai_session_clear_history(void** state)
+{
+    AISession* session = ai_session_create("openai", "gpt-4");
+
+    ai_session_add_message(session, "user", "Message 1");
+    ai_session_add_message(session, "user", "Message 2");
+    ai_session_add_message(session, "assistant", "Response");
+
+    assert_int_equal(3, g_list_length(session->history));
+
+    ai_session_clear_history(session);
+    assert_int_equal(0, g_list_length(session->history));
+
+    ai_session_unref(session);
+}
+
+void
+test_ai_session_set_model(void** state)
+{
+    AISession* session = ai_session_create("openai", "gpt-4");
+    assert_string_equal("gpt-4", session->model);
+
+    ai_session_set_model(session, "gpt-3.5-turbo");
+    assert_string_equal("gpt-3.5-turbo", session->model);
+
+    ai_session_unref(session);
+}
+
+/* ========================================================================
+ * JSON Escape Tests
+ * ======================================================================== */
+
+void
+test_ai_json_escape(void** state)
+{
+    gchar* escaped = ai_json_escape("hello \"world\"");
+    assert_string_equal("hello \\\"world\\\"", escaped);
+    g_free(escaped);
+}
+
+void
+test_ai_json_escape_null(void** state)
+{
+    gchar* escaped = ai_json_escape(NULL);
+    assert_string_equal("", escaped);
+    g_free(escaped);
+}
+
+void
+test_ai_json_escape_empty(void** state)
+{
+    gchar* escaped = ai_json_escape("");
+    assert_string_equal("", escaped);
+    g_free(escaped);
+}
+
+void
+test_ai_json_escape_special_chars(void** state)
+{
+    gchar* escaped = ai_json_escape("line1\nline2\ttab\\backslash\"quote");
+    assert_string_equal("line1\\nline2\\ttab\\\\backslash\\\"quote", escaped);
+    g_free(escaped);
+}
+
+void
+test_ai_json_escape_percent_signs(void** state)
+{
+    /* Critical: % characters in content must be escaped for JSON, not treated as format specifiers */
+    gchar* escaped = ai_json_escape("100% complete with %s and %d format strings");
+    assert_string_equal("100% complete with %s and %d format strings", escaped);
+    g_free(escaped);
+}
+
+void
+test_ai_json_escape_backslash_quote(void** state)
+{
+    /* Test escaped quote handling */
+    gchar* escaped = ai_json_escape("He said \"hello\" and \\ goodbye");
+    assert_string_equal("He said \\\"hello\\\" and \\\\ goodbye", escaped);
+    g_free(escaped);
+}
+
+void
+test_ai_session_api_key_is_copied(void** state)
+{
+    /* Verify that session owns its own copy of the API key */
+    ai_set_provider_key("openai", "sk-test-key-123");
+
+    AISession* session = ai_session_create("openai", "gpt-4");
+    assert_non_null(session);
+    assert_string_equal("sk-test-key-123", session->api_key);
+
+    /* Remove the provider key - session should still have its copy */
+    ai_set_provider_key("openai", NULL);
+    assert_non_null(session->api_key);
+    assert_string_equal("sk-test-key-123", session->api_key);
+
+    ai_session_unref(session);
+}
+
+void
+test_ai_add_provider_update_existing(void** state)
+{
+    /* Add a provider (hash table owns ref) */
+    AIProvider* provider = ai_add_provider("custom", "https://first.api.com/v1", "org1");
+    assert_non_null(provider);
+    assert_string_equal("https://first.api.com/v1", provider->api_url);
+    assert_string_equal("org1", provider->org_id);
+
+    /* Update the same provider (returns ref) */
+    provider = ai_add_provider("custom", "https://second.api.com/v1", "org2");
+    assert_non_null(provider);
+    assert_string_equal("https://second.api.com/v1", provider->api_url);
+    assert_string_equal("org2", provider->org_id);
+    ai_provider_unref(provider);
+}
+
+void
+test_ai_add_provider_null_name_returns_null(void** state)
+{
+    assert_null(ai_add_provider(NULL, "https://api.com/v1", NULL));
+}
+
+void
+test_ai_add_provider_null_url_returns_null(void** state)
+{
+    assert_null(ai_add_provider("test", NULL, NULL));
+}
+
+void
+test_ai_session_create_null_provider_returns_null(void** state)
+{
+    assert_null(ai_session_create("nonexistent", "gpt-4"));
+}
+
+void
+test_ai_session_create_null_model_returns_null(void** state)
+{
+    assert_null(ai_session_create("openai", NULL));
+}
+
+void
+test_ai_session_api_key_null_when_no_key_set(void** state)
+{
+    /* openai has no key set by default */
+    AISession* session = ai_session_create("openai", "gpt-4");
+    assert_non_null(session);
+    assert_null(session->api_key);
+    ai_session_unref(session);
+}
+
+/* ========================================================================
+ * Provider Autocomplete Tests
+ * ======================================================================== */
+
+void
+test_ai_providers_find_forward(void** state)
+{
+    /* Test forward iteration - should return first match */
+    char* result = ai_providers_find("o", FALSE, NULL);
+    assert_non_null(result);
+    assert_string_equal("openai", result);
+    g_free(result);
+}
+
+void
+test_ai_providers_find_forward_perplexity(void** state)
+{
+    /* Test forward iteration for perplexity */
+    char* result = ai_providers_find("p", FALSE, NULL);
+    assert_non_null(result);
+    assert_string_equal("perplexity", result);
+    g_free(result);
+}
+
+void
+test_ai_providers_find_forward_custom(void** state)
+{
+    /* Add a custom provider and test */
+    ai_add_provider("custom", "https://custom.api.com/v1", NULL);
+
+    char* result = ai_providers_find("c", FALSE, NULL);
+    assert_non_null(result);
+    assert_string_equal("custom", result);
+    g_free(result);
+}
+
+void
+test_ai_providers_find_forward_no_match(void** state)
+{
+    /* Test no match */
+    char* result = ai_providers_find("z", FALSE, NULL);
+    assert_null(result);
+}
+
+void
+test_ai_providers_find_forward_partial_match(void** state)
+{
+    /* Test partial match - should return providers starting with "ope" */
+    char* result = ai_providers_find("ope", FALSE, NULL);
+    assert_non_null(result);
+    assert_string_equal("openai", result);
+    g_free(result);
+}
+
+void
+test_ai_providers_find_next(void** state)
+{
+    /* Test that stateless implementation returns same result each call */
+    char* result1 = ai_providers_find("o", FALSE, NULL);
+    assert_non_null(result1);
+    assert_string_equal("openai", result1);
+    g_free(result1);
+
+    /* Second call with same params returns same result (stateless) */
+    char* result2 = ai_providers_find("o", FALSE, NULL);
+    assert_non_null(result2);
+    assert_string_equal("openai", result2);
+    g_free(result2);
+}
+
+void
+test_ai_providers_find_previous(void** state)
+{
+    /* Test that previous=TRUE returns last match in list */
+    /* With only "openai" starting with "o", both FALSE and TRUE return same result */
+    char* result1 = ai_providers_find("o", FALSE, NULL);
+    assert_non_null(result1);
+    assert_string_equal("openai", result1);
+    g_free(result1);
+
+    /* previous=TRUE also returns "openai" (only one match, so first==last) */
+    char* result2 = ai_providers_find("o", TRUE, NULL);
+    assert_non_null(result2);
+    assert_string_equal("openai", result2);
+    g_free(result2);
+}
+
+void
+test_ai_providers_find_null_search_str(void** state)
+{
+    char* result = ai_providers_find(NULL, FALSE, NULL);
+    assert_null(result);
+}
+
+void
+test_ai_providers_find_empty_search_str(void** state)
+{
+    char* result = ai_providers_find("", FALSE, NULL);
+    assert_null(result);
+}
+
+void
+test_ai_providers_find_case_sensitive(void** state)
+{
+    /* Test that matching is case-sensitive */
+    char* result = ai_providers_find("OPENAI", FALSE, NULL);
+    assert_null(result);
+
+    result = ai_providers_find("OpenAI", FALSE, NULL);
+    assert_null(result);
+
+    result = ai_providers_find("openai", FALSE, NULL);
+    assert_non_null(result);
+    assert_string_equal("openai", result);
+    g_free(result);
+}

tests/unittests/test_ai_client.h

@@ -0,0 +1,42 @@
+/*
+ * test_ai_client.h - AI client unit test declarations
+ */
+
+int ai_client_setup(void** state);
+int ai_client_teardown(void** state);
+
+void test_ai_client_init(void** state);
+void test_ai_add_provider(void** state);
+void test_ai_remove_provider(void** state);
+void test_ai_list_providers(void** state);
+void test_ai_set_provider_key(void** state);
+void test_ai_get_provider_key(void** state);
+void test_ai_session_create(void** state);
+void test_ai_session_ref_unref(void** state);
+void test_ai_session_add_message(void** state);
+void test_ai_session_clear_history(void** state);
+void test_ai_session_set_model(void** state);
+void test_ai_json_escape(void** state);
+void test_ai_json_escape_null(void** state);
+void test_ai_json_escape_empty(void** state);
+void test_ai_json_escape_special_chars(void** state);
+void test_ai_json_escape_percent_signs(void** state);
+void test_ai_json_escape_backslash_quote(void** state);
+void test_ai_session_api_key_is_copied(void** state);
+void test_ai_add_provider_update_existing(void** state);
+void test_ai_add_provider_null_name_returns_null(void** state);
+void test_ai_add_provider_null_url_returns_null(void** state);
+void test_ai_session_create_null_provider_returns_null(void** state);
+void test_ai_session_create_null_model_returns_null(void** state);
+void test_ai_session_api_key_null_when_no_key_set(void** state);
+/* Provider autocomplete tests */
+void test_ai_providers_find_forward(void** state);
+void test_ai_providers_find_forward_perplexity(void** state);
+void test_ai_providers_find_forward_custom(void** state);
+void test_ai_providers_find_forward_no_match(void** state);
+void test_ai_providers_find_forward_partial_match(void** state);
+void test_ai_providers_find_next(void** state);
+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_sensitive(void** state);

tests/unittests/ui/stub_ai.c

@@ -0,0 +1,30 @@
+/*
+ * stub_ai.c - Stubs for AI window functions
+ */
+
+#include "ui/window.h"
+#include "ai/ai_client.h"
+
+ProfWin*
+win_create_ai(AISession* session)
+{
+    /* Return NULL to simulate failure in unit tests */
+    (void)session;
+    return NULL;
+}
+
+void
+aiwin_display_response(ProfAiWin* win, const char* response)
+{
+    /* Stub: do nothing */
+    (void)win;
+    (void)response;
+}
+
+void
+aiwin_display_error(ProfAiWin* win, const char* error_msg)
+{
+    /* Stub: do nothing */
+    (void)win;
+    (void)error_msg;
+}

tests/unittests/unittests.c

@@ -36,6 +36,7 @@
 #include "test_form.h"
 #include "test_callbacks.h"
 #include "test_plugins_disco.h"
+#include "test_ai_client.h"
 
 #define muc_unit_test(f) cmocka_unit_test_setup_teardown(f, muc_before_test, muc_after_test)
 
@@ -656,6 +657,43 @@ main(int argc, char* argv[])
         cmocka_unit_test_setup_teardown(test_allow_unencrypted_message_confirms_on_second_attempt, load_preferences, close_preferences),
         cmocka_unit_test_setup_teardown(test_cmd_force_encryption_invalid_policy, load_preferences, close_preferences),
         cmocka_unit_test_setup_teardown(test_allow_unencrypted_message_invalid_mode, load_preferences, close_preferences),
+
+        // AI client tests
+        cmocka_unit_test_setup_teardown(test_ai_client_init, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_add_provider, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_remove_provider, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_list_providers, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_set_provider_key, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_get_provider_key, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_create, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_ref_unref, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_add_message, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_clear_history, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_set_model, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_api_key_is_copied, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_add_provider_update_existing, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_add_provider_null_name_returns_null, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_add_provider_null_url_returns_null, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_create_null_provider_returns_null, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_create_null_model_returns_null, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_session_api_key_null_when_no_key_set, ai_client_setup, ai_client_teardown),
+        /* Provider autocomplete tests */
+        cmocka_unit_test_setup_teardown(test_ai_providers_find_forward, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_providers_find_forward_perplexity, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_providers_find_forward_custom, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_providers_find_forward_no_match, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_providers_find_forward_partial_match, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_providers_find_next, ai_client_setup, ai_client_teardown),
+        cmocka_unit_test_setup_teardown(test_ai_providers_find_previous, ai_client_setup, ai_client_teardown),
+        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_sensitive, 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),
+        cmocka_unit_test(test_ai_json_escape_special_chars),
+        cmocka_unit_test(test_ai_json_escape_percent_signs),
+        cmocka_unit_test(test_ai_json_escape_backslash_quote),
     };
     return cmocka_run_group_tests(all_tests, NULL, NULL);
 }