fix(agent): save conversations to DB, fix Test button hang, wire hasNext/search

## Root cause: _save_conversation() dead code + missing message persistence

### Backend: Conversation persistence (3 critical bugs)
- **app.py**: Replaced early  with  so _save_conversation() executes
  after successful stream — was dead code on normal path
- **app.py**: Added _save_conversation call in HITL resume path (confirm/deny)
- **app.py**: Added broad  that saves conversation (at least user
  message) before re-raising on LLM errors (APIConnectionError etc.)
- **app.py**: _save_conversation now passes user_id from JWT (not hardcoded UUID)
  and includes messages[] in payload
- **agent_conversations.py**: save_conversation endpoint now processes body.messages
  and creates AgentMessage records (idempotent by msg id)

### Frontend: Agent chat sidebar wiring
- AgentChatModel.svelte.ts: added public  derived getter
- AgentChatModel.svelte.ts: added  method
- agent/+page.svelte: wired hasNext={model.conversationsHasNext} (was hardcoded false)
- agent/+page.svelte: wired onsearch to model.searchConversations (was no-op)

### Frontend: LLM Provider Test button hang fix
- ProviderConfig.svelte: resetForm/handleEdit now reset isTesting=false, isProbing=false
- ProviderConfig.svelte: Cancel button calls abortPendingRequests()
- ProviderConfig.svelte: Added AbortController lifecycle — cancels in-flight test/fetch
  requests on modal close or provider switch, preventing stale disabled buttons
- provider_config.integration.test.ts: added 6 abort/reset invariant tests

frontend/src/lib/components/llm/ProviderConfig.svelte

@@ -62,6 +62,16 @@ import { SvelteSet } from "svelte/reactivity";
   let probeResult = $state(null); // { max_images, method } or null
   let probeError = $state("");
 
+  // AbortController for in-flight request cancellation
+  let abortController = $state<AbortController | null>(null);
+
+  function abortPendingRequests() {
+    if (abortController) {
+      abortController.abort();
+    }
+    abortController = new AbortController();
+  }
+
   function isMaskedKey(key) {
     if (!key) return false;
     return key === "********" || key.includes("...");
@@ -78,6 +88,8 @@ import { SvelteSet } from "svelte/reactivity";
   }
 
   function resetForm() {
+    // Cancel any in-flight requests
+    abortPendingRequests();
     formData = {
       name: "",
       provider_type: "openai",
@@ -92,13 +104,17 @@ import { SvelteSet } from "svelte/reactivity";
     };
     editingProvider = null;
     testStatus = { type: "", message: "" };
+    isTesting = false;
     availableModels = [];
     modelsLoadError = "";
     probeResult = null;
     probeError = "";
+    isProbing = false;
   }
 
   function handleEdit(provider) {
+    // Cancel any in-flight requests from previous edit session
+    abortPendingRequests();
     console.log("[ProviderConfig][Action] Editing provider", provider?.id);
     editingProvider = provider;
     // Normalize provider fields to editable form shape.
@@ -118,10 +134,12 @@ import { SvelteSet } from "svelte/reactivity";
       max_output_tokens: provider?.max_output_tokens ?? null,
     };
     testStatus = { type: "", message: "" };
+    isTesting = false;
     availableModels = [];
     modelsLoadError = "";
     probeResult = null;
     probeError = "";
+    isProbing = false;
     showForm = true;
     // Auto-fetch models when editing an existing provider
     if (provider?.base_url) {
@@ -203,7 +221,7 @@ import { SvelteSet } from "svelte/reactivity";
       if (isMaskedKey(testData.api_key)) {
         delete testData.api_key;
       }
-      const result = await requestApi(endpoint, "POST", testData);
+      const result = await requestApi(endpoint, "POST", testData, { signal: abortController?.signal });
 
       if (result.success) {
         testStatus = { type: "success", message: $t.llm.connection_success };
@@ -649,6 +667,7 @@ import { SvelteSet } from "svelte/reactivity";
             type="button"
             class="px-4 py-2 border rounded hover:bg-surface-muted flex-1"
             onclick={() => {
+              abortPendingRequests();
               showForm = false;
             }}
           >

frontend/src/lib/components/llm/__tests__/provider_config.integration.test.ts

@@ -1,9 +1,12 @@
-// #region ProviderConfigIntegrationTest [C:3] [TYPE Module] [SEMANTICS llm, provider-config, integration-test, edit-flow, delete-flow]
-// @PURPOSE: Protect edit, submit, test, and delete interaction contracts in LLM provider settings UI.
+// #region ProviderConfigIntegrationTest [C:3] [TYPE Module] [SEMANTICS llm, provider-config, integration-test, edit-flow, delete-flow, abort]
+// @PURPOSE: Protect edit, submit, test, delete interaction contracts, isTesting reset, and AbortController lifecycle in LLM provider settings UI.
 // @LAYER UI (Tests)
 // @RELATION DEPENDS_ON -> [ProviderConfig]
 // @INVARIANT: Edit action keeps explicit click handler and opens normalized edit form.
 // @INVARIANT: Masked API keys are excluded from save/test/fetch-models payloads.
+// @INVARIANT: isTesting resets to false on modal close, edit switch, and form reset.
+// @INVARIANT: abortPendingRequests() aborts old controller and creates a new one.
+// @INVARIANT: testConnection passes abort signal to requestApi for cancellability.
 
 import { describe, it, expect } from 'vitest';
 import fs from 'node:fs';
@@ -90,4 +93,65 @@ describe('ProviderConfig edit interaction contract', () => {
   });
 });
 // #endregion provider_config_edit_contract_tests:Function
+
+// #region provider_config_isTesting_reset_tests:Function [TYPE Function]
+// @RELATION BINDS_TO -> [EXT:frontend:ProviderConfigIntegrationTest]
+// @PURPOSE: Validate isTesting and isProbing reset, AbortController lifecycle, and Cancel button wiring.
+// @INVARIANT: isTesting = false on edit switch, form reset, and modal close.
+// @INVARIANT: abortPendingRequests() cancels in-flight and creates fresh AbortController.
+// @INVARIANT: testConnection passes AbortSignal via FetchOptions to enable pre-unmount cancellation.
+// @TEST_EDGE: resetForm includes abortPendingRequests + isTesting + isProbing reset
+// @TEST_EDGE: handleEdit includes abortPendingRequests + isTesting + isProbing reset
+// @TEST_EDGE: Cancel button calls abortPendingRequests before hiding modal
+// @TEST_EDGE: testConnection uses abortController?.signal in requestApi call
+describe('ProviderConfig abort/reset invariants', () => {
+  it('resetForm calls abortPendingRequests and resets isTesting + isProbing', () => {
+    const source = fs.readFileSync(COMPONENT_PATH, 'utf-8');
+
+    expect(source).toContain('function resetForm()');
+    expect(source).toContain('abortPendingRequests();');
+    expect(source).toContain('isTesting = false;');
+    expect(source).toContain('isProbing = false;');
+  });
+
+  it('handleEdit calls abortPendingRequests and resets isTesting + isProbing', () => {
+    const source = fs.readFileSync(COMPONENT_PATH, 'utf-8');
+
+    expect(source).toContain('function handleEdit(provider)');
+    expect(source).toContain('abortPendingRequests();');
+    expect(source).toContain('isTesting = false;');
+    expect(source).toContain('isProbing = false;');
+  });
+
+  it('Cancel button calls abortPendingRequests before hiding modal', () => {
+    const source = fs.readFileSync(COMPONENT_PATH, 'utf-8');
+
+    // Cancel button must abort pending requests, not just hide
+    expect(source).toContain('abortPendingRequests();');
+    expect(source).toContain('showForm = false;');
+    // Cancel must appear before Save in the button group
+  });
+
+  it('testConnection passes AbortSignal via FetchOptions to requestApi', () => {
+    const source = fs.readFileSync(COMPONENT_PATH, 'utf-8');
+
+    expect(source).toContain('requestApi(endpoint, "POST", testData, { signal: abortController?.signal })');
+  });
+
+  it('abortPendingRequests aborts existing controller and creates a new one', () => {
+    const source = fs.readFileSync(COMPONENT_PATH, 'utf-8');
+
+    expect(source).toContain('function abortPendingRequests()');
+    expect(source).toContain('abortController.abort();');
+    expect(source).toContain('abortController = new AbortController();');
+  });
+
+  it('defines abortController as nullable $state', () => {
+    const source = fs.readFileSync(COMPONENT_PATH, 'utf-8');
+
+    expect(source).toContain('let abortController = $state<AbortController | null>(null);');
+  });
+
+});
+// #endregion provider_config_isTesting_reset_tests:Function
 // #endregion ProviderConfigIntegrationTest:Module

frontend/src/lib/models/AgentChatModel.svelte.ts

@@ -141,6 +141,7 @@ export class AgentChatModel {
       : "destructive",
   );
   queuePosition = $derived(this._messageQueue.length);
+  conversationsHasNext = $derived(this._conversationsHasNext);
 
   // ── Actions — P1 ───────────────────────────────────────────────
 
@@ -273,6 +274,28 @@ export class AgentChatModel {
     }
   }
 
+  async searchConversations(query: string): Promise<void> {
+    log("AgentChat.Model", "REASON", "Searching conversations", { query });
+    try {
+      this._conversationsPage = 1;
+      const res = await getAssistantConversations(
+        1, 20, false, query
+      );
+      const items = res.items || [];
+      this.conversations = items.map((item: Record<string, unknown>) => ({
+        id: item.conversation_id ?? item.id ?? "",
+        title: item.title ?? "",
+        updated_at: item.updated_at ?? "",
+        message_count: item.message_count ?? 0,
+      }));
+      this._conversationsHasNext = Boolean(res.has_next);
+      this._conversationsPage++;
+    } catch (e: unknown) {
+      this.error = e instanceof Error ? e.message : "Failed to search conversations";
+      log("AgentChat.Model", "EXPLORE", "Search conversations failed", {}, this.error);
+    }
+  }
+
   async loadHistory(conversationId: string | null = null): Promise<void> {
     this.isLoadingHistory = true;
     this.error = null;

frontend/src/routes/agent/+page.svelte

@@ -45,14 +45,14 @@
           conversations={model.conversations}
           currentConversationId={model.currentConversationId}
           isLoading={model.isLoadingHistory}
-          hasNext={false}
+          hasNext={model.conversationsHasNext}
           onselect={(id) => {
             model!.currentConversationId = id;
             model!.loadHistory(id);
           }}
           ondelete={(id) => model!.deleteConversation(id)}
           onloadmore={() => model!.loadConversations(false)}
-          onsearch={() => {}}
+          onsearch={(q: string) => model!.searchConversations(q)}
         />
       {/if}
 
@@ -95,7 +95,7 @@
             conversations={model.conversations}
             currentConversationId={model.currentConversationId}
             isLoading={model.isLoadingHistory}
-            hasNext={false}
+            hasNext={model.conversationsHasNext}
             onselect={(id) => {
               model!.currentConversationId = id;
               model!.loadHistory(id);
@@ -103,7 +103,7 @@
             }}
             ondelete={(id) => model!.deleteConversation(id)}
             onloadmore={() => model!.loadConversations(false)}
-            onsearch={() => {}}
+            onsearch={(q: string) => model!.searchConversations(q)}
           />
         </div>
         <div class="flex-1 bg-black/30" onclick={() => sidebarOpen = false}></div>