fix(chat): 会话已选 LLM 时不再被「全局未激活」误拦，提示按状态细分

发送消息的前置检查只看全局激活配置(chatAgentRef),而真正执行的
runConversationSync 会优先用会话所选/Agent 绑定的配置——两处解析分叉,导致
「会话已选一个有效配置、但全局没有激活配置」时,消息在预检查阶段就被 503
「LLM 未配置」拦下,根本走不到能用所选配置的执行阶段。

- 抽出 resolveChatAgent(conversation) 作为唯一解析入口(会话/Agent 绑定优先、
  全局兜底),send 预检查与后台执行都用它,消除分叉。
- 提示按实际状态细分(chatUnavailableReason):无任何配置→提示添加;有配置但
  未激活→提示激活或为本会话指定一个;而非一律「未配置」。

相邻的 StartTriggeredRun 仍用全局 gate(触发器场景,本次不动)。

验证: 新增两个测试——三态提示区分、会话所选配置在全局无激活时仍能解析出
ChatAgent(回归防护);连本地 PG 实跑通过,server 全量无回归。

server/chat_llm_resolve_test.go

@@ -0,0 +1,97 @@
+package server
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/Autumn-27/artex/db"
+)
+
+// TestChatUnavailableReasonDistinguishesStates pins the operator-facing message
+// to the actual configuration state: nothing configured vs. configured-but-not-
+// activated must read differently so the user knows what to do.
+func TestChatUnavailableReasonDistinguishesStates(t *testing.T) {
+	m, err := NewManager(t.TempDir(), "")
+	if err != nil {
+		t.Skipf("postgres unavailable (%v) — skipping", err)
+	}
+	defer m.Close()
+	td := t.TempDir()
+	s := New(context.Background(), m, td, td, td)
+
+	// Start from a clean profile table; other tests in the shared DB may have left rows.
+	existing, _ := m.pg.ListProfiles()
+	for _, p := range existing {
+		if p.IsDefault {
+			// The active profile cannot be deleted directly; clear the flag first.
+			_, _ = m.pg.Exec(`UPDATE llm_profiles SET is_default=false WHERE id=$1`, p.ID)
+		}
+		_ = m.pg.DeleteProfile(p.ID)
+	}
+
+	if reason := s.chatUnavailableReason(); !strings.Contains(reason, "尚未配置") {
+		t.Fatalf("no-profile reason=%q, want 尚未配置", reason)
+	}
+
+	id, err := m.pg.SaveProfile(&db.LLMProfile{Name: "p1", Format: "anthropic", Model: "claude-x", APIKey: "sk-test"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		_, _ = m.pg.Exec(`UPDATE llm_profiles SET is_default=false WHERE id=$1`, id)
+		_ = m.pg.DeleteProfile(id)
+	})
+
+	// Profile exists but is not activated.
+	if reason := s.chatUnavailableReason(); !strings.Contains(reason, "没有已激活") {
+		t.Fatalf("inactive reason=%q, want 没有已激活", reason)
+	}
+
+	// Once activated, the reason no longer claims a missing/inactive config.
+	if err := m.pg.SetActiveProfile(id); err != nil {
+		t.Fatal(err)
+	}
+	if reason := s.chatUnavailableReason(); strings.Contains(reason, "尚未配置") || strings.Contains(reason, "没有已激活") {
+		t.Fatalf("active reason=%q should not report missing/inactive", reason)
+	}
+}
+
+// TestResolveChatAgentHonoursConversationProfile is the regression guard for the
+// reported bug: a conversation that picked a valid profile must resolve a chat
+// agent even when NO global profile is active, so the send precheck stops
+// rejecting it with "LLM 未配置".
+func TestResolveChatAgentHonoursConversationProfile(t *testing.T) {
+	m, err := NewManager(t.TempDir(), "")
+	if err != nil {
+		t.Skipf("postgres unavailable (%v) — skipping", err)
+	}
+	defer m.Close()
+	td := t.TempDir()
+	s := New(context.Background(), m, td, td, td)
+
+	// Force the global fallback to nil so a non-nil result can ONLY come from the
+	// conversation's own profile — this is exactly the situation the user hit
+	// (no usable global config) and isolates the fix from the test host's env.
+	s.cfgMu.Lock()
+	s.chatAgent = nil
+	s.cfgMu.Unlock()
+
+	id, err := m.pg.SaveProfile(&db.LLMProfile{Name: "conv-pick", Format: "anthropic", Model: "claude-x", APIKey: "sk-test"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = m.pg.DeleteProfile(id) })
+
+	// A conversation that pinned this profile resolves a chat agent despite the
+	// nil global fallback; without the fix the send precheck rejected it outright.
+	conv := &db.Conversation{AgentKey: "mainagent", LLMProfileID: &id}
+	if s.resolveChatAgent(conv) == nil {
+		t.Fatalf("resolveChatAgent(conversation with valid profile) = nil; global fallback wrongly gates the pick")
+	}
+
+	// With neither a pick nor a global fallback there is genuinely nothing to run.
+	if s.resolveChatAgent(&db.Conversation{AgentKey: "mainagent"}) != nil {
+		t.Fatalf("resolveChatAgent with neither pick nor global config should be nil")
+	}
+}

server/conversations.go

@@ -315,9 +315,12 @@ func (s *Server) pgSendConversationMessage(w http.ResponseWriter, r *http.Reques
 		writeErr(w, 400, "消息不能为空")
 		return
 	}
-	ca := s.chatAgentRef()
-	if ca == nil {
-		writeErr(w, 503, "LLM 未配置，无法对话")
+	// Same resolution as the background runner: honour the agent binding / this
+	// conversation's chosen profile before falling back to the global config, so a
+	// conversation that picked a valid LLM is not rejected just because no global
+	// config is active.
+	if s.resolveChatAgent(c) == nil {
+		writeErr(w, 503, s.chatUnavailableReason())
 		return
 	}
 
@@ -390,12 +393,7 @@ func (s *Server) runConversationSync(c *db.Conversation, msg, busyKey string) {
 		s.chatMu.Unlock()
 	}()
 	// precedence: the conversation agent's own binding → this conversation's pin → global.
-	ca := s.chatAgentRef()
-	if eff := s.effectiveProfileForAgent(c.AgentKey, c.LLMProfileID); eff != nil {
-		if pa := s.chatAgentForProfile(*eff); pa != nil {
-			ca = pa
-		}
-	}
+	ca := s.resolveChatAgent(c)
 	if ca == nil {
 		return
 	}

server/server.go

@@ -492,6 +492,37 @@ func (s *Server) effectiveProfileForAgent(agentKey string, pinID *int64) *int64
 	return pinID
 }
 
+// resolveChatAgent picks the ChatAgent for one conversation: the agent's own
+// binding or this conversation's chosen profile first, the global active config
+// only as a fallback. Both the send precheck and the background runner MUST use
+// this — resolving differently in the two paths is how a conversation that had
+// picked a valid profile still got rejected with "LLM 未配置" when no global
+// config was active.
+func (s *Server) resolveChatAgent(c *db.Conversation) *agent.ChatAgent {
+	ca := s.chatAgentRef()
+	if eff := s.effectiveProfileForAgent(c.AgentKey, c.LLMProfileID); eff != nil {
+		if pa := s.chatAgentForProfile(*eff); pa != nil {
+			ca = pa
+		}
+	}
+	return ca
+}
+
+// chatUnavailableReason explains why no ChatAgent could be resolved, so the user
+// knows whether to add a config, activate one, or pick one for this conversation
+// — rather than a flat "not configured" that hides which of those it is.
+func (s *Server) chatUnavailableReason() string {
+	if s.m.pg != nil {
+		if profiles, err := s.m.pg.ListProfiles(); err == nil && len(profiles) == 0 {
+			return "尚未配置 LLM：请到 系统 → LLM 配置 添加一个配置"
+		}
+		if active, err := s.m.pg.ActiveProfile(); err == nil && active == nil {
+			return "没有已激活的 LLM 配置：请到 系统 → LLM 配置 激活一个，或在本对话为该会话指定一个配置"
+		}
+	}
+	return "LLM 未就绪，无法对话：请检查 系统 → LLM 配置是否有可用且已激活的配置"
+}
+
 // providerForProfile returns a cached provider+cfg for a profile id, so every agent
 // bound/pinned to the same profile shares one provider instance (one rate limiter).
 // ok=false when the profile is missing/invalid → caller falls back to the global pair.