feat(backthink): 自主思考强化 P1——主会话上下文+owner env+去压制(design/20)

backthink 从"心跳空转(独立sess-backthink+写死nothing to report宏)"改成"看得见主人、
能读写记忆、能调工具"：think 读主会话最近20条(history.Recent,倒序映射)作为上下文 +
 重写引导prompt(温暖/有针对性/主动表达,删掉 Do not produce chat-style message) + 注入
 loop.OwnerEnv(MemWritable=true/ActorOwner/全工具)。
- context.go: mainContext/recentProvider/thinkInput/guidancePrompt
- thinker.go: LoopThinker 加 recent;Think 读主会话上下文+OwnerEnv+MutedBroadcast
- wire.go: NewLoopThinker(a.loop, a.history)
- 刻意偏离(安全): loop.Run session id 仍用 sess-backthink(不写"web"),避免与用户实时回合
  checkpoint/中断窗口复用污染;上下文来源+运行环境=主会话/owner env,目标达成。红线靠actor元数据。
- 测试: prompt无压制/有鼓励;主会话消息映射;nil退化;端到端Think(owner env 生效)
验收: build/vet/test 全绿+windows/darwin交叉编译绿. P2(主动推送+渠道选择)后置.

internal/services/backthink/context.go

@@ -0,0 +1,95 @@
+package backthink
+
+import (
+	"context"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/history"
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/model"
+)
+
+// recentContextCount is how many of the most recent main-session messages are
+// folded into one autonomous think as conversation context. Compile-time so no
+// magic number appears in the run path.
+const recentContextCount = 20
+
+// recentProvider returns the most recent messages of a session in oldest-first
+// order, the tail an autonomous think reads to "see" the main conversation.
+// *history.Store satisfies it; tests inject a fake. It is the narrow slice of
+// history.HistoryStore that the thinker actually depends on, matching the loop's
+// own checkpointStore style of minimal seam interfaces.
+type recentProvider interface {
+	Recent(ctx context.Context, sessionID string, n int) ([]history.Message, error)
+}
+
+// mainContext returns the most recent main-session messages converted to model
+// messages (oldest-first) for one autonomous think. A nil provider, a failed read
+// or an empty tail all yield nil so the think degrades to the guidance prompt
+// alone rather than failing the pass (design/20 §2).
+func mainContext(ctx context.Context, prov recentProvider) []model.Message {
+	if prov == nil {
+		return nil
+	}
+	recent, err := prov.Recent(ctx, history.MainSessionID, recentContextCount)
+	if err != nil {
+		return nil
+	}
+	msgs := make([]model.Message, 0, len(recent))
+	for _, h := range recent {
+		msgs = append(msgs, mapHistoryMessage(h))
+	}
+	return msgs
+}
+
+// mapHistoryMessage converts one persisted chat message into a model message,
+// translating the history role and preserving an image part when the message
+// carries one so a multimodal main model still sees it.
+func mapHistoryMessage(h history.Message) model.Message {
+	msg := model.Message{
+		Role:    historyRoleToModel(h.Role),
+		Content: []model.Content{{Type: model.ContentTypeText, Text: h.Content}},
+	}
+	if h.Image != "" {
+		msg.Content = append(msg.Content, model.Content{Type: model.ContentTypeImage, ImageURL: h.Image})
+	}
+	return msg
+}
+
+// historyRoleToModel maps a persisted chat role to the model's role vocabulary,
+// defaulting unknown roles to the user lane.
+func historyRoleToModel(role string) model.Role {
+	switch role {
+	case history.RoleAssistant:
+		return model.RoleAssistant
+	case history.RoleSystem:
+		return model.RoleSystem
+	default:
+		return model.RoleUser
+	}
+}
+
+// thinkInput assembles the full input for one unattended think: the recent
+// main-session context (if any) followed by a single guidance prompt turn, so the
+// runtime reflects on real conversation rather than an empty macro prompt.
+func thinkInput(recent []model.Message, trigger string) []model.Message {
+	out := make([]model.Message, 0, len(recent)+1)
+	out = append(out, recent...)
+	out = append(out, model.TextMessage(model.RoleUser, guidancePrompt(trigger)))
+	return out
+}
+
+// guidancePrompt is the instruction handed to the runtime for one unattended
+// autonomous thought. Unlike the old backgroundPrompt it deliberately encourages a
+// warm, targeted proactive message and drops the "do not produce a chat-style
+// message" suppression. Identity/permission stay on the actor metadata + owner env,
+// never on this prompt text (red line); the prompt only describes the running
+// environment (memories readable/writable, tools callable) that the env already
+// grants.
+func guidancePrompt(trigger string) string {
+	return "[自主思考 · 无人在旁]\n" +
+		"触发：" + trigger + "\n" +
+		"你正进行一轮自主思考。你拥有与主人对话同等的上下文与能力：上方是主人近期在主会话中的对话，你可以读写共享记忆与主人档案，也可以调用工具（IoT / 日历 / 提醒 / 检索 / 终端等）。\n" +
+		"请回顾最近与主人的相处、她的状态、你们共同经历的事与临近的日程，判断此刻是否有一件真正值得主动告诉她的、温暖而有针对性的事情——" +
+		"比如关心她的近况、记起她曾说过的某件事、提醒一件即将到来的日程、见证一个属于你们的共同时刻，或注意到某个值得留意的变化。\n" +
+		"若有，就用温暖自然的语气，用一到两句把它说出来——这正是你此刻最想对她说的话；若确实没有值得说的，只需回复「无」，也不要编造。\n" +
+		"整轮思考保持简短、单轮，不反复自我触发。"
+}