feat(agent): Agent 工作台 - 计划插话记忆、统一模型选择器并修复摘要与视频入库

将计划清单、运行中插话和个人记忆接入云端 Agent；全站模型选择器统一为左右二级菜单。画布摘要按预算截断不再整轮拒绝，首页视频未知宽高可入库。README 补充贡献者 morrow。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/app/cloud_agent_working_context.go

@@ -0,0 +1,89 @@
+package app
+
+import (
+	"encoding/json"
+	"strings"
+)
+
+const (
+	cloudAgentHistoryKeepRounds = 10
+	cloudAgentHistoryMaxBytes   = 64000
+)
+
+func isCloudAgentContinuationMessage(message providerTextMessage) bool {
+	if message.Role != "user" {
+		return false
+	}
+	content := strings.TrimSpace(message.Content)
+	return strings.HasPrefix(content, "上一轮真实执行记录") || strings.HasPrefix(content, "上一轮已结束")
+}
+
+func cloudAgentHistoryUserInstructionCount(history []providerTextMessage) int {
+	count := 0
+	for _, message := range history {
+		if message.Role == "user" && !isCloudAgentContinuationMessage(message) {
+			count++
+		}
+	}
+	return count
+}
+
+func cloudAgentHistoryJSONSize(history []providerTextMessage) int {
+	raw, err := json.Marshal(history)
+	if err != nil {
+		return 0
+	}
+	return len(raw)
+}
+
+func dropOldestCloudAgentHistoryRound(history []providerTextMessage) []providerTextMessage {
+	if len(history) == 0 {
+		return history
+	}
+	if isCloudAgentContinuationMessage(history[0]) || history[0].Role != "user" {
+		return history[1:]
+	}
+	index := 1
+	for index < len(history) {
+		if history[index].Role == "user" && !isCloudAgentContinuationMessage(history[index]) {
+			break
+		}
+		index++
+	}
+	return history[index:]
+}
+
+// trimCloudAgentTextHistory 只把最近若干轮用户对话留给模型。
+// 个人记忆、更早轮次和上一轮工具流水不进工作上下文；超字节上限时从最旧一轮往下丢。
+func trimCloudAgentTextHistory(history []providerTextMessage, keepRounds, maxBytes int) []providerTextMessage {
+	if keepRounds <= 0 {
+		keepRounds = cloudAgentHistoryKeepRounds
+	}
+	if maxBytes <= 0 {
+		maxBytes = cloudAgentHistoryMaxBytes
+	}
+	if len(history) == 0 {
+		return history
+	}
+	start := 0
+	seen := 0
+	for index := len(history) - 1; index >= 0; index-- {
+		if history[index].Role != "user" || isCloudAgentContinuationMessage(history[index]) {
+			continue
+		}
+		seen++
+		if seen == keepRounds {
+			start = index
+			break
+		}
+	}
+	trimmed := append([]providerTextMessage{}, history[start:]...)
+	for cloudAgentHistoryJSONSize(trimmed) > maxBytes && cloudAgentHistoryUserInstructionCount(trimmed) > 1 {
+		next := dropOldestCloudAgentHistoryRound(trimmed)
+		if len(next) >= len(trimmed) {
+			break
+		}
+		trimmed = next
+	}
+	return trimmed
+}