cdrop — 跨 OS 剪贴板与文件传输服务

Commilitia Drop：自托管的跨设备剪贴板同步与点对点文件传输。

- 后端 Go（chi / SQLite WAL / SSE Hub / WebRTC signaling + 状态机 / Relay ring buffer），编译进单个 distroless 镜像（前端 go:embed）。
- 前端 React + TanStack Router + Zustand，自实现 SSE + WebRTC P2P，NAT 受阻时回退服务端中继；聚珍（Juzhen）CJK 综合排版。
- 桌面端 Wails v2（macOS / Windows），瘦客户端复用 web。
- 鉴权 OIDC PKCE（自建 Casdoor 等），refresh_token 信封加密存系统密钥库；iOS Shortcut 用 HS256 scoped token。

架构文档与变更记录见 docs 分支（PROJECT_BRIEF / FRONTEND_DESIGN / CHANGELOG）。

本次为公开发布初始提交：完整开发历史（含部署细节）留存于私有归档，公开仓库自此干净起步。

internal/transfer/state.go

@@ -0,0 +1,54 @@
+package transfer
+
+const (
+	StatePending     = "PENDING"
+	StateAccepted    = "ACCEPTED"
+	StateP2PActive   = "P2P_ACTIVE"
+	StateRelayActive = "RELAY_ACTIVE"
+	StateDone        = "DONE"
+	StateFailed      = "FAILED"
+	StateCancelled   = "CANCELLED"
+)
+
+const (
+	ModeP2P   = "p2p"
+	ModeRelay = "relay"
+)
+
+// AutoAcceptThreshold is the file size at/under which the receiver may
+// silently auto-accept a transfer. brief §2: "> 100 MB 二次确认".
+const AutoAcceptThreshold = 100 * 1024 * 1024
+
+// IsValidTransition reports whether a transfer may move from→to.
+//
+// Forward-only: any state can advance to a "later" state, but never go back.
+// We're permissive because client→server timing races are real:
+//   - sender's /p2p can land before receiver's /accept commits → PENDING → P2P_ACTIVE
+//   - either side may call /done before /p2p ever fired → ACCEPTED → DONE
+// Strict ordering would surface as 409s the user can't recover from.
+//
+// Terminal states (DONE / FAILED / CANCELLED) accept no further transitions.
+func IsValidTransition(from, to string) bool {
+	switch from {
+	case StatePending:
+		return to == StateAccepted || to == StateP2PActive || to == StateRelayActive ||
+			to == StateCancelled || to == StateFailed
+	case StateAccepted:
+		return to == StateP2PActive || to == StateRelayActive ||
+			to == StateDone || to == StateCancelled || to == StateFailed
+	case StateP2PActive:
+		// P2P 失败自动 fallback 到 Relay (brief §2).
+		return to == StateRelayActive || to == StateDone ||
+			to == StateFailed || to == StateCancelled
+	case StateRelayActive:
+		return to == StateDone || to == StateFailed || to == StateCancelled
+	case StateDone, StateFailed, StateCancelled:
+		return false
+	}
+	return false
+}
+
+// IsTerminal reports whether the state is final (no further transitions).
+func IsTerminal(state string) bool {
+	return state == StateDone || state == StateFailed || state == StateCancelled
+}