init: OpenSpec project scaffolding with proposal, design, specs, tasks

- 7 capabilities: agent-registry, task-router, receipt-protocol,
  forgejo-integration, matrix-chatops, agent-adapter, orchestrator-core
- Tech stack: Rust + axum + zigbuild (single binary)
- Forgejo as task source of truth
- Matrix as real-time ChatOps layer
- Adapter pattern for multi-agent type support

openspec/changes/agent-fleet-platform/specs/receipt-protocol/spec.md

@@ -0,0 +1,41 @@
+## ADDED Requirements
+
+### Requirement: Structured receipt format
+Agent 完成任务后 SHALL 回写结构化 receipt。Receipt 包含：task_id、agent_id、status（completed / failed / partial）、duration_seconds、summary、artifacts（PR URL、文件路径等）、error（失败时）。
+
+#### Scenario: Successful task completion with PR
+- **WHEN** Agent 完成代码任务并创建了 PR #15
+- **THEN** Agent SHALL 提交 receipt：`{status: "completed", artifacts: [{type: "pr", url: "https://forgejo.example/repo/pulls/15"}], summary: "..."}`
+
+#### Scenario: Partial completion
+- **WHEN** Agent 完成了部分工作但未能全部完成
+- **THEN** Agent SHALL 提交 receipt：`{status: "partial", summary: "完成 3/5 个文件修改，test_auth.ts 超时", artifacts: [...]}`
+
+### Requirement: Receipt delivery channels
+Receipt SHALL 通过至少一个持久化渠道回写：Forgejo Issue comment（必须）+ Matrix 通知（可选）。
+
+#### Scenario: Receipt written as Issue comment
+- **WHEN** Agent 提交 receipt
+- **THEN** Orchestrator SHALL 在对应 Issue 下创建结构化 comment，包含 status emoji + summary + artifact links
+
+#### Scenario: Receipt triggers Matrix notification
+- **WHEN** Receipt 写入成功
+- **THEN** Orchestrator SHALL 向 Matrix 协同房间发送通知消息，包含任务状态和关键信息
+
+### Requirement: Receipt validation
+Orchestrator SHALL 验证 receipt 中的 artifact 声明（如 PR 是否真实存在）。
+
+#### Scenario: PR artifact validation
+- **WHEN** Receipt 声明创建了 PR #15
+- **THEN** Orchestrator SHALL 通过 Forgejo API 验证 PR #15 确实存在，若不存在 SHALL 将任务标记为 `failed` 并通知 Agent
+
+#### Scenario: Comment artifact validation
+- **WHEN** Receipt 声明在某个文件中做了修改
+- **THEN** Orchestrator SHALL 验证对应 commit/PR 包含该修改
+
+### Requirement: No-trust policy
+系统 SHALL NOT 仅凭 Agent 的文本输出判定任务完成。只有结构化 receipt + artifact 验证通过才算 `completed`。
+
+#### Scenario: Agent says done without receipt
+- **WHEN** Agent 在 Matrix 发消息说"任务完成了"但未提交 receipt
+- **THEN** 任务 SHALL 保持 `running` 状态，超时后按 `failed` 处理