feat: dual execution model (SSH CLI + HTTP pull)

- ExecutionMode enum: SshCli (orchestrator dispatches) | HttpPull (agent pulls)
- SSH CLI executor: spawn remote agents via ssh + CLI template
- Local subprocess as SSH special case (localhost)
- HostConfig with capability matching and load-based selection
- Dispatch loop: scan created tasks → select host → execute → update
- CliAdapterConfig: CLI templates for Codex and Claude Code
- Structured prompt construction (Issue → goal/constraints/validation)
- Output parsers: Codex JSON, Claude Code JSON, raw fallback
- TaskStatus::ReviewPending + review_count loop limit
- Forgejo webhook: pull_request (opened→review_pending, merged→completed)
- Forgejo webhook: push events (task/* branch → last_activity_at)
- HTTP API: dequeue only returns http_pull tasks
- HTTP API: status update only for http_pull mode
- Token auth config for http_pull agents
- Adapter module rewritten: AgentAdapter trait removed → config-driven CLI templates
- New fields: execution_mode, assigned_host, branch_name, pr_title, last_activity_at, review_count
- 30/30 tests pass

openspec/changes/adapter-cross-machine-revision/specs/task-assignment-protocol/spec.md

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+## ADDED Requirements
+
+### Requirement: Agent task dequeue (pull model)
+Agent SHALL 通过 `POST /api/v1/tasks/dequeue` 主动拉取任务。Orchestrator 根据 Agent 声明的 capabilities 匹配最优任务，原子性地分配给该 Agent。
+
+#### Scenario: Agent dequeues a matching task
+- **WHEN** Agent `worker-03` 发送 `POST /api/v1/tasks/dequeue`，body 包含 `{agent_id: "worker-03", capabilities: ["code:rust", "review"]}`
+- **THEN** Orchestrator SHALL 在单个事务中找到 status=created 且匹配 capabilities 的最高优先级任务
+- **AND** 将该任务状态转为 `assigned`，assigned_agent_id 设为 `worker-03`
+- **AND** 返回任务详情 JSON
+
+#### Scenario: No matching task available
+- **WHEN** Agent 发送 dequeue 但无匹配任务
+- **THEN** Orchestrator SHALL 返回 204 No Content
+
+### Requirement: Agent task status update
+Agent 执行过程中 SHALL 通过 `POST /api/v1/tasks/{task_id}/status` 更新任务状态。
+
+#### Scenario: Agent starts execution
+- **WHEN** Agent 开始执行任务，发送 `POST /api/v1/tasks/org/repo#42/status` body `{status: "running"}`
+- **THEN** Orchestrator SHALL 将任务状态更新为 `running`，记录 started_at
+
+#### Scenario: Agent reports progress
+- **WHEN** Agent 发送状态更新但任务已不在 assigned 给该 Agent
+- **THEN** Orchestrator SHALL 返回 403 Forbidden
+
+### Requirement: Single task detail query
+Orchestrator SHALL 提供 `GET /api/v1/tasks/{task_id}` 返回单个任务详情。
+
+#### Scenario: Query existing task
+- **WHEN** 发送 `GET /api/v1/tasks/org/repo#42`
+- **THEN** 返回任务完整信息 JSON（包含所有字段和事件历史）
+
+#### Scenario: Query non-existent task
+- **WHEN** 发送 `GET /api/v1/tasks/nonexistent`
+- **THEN** 返回 404 Not Found
+
+### Requirement: Agent authentication
+Agent 调用任务相关 API（dequeue、status update、receipt）时 SHALL 携带注册时获得的 token。Orchestrator SHALL 验证 token 有效性。
+
+#### Scenario: Valid token
+- **WHEN** Agent 携带有效 token 调用 dequeue
+- **THEN** 请求正常处理
+
+#### Scenario: Invalid or missing token
+- **WHEN** Agent 不携带 token 或 token 无效
+- **THEN** 返回 401 Unauthorized
+
+### Requirement: Non-PR task completion endpoint
+对于不产生 PR 的任务（research、review 等），Agent SHALL 通过 `POST /api/v1/tasks/{task_id}/complete` 显式提交完成，并附带 receipt。
+
+#### Scenario: Agent completes a non-PR task
+- **WHEN** Agent 发送 `POST /api/v1/tasks/org/repo#42/complete`，附带 receipt
+- **THEN** Orchestrator SHALL 验证 receipt（与 `POST /api/v1/receipts` 相同验证逻辑）
+- **AND** 任务状态转为 `completed`
+
+#### Scenario: Non-owner attempts to complete
+- **WHEN** 非 assigned Agent 尝试 complete
+- **THEN** 返回 403 Forbidden
+
+### Requirement: Review loop limit
+任务在 `running` ↔ `review_pending` 之间循环 SHALL 有最大次数限制，防止死循环。
+
+#### Scenario: Review loop exceeds limit
+- **WHEN** 任务的 review 循环次数超过 `max_retries`
+- **THEN** Orchestrator SHALL 将任务标记为 `failed`
+- **AND** 在对应 Issue 添加评论说明超限原因