feat: session persistence + prompt pipe

[Jonnytoshen]

变更内容

• Session 持久化：新增 src/session/store.ts，支持将对话消息落盘；新增 pnpm run continue（--continue 参数）用于恢复上次会话。
• Prompt Pipe：新增 src/context/prompt-builder.ts，将原本内联的 system prompt 字符串重构为可组合的 PromptBuilder 管道（coreRules / toolGuide / deferredTools / sessionContext），并支持 debug 输出各模块状态。

Commits

• feat(session): add session persistence and --continue flag
• feat(prompt): introduce PromptBuilder pipe for system prompt assembly

[Copilot]

Pull request overview

This PR adds two user-facing capabilities to the CLI agent: persisting conversation history across runs, and restructuring the system prompt into a composable “PromptBuilder” pipeline to make prompt assembly more maintainable and inspectable.

Changes:

• Introduces a JSONL-based SessionStore to append/load conversation messages and a pnpm run continue entrypoint to resume the last session.
• Refactors the inline system prompt into a PromptBuilder pipeline (coreRules, toolGuide, deferredTools, sessionContext) with a debug display of pipe status.
• Updates gitignore to exclude persisted session files.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/session/store.ts	Adds JSONL session persistence (append/load/exists) for chat messages.
src/index.ts	Wires session restore/persist flow into the CLI loop and switches system prompt creation to PromptBuilder.
src/context/prompt-builder.ts	Adds a pipe-based system prompt builder and predefined pipe functions.
package.json	Adds continue script to run the CLI with --continue.
.gitignore	Ignores the .sessions directory used for persisted sessions.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.