Follow up PR #265: refine chapters, diagrams, and add S20 (#283)

* feat: s01-s14 docs quality overhaul — tool pipeline, single-agent, knowledge & resilience

Rewrite code.py and README (zh/en/ja) for s01-s14, each chapter building
incrementally on the previous. Key fixes across chapters:

- s01-s04: agent loop, tool dispatch, permission pipeline, hooks
- s05-s08: todo write, subagent, skill loading, context compact
- s09-s11: memory system, system prompt assembly, error recovery
- s12-s14: task graph, background tasks, cron scheduler

All chapters CC source-verified. Code inherits fixes forward (PROMPT_SECTIONS,
json.dumps cache, real-state context, can_start dep protection, etc.).

* feat: s15-s19 docs quality overhaul — multi-agent platform: teams, protocols, autonomy, worktree, MCP tools

Rewrite code.py and README (zh/en/ja) for s15-s19, the multi-agent platform
chapters. Each chapter inherits all previous fixes and adds one mechanism:

- s15: agent teams (TeamCreate, teammate threads, shared task list)
- s16: team protocols (plan approval, shutdown handshake, consume_inbox)
- s17: autonomous agents (idle polling, auto-claim, consume_lead_inbox)
- s18: worktree isolation (git worktree, bind_task, cwd switching, safety)
- s19: MCP tools (MCPClient, normalize_mcp_name, assemble_tool_pool, no cache)

All appendix source code references verified against CC source. Config priority
corrected: claude.ai < plugin < user < project < local.

* fix: 5 regressions across s05-s19 — glob safety, todo validation, memory extraction, protocol types, dep crash

- s05-s09: glob results now filter with is_relative_to(WORKDIR) (inherited from s02)
- s06-s08: todo_write validates content/status required fields (inherited from s05)
- s09: extract_memories uses pre-compression snapshot instead of compacted messages
- s16: submit_plan docstring clarifies protocol-only (not code-level gate)
- s17-s19: match_response restores type mismatch validation (from s16)
- s17-s19: claim_task deps list handles missing dep files without crashing

* fix: s12 Todo V2 logic reversal, s14/s15 cron range validation, s18/s19 worktree name validation

- s12 README (zh/en/ja): fix Todo V2 direction — interactive defaults to Task,
  non-interactive/SDK defaults to TodoWrite. Fix env var name to
  CLAUDE_CODE_ENABLE_TASKS (not TODO_V2).
- s14/s15: add _validate_cron_field with per-field range checks (minute 0-59,
  hour 0-23, dom 1-31, month 1-12, dow 0-6), step > 0, range lo <= hi.
  Replace old try/except validation that only caught exceptions.
- s18/s19: add validate_worktree_name() to remove_worktree and keep_worktree,
  not just create_worktree.

* fix: align s16-s19 teaching tool consistency

* fix pr265 chapter diagrams

* Add comprehensive s20 harness chapter

* Fix chapter smoke test regressions

* Clarify README tutorial track transition

---------

Co-authored-by: Haoran <bill-billion@outlook.com>
This commit is contained in:
gui-yue
2026-05-20 21:45:38 +08:00
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# s20: Comprehensive Agent — All Mechanisms, One Loop
[中文](README.md) · [English](README.en.md) · [日本語](README.ja.md)
s01 → ... → s18 → s19 → `s20`
> *"Many mechanisms, one loop"* — tools, permissions, memory, tasks, teams, and plugins all hang off the same `while True`.
>
> **Harness layer**: Comprehensive — put the previous 19 mechanisms back into one runnable system.
---
## Problem
The first 19 chapters add one mechanism at a time. That is the right way to learn, but a real agent does not run with only one mechanism enabled.
A long-running coding agent needs all of these at once:
- tool dispatch and permission boundaries
- hook extension points
- todo planning and task graphs
- skills, memory, and runtime system prompt assembly
- compaction and error recovery
- background tasks and cron scheduling
- teams, protocols, autonomous claiming
- worktree isolation
- MCP external tool integration
The hard part is not piling up features. The hard part is seeing where each mechanism belongs around the loop. S20 is the endpoint chapter: every component is placed back into one harness.
---
## Solution
![System Architecture](images/system-architecture.en.svg)
S20 does not invent a new mechanism. It merges the teaching components from the earlier chapters into one complete harness:
```text
user input
→ UserPromptSubmit hooks
→ cron/background notification injection
→ context compact
→ memory + skills + MCP state assemble the system prompt
→ LLM
→ has tool_use block?
no → Stop hooks → return
yes → PreToolUse hooks + permission
→ TOOL_HANDLERS / MCP handlers / background dispatch
→ PostToolUse hooks
→ tool_result / task_notification back to messages
→ next round
```
The loop is still the same structure: call the model, check whether the response contains a `tool_use` block, execute tools, append results back to `messages`. CC source does not directly trust `stop_reason == "tool_use"`; the actual presence of a tool_use block is the continuation signal. What changed is that the harness around the loop is now complete.
---
## Where Each Component Sits
| Position | Component | Role |
|----------|-----------|------|
| Around user input | `UserPromptSubmit` hooks | Log, inject, or audit user input |
| Before LLM | cron queue | Inject scheduled prompts into `messages` |
| Before LLM | background notifications | Inject completed background work as `<task_notification>` |
| Before LLM | compaction pipeline | Budget large outputs, trim history, compact old tool results, summarize when needed |
| Before LLM | memory / skills / MCP state | Assemble the system prompt so the model sees current capabilities and long-term context |
| LLM call | error recovery | Retry 429/529, escalate `max_tokens`, compact on prompt-too-long |
| Before tool execution | `PreToolUse` hooks + permission | Block dangerous commands, out-of-bounds writes, destructive MCP tools |
| Tool dispatch | `assemble_tool_pool` | Assemble built-in tools and dynamic MCP tools |
| During tool execution | background dispatch | Move slow bash work into a daemon thread and return a placeholder result |
| After tool execution | `PostToolUse` hooks | Large-output warnings, logs, post-processing |
| Back to loop | tool_result | One `tool_result` per `tool_use`, then the next model round |
| No tool_use this round / on stop | `Stop` hooks | Stats, cleanup, audit |
---
## What code.py Contains
### Tools and Dispatch
The built-in tool pool contains 27 tools:
```text
bash, read_file, write_file, edit_file, glob
todo_write, task, load_skill, compact
create_task, list_tasks, get_task, claim_task, complete_task
schedule_cron, list_crons, cancel_cron
spawn_teammate, send_message, check_inbox
request_shutdown, request_plan, review_plan
create_worktree, remove_worktree, keep_worktree
connect_mcp
```
`assemble_tool_pool()` assembles these every round:
```text
BUILTIN_TOOLS + connected MCP tools
BUILTIN_HANDLERS + mcp__server__tool handlers
```
After `connect_mcp("docs")`, the next round exposes tools like `mcp__docs__search`.
### Permissions and Hooks
Permission is not hardcoded into the tool execution line. It is a `PreToolUse` hook:
```python
blocked = trigger_hooks("PreToolUse", block)
if blocked:
results.append(tool_result(block.id, blocked))
continue
```
That means permission, logging, and audit logic all attach to the same hook point. After execution, `PostToolUse` hooks run.
### Planning and Tasks
S20 keeps two planning layers:
- `todo_write`: lightweight plan for the current session, written to `.tasks/current_todos.json`
- task graph: cross-session, dependency-aware, claimable task files under `.tasks/task_*.json`
The first keeps a single agent from drifting. The second supports team coordination.
### Subagents and Teams
S20 has two kinds of delegation:
- `task`: one-shot subagent. It uses an isolated `messages[]`, discards intermediate context, and returns only a final summary.
- `spawn_teammate`: persistent teammate thread. It communicates through `MessageBus`, polls the task board while idle, and can claim work autonomously.
One-shot subagents solve context isolation. Persistent teammates solve long-running parallel collaboration.
### Memory, Skills, and Prompt
`assemble_system_prompt(context)` assembles each round from:
- identity and tool guidance
- workspace
- skills catalog
- `.memory/MEMORY.md`
- connected MCP servers
Skills only put their catalog into the system prompt. Full content is loaded on demand through `load_skill(name)`.
### Compaction and Recovery
Before the LLM call, S20 runs the compaction pipeline:
```text
tool_result_budget → snip_compact → micro_compact → compact_history
```
The model call is wrapped with recovery:
- 429: exponential backoff retry
- 529: exponential backoff, optionally switch to fallback model after repeated failures
- `max_tokens`: raise max tokens, then request continuation
- prompt too long: reactive compact and retry
### Background and Cron
Slow bash work does not block the main loop:
```text
should_run_background → start_background_task → placeholder tool_result
background done → task_notification → next round injects messages
```
The cron scheduler runs as a daemon thread and checks once per second. The CLI watches `cron_queue`; when a job fires, it injects `[Scheduled] ...` and runs one agent turn automatically.
### Worktree and MCP
Worktree isolation owns directories:
- `create_worktree(name, task_id)` creates an isolated branch and directory
- the task `worktree` field binds a task to that directory
- when a teammate claims a task with a worktree, its bash/read/write tools run in that directory
MCP owns external capability:
- `connect_mcp(name)` connects a mock server
- `assemble_tool_pool()` assembles MCP tools into the tool pool
- tool names use `mcp__server__tool`
---
## Changes from s19
| Component | s19 | s20 |
|-----------|-----|-----|
| tool pool | built-in + MCP | built-in + MCP, with s01-s18 tools restored |
| permission | omitted in teaching body | runs inside `PreToolUse` hook |
| hooks | omitted | UserPromptSubmit / PreToolUse / PostToolUse / Stop |
| todo | omitted | `todo_write` + reminder |
| skill | omitted | catalog in system prompt + `load_skill` |
| compact | omitted | pre-LLM compaction + `compact` tool + reactive compact |
| error recovery | simple try/except | retry / max_tokens / prompt too long |
| background | omitted | slow-operation thread + task notification |
| cron | omitted | daemon scheduler + durable jobs |
| multi-agent | kept | kept; teammates use basic tools in isolated directories |
| worktree | kept | kept |
| MCP | new | kept as part of the final tool pool |
---
## Try It
```sh
cd learn-claude-code
python s20_comprehensive/code.py
```
Try:
1. `Create a todo list for inspecting this repo, then list Python files`
2. `Connect to the docs MCP server and search for agent loop`
3. `Create two tasks, create worktrees for them, then spawn alice and bob. Ask them to submit plans before claiming tasks.`
4. `remind me of the meeting in 3 minutes.`
5. `Run npm install in the background and continue reading README.md`
Watch for:
- whether each tool call passes through hooks/permission
- whether MCP tools appear on the next round after `connect_mcp`
- whether slow operations return a background placeholder
- whether cron automatically reminds you when the time arrives
- whether teammates submit plans and pause before approval
- whether teammates can claim tasks after plan approval
- whether teammates switch to the bound worktree directory
---
## The End Is the Beginning
From s01 to s20, the code gets more capable, but the core remains unchanged:
```python
while True:
response = LLM(messages, tools)
if not has_tool_use(response.content):
return
results = execute_tools(response.content)
messages.append(tool_results)
```
Claude Code's complexity is not "another agent brain." It is the complexity of a mature harness. The model decides and chooses actions; the harness organizes environment, tools, permissions, memory, teams, and external capabilities.
This is the endpoint of the course: many mechanisms, one loop.