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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# s02: Tool Use — Add a Tool, Add Just One Line
[中文](README.md) · [English](README.en.md) · [日本語](README.ja.md)
s01 → `s02` → [s03](../s03_permission/) → s04 → ... → s20
> *"Add a tool, add just one handler"* — The loop stays the same. Register the new tool in the dispatch map and you're done.
>
> **Harness Layer**: Tool Dispatch — Expanding the model's reach.
---
## Only One Tool: Bash
The s01 Agent has only one tool: bash. To read a file, `cat`; to write, `echo "..." > file.py`; to edit, `sed`.
The model thinks "read this file" but has to spell out `cat path/to/file`. An extra layer of translation that wastes tokens and invites errors.
---
## Overview: Tool Dispatch
![Tool Dispatch](images/tool-dispatch.en.svg)
The s01 loop is fully preserved (LLM call, stop_reason check, message append — not a single word changed). The only change is in that one line of tool execution: `run_bash()` is replaced with `TOOL_HANDLERS[block.name]()` dispatch lookup.
Adding a tool to the Agent requires just two things:
1. **Define the tool**: Add one entry to the `TOOLS` array
2. **Register the handler**: Add one mapping in the `TOOL_HANDLERS` dict
---
## From 1 Tool to 5 Tools
s01 had only bash:
```python
TOOLS = [{"name": "bash", ...}]
def run_bash(command): ...
```
s02 expands to 5 tools, each independently defined:
```python
TOOLS = [
{"name": "bash", "description": "Run a shell command.", ...},
{"name": "read_file", "description": "Read file contents.", ...},
{"name": "write_file", "description": "Write content to file.", ...},
{"name": "edit_file", "description": "Replace text in file once.", ...},
{"name": "glob", "description": "Find files by pattern.", ...},
]
```
Each tool has its own implementation function:
```python
def run_read(path, limit=None):
lines = safe_path(path).read_text().splitlines()
if limit:
lines = lines[:limit]
return "\n".join(lines)
def run_write(path, content):
safe_path(path).write_text(content)
return f"Wrote {len(content)} bytes to {path}"
def run_edit(path, old_text, new_text):
text = safe_path(path).read_text()
if old_text not in text:
return "Error: text not found"
safe_path(path).write_text(text.replace(old_text, new_text, 1))
return f"Edited {path}"
def run_glob(pattern):
import glob as g
return "\n".join(g.glob(pattern, root_dir=WORKDIR))
```
---
## Tool Dispatch
```python
TOOL_HANDLERS = {
"bash": run_bash,
"read_file": run_read,
"write_file": run_write,
"edit_file": run_edit,
"glob": run_glob,
}
# Only one line changed in the loop — from hardcoded run_bash to dispatch lookup:
for block in response.content:
if block.type == "tool_use":
handler = TOOL_HANDLERS[block.name] # lookup
output = handler(**block.input) # call
results.append(...)
```
Adding a tool = one entry in `TOOLS` array + one line in `TOOL_HANDLERS` dict. The loop stays the same.
---
## Multiple Tool Calls
The model often returns multiple tool_use calls at once — "read a.py and b.py, then list all .py files".
The teaching version executes them one by one in the original `response.content` order. CC's approach is more complex: it slices the original order into consecutive batches, where concurrency-safe tools within a batch run in parallel, and batches are strictly sequential (see appendix).
---
## Quick Reference
| Concept | One-Liner |
|---------|-----------|
| TOOL_HANDLERS | Tool name → handler function dict. Add a tool = add one mapping line |
| Tool Definition | JSON schema telling the model "what I can do" |
| Multiple tool calls | Model may return multiple tool_use at once; teaching version executes them in original order |
| Loop Unchanged | s01's `while True` loop — not a single line changed |
---
## Changes from s01
| Component | Before (s01) | After (s02) |
|-----------|-------------|-------------|
| Tool count | 1 (bash) | 5 (+read, write, edit, glob) |
| Tool execution | Hardcoded `run_bash()` | TOOL_HANDLERS dispatch lookup |
| Path safety | None | safe_path validation (file tools only) |
| Loop | `while True` + `stop_reason` | Identical to s01 |
---
## Try It
```sh
cd learn-claude-code
python s02_tool_use/code.py
```
Try these prompts:
1. `Read the file README.md and tell me what this project is about`
2. `Create a file called test.py that prints "hello", then read it back`
3. `Find all Python files in this directory`
4. `Read both README.md and requirements.txt, then create a summary file`
What to watch for: When does the model call just one tool, and when does it call multiple at once? Are multiple tool calls executed in the correct order?
---
## What's Next
The Agent now has 5 specialized tools. File tools are protected by `safe_path`, but bash is unrestricted — `rm -rf /` still runs.
→ s03 Permission: Add a gate before tool execution — is this operation safe? Does it need user approval?
<details>
<summary>Dive into CC Source Code</summary>
> The following is based on a review of CC source code `Tool.ts`, `tools.ts`, `toolOrchestration.ts`, `toolExecution.ts`, and `StreamingToolExecutor.ts`.
### 1. Tool Definition Approach
**Teaching version**: `TOOLS` array + `TOOL_HANDLERS` dict. Definition and implementation are separate.
**CC**: Each tool is an independent object created by `buildTool()`, containing schema, validation, permissions, and execution. `getAllBaseTools()` aggregates all tools.
The teaching version's separation is clearer for teaching — readers immediately see "add a tool = two definitions".
### 2. Concurrency Safety: isConcurrencySafe()
![Tool Concurrency](images/concurrency-comparison.en.svg)
The teaching version executes tools one by one in original order, without concurrency. CC uses `isConcurrencySafe(input)` to determine concurrency — note this isn't simply "read-only vs write", but judges by specific input:
| | isReadOnly | isConcurrencySafe |
|---|---|---|
| FileRead | true | true |
| Glob | true | true |
| Bash `ls` | true | **true** ← key difference |
| Bash `rm` | false | false |
| TaskCreate | false | **true** ← modifies state but can be concurrent (introduced in s12) |
CC's Bash tool's `isConcurrencySafe` equals `isReadOnly` — read-only commands can be concurrent, write commands cannot. TaskCreate modifies task files, but each writes a different file, so it can be concurrent.
### 3. Partition Algorithm
CC's `partitionToolCalls()` (`toolOrchestration.ts:91-115`) doesn't split into two groups — it batches tool calls **by consecutive blocks**:
```
[read A, read B, glob *.py, bash "rm x", read C]
→ batch1(concurrent): [read A, read B, glob *.py]
→ batch2(serial): [bash "rm x"]
→ batch3(concurrent): [read C]
```
Consecutive concurrency-safe calls are grouped into the same batch for truly concurrent execution (`toolOrchestration.ts:152-176`, with a concurrency limit). When a non-concurrency-safe call is encountered, a new batch starts for serial execution. Batches are strictly sequential.
### 4. Validation Pipeline
Each tool call in CC goes through a strict 5-step validation (`toolExecution.ts`):
1. **Zod schema validation** (`614-680`, teaching version uses JSON Schema): parameter type/structure check
2. **Tool-level validateInput()** (`682-733`): parameter value validation (e.g., is the path within the working directory)
3. **PreToolUse hooks** (`800-862`, covered in s04): hooks can return messages, modify input, or block execution
4. **Permission check** (`921-931`, core topic of s03): canUseTool + checkPermissions → allow/deny/ask
5. **Execute tool.call()** (`1207-1222`)
The teaching version omits Zod (uses JSON Schema), omits validateInput (uses safety functions), but preserves the permission check and hook concepts.
### 5. Streaming Tool Execution
CC's `StreamingToolExecutor` (`StreamingToolExecutor.ts`) starts tools while the model is still generating — no waiting for the model to finish. `read_file` might complete while the model is still outputting "Let me analyze". The teaching version doesn't implement this, consistent with s01's goal — conceptual clarity, not peak performance.
### 6. Tool Result Persistence
Each tool has a `maxResultSizeChars` field. Results exceeding this threshold are persisted to disk, and the model sees a preview + file path. FileRead is special — set to `Infinity`, preventing file read output from being persisted again. Specifically, if FileRead's result exceeds the threshold and gets persisted, the model's next read of that persisted file would trigger another persistence → infinite loop (read file → persist → re-read → re-persist → ...).
</details>
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