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>
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# s08: Context Compact — Context Will Fill Up, Have a Way to Make Room
[中文](README.md) · [English](README.en.md) · [日本語](README.ja.md)
s01 → s02 → s03 → s04 → s05 → s06 → s07 → `s08` → [s09](../s09_memory/) → s10 → ... → s20
> *"Context will fill up — have a way to make room"* — Four-layer compression pipeline: cheap first, expensive last.
>
> **Harness Layer**: Compression — clean memory, unlimited sessions.
---
## The Problem
The agent is running along, then freezes.
It has bash, read, write — all the capabilities it needs. But it read a 1000-line file (~4000 tokens), then read 30 more files, ran 20 commands. Every command's output, every file's contents, all pile up in the `messages` list.
The context window is finite. Once full, the API outright rejects the call: `prompt_too_long`.
Without compression, an agent simply cannot work on large projects.
---
## The Solution
![Compact Overview](images/compact-overview.en.svg)
The hook structure, skill loading, and sub-Agent from s07 are preserved, with some tools omitted to focus on compaction. The core change: insert three pre-processors (0 API calls) before each LLM call, trigger an LLM summary (1 API call) when tokens still exceed the threshold, and emergency-trim if the API throws an error.
Core design: cheap first, expensive last.
---
## How It Works
![Four-layer compression pipeline](images/compaction-layers.en.svg)
### L1: snip_compact — Trim Irrelevant Old Conversation
The agent ran 80 turns of conversation, accumulating 160 `messages`. The very first "help me create hello.py" is barely relevant to current work, yet it still occupies space.
Message count exceeds 50 → keep the first 3 (initial context) and the last 47 (current work), trim the middle:
```python
def snip_compact(messages, max_messages=50):
if len(messages) <= max_messages:
return messages
keep_head, keep_tail = 3, max_messages - 3
snipped = len(messages) - keep_head - keep_tail
placeholder = {"role": "user",
"content": f"[snipped {snipped} messages from conversation middle]"}
return messages[:keep_head] + [placeholder] + messages[-keep_tail:]
```
Entire messages are trimmed, but `tool_result` content within remaining messages keeps accumulating — message #34 may still hold 30KB of old file contents. → L2.
### L2: micro_compact — Placeholder for Old Tool Results
![Old results placeholder](images/micro-compact.en.svg)
The agent read 10 files consecutively. The full contents of reads 17 are still sitting in context, no longer needed, but hogging large amounts of space.
Keep only the 3 most recent `tool_result` entries intact; replace older ones with a one-line placeholder:
```python
KEEP_RECENT_TOOL_RESULTS = 3
def micro_compact(messages):
tool_results = collect_tool_result_blocks(messages)
if len(tool_results) <= KEEP_RECENT_TOOL_RESULTS:
return messages
for _, _, block in tool_results[:-KEEP_RECENT_TOOL_RESULTS]:
if len(block.get("content", "")) > 120:
block["content"] = "[Earlier tool result compacted. Re-run if needed.]"
return messages
```
Old results are cleared, but a single new result can be 500KB — one `cat` of a large file can max out the context. → L3.
### L3: tool_result_budget — Persist Large Results to Disk
![Large results to disk](images/layer1-budget.en.svg)
The model read 5 large files in one go; all `tool_result` blocks in the last user message total 500KB.
Sum the size of all `tool_result` blocks in the last user message. If over 200KB → sort by size, starting from the largest, persist to `.task_outputs/tool-results/`, keeping only a `<persisted-output>` marker + a 2000-character preview in context. The model sees the marker and knows the full content is on disk, re-reading it when needed.
```python
def tool_result_budget(messages, max_bytes=200_000):
last = messages[-1]
blocks = [(i, b) for i, b in enumerate(last["content"])
if b.get("type") == "tool_result"]
total = sum(len(str(b.get("content", ""))) for _, b in blocks)
if total <= max_bytes:
return messages
ranked = sorted(blocks, key=lambda p: len(str(p[1].get("content", ""))), reverse=True)
for idx, block in ranked:
if total <= max_bytes:
break
block["content"] = persist_large_output(block["tool_use_id"], str(block["content"]))
total = recalculate_total(blocks)
return messages
```
The first three layers are all plain-text / structural operations — 0 API calls — but they cannot "understand" conversation content. Context may still be too large. → L4.
### L4: compact_history — Full LLM Summary
![Full LLM summary](images/auto-compact.en.svg)
All three previous layers have run, but after 30 minutes of continuous work on a huge project, tokens still exceed the threshold.
Three-step process:
1. **Save transcript**: Write the full conversation to `.transcripts/` in JSONL format. The transcript preserves a recoverable record, but the model's active context only contains the summary. For the model's current reasoning, the details are no longer in context. The teaching code does not provide a transcript retrieval tool.
2. **LLM generates summary**: Send conversation history to the LLM, asking it to preserve key information: current goals, important findings, modified files, remaining work, user constraints, etc.
3. **Replace message list**: All old messages are replaced with a single summary. The teaching version only keeps the summary; the real Claude Code re-attaches some recent files, plans, agent/skill/tool context after compaction.
```python
def compact_history(messages):
transcript_path = write_transcript(messages) # Save full conversation first
summary = summarize_history(messages) # LLM generates summary
return [{"role": "user",
"content": f"[Compacted]\n\n{summary}"}]
```
**Circuit breaker**: After 3 consecutive failures, stop retrying to prevent an infinite loop wasting API calls.
### Reactive: reactive_compact
Sometimes the API still returns `prompt_too_long` (413) — when context grows faster than compression triggers.
This triggers **reactive_compact**: more aggressive than compact_history, it retreats from the tail, trimming to an API-acceptable size with byte-level precision, keeping only the last 5 messages + summary.
```python
def reactive_compact(messages):
transcript = write_transcript(messages)
summary = summarize_history(messages)
tail = messages[-5:]
return [{"role": "user",
"content": f"[Reactive compact]\n\n{summary}"}, *tail]
```
Reactive compact has a retry limit (default 1). If it still fails, an exception is raised instead of looping forever. Full error recovery is deferred to s11.
### Putting It All Together
```python
def agent_loop(messages):
reactive_retries = 0
while True:
# Three pre-processors (0 API calls)
# Order: budget first, so large content is persisted before placeholders
messages[:] = tool_result_budget(messages) # L3: persist large results
messages[:] = snip_compact(messages) # L1: trim middle
messages[:] = micro_compact(messages) # L2: old result placeholders
# Still too much? LLM summary (1 API call)
if estimate_token_count(messages) > THRESHOLD:
messages[:] = compact_history(messages)
try:
response = client.messages.create(...)
except PromptTooLongError:
if reactive_retries < MAX_REACTIVE_RETRIES:
messages[:] = reactive_compact(messages) # Emergency
reactive_retries += 1
continue
raise # retry limit exceeded, raise exception
# ... tool execution ...
# compact tool: when the model actively calls it, triggers compact_history
if block.name == "compact":
messages[:] = compact_history(messages)
results.append({..., "content": "[Compacted. History summarized.]"})
messages.append({"role": "user", "content": results})
break # end current turn, start fresh with compacted context
```
**The order must not be swapped.** L3 (budget) runs before L2 (micro) because micro replaces old large tool_results with one-line placeholders — budget must persist the full content before that happens. This is why CC source puts `applyToolResultBudget` first.
---
## Changes From s07
| Component | Before (s07) | After (s08) |
|-----------|-------------|-------------|
| Context management | None (context grows unbounded) | Four-layer compression pipeline + emergency |
| New functions | — | snip_compact, micro_compact, tool_result_budget, compact_history, reactive_compact |
| Tools | bash, read_file, write_file, edit_file, glob, todo_write, task, load_skill (8) | 8 + compact (9) |
| Loop | LLM call → tool execution | Three pre-processors before each turn + threshold-triggered compact_history |
| Design principle | — | Cheap first, expensive last |
---
## Try It
```sh
cd learn-claude-code
python s08_context_compact/code.py
```
Try these prompts:
1. `Read the file README.md, then read code.py, then read s01_agent_loop/README.md` (read multiple files consecutively, observe L2 compressing old results)
2. `Read every file in s08_context_compact/` (read a large amount of content at once, observe L3 persisting to disk)
3. Chat for 20+ turns, observe whether `[auto compact]` or `[reactive compact]` appears
What to watch for: After each tool execution, are old `tool_result` entries compressed? When tokens exceed the threshold after extended conversation, is summarization triggered automatically?
---
## What's Next
Context compression lets an agent run for a long time without crashing. But after each compression, the preferences and constraints the user told it are also lost. Can we let the agent selectively remember important things?
s09 Memory → three subsystems: choosing what to remember, extracting key information, consolidating and organizing. Across compressions, across sessions.
<details>
<summary>Deep Dive Into CC Source Code</summary>
> The following is based on analysis of CC source code `compact.ts`, `autoCompact.ts`, `microCompact.ts`, and `query.ts`.
### Execution Order Comparison
The teaching version labels layers L1/L2/L3/L4 for pedagogical clarity, but actual execution order does not match the numbering:
| Dimension | Teaching Version | Claude Code |
|-----------|-----------------|-------------|
| Execution order | budget → snip → micro → auto | budget → snip → micro → collapse → auto (`query.ts:379-468`) |
| snip_compact | Keep head 3 + tail 47 | CC only enables on main thread; implementation not in open-source repo (`HISTORY_SNIP` feature gate), but interface is visible: `snipCompactIfNeeded(messages)``{ messages, tokensFreed, boundaryMessage? }`, also exposes `SnipTool` for model-initiated snipping. Teaching version's 3/47 are simplified parameters |
| micro_compact | Text placeholder replacement | Two paths: time-based clears content directly, cached uses API `cache_edits` (legacy path removed) |
| micro_compact whitelist | By position (most recent 3) | time-based triggers by time threshold; cached triggers by count (`microCompact.ts`) |
| tool_result_budget | 200KB characters | 200,000 characters (`toolLimits.ts:49`) |
| compact_history threshold | Character count estimate | Precise tokens: `contextWindow - maxOutputTokens - 13_000` |
| Summary requirements | 5 categories of info | 9 sections + `<analysis>`/`<summary>` dual tags |
| Compression prompt | Simple prompt | Double-ended hard guardrails forbidding tool calls |
| PTL retry | Yes (simplified) | `truncateHeadForPTLRetry()` retreats by message groups (`compact.ts:243-290`) |
| Post-compaction recovery | None (teaching version only keeps summary) | Auto re-read recent files, plans, agent/skill/tool context |
| Circuit breaker | 3 times | 3 times (`autoCompact.ts:70`) |
| Reactive retry | 1 time | CC has more granular tiered retries |
### Execution Order Details
The real order in CC source `query.ts`:
1. `applyToolResultBudget` (L379): persist large results first, ensuring full content is saved
2. `snipCompact` (L403): trim middle messages
3. `microcompact` (L414): old result placeholders
4. `contextCollapse` (L441): independent context management system (not in teaching version)
5. `autoCompact` (L454): LLM full summary
The teaching version's budget → snip → micro order matches this. The teaching version does not have the contextCollapse mechanism.
### Full Constant Reference
| Constant | Value | Source File |
|----------|-------|-------------|
| `AUTOCOMPACT_BUFFER_TOKENS` | 13,000 | `autoCompact.ts:62` |
| `MAX_CONSECUTIVE_AUTOCOMPACT_FAILURES` | 3 | `autoCompact.ts:70` |
| `MAX_OUTPUT_TOKENS_FOR_SUMMARY` | 20,000 | `autoCompact.ts:30` |
| `POST_COMPACT_TOKEN_BUDGET` | 50,000 | `compact.ts:123` |
| `POST_COMPACT_MAX_FILES_TO_RESTORE` | 5 | `compact.ts:122` |
| `POST_COMPACT_MAX_TOKENS_PER_FILE` | 5,000 | `compact.ts:124` |
| Time micro_compact interval | 60 minutes | `timeBasedMCConfig.ts` |
| `MAX_COMPACT_STREAMING_RETRIES` | 2 | `compact.ts:131` |
### contextCollapse and sessionMemoryCompact
CC source code has two additional mechanisms not covered in this teaching version:
- **contextCollapse**: An independent context management system that, when enabled, suppresses proactive autocompact (`autoCompact.ts:215-222`), with collapse's commit/blocking flow taking over context management. Manual `/compact` and reactive fallback remain independent paths, unaffected by contextCollapse.
- **sessionMemoryCompact**: Before compact_history, CC first attempts a lightweight summary using existing session memory (covered in s09) without calling the LLM. This mechanism becomes clearer after learning s09.
### What Does the Compression Prompt Look Like?
CC's compression prompt has two hard requirements:
1. **Absolutely no tool calls**: It begins with `CRITICAL: Respond with TEXT ONLY. Do NOT call any tools.`, and appends another REMINDER at the end
2. **Analyze first, then summarize**: The model must first reason in an `<analysis>` tag, then output the formal summary in a `<summary>` tag. The analysis is stripped during formatting
### Teaching Version Simplifications Are Intentional
- micro_compact uses text placeholders → we don't have API-level `cache_edits` access
- Tokens estimated via character count → precise tokenizers are out of scope
- Post-compaction recovery omitted → teaching version only keeps summary, does not auto re-attach files
- Two auxiliary mechanisms not covered → they fall in the 10% detail category
The core design principle, cheap first, expensive last, is fully preserved.
</details>
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