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>

s14_cron_scheduler/images/cron-scheduler-overview.en.svg

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+  <defs>
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+      <stop offset="0%" stop-color="#1e3a5f"/><stop offset="100%" stop-color="#4f46e5"/>
+    </linearGradient>
+    <marker id="arrow" viewBox="0 0 10 10" refX="10" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
+      <path d="M 0 0 L 10 5 L 0 10 z" fill="#555"/>
+    </marker>
+    <marker id="arrow-indigo" viewBox="0 0 10 10" refX="10" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M 0 0 L 10 5 L 0 10 z" fill="#4f46e5"/>
+    </marker>
+  </defs>
+
+  <rect width="760" height="480" fill="#fafbfc" rx="8"/>
+
+  <!-- Title -->
+  <rect x="0" y="0" width="760" height="44" fill="url(#header)" rx="8"/>
+  <rect x="0" y="36" width="760" height="8" fill="url(#header)"/>
+  <text x="380" y="28" fill="#fff" font-size="15" font-weight="700" text-anchor="middle">Cron Scheduler — Independent scheduler thread + cron_queue injection point</text>
+
+  <!-- Legend -->
+  <rect x="40" y="56" width="12" height="10" rx="2" fill="#f8fafc" stroke="#94a3b8" stroke-width="1"/>
+  <text x="58" y="66" fill="#64748b" font-size="10" font-weight="600">s10-s13 retained</text>
+  <rect x="160" y="56" width="12" height="10" rx="2" fill="#eef2ff" stroke="#4f46e5" stroke-width="1"/>
+  <text x="178" y="66" fill="#4f46e5" font-size="10" font-weight="600">s14 new</text>
+
+  <!-- ===== Row 1: Full Agent Loop Chain ===== -->
+
+  <!-- consume_cron_queue (s14 new, indigo) -->
+  <rect x="30" y="100" width="95" height="48" rx="8" fill="#eef2ff" stroke="#4f46e5" stroke-width="2"/>
+  <text x="77" y="120" fill="#312e81" font-size="9" font-weight="700" text-anchor="middle">consume</text>
+  <text x="77" y="134" fill="#312e81" font-size="9" font-weight="700" text-anchor="middle">cron_queue</text>
+  <text x="77" y="144" fill="#94a3b8" font-size="7" text-anchor="middle">★ s14 injection</text>
+
+  <line x1="125" y1="124" x2="143" y2="124" stroke="#555" stroke-width="1.5" marker-end="url(#arrow)"/>
+
+  <!-- messages (s10) -->
+  <rect x="146" y="100" width="80" height="48" rx="8" fill="#f8fafc" stroke="#94a3b8" stroke-width="1.2"/>
+  <text x="186" y="128" fill="#1e3a5f" font-size="10" font-weight="600" text-anchor="middle">messages</text>
+
+  <line x1="226" y1="124" x2="244" y2="124" stroke="#555" stroke-width="1.5" marker-end="url(#arrow)"/>
+
+  <!-- prompt + cache (s10) -->
+  <rect x="247" y="94" width="115" height="60" rx="8" fill="#f8fafc" stroke="#94a3b8" stroke-width="1.2"/>
+  <text x="304" y="116" fill="#1e3a5f" font-size="9" font-weight="600" text-anchor="middle">prompt + cache</text>
+  <text x="304" y="130" fill="#94a3b8" font-size="8" text-anchor="middle">assemble_system_prompt</text>
+  <text x="304" y="142" fill="#94a3b8" font-size="8" text-anchor="middle">(s10)</text>
+
+  <line x1="362" y1="124" x2="380" y2="124" stroke="#555" stroke-width="1.5" marker-end="url(#arrow)"/>
+
+  <!-- LLM call (s11 retry) -->
+  <rect x="383" y="94" width="100" height="60" rx="8" fill="#f8fafc" stroke="#94a3b8" stroke-width="1.2"/>
+  <text x="433" y="116" fill="#1e3a5f" font-size="9" font-weight="600" text-anchor="middle">LLM (try/except)</text>
+  <text x="433" y="130" fill="#94a3b8" font-size="8" text-anchor="middle">with_retry</text>
+  <text x="433" y="142" fill="#94a3b8" font-size="8" text-anchor="middle">(s11)</text>
+
+  <line x1="483" y1="124" x2="501" y2="124" stroke="#555" stroke-width="1.5" marker-end="url(#arrow)"/>
+
+  <!-- TOOL DISPATCH (expanded) -->
+  <rect x="504" y="88" width="220" height="72" rx="8" fill="#f8fafc" stroke="#94a3b8" stroke-width="1.2"/>
+  <text x="614" y="106" fill="#1e3a5f" font-size="10" font-weight="600" text-anchor="middle">TOOL DISPATCH</text>
+  <text x="519" y="122" fill="#2563eb" font-size="8">fast → sync (bash, read, write)</text>
+  <text x="519" y="134" fill="#ea580c" font-size="8">slow → background thread (s13)</text>
+  <text x="519" y="146" fill="#4f46e5" font-size="8" font-weight="600">cron → schedule_cron, list, cancel (s14)</text>
+  <text x="519" y="156" fill="#2563eb" font-size="8">task → create, list, claim, complete (s12)</text>
+
+  <!-- Loop back arrow -->
+  <path d="M 724 124 L 748 124 L 748 170 L 77 170 L 77 148" fill="none" stroke="#94a3b8" stroke-width="1" marker-end="url(#arrow)" stroke-dasharray="5,4"/>
+  <text x="400" y="183" fill="#94a3b8" font-size="9" text-anchor="middle">loop back: tool_results → next turn</text>
+
+  <!-- ===== Row 2: Cron Scheduler Thread (indigo) ===== -->
+  <rect x="30" y="206" width="250" height="90" rx="8" fill="#eef2ff" stroke="#4f46e5" stroke-width="2"/>
+  <text x="155" y="226" fill="#312e81" font-size="11" font-weight="700" text-anchor="middle">cron_scheduler_loop (daemon thread)</text>
+  <text x="48" y="244" fill="#4f46e5" font-size="9">time.sleep(1) → cron_matches(job.cron, now)</text>
+  <text x="48" y="258" fill="#4f46e5" font-size="9">match → cron_queue.append(job)</text>
+  <text x="48" y="272" fill="#6b7280" font-size="8">minute_marker prevents double-fire per minute</text>
+  <text x="48" y="286" fill="#6b7280" font-size="8">one-shot jobs auto-delete after firing</text>
+
+  <!-- Arrow: scheduler → cron_queue -->
+  <path d="M 155 296 L 155 330" fill="none" stroke="#4f46e5" stroke-width="1.5" marker-end="url(#arrow-indigo)"/>
+
+  <!-- cron_queue (indigo) -->
+  <rect x="60" y="333" width="200" height="38" rx="8" fill="#eef2ff" stroke="#4f46e5" stroke-width="2"/>
+  <text x="160" y="352" fill="#312e81" font-size="10" font-weight="700" text-anchor="middle">cron_queue</text>
+  <text x="160" y="364" fill="#4f46e5" font-size="8" text-anchor="middle">cron_lock · scheduler writes · loop reads</text>
+
+  <!-- Arrow: cron_queue → consume_cron_queue (connects to top row) -->
+  <path d="M 77 333 L 77 318 L 18 318 L 18 124 L 30 124" fill="none" stroke="#4f46e5" stroke-width="2" marker-end="url(#arrow-indigo)"/>
+  <text x="95" y="313" fill="#4f46e5" font-size="8" font-weight="600" text-anchor="middle">next agent_loop consumes</text>
+
+  <!-- ===== Row 2 Right: CronJob + Storage ===== -->
+  <rect x="320" y="206" width="410" height="90" rx="8" fill="#eef2ff" stroke="#4f46e5" stroke-width="2"/>
+  <text x="525" y="226" fill="#312e81" font-size="11" font-weight="700" text-anchor="middle">CronJob + Persistence</text>
+  <text x="338" y="244" fill="#4f46e5" font-size="9" font-weight="600">CronJob dataclass:</text>
+  <text x="455" y="244" fill="#6b7280" font-size="8">id, cron, prompt, recurring, durable</text>
+  <text x="338" y="260" fill="#4f46e5" font-size="9" font-weight="600">Durable → .scheduled_tasks.json</text>
+  <text x="560" y="260" fill="#6b7280" font-size="8">restored via load_durable_jobs after restart</text>
+  <text x="338" y="276" fill="#4f46e5" font-size="9" font-weight="600">Session-only → memory only</text>
+  <text x="530" y="276" fill="#6b7280" font-size="8">lost when process exits</text>
+  <text x="338" y="292" fill="#ef4444" font-size="9" font-weight="600">⚠ Process exit = scheduler stops (not OS-level crontab)</text>
+
+  <!-- ===== Row 3: 5-field cron reference ===== -->
+  <rect x="30" y="390" width="700" height="76" rx="6" fill="#f8fafc" stroke="#e2e8f0" stroke-width="1"/>
+  <text x="60" y="412" fill="#1e3a5f" font-size="11" font-weight="600">5-field Cron Expression</text>
+  <rect x="60" y="422" width="52" height="16" rx="3" fill="#eef2ff" stroke="#4f46e5" stroke-width="1"/>
+  <text x="86" y="434" fill="#4f46e5" font-size="9" text-anchor="middle">*</text>
+  <rect x="118" y="422" width="52" height="16" rx="3" fill="#eef2ff" stroke="#4f46e5" stroke-width="1"/>
+  <text x="144" y="434" fill="#4f46e5" font-size="9" text-anchor="middle">*</text>
+  <rect x="176" y="422" width="52" height="16" rx="3" fill="#eef2ff" stroke="#4f46e5" stroke-width="1"/>
+  <text x="202" y="434" fill="#4f46e5" font-size="9" text-anchor="middle">*</text>
+  <rect x="234" y="422" width="52" height="16" rx="3" fill="#eef2ff" stroke="#4f46e5" stroke-width="1"/>
+  <text x="260" y="434" fill="#4f46e5" font-size="9" text-anchor="middle">*</text>
+  <rect x="292" y="422" width="52" height="16" rx="3" fill="#eef2ff" stroke="#4f46e5" stroke-width="1"/>
+  <text x="318" y="434" fill="#4f46e5" font-size="9" text-anchor="middle">*</text>
+  <text x="60" y="455" fill="#94a3b8" font-size="8">min</text>
+  <text x="130" y="455" fill="#94a3b8" font-size="8">hour</text>
+  <text x="194" y="455" fill="#94a3b8" font-size="8">day</text>
+  <text x="254" y="455" fill="#94a3b8" font-size="8">month</text>
+  <text x="310" y="455" fill="#94a3b8" font-size="8">dow</text>
+
+  <text x="380" y="434" fill="#475569" font-size="9">*/5 * * * * → every 5 minutes</text>
+  <text x="380" y="450" fill="#475569" font-size="9">0 9 * * 1-5 → weekdays 9:00</text>
+  <text x="560" y="434" fill="#475569" font-size="9">0 9 * * * → daily 9:00</text>
+  <text x="560" y="450" fill="#475569" font-size="9">Supports: *, */N, N, N-M, N,M,...</text>
+</svg>