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>

s18_worktree_isolation/images/worktree-overview.en.svg

@@ -0,0 +1,103 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 450" font-family="system-ui, -apple-system, sans-serif">
+  <defs>
+    <linearGradient id="header" x1="0" y1="0" x2="1" y2="0">
+      <stop offset="0%" stop-color="#1e3a5f"/><stop offset="100%" stop-color="#b45309"/>
+    </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-amber" 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="#b45309"/>
+    </marker>
+    <marker id="arrow-green" 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="#16a34a"/>
+    </marker>
+  </defs>
+
+  <rect width="760" height="450" 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">Worktree Isolation — Git Worktree + Task-Directory Binding + Event Log</text>
+
+  <!-- Legend -->
+  <rect x="40" y="56" width="12" height="10" rx="2" fill="#f0f4ff" stroke="#2563eb" stroke-width="1"/>
+  <text x="58" y="66" fill="#2563eb" font-size="10" font-weight="600">s17 Preserved</text>
+  <rect x="160" y="56" width="12" height="10" rx="2" fill="#fffbeb" stroke="#b45309" stroke-width="1"/>
+  <text x="178" y="66" fill="#b45309" font-size="10" font-weight="600">s18 New</text>
+
+  <!-- ===== Row 1: Lead Loop (s17 preserved) ===== -->
+  <rect x="20" y="90" width="70" height="40" rx="8" fill="#eef2ff" stroke="#4f46e5" stroke-width="1.5"/>
+  <text x="55" y="114" fill="#4f46e5" font-size="8" font-weight="600" text-anchor="middle">turn</text>
+
+  <line x1="90" y1="110" x2="104" y2="110" stroke="#555" stroke-width="1.5" marker-end="url(#arrow)"/>
+
+  <rect x="107" y="90" width="70" height="40" rx="8" fill="#f0f4ff" stroke="#2563eb" stroke-width="1.5"/>
+  <text x="142" y="114" fill="#1e3a5f" font-size="10" font-weight="600" text-anchor="middle">messages</text>
+
+  <line x1="177" y1="110" x2="191" y2="110" stroke="#555" stroke-width="1.5" marker-end="url(#arrow)"/>
+
+  <rect x="194" y="86" width="80" height="48" rx="8" fill="#f0f4ff" stroke="#2563eb" stroke-width="1.5"/>
+  <text x="234" y="114" fill="#1e3a5f" font-size="9" font-weight="600" text-anchor="middle">prompt</text>
+
+  <line x1="274" y1="110" x2="288" y2="110" stroke="#555" stroke-width="1.5" marker-end="url(#arrow)"/>
+
+  <rect x="291" y="86" width="70" height="48" rx="8" fill="#f0f4ff" stroke="#2563eb" stroke-width="1.5"/>
+  <text x="326" y="114" fill="#1e3a5f" font-size="9" font-weight="600" text-anchor="middle">LLM</text>
+
+  <line x1="361" y1="110" x2="375" y2="110" stroke="#555" stroke-width="1.5" marker-end="url(#arrow)"/>
+
+  <rect x="378" y="76" width="356" height="70" rx="8" fill="#f0f4ff" stroke="#2563eb" stroke-width="1.5"/>
+  <text x="556" y="94" fill="#1e3a5f" font-size="10" font-weight="600" text-anchor="middle">TOOL DISPATCH (s17 + s18)</text>
+  <text x="394" y="110" fill="#2563eb" font-size="8">bash · read · write · task(4) · send · inbox</text>
+  <text x="394" y="123" fill="#7c3aed" font-size="8" font-weight="700">request_shutdown · request_plan · review_plan</text>
+  <text x="394" y="136" fill="#b45309" font-size="8" font-weight="700">★ create_worktree · remove_worktree · keep_worktree</text>
+
+  <!-- Loop back -->
+  <path d="M 734 110 L 748 110 L 748 150 L 55 150 L 55 130" fill="none" stroke="#94a3b8" stroke-width="1" marker-end="url(#arrow)" stroke-dasharray="5,4"/>
+
+  <!-- ===== Row 2: Worktree Topology (s18 new) ===== -->
+  <rect x="30" y="172" width="700" height="215" rx="8" fill="#fffbeb" stroke="#b45309" stroke-width="2"/>
+  <text x="380" y="194" fill="#78350f" font-size="11" font-weight="700" text-anchor="middle">Worktree Isolation (s18 new: each task gets its own directory + branch)</text>
+
+  <!-- Main repo box -->
+  <rect x="230" y="208" width="300" height="36" rx="6" fill="#fff" stroke="#b45309" stroke-width="1.5"/>
+  <text x="380" y="231" fill="#78350f" font-size="10" font-weight="600" text-anchor="middle">Main repo (.tasks/ + .worktrees/ + .mailboxes/)</text>
+
+  <!-- Arrow: Main repo → Worktree 1 (Alice) -->
+  <line x1="310" y1="244" x2="178" y2="272" stroke="#b45309" stroke-width="1.5" marker-end="url(#arrow-amber)"/>
+  <text x="200" y="262" fill="#b45309" font-size="7" font-weight="600" transform="rotate(-12 200 262)">create + bind</text>
+
+  <!-- Arrow: Main repo → Worktree 2 (Bob) -->
+  <line x1="450" y1="244" x2="582" y2="272" stroke="#b45309" stroke-width="1.5" marker-end="url(#arrow-amber)"/>
+  <text x="530" y="252" fill="#b45309" font-size="7" font-weight="600" transform="rotate(12 530 252)">create + bind</text>
+
+  <!-- Worktree 1: Alice -->
+  <rect x="50" y="275" width="255" height="78" rx="6" fill="#fff" stroke="#16a34a" stroke-width="1.5"/>
+  <text x="177" y="294" fill="#166534" font-size="10" font-weight="700" text-anchor="middle">Alice: .worktrees/auth/</text>
+  <text x="65" y="310" fill="#374151" font-size="8">branch: wt/auth-refactor</text>
+  <text x="65" y="324" fill="#374151" font-size="8">Task: Refactor auth module</text>
+  <text x="65" y="344" fill="#16a34a" font-size="8" font-weight="600">✓ Isolated, no impact on Bob or main repo</text>
+
+  <!-- Worktree 2: Bob -->
+  <rect x="455" y="275" width="255" height="78" rx="6" fill="#fff" stroke="#16a34a" stroke-width="1.5"/>
+  <text x="582" y="294" fill="#166534" font-size="10" font-weight="700" text-anchor="middle">Bob: .worktrees/ui/</text>
+  <text x="470" y="310" fill="#374151" font-size="8">branch: wt/ui-login</text>
+  <text x="470" y="324" fill="#374151" font-size="8">Task: Refactor UI login page</text>
+  <text x="470" y="344" fill="#16a34a" font-size="8" font-weight="600">✓ Isolated, no impact on Alice or main repo</text>
+
+  <!-- Event log + Lifecycle -->
+  <rect x="50" y="362" width="310" height="20" rx="4" fill="#fef3c7" stroke="#d97706" stroke-width="1"/>
+  <text x="205" y="376" fill="#92400e" font-size="8" text-anchor="middle">Event log: .worktrees/events.jsonl → create / remove / keep</text>
+
+  <rect x="400" y="362" width="310" height="20" rx="4" fill="#fef3c7" stroke="#d97706" stroke-width="1"/>
+  <text x="555" y="376" fill="#92400e" font-size="8" text-anchor="middle">Cleanup: keep (preserve branch for review) / remove (delete + mark done)</text>
+
+  <!-- ===== Row 3: Bottom notes ===== -->
+  <rect x="30" y="400" width="700" height="42" rx="6" fill="#f8fafc" stroke="#e2e8f0" stroke-width="1"/>
+  <rect x="50" y="412" width="12" height="10" rx="2" fill="#f0f4ff" stroke="#2563eb" stroke-width="1"/>
+  <text x="70" y="422" fill="#475569" font-size="10">s17: idle_poll + auto_claim + protocols + WORK/IDLE lifecycle</text>
+  <rect x="50" y="426" width="12" height="10" rx="2" fill="#fffbeb" stroke="#b45309" stroke-width="1"/>
+  <text x="70" y="436" fill="#475569" font-size="10">s18: create_worktree + bind_task + remove/keep + events.jsonl (Lead 14→17)</text>
+</svg>