feat: complete phase 2 -- multi-agent routing, interrupt TTL, escalation, templates

- Intent classification with LLM structured output (single/multi/ambiguous)
- Discount agent with apply_discount and generate_coupon tools
- Interrupt manager with 30-min TTL auto-expiration and retry prompts
- Webhook escalation module with exponential backoff retry (max 3)
- Three vertical industry templates (e-commerce, SaaS, fintech)
- Template loading in AgentRegistry
- Enhanced supervisor prompt with dynamic agent descriptions
- 153 tests passing, 90.18% coverage

docs/phases/phase-2-dev-log.md

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+# Phase 2: Multi-Agent Routing + Safety Layer -- Development Log
+
+> Status: COMPLETED
+> Phase branch: `phase-2/multi-agent-safety`
+> Date started: 2026-03-30
+> Date completed: 2026-03-30
+> Related plan section: [Phase 2 in DEVELOPMENT-PLAN](../DEVELOPMENT-PLAN.md#phase-2-多-agent-路由--安全层-第-3-4-周)
+
+## What Was Built
+
+- **Intent Classification** (`app/intent.py`): LLM structured output-based intent classifier with Pydantic models (`IntentTarget`, `ClassificationResult`). Supports single-intent, multi-intent, and ambiguity detection with configurable confidence threshold.
+- **Discount Agent** (`app/agents/discount.py`): Mock agent with `apply_discount` (write + interrupt) and `generate_coupon` (read) tools. Validates discount range (1-100%).
+- **Interrupt Manager** (`app/interrupt_manager.py`): TTL-based interrupt tracking with 30-minute auto-expiration. Provides `register`, `check_status`, `resolve`, `cleanup_expired`, and `generate_retry_prompt` methods. Complements SessionManager.
+- **Webhook Escalation** (`app/escalation.py`): HTTP POST escalation with exponential backoff retry (max 3 attempts). Includes `WebhookEscalator` and `NoOpEscalator` implementations behind `EscalationService` protocol.
+- **Enhanced Supervisor Routing** (`app/graph.py`): Supervisor prompt now includes dynamic agent descriptions. Intent classifier attached to graph for use by ws_handler routing layer. Multi-intent hint injection for sequential execution.
+- **Vertical Templates**: Three industry YAML templates (e-commerce, SaaS, fintech) in `backend/templates/`.
+- **Template Loading** (`app/registry.py`): `load_template()` and `list_templates()` class methods for template-based agent configuration.
+- **WebSocket Integration** (`app/ws_handler.py`): Ambiguous intent sends clarification message. Interrupt TTL checked before resume -- expired interrupts return retry prompt. Interrupt manager registration on interrupt detection.
+
+## Code Structure
+
+New files:
+- `backend/app/intent.py` -- Intent classification models and LLM classifier
+- `backend/app/agents/discount.py` -- Discount agent tools
+- `backend/app/interrupt_manager.py` -- Interrupt TTL management
+- `backend/app/escalation.py` -- Webhook escalation with retry
+- `backend/templates/e-commerce.yaml` -- E-commerce agent template
+- `backend/templates/saas.yaml` -- SaaS agent template
+- `backend/templates/fintech.yaml` -- Fintech agent template
+
+Modified files:
+- `backend/app/graph.py` -- Intent classifier integration, dynamic supervisor prompt
+- `backend/app/agents/__init__.py` -- Registered discount tools
+- `backend/app/agents/fallback.py` -- Updated capability list
+- `backend/app/registry.py` -- Template loading methods
+- `backend/app/config.py` -- Webhook, template settings
+- `backend/app/ws_handler.py` -- Interrupt manager + intent classification integration
+- `backend/app/main.py` -- Wiring new modules, template loading, version bump to 0.2.0
+- `backend/agents.yaml` -- Added discount agent
+- `backend/pyproject.toml` -- Added httpx to main dependencies
+
+Test files added:
+- `tests/unit/test_intent.py` (11 tests)
+- `tests/unit/test_discount.py` (13 tests)
+- `tests/unit/test_interrupt_manager.py` (14 tests)
+- `tests/unit/test_escalation.py` (11 tests)
+- `tests/unit/test_templates.py` (9 tests)
+
+Test files updated:
+- `tests/unit/test_graph.py` -- Tests for classifier attachment and classify_intent
+- `tests/unit/test_ws_handler.py` -- Tests for interrupt manager and clarification flow
+- `tests/unit/test_main.py` -- Updated version check
+
+## Test Coverage
+
+- Total tests: 153 (87 Phase 1 + 66 Phase 2)
+- Overall coverage: 90.18%
+- New module coverage:
+  - intent.py: 100%
+  - discount.py: 96%
+  - interrupt_manager.py: 100%
+  - escalation.py: 100%
+  - graph.py: 100%
+  - registry.py: 97%
+
+## Deviations from Plan
+
+- Multi-intent handling uses supervisor prompt hint injection rather than a fully custom pre-routing graph node. This is simpler and leverages the existing `langgraph-supervisor` routing rather than fighting it.
+- Webhook escalation is wired to main.py app.state but not yet connected to a specific agent tool (escalation trigger). The module is ready for use -- integration with fallback agent's escalation path is straightforward but deferred to avoid scope creep.
+- The `escalate_to_human` tool mentioned in the plan was not created. The escalation module works standalone and can be triggered from ws_handler or agent tools in Phase 5.
+
+## Known Issues / Tech Debt
+
+- SaaS and fintech templates reference tool names (`get_account_status`, `change_plan`, etc.) that don't have implementations. These are configuration blueprints for future use.
+- Interrupt manager cleanup is not called on a schedule -- `cleanup_expired()` exists but no periodic task invokes it. Consider adding a background task in Phase 5.
+- `main.py` coverage is 44% due to lifespan requiring real DB connection. Integration tests would cover this.