Phase 40: Routing Engine + Policy

- RoutingEngine with RouteDecision (model_pattern → provider)
- config/routing.toml: rules, fallback chain, cost gating
- Per-provider Usage tracking in /v1/usage response
- 12 gateway tests green

config/routing.toml

@@ -0,0 +1,61 @@
+# Phase 40: Routing Engine Configuration
+#
+# Human-editable rules for model → provider routing.
+# Matching order: first match wins.
+
+[[rule]]
+model_pattern = "gpt-4*"
+provider = "openrouter"
+max_tokens = 4096
+temperature = 0.7
+
+[[rule]]
+model_pattern = "claude*"
+provider = "claude"
+max_tokens = 4096
+temperature = 0.7
+
+[[rule]]
+model_pattern = "gemini*"
+provider = "gemini"
+max_tokens = 8192
+temperature = 0.9
+
+[[rule]]
+model_pattern = "qwen3.5*"
+provider = "ollama"
+max_tokens = 4096
+temperature = 0.3
+
+[[rule]]
+model_pattern = "qwen3*"
+provider = "ollama"
+max_tokens = 2048
+temperature = 0.3
+
+[[rule]]
+model_pattern = "gpt-oss*"
+provider = "ollama"
+temperature = 0.1
+
+[[rule]]
+model_pattern = "*"
+provider = "ollama"
+temperature = 0.5
+
+# Fallback chain: if primary fails, try these in order
+fallback = ["ollama", "openrouter"]
+
+# Cost gating (tokens = cents per 1M)
+[cost]
+ollama = 0
+openrouter = 15
+claude = 15
+gemini = 0
+
+# Daily budget per provider (cents)
+[daily_budget]
+ollama = 0
+openrouter = 1000
+claude = 500
+gemini = 0