feat: add route-aware pricing estimates (#1695)

Salvaged from PR #1563 by @kshitijk4poor. Cherry-picked with authorship preserved.

- Route-aware pricing architecture replacing static MODEL_PRICING + heuristics
- Canonical usage normalization (Anthropic/OpenAI/Codex API shapes)
- Cache-aware billing (separate cache_read/cache_write rates)
- Cost status tracking (estimated/included/unknown/actual)
- OpenRouter live pricing via models API
- Schema migration v4→v5 with billing metadata columns
- Removed speculative forward-looking entries
- Removed cost display from CLI status bar
- Threaded OpenRouter metadata pre-warm

Co-authored-by: kshitij <82637225+kshitijk4poor@users.noreply.github.com>

tests/agent/test_usage_pricing.py

@@ -0,0 +1,101 @@
+from types import SimpleNamespace
+
+from agent.usage_pricing import (
+    CanonicalUsage,
+    estimate_usage_cost,
+    get_pricing_entry,
+    normalize_usage,
+)
+
+
+def test_normalize_usage_anthropic_keeps_cache_buckets_separate():
+    usage = SimpleNamespace(
+        input_tokens=1000,
+        output_tokens=500,
+        cache_read_input_tokens=2000,
+        cache_creation_input_tokens=400,
+    )
+
+    normalized = normalize_usage(usage, provider="anthropic", api_mode="anthropic_messages")
+
+    assert normalized.input_tokens == 1000
+    assert normalized.output_tokens == 500
+    assert normalized.cache_read_tokens == 2000
+    assert normalized.cache_write_tokens == 400
+    assert normalized.prompt_tokens == 3400
+
+
+def test_normalize_usage_openai_subtracts_cached_prompt_tokens():
+    usage = SimpleNamespace(
+        prompt_tokens=3000,
+        completion_tokens=700,
+        prompt_tokens_details=SimpleNamespace(cached_tokens=1800),
+    )
+
+    normalized = normalize_usage(usage, provider="openai", api_mode="chat_completions")
+
+    assert normalized.input_tokens == 1200
+    assert normalized.cache_read_tokens == 1800
+    assert normalized.output_tokens == 700
+
+
+def test_openrouter_models_api_pricing_is_converted_from_per_token_to_per_million(monkeypatch):
+    monkeypatch.setattr(
+        "agent.usage_pricing.fetch_model_metadata",
+        lambda: {
+            "anthropic/claude-opus-4.6": {
+                "pricing": {
+                    "prompt": "0.000005",
+                    "completion": "0.000025",
+                    "input_cache_read": "0.0000005",
+                    "input_cache_write": "0.00000625",
+                }
+            }
+        },
+    )
+
+    entry = get_pricing_entry(
+        "anthropic/claude-opus-4.6",
+        provider="openrouter",
+        base_url="https://openrouter.ai/api/v1",
+    )
+
+    assert float(entry.input_cost_per_million) == 5.0
+    assert float(entry.output_cost_per_million) == 25.0
+    assert float(entry.cache_read_cost_per_million) == 0.5
+    assert float(entry.cache_write_cost_per_million) == 6.25
+
+
+def test_estimate_usage_cost_marks_subscription_routes_included():
+    result = estimate_usage_cost(
+        "gpt-5.3-codex",
+        CanonicalUsage(input_tokens=1000, output_tokens=500),
+        provider="openai-codex",
+        base_url="https://chatgpt.com/backend-api/codex",
+    )
+
+    assert result.status == "included"
+    assert float(result.amount_usd) == 0.0
+
+
+def test_estimate_usage_cost_refuses_cache_pricing_without_official_cache_rate(monkeypatch):
+    monkeypatch.setattr(
+        "agent.usage_pricing.fetch_model_metadata",
+        lambda: {
+            "google/gemini-2.5-pro": {
+                "pricing": {
+                    "prompt": "0.00000125",
+                    "completion": "0.00001",
+                }
+            }
+        },
+    )
+
+    result = estimate_usage_cost(
+        "google/gemini-2.5-pro",
+        CanonicalUsage(input_tokens=1000, output_tokens=500, cache_read_tokens=100),
+        provider="openrouter",
+        base_url="https://openrouter.ai/api/v1",
+    )
+
+    assert result.status == "unknown"