fix(messages): fall back to stripped model name for cost calculation

[JasonCZMeng]

Summary

When providers like OpenRouter return model names with a date suffix (e.g. openai/gpt-5.2-20251211), genai-prices doesn't recognize them and ModelResponse.cost() raises LookupError. This causes operation.cost to be missing from traces.

Fix

Added a fallback in ModelResponse.cost(): when the initial calc_price lookup fails, strip the trailing -YYYYMMDD date suffix from the model name and retry. The regex -\d{8}$ matches exactly 8-digit date suffixes at the end of the string.

The fallback chain is now:

1. Try with provider_api_url (most specific)
2. Try with provider_id
3. Strip date suffix → try with provider_api_url
4. Strip date suffix → try with provider_id
5. Raise LookupError

Tests

• test_strip_model_date_suffix: Unit test for the suffix stripping helper
• test_model_response_cost_with_date_suffix: Integration test verifying ModelResponse.cost() works with date-suffixed model names

Fixes #4839

[devin-ai-integration]

Devin Review found 2 potential issues.

View 4 additional findings in Devin Review.

[devin-ai-integration]

🟡 Duplicate try/except LookupError blocks violate rule:894 and cause inconsistent error messages

The cost() method repeats the same two-step fallback pattern (try provider_api_url, then try provider_id) twice — once for the original model name and once for the normalized (date-stripped) name. This violates rule:894 from pydantic_ai_slim/pydantic_ai/AGENTS.md ("Consolidate try/except blocks catching the same exception into one block") and rule:559 from agent_docs/index.md ("Consolidate duplicate logic across conditional branches").

Beyond the style violation, there's also an inconsistency: when the model name has a date suffix and all lookups fail, the final unwrapped calc_price on line 1808 raises a LookupError with calc_price's own message (referencing the normalized name). But when there's no date suffix, the explicit raise LookupError(...) on line 1814 references the original name. A loop-based consolidation would fix both issues.

Suggested change

	try:
	return calc_price(
	self.usage,
	self.model_name,
	provider_id=self.provider_name,
	genai_request_timestamp=self.timestamp,
	)
	except LookupError:
	pass
	# Some providers (e.g. OpenRouter) return model names with a date suffix
	# like "openai/gpt-5.2-20251211". Strip the suffix and retry.
	normalized = _strip_model_date_suffix(self.model_name)
	if normalized != self.model_name:
	if self.provider_url:
	try:
	return calc_price(
	self.usage,
	normalized,
	provider_api_url=self.provider_url,
	genai_request_timestamp=self.timestamp,
	)
	except LookupError:
	pass
	return calc_price(
	self.usage,
	normalized,
	provider_id=self.provider_name,
	genai_request_timestamp=self.timestamp,
	)
	raise LookupError(f'Could not find pricing for model {self.model_name!r}')
	# Build candidate model names: original first, then date-stripped variant.
	names = [self.model_name]
	normalized = _strip_model_date_suffix(self.model_name)
	if normalized != self.model_name:
	names.append(normalized)
	for name in names:
	if self.provider_url:
	try:
	return calc_price(
	self.usage,
	name,
	provider_api_url=self.provider_url,
	genai_request_timestamp=self.timestamp,
	)
	except LookupError:
	pass
	try:
	return calc_price(
	self.usage,
	name,
	provider_id=self.provider_name,
	genai_request_timestamp=self.timestamp,
	)
	except LookupError:
	pass
	raise LookupError(f'Could not find pricing for model {self.model_name!r}')

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[devin-ai-integration]

🟡 Test directly tests private _strip_model_date_suffix function instead of public API

test_strip_model_date_suffix imports and tests _strip_model_date_suffix (a private function prefixed with _) directly. This violates rule:177 from tests/AGENTS.md: "Test through public APIs, not private methods (prefixed with _) or helpers." The date-stripping behavior should be tested through the public ModelResponse.cost() method (which is what test_model_response_cost_with_date_suffix already does), making this test redundant.

Prompt for agents

Remove the test_strip_model_date_suffix function (lines 1392-1407 in tests/test_messages.py) entirely. The date-stripping logic it tests is an internal implementation detail of ModelResponse.cost(), and is already exercised through the public API by test_model_response_cost_with_date_suffix. If additional edge-case coverage is desired (e.g. short numeric suffixes not being stripped), add those as additional test cases within test_model_response_cost_with_date_suffix by constructing ModelResponse objects with those model names.

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