fix(models): correct retry semantics and Anthropic streaming

[git-jxj]

Summary

This PR fixes three retry issues in model API calls:

• retries=0 returned None without invoking the wrapped call, while retries=None raised TypeError.
• Non-recoverable client errors were retried with the normal delay before reaching backend error handling.
• Anthropic streaming requests were only protected while creating the stream; failures while consuming it escaped without retrying.

The changes cover synchronous and asynchronous paths across the affected OpenAI-compatible, OpenAI Responses, Anthropic, and LiteLLM backends.

Root Cause

retry_call() and async_retry_call() iterated directly over range(retries). Zero or negative values produced no attempts, and None was not accepted by range().

The helpers caught every Exception, including deterministic 400/401/403/404/422 client failures. Backend-specific handlers only saw those exceptions after all configured attempts and delays had been exhausted.

For Anthropic streaming, messages.create() ran inside the retry helper but collect_stream_response() ran afterward. Once create() returned a stream object, an interrupted stream was outside the retry boundary.

Changes

• Treat retries as the total attempt count, default None to 3, and clamp values below 1 to one attempt.
• Add no_retry_exceptions support to synchronous and asynchronous retry helpers.
• Bypass retries for non-recoverable 400/401/403/404/422 SDK errors.
• Keep rate limits, conflicts, timeouts, connection failures, and server errors retryable.
• Apply the exception policy to OpenAI-compatible, OpenAI Responses, Anthropic, and LiteLLM call sites.
• Move Anthropic stream creation and complete stream consumption into one retryable operation.
• Discard partial output from failed Anthropic attempts before issuing a fresh request.
• Add synchronous and asynchronous regression tests for helper semantics, backend exception policies, and interrupted Anthropic streams.

Reproduction

On the unmodified main branch:

retry_call(lambda: "x", retries=0)    -> None
retry_call(lambda: "x", retries=None) -> TypeError
BadRequest with retries=5              -> 5 attempts
Authentication/NotFound, retries=5     -> 5 attempts
Anthropic interrupted stream           -> ConnectionError after attempt 1

The new regression suite reports 15 failures against the old source, including all three behaviors above.

After this change:

retries=0                              -> one call, returns "x"
retries=None                           -> uses the default attempt count
non-recoverable client error           -> one attempt
transient connection error             -> retries to the configured attempt count
Anthropic interrupted stream           -> attempt 2 returns the complete response

Validation

Targeted regression tests:

python -m pytest \
  tests/test_function_utils.py \
  tests/models/test_no_retry_exceptions.py \
  tests/models/test_anthropic_stream_retry.py -q

Result:

58 passed

Model-layer regression suite:

python -m pytest tests/models -q

Result:

78 passed

CI smoke test:

python -m pytest tests/cli/test_all.py::TestRun::test_ci_lite -v -s -p no:warnings

Result:

1 passed

All configured pre-commit checks also passed:

flake8, ruff check, yapf, trailing whitespace, YAML, end-of-file,
requirements, quote normalization, merge-conflict, and line-ending checks

Scope

This change does not alter request payloads, configured retry intervals, or the number of attempts for values greater than zero. Rate limits and transient transport/server failures remain retryable. The new stream-consumption retry boundary is limited to Anthropic; unrelated backend streaming behavior is unchanged.

[Yunnglin]

LGTM!