feat(agent): identify Python SDK traffic in user agent

[LukasParke]

Appends the openrouter-agent-sdk distribution name and version to the generated SDK's User-Agent so agent traffic is distinguishable from plain openrouter-python traffic.

speakeasy-sdk/python 1.1.22 2.914.0 1.0.0 openrouter openrouter-agent-sdk/0.8.0

Behavior

• The token is appended only when sdk_configuration.user_agent is still the generated default (openrouter._version.__user_agent__). An explicit user_agent= kwarg, or a hook that rewrites the value during sdk_init, keeps its value untouched.
• importlib.metadata.PackageNotFoundError falls back to the bare distribution name rather than emitting a wrong or empty version.
• Appending is idempotent.

Language-specific identity

.upstreamer/upstreamer.md gains divergence #7: Python appends the PyPI distribution name (openrouter-agent-sdk), TypeScript the npm package name (@openrouter/agent), Go the module path (github.com/OpenRouterTeam/go-agent). The porting automation must not converge this token toward the TypeScript literal.

Tests

tests/unit/test_user_agent.py — six cases: default append, idempotence, explicit user_agent= override (alongside hooks), hook-set user agent preserved, PackageNotFoundError fallback, and a wire-level httpx.MockTransport assertion that the header reaches the transport through call_model together with the existing x-openrouter-callmodel marker.

Verification

.upstreamer/scripts/verify.sh — PASS: 0 failures

uv sync --frozen --all-extras     pass
uv lock --check                   pass
ruff check / ruff format --check  pass
mypy src tests                    pass
pytest tests/unit --cov-fail-under=83   pass
required public API (31 symbols)  pass