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feat(stargate): route decision model requests /v1/decisions and /v1/systemone - #2982
Decision models answer typed questions (predicate or noul, choice, score, box) with probabilities instead of generated text. LiteLLM exposes them on POST /v1/decisions (OpenAI Decisions format) and POST /v1/systemone (System One format). The LLM stack rejected both routes. This work adds them as pure passthrough, non-streaming routes routed by model, with no translation between the formats and no engine-specific code. It is split into four stacked pull requests, as requested in review of the single pull request: #2965 (now closed).
Stack, in merge order: 1 llm-api-gateway (#2981), 2 Stargate, with its test-only mock server (#2982), 3 vanity-gateway (#2983), 4 sample backend, BDD and shared docs (#2984).
This is part 2 of 4: Stargate, plus the test tooling around it.
mock-dynamo is a fake model server that lives next to Stargate and is used only by tests. It answers requests with canned replies, so Stargate's tests and the end-to-end script can run without a GPU or a real model. It is never shipped.
The mock integration run is the local run that src/libraries/rust/stargate/AGENTS.md requires for Stargate changes: scripts/e2e-last-cluster.sh starts the gateway, Stargate, Pylon and mock-dynamo together and sends real requests through them.
It builds on part 1 because the e2e script builds the gateway and exercises both routes through it.
Assumptions to confirm
Stargate needs no Pylon change. Pylon forwards request headers by a denylist on every path except /v1/messages, so TypeSafe-Danger-Zone-Images and vendor headers reach the backend. A contract test proves it over every transport.
Size limits are unchanged: Stargate has no axum body limit, but its retry replay buffer rejects a Content-Length above 64 MiB with 413 (tested). A 13 MB image request is tested.
Test tooling. The Stargate dev auth fixture gets an optional invocation call, and the Stargate copy of llm_gateway.proto gets the matching messages, so the mock integration run can declare per-model uris. The messages match the source proto (the unused tokenizer field is reserved in this copy). The call stays unimplemented unless a test configures it. Test tokens are fixed fake strings.
The mock integration gate has no route-addition exemption in AGENTS.md, so it was run. The performance gate comparison was not run: this change adds two route registrations and no code on existing routes, and the repo has no automated baseline versus candidate tooling. Please say if you want a comparison.
What changed
Two route constants and two route registrations in http_proxy.rs.
Contract tests over raw QUIC, HTTP/3 and WebTransport, direct and reverse: header passthrough, a 13 MB body byte for byte, backend 429 and 400 unchanged and not retried, missing required headers, the 413 replay limit, and the router error marker.
mock-dynamo (the test-only fake model server above) serves canned answers by question type, echoes selected headers and a SHA-256 of the body, and has canned 429 and 400 triggers.
The last-cluster e2e script gets a decision case that compares full bodies and digests.
Stargate contract docs and the data flow diagram list the routes.
Customer Release Notes
Added beta support for /v1/decisions and /v1/systemone in Stargate.
Plan Summary
Not applicable.
Usage
Not applicable.
Testing
Ran, all passing: cargo fmt, clippy with -D warnings, stargate_integration decision tests, mock-dynamo tests, the pylon-lib tunnel tests, and the mock integration run (scripts/e2e-last-cluster.sh, all last-cluster cases and both decision routes). The same suites ran on a Linux x86_64 host with identical results. The e2e mutation checks (one changed payload byte, a changed canned field, a wrong Retry-After) each fail as expected.
Real engine run: the gateway, Stargate and Pylon (passthrough backend kind) in front of vLLM (nightly 0.33.0rc1.dev178, model Qwen3-0.6B) on a Linux host. Both routes returned 200 with the same labels and probabilities within 0.05 of a direct call to vLLM. vLLM's own 400 (BadRequestError, and an extra-field Bad Request) and 404 (NotFoundError) bodies came back byte for byte with the same status. A 64-question request was accepted, and a model not declared in the dev auth fixture got the gateway's own 404.
Not run: the performance regression comparison (see Assumption 4); a full Bazel build.
Notes
A Stargate-generated error that is a bare status (replay 413, transport 502 to 504) has no X-Stargate-Error-Code. Marking all of them is a follow-up that would let the gateway drop its empty-body heuristic.
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Walkthrough
Stargate adds /v1/decisions and /v1/systemone proxy support, mock endpoint behavior, and an authorization RPC for invocation routing. Contract tests, end-to-end checks, and API documentation cover the new routes and request handling.
Changes: Decision routes and invocation authorization
Layer / File(s)
Summary
Invocation authorization contract and handler crates/proto/proto/llm_gateway.proto, crates/stargate/src/bin/stargate-dev-auth.rs
The protocol adds AuthLlmInvocation. stargate-dev-auth implements the RPC with optional invocation configuration, authorization checks, response fields, metrics, and tests.
Mock Decisions and System One endpoints crates/mock-dynamo/src/main.rs, crates/mock-dynamo/src/openai.rs, crates/mock-dynamo/src/sha256.rs, crates/mock-dynamo/src/test_control.rs, crates/mock-dynamo/src/tests.rs
mock-dynamo registers both endpoints and returns route-specific answers and errors. Responses echo request details, including body length and SHA-256. Tests cover response shapes, counters, errors, and large request bodies.
Stargate registers both POST routes. Tests cover forwarding across tunnel protocols, request validation, body limits, overload handling, and unknown models. The API contract and system diagram list the routes, and the header-filter test checks forwarding of additional headers.
The script configures invocation credentials and gateway authentication, tests success and error responses through the stack, and checks forwarded request data and backend counts. The --decisions-only option skips the affinity cases while retaining decision-route checks.
NVIDIA/nvcf#2981: Adds the upstream decision handlers that these Stargate routes and end-to-end tests reach.
Suggested reviewers:famousdirector, barrygreengus
Merge Risk: Low · previous review 2044b
The new routes have no established forwarding defect, but an empty development-auth client token would allow requests with only service authorization. Validate that configuration before startup.
Pre-merge checks: 4 · 1
Failed checks: 1 warning
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Docstring coverage is 30.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…
Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed checks: 4 passed
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Title check
The title uses the feat type with the required stargate scope and follows Conventional Commits format. The change adds /v1/decisions and /v1/systemone as non-streaming passthrough routes in Stargate, …
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The title uses the feat type with the required stargate scope and follows Conventional Commits format. The change adds /v1/decisions and /v1/systemone as non-streaming passthrough routes in Stargate, with registrations, mock-dynamo support, contract tests, and docs. The feat type fits because this adds a new beta capability that appears in release notes. The title accurately reflects the primary change.
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Decision models answer typed questions and are served from /v1/decisions
and /v1/systemone. Stargate needs both paths so the LLM gateway can send
them through the same model routing, retry and tunnel path as the other
OpenAI-compatible routes. Pylon already forwards vendor headers on every
path except /v1/messages, so no Pylon change is needed.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
Cover /v1/decisions and /v1/systemone over raw QUIC, HTTP/3 and
WebTransport, direct and reverse: vendor headers reach the backend, a
13 MB base64 body arrives byte-identical, backend 429 and 400 bodies are
passed through unretried, missing required headers return 400 without an
upstream call, an oversized Content-Length returns 413, and routing and
overload rejections carry x-stargate-error-code. The Pylon header policy
test also asserts the vendor headers are forwarded.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
Mock-based integration runs need a backend for the new decision routes.
Both handlers return a canned answer in each route's documented shape,
echo the request headers and body length so a test can prove vendor
headers survive the tunnel, and serve 429 (Retry-After: 7) and 400
errors on request via ?mock_error=. The routes accept bodies up to
16 MiB so base64 image requests are not cut off by axum's 2 MB default.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
The LLM API gateway only serves a decision route for a model whose
function declares the route in its uris, and it learns the uris from the
invocation auth call. The dev auth fixture answered only worker auth, so
no loopback run could exercise the decision routes through the gateway.
An optional invocation section now enables the invocation RPC with a
fixed client token and per-model uris. Without it the RPC stays
unimplemented as before.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
Stargate changes need a loopback run through the real path. The script
now also posts /v1/decisions and /v1/systemone through the gateway,
Stargate, Pylon and mock-dynamo, with the gateway authenticating against
the dev auth fixture that declares both routes. It checks the 200 body,
that the TypeSafe-Danger-Zone-Images vendor header and a 13 MB base64
body reach the backend, and that a backend 429 with Retry-After and a
backend 400 come back unchanged and unretried. --decisions-only runs
just this case.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
The canned answers copied the question type but always used the
predicate shape (Decisions) or the noul shape (System One), so a choice,
score or box question got an answer a client could not parse as that
type. Answers now follow each type's documented shape, read from the
question loosely so unexpected fields never fail a request.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
An end to end run can only prove a large base64 body arrived unchanged
if the backend reports more than its length. The decision echo now
includes the SHA-256 of the received body, computed in a small local
implementation so no dependency is added.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
The decision case only checked a few fields, so a changed image payload
or a rewritten error body could pass. It now compares the SHA-256 the
backend reports with the digest of the body the gateway should forward,
and the complete 200, 400 and 429 bodies and the Retry-After value with
the canned responses.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
The gateway contract lists the endpoints Stargate proxies and the body rules
for each. Both new routes must carry valid JSON and need no stream field.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Review comments at
@src/libraries/rust/stargate/crates/stargate/src/bin/stargate-dev-auth.rs:
- Line 75: Update DevAuth::new to reject an empty invocation.client_token when
invocation is configured, matching its existing validation of serviceToken,
workerToken, and routingKey. Keep the validation conditional on invocation being
present.
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An omitted proto3 string is empty, so a configured empty clientToken would
authorize a request that carries only the service token. The fixture now
rejects it at startup, like the other tokens.
Relates to #2921
Signed-off-by: Sachin Prabhakar <saprabhakar@nvidia.com>
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Posting the prior reviewer's prepared review against the unchanged commit below. Validation results are from that review; I have not rerun those checks.
Reviewed at 9783110. Validated locally: cargo fmt and clippy (-D warnings) are clean, the mock-dynamo, stargate-dev-auth, decision contract, queue-mismatch sanitization, and Pylon header filter tests pass, and scripts/e2e-last-cluster.sh --decisions-only passes for both routes through the gateway, Stargate, Pylon, and mock-dynamo. The revision-level performance comparison was not run. The route wiring works; the main gaps are error classification for Pylon-generated errors, Pylon request observation, and the validation record.
Findings outside the diff:
Major: the Stargate AGENTS.md gates are not met while the PR is marked ready. The integration record lacks the tested commit, exact commands and environment, binaries or images, policy (wait-and-widen, flag off), workload, and artifact links. The performance gate was skipped although baseline and candidate builds differ. These routes make 13 MB+ bodies the normal case, and each one is fully buffered in Stargate's replay buffer (retry/replay.rs:69, an uncapped Vec::new() that grows by doubling, so peak is up to about 2x the body) and again in Pylon's read_request_body. Please record the run details and either run a scoped resource benchmark (Stargate and Pylon RSS and latency with 13 MB decision bodies at fixed concurrency) or record an explicit approval to skip it.
Major (cross-PR): the gateway in #2981 forwards the caller's Authorization, X-Api-Key, Proxy-Authorization, and Cookie to the decision backend. Stargate only strips x-stargate-* headers, and Pylon forwards authorization on every path except /v1/messages, which uses an allowlist (pylon-lib/src/quic_http_tunnel/core.rs:984). Client credentials therefore reach the model server on /v1/decisions and /v1/systemone. Pylon likely needs a matching strip rule for the decision paths, with a test.
Nit: the PR body does not follow the root PR template and has no ## Issues section; the #2921 reference sits under References instead.
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Major: Pylon-generated errors on these routes reach the client as if the model server sent them. Pylon answers a local connect failure (core.rs:893) and an unadmitted model generation (core.rs:739) with a problem+json body. When Stargate exhausts retries, it passes those through: is_internal_capacity_rejection (retry.rs:188) only covers queue mismatch and rewrite saturation, and the retry headers are stripped, so the response has a body and no X-Stargate-Error-Code. The gateway in #2981 treats any non-empty unmarked error as the backend's, so with the decision backend down the client gets an RFC 7807 body with internal Pylon wording, in neither the OpenAI nor the FastAPI shape. #2981 also treats bare 400s and client-controlled Stargate headers as backend errors. One fix covers both: have Stargate mark every router- or Pylon-generated final error with X-Stargate-Error-Code. Please also add a backend-down contract test here for both decision routes.
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Major: the assumption that Pylon needs no change is incomplete. request_observation_endpoint in pylon-lib/src/quic_http_tunnel/core.rs:1157 only maps chat, responses, and embeddings, so requests on these two routes get no TunnelRequestObserver. That means no Pylon request-state or terminal metrics (observe_request_transition) and no input-token live-request accounting in PylonRuntimeState, which feeds queue estimates and load signals. Image-heavy decision traffic would be invisible to Pylon dashboards and load signals, and the new request path would lack the RED metrics the repo requires. Suggest a non-streaming Decisions observation endpoint handled like Embeddings, with a test, or an explicit documented decision to leave it out. /v1/messages has the same gap today.
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Minor: malformed or non-JSON bodies get a 200 with empty answers here, while real FastAPI or LiteLLM backends return 400 or 422, as does the sample backend in #2984. Any test that does not check the digest would pass with a body corrupted in transit. Suggest returning the route's native 400 when parsing fails.
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Minor: counters are emitted before the mock_error branch, so canned 429 and 400 responses still report processed tokens on the stats stream and inflate Pylon load stats in mock runs. These handlers also skip the configured pacing (prepare_request and token delay), so decision requests always finish instantly, and any benchmark campaign that includes them measures zero backend time. Suggest emitting counters only on success and applying the configured input-based delay.
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Nit: this fixture and the sample backend in #2984 (the other side of this contract) disagree. Here the echo key is body_len and absent headers echo as null; the sample uses body_length and omits absent headers. A System One 429 here has detail as a string; the sample uses an array. Empty questions return [] here and a default predicate there. Score is an integer 0 here and a weighted float there. Aligning them would make stack-level assertions mean the same thing against either backend.
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Nit: this assertion can never fail, because the mock never sets x-stargate-upstream-retryable. There is also no negative test that a body over the 16 MiB route limit returns 413.
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FamousDirector
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Why
Decision models answer typed questions (predicate or noul, choice, score, box) with probabilities instead of generated text. LiteLLM exposes them on
POST /v1/decisions(OpenAI Decisions format) andPOST /v1/systemone(System One format). The LLM stack rejected both routes. This work adds them as pure passthrough, non-streaming routes routed bymodel, with no translation between the formats and no engine-specific code. It is split into four stacked pull requests, as requested in review of the single pull request: #2965 (now closed).Stack, in merge order: 1 llm-api-gateway (#2981), 2 Stargate, with its test-only mock server (#2982), 3 vanity-gateway (#2983), 4 sample backend, BDD and shared docs (#2984).
This is part 2 of 4: Stargate, plus the test tooling around it.
src/libraries/rust/stargate/AGENTS.mdrequires for Stargate changes:scripts/e2e-last-cluster.shstarts the gateway, Stargate, Pylon and mock-dynamo together and sends real requests through them.It builds on part 1 because the e2e script builds the gateway and exercises both routes through it.
Assumptions to confirm
/v1/messages, soTypeSafe-Danger-Zone-Imagesand vendor headers reach the backend. A contract test proves it over every transport.Content-Lengthabove 64 MiB with 413 (tested). A 13 MB image request is tested.llm_gateway.protogets the matching messages, so the mock integration run can declare per-modeluris. The messages match the source proto (the unusedtokenizerfield is reserved in this copy). The call stays unimplemented unless a test configures it. Test tokens are fixed fake strings.AGENTS.md, so it was run. The performance gate comparison was not run: this change adds two route registrations and no code on existing routes, and the repo has no automated baseline versus candidate tooling. Please say if you want a comparison.What changed
http_proxy.rs.Customer Release Notes
Added beta support for
/v1/decisionsand/v1/systemonein Stargate.Plan Summary
Not applicable.
Usage
Not applicable.
Testing
Ran, all passing:
cargo fmt, clippy with-D warnings,stargate_integrationdecision tests, mock-dynamo tests, the pylon-lib tunnel tests, and the mock integration run (scripts/e2e-last-cluster.sh, all last-cluster cases and both decision routes). The same suites ran on a Linux x86_64 host with identical results. The e2e mutation checks (one changed payload byte, a changed canned field, a wrongRetry-After) each fail as expected.Real engine run: the gateway, Stargate and Pylon (passthrough backend kind) in front of vLLM (nightly 0.33.0rc1.dev178, model Qwen3-0.6B) on a Linux host. Both routes returned 200 with the same labels and probabilities within 0.05 of a direct call to vLLM. vLLM's own 400 (
BadRequestError, and an extra-fieldBad Request) and 404 (NotFoundError) bodies came back byte for byte with the same status. A 64-question request was accepted, and a model not declared in the dev auth fixture got the gateway's own 404.Not run: the performance regression comparison (see Assumption 4); a full Bazel build.
Notes
X-Stargate-Error-Code. Marking all of them is a follow-up that would let the gateway drop its empty-body heuristic.References
Relates to #2921
Related Pull Requests
Part 2 of 4. Builds on #2981 (llm-api-gateway). Next: #2983, #2984.
Dependencies
None.