🤖 tests: fuzz gateway, provider routing, and stream error paths; fix error-serialization bugs - #4021
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…am error paths Deterministic seeded fuzz tests (no new deps) covering: - gateway stream usage/finishReason normalization (hostile upstream payloads) - model string parsing/normalization idempotence + prototype-pollution keys - refusal-fallback chain sanitization (bounded, deduped, acyclic) - error extraction/clamping/429 classification with hostile thrown values - pure route resolution with garbage priorities/overrides - Coder gateway catalog parsing and model-id mapper roundtrips - StreamManager chaos: hostile chunk streams must settle with a terminal event, leak no unhandled rejections, and never wedge the workspace Fixes found by fuzzing: - getErrorMessage could throw despite its non-throwing contract: String(error) on a hostile Proxy/throwing toString escaped the guard (it runs in stream-failure paths where a throw masks the real provider error) - getErrorMessage degraded cyclic/BigInt provider error payloads to "[object Object]" because bare JSON.stringify threw; now serializes with a cycle-safe replacer so the payload's actual fields survive - StreamManager error-part fallback used bare JSON.stringify, replacing cyclic provider errors with a serialization TypeError; now uses getErrorMessage
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- getErrorMessage: track only the ancestor chain when serializing so shared (non-cyclic) sibling references stay intact; only true cycles become [Circular] - streamManager: route tool-error payload serialization through getErrorMessage so cyclic/BigInt tool errors stay recoverable tool errors - flatUsageToV3: sanitize non-finite token counts (NaN/Infinity) to undefined so they cannot leak into usage/cost arithmetic; fuzz asserts finiteness - gateway model-id mappers: reject leading/trailing separators (slash and dot) so empty origins/model ids cannot form invalid canonical identities; fuzz asserts non-empty parts - chaos test: actually start and settle a second stream on the same workspace to exercise the reuse path
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Summary
Adds a deterministic fuzzing/chaos pass over the AI Gateway integration, provider routing/resolution, refusal-fallback logic, and stream error handling — and fixes three error-path bugs the campaign surfaced (all in how hostile provider error payloads are stringified/propagated).
Background
A faulty upstream provider recently hung/broke the agent loop until manual intervention, suggesting hidden edge cases in provider failure handling. This PR probes the mux-owned failure surfaces with seeded fuzz tests: gateway payload normalization, model-string parsing, fallback-chain resolution, route resolution, Coder gateway catalog parsing, error classification, and StreamManager's chunk-consumption loop.
Implementation
src/common/utils/testing/fuzzHelpers.ts: dependency-free seeded PRNG (mulberry32) plus hostile value/string generators (prototype-pollution keys, lone surrogates, cyclic objects, BigInt, throwing getters/Proxies). Every fuzz test reports its seed, so failures replay deterministically.*.fuzz.test.ts/ chaos suites asserting totality (never throw), idempotence (normalization survives persist/reload round-trips), boundedness (fallback chains ≤ 3, deduped, acyclic; clamped errors stay clamped), and terminal settlement (every hostile stream ends in a terminal event with zero unhandled rejections and no wedged workspace; 40 seeded iterations againstStreamManagerwith malformed deltas, unknown chunk types, mid-stream throws, truncation, and garbage usage payloads).Fixes found by the campaign:
getErrorMessagecould throw despite its non-throwing contract: theString(error)fallback sat outside the try, so a hostile Proxy / throwingtoStringescaped — in stream-failure paths this masks the real provider error.getErrorMessagedegraded cyclic/BigInt provider payloads to"[object Object]"because bareJSON.stringifythrew; it now serializes with a cycle/BigInt-safe replacer so the payload's actual fields survive to the UI.StreamManager's error-chunk fallback used bareJSON.stringify(errorObj), replacing cyclic provider errors with aConverting circular structure to JSONTypeError; it now routes throughgetErrorMessage(regression test included).Validation
"[object Object]"degradation for circular error objects, which this PR intentionally improves.Risks
Low. Production changes are confined to error-message serialization fallbacks (
errors.ts, oneStreamManagererror-part branch); behavior only changes for error payloads that previously crashed serialization or degraded to"[object Object]". Affected area: error reporting in stream-failure paths. UTF-8/SSE byte-boundary decoding lives inside the AI SDK (not mux-owned), so it is intentionally out of scope; socket-level fault injection against a live gateway would need an integration harness and is noted as follow-up material.Generated with
xum• Model:anthropic:claude-fable-5• Thinking:xhigh• Cost:$13.41