slice-3 §7.4: external golden JSON fixtures + a new integration-test
file locking the exact on-wire bytes produced by each slice-3 encode_*
function. The inline round-trip tests in protocol.rs use String::contains
(substring) which cannot catch field-order drift, stray fields, or number
formatting changes — all of which the Envelope Serialize impl promises to
keep stable (protocol.rs:115-118: "field order is pinned to make the wire
bytes deterministic"). These fixtures make that promise load-bearing.
5 fixtures cover the 5 new event kinds (spec §3.2-3.3):
speech_started, speech_stopped, function_call,
function_call_output, tools.update.
Each fixture asserts (a) encode_* output equals the fixture bytes exactly
(string equality, not serde_json::Value equality — the latter would
erase the field-order pinning the serializer guarantees), and (b) the
fixture decodes back to the expected DecodedPayload variant with the
expected fields.
Plus a forwards-compat re-assertion: unknown wire type -> DecodedPayload::Unknown
(via FrameKind's #[serde(other)]), not an error — the foundation of the
slice-2 §3.4 "drop + observe" posture that lets a future-protocol brain
not crash an older core.
On first run the golden test caught real drift: serde_json (without
preserve_order) alphabetizes nested object keys, so tools.update's tools
array serializes description-before-name, not input order. Fixture
corrected to lock the actual contract.
11 new tests, all green. cargo fmt + clippy -D warnings clean.
568934177d