TokenPak v1.3.9

Added — TIP-SC+2: streaming semantics invariants

SC+2 extends the conformance matrix from SC+1's non-stream invariants (I1–I5) into the streaming (SSE) path. Three invariants land this phase — the narrowest deliberate scope that covers the highest-value streaming guarantees. Two more (streaming byte-identity of the response-side accumulator; streaming error-frame shape) are deferred to SC+3.

Shipped invariants:

• I6 SSE frame-ordering (blocking). Every complete Anthropic-style SSE frame forwarded to the client is notified to the conformance observer exactly once, in receipt order. No reordering, no drops, no synthesis. On claude-code-* routes, byte-identity per-frame. 9 tests covering parser primitives + multi-chunk split frames + observer receipt order + route-class propagation.
• I7 streaming cache-attribution causality (blocking). The streaming analog of SC+1 I2. cache_origin classification from the message_start frame's usage block respects the "who placed the markers" rule — 'proxy' iff TokenPak inserted the cache_control headers, 'client' iff the client already did, 'unknown' otherwise. Includes the explicit over-claim negative: upstream reports cache hits that neither side admits to seeding → never attribute to proxy. 5 tests.
• I10 streaming telemetry completeness (blocking). Monitor.log fires exactly once per streamed request, post-message_stop, with input_tokens from message_start and output_tokens from the final message_delta. Fire-once and ordering contract locked; single mid-stream telemetry event would double-count or emit partial rows. 4 tests including the end-to-end ordering-contract exercise.

Infrastructure:

• tokenpak/services/diagnostics/conformance/__init__.py — new on_stream_event(route_class, event_type, frame) callback on ConformanceObserver + notify_stream_event(...) free helper. Ship-safe no-op when no observer installed.
• parse_sse_frames(buf) helper — minimal, deterministic byte-in/tuple-out SSE parser. Consumed by both the production chokepoint (to extract event_type before notifying) and test harnesses (to reconstruct frame sequences). Tolerates LF-only and CRLF terminators; returns partial-frame remainder for chunk-accumulation patterns.
• tokenpak/proxy/server.py — streaming forward loop now accumulates an observer-only byte buffer alongside the existing sse_buffer, parses complete frames on each chunk, and calls notify_stream_event per frame. Zero overhead when no observer is installed (one attr lookup on threading.local).

Deferred:

• I8 streaming byte-identity of the response-side accumulator — mostly subsumed by SC+1 I1 for the request side; the response-side streaming analog is niche.
• I9 streaming error-frame shape — requires a minor error.schema.json extension to cover SSE error events; registry is frozen for this phase.

Conformance matrix status: 102 tests green (84 SC + SC+1 + 18 new SC+2) across 3.10/3.11/3.12.