nx_h2_stream.nx

nx_h2_stream.nx -- TUTOR-BOOTSTRAP SCAFFOLD (Claude, authored under the R4-H2 HTTP/2-transport-ladder workflow), NOT credited as team self-authoring. R4-H2-004 of the sovereign HTTP/2 transport ladder (knowledge/specs/2026-06-13-http2-transport-ladder.md). The HTTP/2 stream state machine (RFC 9113 §5.1). Unlike the lower rungs this organ emits no wire bytes -- it is the BEHAVIOURAL automaton that RFC 9113 §5.1 dictates: idle -> open -> half-closed(local|remote) -> closed, driven by the HEADERS / DATA / RST_STREAM / END_STREAM events the frame codec produces and consumes. The TRANSITION TABLE is the allowed internet-boundary requirement (a peer that disagrees about the legal transitions cannot interoperate, exactly as it must agree on the frame bytes); the IMPLEMENTATION is pure NishiLang via nx_cc -> nxasm_x86: no gcc, no openssl, no nghttp2. FOUNDED ON (composes, does not reinvent -- anti-orphan law): - nx_h2_frame.nx (R4-H2-003, GREEN): we import it EXACTLY ONCE. It transitively splices nx_hpack.nx -> nx_str.nx -> syscalls.nx, so we inherit sys_mmap / sys_write / sys_exit / sys_openat_append / sys_close from that single import (importing nx_hpack / nx_str / nx_syscalls directly TOO would be the RC6 double-import landmine). The frame type codes (DATA=0x00, HEADERS=0x01, RST_STREAM=0x03) and the END_STREAM flag (0x01) that DRIVE this automaton are exactly the ones nx_h2_frame.nx emits, so the SM and the codec cannot disagree (single source of truth). No floating capability: the frame codec founds this stream machine; flow control (R4-H2-005) founds on this next. BACK-FILL: the team RE-AUTHORS this from the DATA spec via the emitter-of-emitters (X-AUT-006c/e/f) -- this hand-authored scaffold is the sanctioned one-time bootstrap only (meter-integrity, mirror nx_frame_codec.nx:13-16 / nx_h2_frame.nx:31-34). GATE (main): asserts the RFC 9113 §5.1 transition table is the "known answer". The canonical client-GET no-body trajectory: new(1)==IDLE, send_headers(IDLE, END_STREAM)==HC_LOCAL (open transited instantaneously per the "immediately half-closed" rule), recv_headers(HC_LOCAL)==HC_LOCAL, recv_data(HC_LOCAL, END_STREAM)==CLOSED. The with-body branch: send_headers(IDLE, no-END_STREAM)==OPEN, send_data(OPEN, END_STREAM)==HC_LOCAL. RST from any non-idle state -> CLOSED. Stream-id parity: 1/3/0x7FFFFFFF are client (odd, nonzero, <=2^31-1), 0/2 are not. PLUS TAMPER / illegal- transition cases on a SEPARATE state value (the canonical KAT states are never