nx_h2_flow.nx

nx_h2_flow.nx -- TUTOR-BOOTSTRAP SCAFFOLD (Claude, authored under the R4-H2 HTTP/2-transport-ladder workflow), NOT credited as team self-authoring. R4-H2-005 of the sovereign HTTP/2 transport ladder (knowledge/specs/2026-06-13-http2-transport-ladder.md). HTTP/2 flow control (RFC 9113 §5.2 / §6.9). Like the stream state machine this organ emits almost no wire bytes -- it is the WINDOW ARITHMETIC the RFC dictates: a connection window (stream 0) and a per-stream window each initialised to SETTINGS_INITIAL_WINDOW_SIZE (default 65535), debited by the ENTIRE payload of every DATA frame (and ONLY DATA frames, §5.2.1), replenished by WINDOW_UPDATE increments, with the hard ceiling 2^31-1. The VALUE SEMANTICS are an allowed internet-boundary requirement (a peer that disagrees about when a window is exhausted or overflowed 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): imported 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 / nx_tls13 directly TOO would be the RC6 double-import landmine). The WINDOW_UPDATE builder h2_frame_write_window_update (§6.9, type 0x08, 4-octet payload), the big-endian helpers, and the SETTINGS INITIAL_WINDOW_SIZE param emitter all live in nx_h2_frame.nx -- this rung emits the SAME WINDOW_UPDATE bytes the codec does (single source of truth), it does NOT re-roll its own builder. No floating capability: the frame codec founds this flow-control layer; the conformance + ALPN-h2 rung (R4-H2-006) 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 / nx_h2_stream.nx:27-30). GATE (main): asserts the RFC 9113 §6.9 known-answers byte-exact AND the window arithmetic. WINDOW_UPDATE +65535 on the connection (stream 0) and on stream 1, WINDOW_UPDATE +2147483647 (max) on stream 1, the SETTINGS INITIAL_WINDOW_SIZE =65535 frame -- all built by the composed nx_h2_frame builders. Value math: init -> 65535; consume(65535, 100) -> 65435; apply_window_update(0, 65535) -> 65535; is_data_frame(DATA 0x00)==1 / (HEADERS 0x01)==0; apply_settings_initial