Client now sends the last 4 ticks' actions per packet (newest-first,
already-supported by net_codec's wire format from Phase 1) instead of a
single action with no redundancy. Server gains a real per-slot ring
buffer (new InputJitterBuffer class, scripts/input_jitter_buffer.gd) that
consumes exactly one sequence number per physics tick: repeats the last
action on a starve, zeroes only after a sustained 500ms stall, and
reports real input_buffer_depth/last_input_seq/echo_client_send_ms in
every snapshot instead of the hardcoded zeros Phase 2 shipped with.
InputJitterBuffer is a standalone, scene-free RefCounted (same pattern as
net_codec.gd/net_interpolator.gd) specifically so it's unit-testable
against scripted arrival traces (tests/cases/test_input_jitter_buffer.gd):
sequential consumption, redundancy surviving a 3-packet burst loss (3.1's
own acceptance criterion), starvation repeat-then-zero timing, stale/
reordered packet handling, buffered-depth reporting, and ring-wraparound
slot-tagging safety.
One real bug found wiring this into a live match: the server's ring
buffer started counting its own "expected sequence" from 0 the instant a
player's slot was created - well before that player's first real packet
could possibly have arrived (connection handshake, arena/ship spawn all
take real time first). Since both sides only ever advance monotonically
with no resync mechanism, that gap between the server's arbitrary local
counter and the client's actual from-1 sequence numbers never closed,
so the ship simply never received the client's input (0m movement in a
two-process test). Fixed by seeding the buffer's expected-sequence
counter from the client's own numbering on first real ingest, rather
than assuming a shared from-zero baseline.
Verified with real two-process runs: clean baseline movement restored,
zero starvation observed under 25% random simulated input loss (well
above what redundancy-4 needs to fully absorb), and correct starve-then-
stall behaviour confirmed under 100% loss as a sanity check that the
mechanism isn't a silent no-op. Full regression suite, including the
net-sim-latency milestone gate, re-run clean.
Lands tasks 1.0-1.8 of multiplayer-todo.md: the pure-function test runner,
net_codec (wire format quantizers/pack-unpack), NetworkManager (ENet
transport, manual polling, min-RTT clock sync), MatchNet (handshake,
protocol/tick-rate gating, roster with team+ready state), lobby.tscn (team
columns, switch team, ready toggle), server_boot.tscn (headless dedicated
server with structured logging and an overrun watchdog), and main_menu.gd's
Host/Join-by-IP UI (connecting overlay, cancel, bounded failure path).
Followed by an adversarial review (Opus subagent) that found and fixed two
real bugs - an unvalidated player_name broadcast that let one client's
oversized name head-of-line-block the reliable channel for everyone, and a
server-side roster leak across a host/re-host cycle - plus three gaps in
the test suite itself where a claim of "verified" wasn't actually backed
by what the test checked. All five two-process smoke tests plus the
pure-function suite are green with the strengthened assertions in place.
Josh Creek