Piik/docs/project-memory.md

Project Memory

Last updated: 2026-08-19

Confirmed Intent

• Build low-latency game screen sharing for one broadcaster and a small trusted group; public or large broadcasts belong on OBS/Twitch-class services.
• Viewers join from normal desktop/mobile browsers. A later native sender may share encoding and improve capture/audio without changing the Web viewer requirement.
• Use a small central service for access, rooms, signaling, deterministic topology, STUN/TURN, and observability while clients carry media whenever practical.
• Minimize server bandwidth. Automatic, viewer-transparent routing follows direct P2P, measured peer assistance, then enabled user-operated/central SFU fallback under deterministic budgets; TURN is transport chosen per edge, not a topology.
• Host/native roots have at most two downstream edges; browser relays have one. An SFU is only a virtual parent for one or two necessary roots, which retain bounded peer descendants; a zero-descendant viewer consumes the same root cap only when no reliable relay root exists. A long-term native/object path should reuse one encode, while browsers re-encode.
• Two-tree packet/layer striping may reduce endpoint upload toward one stream bitrate, but needs a bounded multi-parent, loss, sync, churn, and latency experiment; it is not in the current full-stream chains.
• Shared encoding reduces compute, not each viewer's last-hop copy. Automatic quality uses shared HIGH plus exactly one on-demand LOW whenever verified weak paths exist; all weak paths share it and recovery stops it. An unavailable efficient second encoder fails closed for that attempt while protecting HIGH, but a supported sender cohort that cannot start LOW reliably fails controller acceptance and must be optimized or marked unsupported. SVC has no software fallback.
• Keep decisions, snapshots, research, code, AGENTS.md, and .codex/ in Git; rewrite memory/status in place. Research current primary sources before material work and reject speculative machinery.

Current Recommendation

• Keep desktop Chrome/Edge and the responsive Web viewer as the baseline. Validate Android Chrome and iOS Safari as leaves.
• Use direct host P2P for one or two viewers. Keep ADR-0004 off for broad production traffic: two mobile leaves can consume both host roots. Use the exact-room allowlist only on an isolated canary until its resource, quality, recovery, TURN, and browser/mobile gates pass.
• Browser relays resend remote MediaStreamTrack values and re-encode at each hop; WebRTC does not guarantee a shared encoder across peer connections, so measure the cost.
• Keep browser experiments bounded; spike native RTP relay, encoded-object striping, SVC, and FEC separately.
• Plan a separate native-sender ADR regardless of browser relay results. One encode may feed at most two WebRTC packetizers, reducing encode work but not per-edge upload; it cannot rescue a failed browser gate.
• Optional single-node SFU capacity is failure-only final fallback; it never defaults to whole-room fanout. Stable dual-TURN host roots are only a future exact-room shadow comparison against the same SFU roots, with real hop/egress and E2EE/operator accounting, until evidence amends ADR-0005. PR #12's whole-room SFU mode is superseded.
• Keep ADR-0005 routing default-off: discrete failures drive peer/SFU recovery, full host fanout uses break-before-make, and mobile/iPad clients stay leaves. PR #20 prewarm passes locally; public transport/load gates remain.
• Local reparenting is a later candidate: start with unassigned relay admission rescue; do not block current work.
• Prefer direct UDP, then TURN/UDP, with TURN/TCP required; optional TURN/TLS defaults to 5349, while 443 needs a dedicated address or validated L4/SNI routing.
• Treat video settings as ceilings and degradation as unclassified. The first local A+B alignment foundation covers same-tick capture/outbound identity, windows, deltas, remote linkage, and path; next derive codec profile/parameters/scalabilityMode, then add minimal authenticated C, a two-state controller, and shared LOW. Never use UA or a composite score.
• Reported poor movie/video audio is unclassified. After video A+B, separately diagnose audio A/B/C and A/V sync across capture settings, codec/fmtp, actual bitrate, loss, jitter, concealment, and jitter buffer. maxBitrate is not quality-up; do not expand runtime before evidence. See docs/research/browser-screen-audio-quality.md.
• Do not add custom scene detection or dynamic-FPS control until WebRTC statistics and host resource measurements prove a material gap. Keep browser codec order until target hardware proves a more efficient common codec.
• Keep room policy deployment-driven: public/password-only rooms are random and temporary; password plus SQLite enables sequential persistent rooms and reusable stopped links.
• Deferred architecture audit: docs/maintenance.md.

Current Implementation

• The repository is one npm package using Node.js 24, React, TypeScript, Vite, native WebRTC, ws, Zod, Vitest, and separate coturn.
• Production 769de201f7cc at https://share.bonfire.icu has equal entry actions, default-closed details, bounded clarity-first quality, live source/quality changes, pause, and sender warnings.
• Production still uses one host RTCPeerConnection per viewer because peer assistance and LiveKit are unconfigured; above two viewers it still exceeds the target host-edge budget. Its real game-capture quality/pause cycle remains unverified.
• Access uses optional ACCESS_PASSWORD, a 12-hour stateless HMAC HttpOnly Strict cookie, internal host token, role-bound signaling, Origin/payload checks, and no accounts/JWT/session map.
• With ROOM_DATABASE_PATH and the password, SQLite stores room ID and host-token digest; links persist and room 1 survived deployment. Without it, rooms are temporary.
• Production uses nginx, Node.js 24.19.0, and authenticated coturn 4.17.2 at turn.bonfire.icu:3478; public STUN, TURN/UDP, TURN/TCP, and relay-only traffic pass. TURN/TLS is off.
• The default-off ADR-0005 controller has no production peer/SFU configuration. PEER_ASSISTED_ROOM_IDS restricts exact canary rooms; unlisted rooms stay P2P and empty/missing means all.
• When enabled, peer recovery precedes allowlisted SFU; session revisions prepare/commit/abort and active SFU gets one token refresh before failback. Browser relays re-encode; native sharing is outside product code.
• Chrome 151/LiveKit localhost A/B cut failure-to-active/render from 1.481/2.257 seconds to 0.200/0.320; 31 new frames and 25 ms sampling kept host edges at two. It is headless synthetic 720p30 and includes SDK/network prewarm, not public-network evidence.
• Draft native ladder #16/#18/#22/#23/#25/#28 has one bounded Chrome 720p30 loop: one WebCodecs object feeds two Pion/browser legs, applies an experiment-only minimum stock-GCC target, and recovers one isolated loss. It does not prove one hardware encode.
• Stock Pion GCC plus negotiated RTX is a no-go. The no-RTX candidate can distort loss statistics and stays outside product code until audio, heterogeneous estimates, broader loss, TURN/reconnect, and browser-diversity gates pass; do not add custom congestion control to bypass them.
• Chrome 151 short synthetic 1/3/5/8 runs kept host edges at two, relay edges at one, and all viewers decoding; a three-viewer relay close recovered in 5.32 seconds. This proves topology/control only, not quality, load, endurance, or silent partitions.
• The current quality stack uses one strict, non-persistent QualitySettings value with bounded ceilings and clarity/balanced/fluid preference. Sender readback and limitation warnings remain manual diagnostics. ADR-0007's automatic per-path HIGH/FALLBACK and unique on-demand shared LOW are accepted mainline behavior, but the C report, state controller, and LOW runtime are unimplemented.
• Chrome 151 synthetic 720p30 propagated balanced/clarity to one host and three viewers without changing peer identities; all viewers kept decoding and fanout stayed host two/relay one. This proves control continuity only.
• The first local A+B alignment foundation binds host capture settings to one uniquely matched outbound track in the same tick, follows remoteId and the RTP-specific transport/candidate pair, and blocks stale generations across source replacement. Adjacent getStats() deltas rebase on first, empty, ambiguous, changed-identity, or reset intervals. Codec evidence remains MIME-only; this is not the complete A+B contract.
• Release 769de201f7cc passed CI/hygiene/typecheck, 22 files/274 tests, both builds, zero production dependency vulnerabilities, atomic activation, public health/access, exact bundle, and service/log checks.

Provisional Quality Targets

• Controlled direct path at RTT no more than 40 ms and loss no more than 1%: glass-to-glass p50 no more than 150 ms and p95 no more than 250 ms.
• Regional TURN/UDP under the same endpoint conditions: glass-to-glass p95 no more than 350 ms.
• First picture within 3 seconds after a watch request, excluding explicit permission time.
• A 60 fps profile must not remain below 50 decoded fps for more than 5 seconds without a visible downgrade or limiting reason.

These are measurement gates, not performance claims.

Open Decisions

• Sustainable viewer count by broadcaster and relay hardware, quality profile, network class, and media route; use instrumented 1/3/5/8 comparisons rather than a 1:8 claim.
• Whether ADR-0004 passes fanout, re-encoding, depth-four latency, reparenting, silent-partition, and mobile-leaf gates.
• Whether ADR-0005 standby gains persist across public LiveKit UDP/ICE-TCP/TURN, rollback, reconnect, restart, egress, load, and browser-matrix gates.
• Exact mobile lifecycle behavior and whether Windows per-application audio is required for the first release.
• Project license and distribution model, which determines whether GPL/AGPL sources can move beyond study-only use.
• Initial deployment regions and expected mainland China, Hong Kong, and overseas network mix.
• Whether voice chat ever enters scope or Screener stays complementary to an existing voice application.
• Exact evidence thresholds/windows and the native hardware matrix for ADR-0007; #28's minimum-of-two rule is not a candidate.

Source Of Truth

• Documentation index and current phase: docs/README.md and docs/status.md
• Requirements and design: docs/需求理解.md and docs/方案设计.md
• Media research: docs/research/, indexed by docs/README.md
• Architecture: ADR-0001/0002, proposed ADR-0004/0005, accepted ADR-0007, and rejected/superseded ADR-0003
• Deployment and maintenance: docs/deployment.md, docs/maintenance.md, AGENTS.md, and .codex/