every.channel: sanitized baseline

evolution/proposals/ECP-0037-cross-os-determinism.md

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+# ECP-0037: Cross-OS Determinism Testing (macOS + Linux)
+
+Status: Draft
+Author: Codex
+Reviewers: founder@every.channel
+Created: 2026-02-07
+
+## Decision
+
+Add an explicit cross-OS determinism test workflow for the CMAF ladder pipeline.
+
+We will treat the determinism target as:
+
+- identical output bytes for `init.mp4` and `segment_*.m4s` for the same synthetic input,
+- given the same ffmpeg/x264 build and the same every.channel version,
+- across macOS and Linux.
+
+## Motivation
+
+- Our core thesis depends on multiple independent nodes producing byte-identical artifacts.
+- Without automated cross-OS checks, determinism will silently regress.
+
+## Scope
+
+In scope:
+- Keep an ignored Rust test that produces a deterministic synthetic TS and verifies:
+  - bit-identical outputs across two runs on one host,
+  - keyframe alignment at segment boundaries.
+- Add a script that exports a canonical test input and compares outputs from two machines.
+
+Out of scope:
+- Perfect determinism across different ffmpeg/x264 versions.
+- Hardware encoder determinism.
+
+## Implementation
+
+- Local test: `crates/ec-node/tests/determinism_cmaf_ladder.rs`
+- Cross-OS procedure:
+  1. On macOS and Linux, run the same nix flake dev environment (pins ffmpeg).
+  2. Run `cargo test -p ec-node --test determinism_cmaf_ladder -- --ignored --nocapture`.
+  3. Emit a JSON summary of sha256s per variant (init + segments) into `tmp/determinism/<os>.json`.
+  4. Compare the JSON across OS.
+
+## Notes
+
+- Even with pinned ffmpeg, Apple vs Linux libc may still perturb behavior.
+- If cross-OS byte equality fails but in-host determinism holds, we can treat it as:
+  - still useful for availability (single-encoder determinism),
+  - but not sufficient for multi-source "same bytes" dedupe.
+