test(sdk): characterization baseline for the network layer refactor

[cyaiox]

Phase T of the authoritative-server network refactor: pin current
behavior before restructuring so the migration is provably invisible.

• characterization-api/wire/flow specs: public API surface, golden-byte
  wire format (translation round-trips, 12KB chunking, engineToCrdt
  dumps, comms envelope), and 3-engine message flow incl. current
  quirks (echo-to-sender, any-peer hydration responder)
• defects-red spec: 13 it.failing tests, one per known defect, each
  asserting the CORRECT behavior and confirmed failing today; phases
  flip them green as fixes land
• shared utils: 3-engine harness extracted from the connectivity spec,
  convergence oracle (cross-engine networked-state equality), hex helper

Claude-Session: https://claude.ai/code/session_01Kzo6zwrn1CA79S4RN1dgsU

🤖 Generated with Claude Code

https://claude.ai/code/session_01Kzo6zwrn1CA79S4RN1dgsU

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📚 Stack (splits #1505 — merge top-down within each stack)

Network layer (each PR is one self-contained, independently-green commit):

1. test(sdk): characterization baseline for the network layer refactor #1518 test harness — characterization baseline + red defect suite (this stack's root)
2. [DO NOT MERGE] refactor(sdk): network layer foundations — break cycles, single isServer, logging discipline #1519 foundations — cycle break, single isServer, logging discipline
3. [DO NOT MERGE] feat(sdk): hydration FSM — deterministic late-join and reconnect convergence #1520 hydration FSM — late-join/reconnect correctness
4. [DO NOT MERGE] feat(sdk): default-deny server validation, fixed correction path, O(1) entity lookup #1521 validator — default-deny, correction path, entity index
5. [DO NOT MERGE] refactor(sdk): unify CRDT codec into a parse-once pipeline #1522 codec — parse-once pipeline (wire goldens byte-identical)
6. [DO NOT MERGE] feat(sdk): clients target the authoritative server; registry collisions; players dedupe #1523 topology — targeted sends, registry collisions, players dedupe
7. [DO NOT MERGE] refactor(sdk): parameterize network boot, document the host contract #1524 boot + host-conformance doc
8. [DO NOT MERGE] refactor(sdk): ponytail sweep — delete what the refactor no longer needs #1525 simplification sweep (−95 lines)

sdk-commands (independent of the stack above):

• feat(sdk-commands): namespace and durably persist local dev storage per project #1526 world-storage namespacing (pre-existing WIP, carried from the working tree)
• [DO NOT MERGE] fix(sdk-commands): make the local hammurabi dev server reliable #1527 local dev-server reliability (depends on feat(sdk-commands): namespace and durably persist local dev storage per project #1526)

After a parent squash-merges, the child needs git rebase --onto origin/auth-server <old-parent> <child> — ping the session and it gets restacked.

[github-actions]

Test this pull request

• The @dcl/sdk package can be tested in scenes by running

  npm install "https://sdk-team-cdn.decentraland.org/@dcl/js-sdk-toolchain/branch/stack/01-test-harness/dcl-sdk-7.25.1-31013678086.commit-cf9cd20.tgz"

• The @dcl/js-runtime package can be tested in scenes by running

  npm install "https://sdk-team-cdn.decentraland.org/@dcl/js-sdk-toolchain/branch/stack/01-test-harness/@dcl/js-runtime/dcl-js-runtime-7.25.1-31013678086.commit-cf9cd20.tgz"

• To test with npx init

  export SDK_COMMANDS="https://sdk-team-cdn.decentraland.org/@dcl/js-sdk-toolchain/branch/stack/01-test-harness/dcl-sdk-commands-7.25.1-31013678086.commit-cf9cd20.tgz"
  npx $SDK_COMMANDS init

• The /changerealm command to test test in-world

  /changerealm https://sdk-team-cdn.decentraland.org/ipfs/stack/01-test-harness-e2e
  

• You can preview this build entering:
  https://playground.decentraland.org/?sdk-branch=stack/01-test-harness