Project editor example: asynchronous engine, Forum viewer and three games

[concordia-claw]

Summary

This builds on the editor teaching example (google-deepmind#389, whose branch is this PR's base). It holds the tutorial work's changes outside the core library. The core changes are in google-deepmind#396.

• --engine asynchronous. The launcher gives every instance one shared ReactiveMeasurements, as examples/social_media does. The object is host-owned and never written to a project.

• Forum viewer. Forum in the central viewer renders the running game master's standard ForumState (to_html). Without a forum, it explains how to get one.

• --title. Sets the editor heading.

• Three bundled games in projects/, one per engine:

  • royal-cake.json: situated game master, sequential engine.
  • royal-pond.json: a commons dilemma on the contrib simultaneous game master, in 15-minute rounds.
  • crumbleton-forum.json: the asynchronous social media game master.

  A new test checks that each one loads and builds without model calls.

• Mock label. The no-model label now reads "NoLanguageModel · no model API calls" instead of "Free mock". Concordia itself is always free; the label should say what NoLanguageModel avoids.

• README. Covers the engine choice: sequential is for turn-based games with one entity per step, simultaneous lets every player act in the same step, and asynchronous lets each player act at its own pace. It also covers the generic simulation prefab and the three games.

Dependency

royal-pond.json sets start_time, use_variable_increments and call_to_action on GameMasterSimultaneous, so it needs google-deepmind#396.

• On this branch's current core, the editor rejects those fields, and test_bundled_projects_load_and_build[royal-pond.json…] fails. Every other example test passes (78 of 79).
• On upstream main plus Add params/get inspection and runtime-editable game master state google-deepmind/concordia#396, all 79 example tests pass.

Test plan

• pytest examples/project_editor on upstream main plus Add params/get inspection and runtime-editable game master state google-deepmind/concordia#396: 79 passed.
• The same tests on this branch's core: 78 passed, plus the one expected failure described above.
• pyrefly check examples/project_editor/*.py (1.2.0) and pylint --errors-only examples/project_editor are clean on both cores.
• Live runs of all three projects with DeepSeek V4.1 Flash on Together AI cost about $0.28 together.

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