S3-094: Implement authoritative multiplayer simulation

Parent and ownership

Parent epic: https://github.com/stacksjs/the-settlers-iii-remake/issues/14 Source owner: stacksjs/the-settlers-iii-remake. Master roadmap: https://github.com/stacksjs/the-settlers-iii-remake/issues/4.

Problem and observable result

Validate costs, ownership, ordering, and rates server-side. Advance authoritative ticks. Send visibility-filtered updates only.

The current application is a browser prototype. Passing the Riverlands campaign does not establish original-game or native parity. This issue is complete only when its stated behavior has retained evidence.

Evidence and interfaces

Versioned save envelopes and seeded command logs preserve complete simulation state. Online matches run authoritatively in Bun and emit visibility-filtered updates to authenticated clients.

• https://github.com/stacksjs/the-settlers-iii-remake/blob/884406e97f912d18a50a33734b535a27dd25531d/resources/game/controller.ts
• https://github.com/stacksjs/stacks/tree/c8e9b2755edeead39ecf6aa540014a7642ff7149/storage/framework/core/realtime

Pin the inspected revisions and fixture hashes in the implementation evidence. Original-game observations govern rules and timing. JSettlers is implementation evidence, not an authoritative balance specification. Unknown values remain explicitly unverified.

Acceptance criteria

• Validate costs, ownership, ordering, and rates server-side.
• Advance authoritative ticks.
• Send visibility-filtered updates only.
• The visible result agrees with the underlying simulation or platform state, including failure paths.
• Tests exercise the maintained public interface and retain reproducible fixtures or execution receipts.

Test matrix

• Submit unauthorized or repeated commands.
• Inspect network payloads for concealed state.
• Exercise invalid input, cancellation or interruption, and repeated execution where this interface permits them.
• Verify determinism/conservation for simulation changes and resource ownership/disposal for platform changes.
• Run owning-repository lint, relevant type checks and tests. Capture actual native output for native capability claims.

Scope constraints

Implement this behavior as a complete verifiable slice. Do not silently expand into adjacent tickets or substitute simplified gameplay. Keep the shared TypeScript simulation, shared stx signals, and ts-css conventions. Native gameplay and HUD must not depend on a WebView. HomeOS reuse must not introduce a kernel dependency into the game. Existing unrelated edits and authored guidance must be preserved.

Blocked by

• https://github.com/stacksjs/the-settlers-iii-remake/issues/38
• https://github.com/stacksjs/the-settlers-iii-remake/issues/95

Upstream release and adoption

Application behavior belongs here. If a reproduction identifies a framework defect, repair and release its owning source first, update Stacks where affected, then install the verified packages here.

No node_modules edits, copied runtimes, generated-source string patches, fabricated globals, successful no-op implementations, or skipped release gates. Push tested conventional commits as Chris to the owning origin/main without coauthor trailers or force pushes.

Completion evidence

• Implementation commits and relevant upstream issue links.
• Exact checks and results, fixture hashes, and screenshots/native execution evidence where applicable.
• Published package versions, downstream lockfile identity, and release receipts when affected.
• Remaining limitations stated explicitly. Partial work does not close this issue.

Partial progress on the authoritative match (commit 6418bc5): the server owns the Session, stamps tick, player and sequence, validates orders with the engine, advances in 250 ms turns and publishes them over Stacks realtime (emit plus createBroadcastResponse). Each client replays the turns, compares the checksum every turn and resyncs from a snapshot on any gap or mismatch (browser test: 20 verified turns each, no resync, then recovery after a dropped connection). Open and stated in docs/multiplayer.md: visibility-filtered updates (clients hold the whole world), cost and rate validation beyond the engine's own checks, and scale-out beyond one process.