Verify multi-site id honor in MCP .wsb channel; document cross-repo root cause of duplicate/first-only launch

[Copilot]

When asked to launch multiple banks (kb 국민은행과 우리은행 인터넷 뱅킹을 실행하려 해.), only the first bank opens, and in Spork command-line mode the site opens twice. This traces the multi-argument path MCP → tablecloth-prepare.ps1 → SporkBootstrap → Spork.exe and pins the failure downstream.

Findings

• The MCP already honors multiple ids. Both Tools/SandboxTools.cs (BuildWsb) and node/src/tools/sandbox-tools.ts (buildWsb) emit every id, space-joined, in a single assignment:

  $env:TABLECLOTH_SITE_IDS = 'Hometax ShinhanBank';

• "Only first bank" is downstream in TableCloth/tools/no-install/tablecloth-prepare.ps1: Start-Process $launcher -ArgumentList @('--site-ids', $SiteIds) flattens the value into separate argv tokens (reproduced with pwsh), and Spork.Bootstrapper/BootstrapOptions.cs (case "--site-ids": siteIds = value) keeps only the first — the rest are dropped.
• "Duplicate open" is downstream in Spork command-line mode; already addressed on TableCloth main (removed OpenWebSiteStep from StepsComposer), pending release. With one id surviving, that single site is opened twice by the older runner — the same underlying behavior.

Changes

• node/test/conformance.mjs — added a generate_wsb(["Hometax","ShinhanBank"]) regression check asserting both builds keep all ids, in a single TABLECLOTH_SITE_IDS assignment, space-joined, byte-identical across .NET/Node.
• SPEC.md §7 — documented the multi-id honor contract (all ids preselected, assigned once; each site opened once end-to-end).
• TROUBLESHOOTING.md — Known-issue entry: MCP boundary is correct; exact downstream root causes and fixes.

Scope

The MCP's half of the path is correct and now regression-tested. The runtime fix (preserve all ids when forwarding --site-ids; keep the landed single-open fix) belongs to the yourtablecloth/TableCloth runner/prepare script and its next release, outside this repository.

• Fixes 여러 은행 열기 지원이 동작하지 않음 + 중복된 웹 사이트 열림 #2

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