feat(copilot): add a docs-backed platform agent - #5948

Summary

Copilot can now delegate Sim product questions to a dedicated platform agent. Documented behavior is grounded in Sim's public docs, while workspace-access questions can use the live list_user_workspaces tool supplied by the focused dependency in #6227.

• Docs corpus (docs/): a generated manifest synced from apps/docs/content/docs/en defines a read-only VFS tree. glob lists it, read fetches pages from docs.sim.ai, and single-page grep searches within a page. Academy and API-reference remain deliberately unmounted.
• search_docs server tool replaces search_documentation: vector search supports optional page/section path scoping and bounded topK, and reports filtered-result shortfalls explicitly.
• Platform agent surface: the generated catalog and Copilot UI recognize the platform subagent, while retired search_documentation and get_platform_actions ids stay permanently chip-hidden for historical chat replay.
• Hardening: trailing-slash docs globs resolve consistently, oversized single-line pages fail with grep guidance, and handler tests cover docs routing, errors, truncation, and dispatch.
• @Docs tagging remains inert: the wire context kind stays as a documented future seam, but the server continues to drop it; the platform agent uses the docs VFS and search_docs instead.

Depends on #6227 for the updated list_user_workspaces result. The companion Mothership agent consumes that result in simstudioai/mothership#371, which in turn depends on simstudioai/mothership#393.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• Other: ___________

Testing

• bun --cwd apps/sim test lib/copilot/tools/handlers/workflow/queries.test.ts lib/copilot/tools/tool-display.test.ts — 74 tests passed across this branch and its focused dependency.
• bun run check:api-validation passed.
• bunx biome check passed for the changed Sim files.
• bun run scripts/sync-tool-catalog.ts --check --input=../mothership/copilot/contracts/tool-catalog-v1.json passed.
• The existing manifest, docs search, VFS routing, truncation, and dispatch tests continue to cover the documentation path; docs-manifest:check prevents manifest drift in CI.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

Screenshots/Videos

UI impact is chip text only: docs reads render as Section/page (for example, "Read Workflows/agent") and docs searches as "Searching Sim docs for "..."".

Related: simstudioai/mothership#371

Post-Deploy Monitoring & Validation

Merge and deploy #6227 and simstudioai/mothership#393 before the platform-agent PRs. For the first 24 hours after both platform PRs deploy, the Copilot/platform owner should watch request logs for platform, list_user_workspaces, tool-not-found or denied failures, and repeated delegation. Healthy behavior is a direct workspace-list call for access and role questions, exactly one current workspace in scoped chats, and docs-backed answers for product behavior. Removing the platform allowlist entry in the companion PR disables the live lookup independently.