feat(vercel-functions): WebSocket guidance + SSE/streaming clarification

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Stacked on #103 (manifest-ci-gate). Review/merge that first; this PR retargets to main automatically once it lands. The diff here is websockets content only — the workflow manifest correction lives in #103.

Summary

Vercel Functions now serve WebSocket connections natively (changelog, docs). This documents WebSockets across the skill set, steers users away from third-party realtime services and polling workarounds, and corrects the common belief that streaming/SSE needs the Edge runtime.

Changes

• vercel-functions — new ## WebSockets section:
  • Request lifecycle (GET + Upgrade → Routing Middleware/rewrites/Firewall/rate limits), instance pinning + Fluid Compute concurrency, Active CPU pricing.
  • Examples: ws server, Socket.IO server + client (with the transports: ['websocket'] / path gotcha), Next.js experimental_upgradeWebSocket() from @vercel/functions, plus Express/Hono/Nitro and Python (FastAPI / python-socketio) notes.
  • Reconnect-with-backoff client example and persistent-state guidance (no instance affinity → external store, e.g. Marketplace Redis).
  • Discovery wiring: importPatterns (ws, socket.io, socket.io-client), retrieval, docs, and promptSignals — including workaround terms (long polling, pusher, pubnub, ably) so prompts reaching for a websocket substitute surface the native guidance.
• vercel-functions Streaming — explicit callout that SSE/streaming works on the default Node.js runtime; no runtime = 'edge' needed.
• knowledge-update — corrects the stale "Functions can't hold WebSocket connections" belief, adds that streaming/SSE is not Edge-exclusive, and reinforces that Edge is inferior in nearly every case.
• lexical-index — adds polling/long-polling/pusher/ably to the realtime synonym group for the lexical fallback.
• vercel.md — adds WebSockets to the Core Platform compute list and the Functions decision matrix.

Not labeled as beta, per request.

Verification

• bun test → 878 pass, 0 fail; bun run validate passes; build:manifest:check + build:from-skills:check clean.

🤖 Generated with Claude Code

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Note

Low Risk
Documentation and generated skill metadata only; no runtime or application code paths change.

Overview
Documents native WebSockets on Vercel Functions and steers agents away from third-party realtime services and long-polling workarounds, while correcting the belief that streaming/SSE requires runtime = 'edge'.

vercel-functions adds a WebSockets section (ws, Socket.IO client/server gotchas, Next.js experimental_upgradeWebSocket(), reconnect/backoff, external store for state) plus discovery: websockets docs, importPatterns for ws / socket.io, retrieval aliases/intents, and promptSignals for websocket and long-polling terms. The Streaming section now states SSE/ReadableStream work on default Node.js (Fluid Compute).

knowledge-update adds bullets that Functions support WebSockets, streaming is not Edge-exclusive, and Edge should not be the default choice.

lexical-index expands the realtime synonym group with polling / long-polling. vercel.md lists WebSockets on the platform and in the Functions decision matrix. Regenerated skill-manifest.json / skill-catalog.md reflect the metadata changes.

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