fix(tui): attach explicitly subscribes to /global/event SSE - #2

Problem

When opencode runs in attach mode (opencode attach <url>), externally-triggered session activity never renders in the TUI. Specifically: if peer A POSTs to /session/<id>/prompt_async while peer B is attached to that same session, the daemon processes the wake (the LLM runs, the assistant message is written to opencode.db) but peer B's screen shows nothing.

Verified in production by grunt-it (hivemind anomalyco#221):

• daemon log shows service=bus type=message.updated publishing after the POST
• curl <daemon>/session/<id>/message returns the new messages
• attach client TUI displays nothing
• only ONE TCP connection per attach client to the daemon (the RPC channel) — no SSE connection observed

Root cause

attach.ts calls tui({...}) without passing events. The SDKProvider's onMount has a fallback path:

if (props.events) {
  const unsub = await props.events.subscribe(handleEvent)
  ...
} else {
  startSSE()
}

startSSE() is an async IIFE that calls sdk.global.event({ sseMaxRetryAttempts: 0 }) and forwards events to the local emitter. In practice this fallback is silent on failure — the outer .catch(() => {}) (line 108 of context/sdk.tsx) swallows every error including the SSE-connect failure I observed in production.

Fix

attach.ts now explicitly creates an EventSource that subscribes to /global/event via the SDK, mirroring how the local-worker case in thread.ts wires events: createEventSource(client). Caller (SDKProvider) sees props.events defined and uses the explicit subscription instead of the silent fallback.

The new createAttachEventSource is intentionally one-shot (no reconnect loop). Reconnect-on-disconnect can be a follow-up; the silent fallback is the immediate bug.

Verification

• bun typecheck from packages/opencode passes.
• End-to-end manual test requires a rebuilt binary; tracked in hivemind #222 Phase 2 patch 2c verification.

Notes for upstream (anomalyco/opencode)

Will open an equivalent PR against anomalyco/opencode:dev once we've verified the fix end-to-end on a built binary. The bug exists in upstream too.