fix(opencode): fix SSE listener leak causing MaxListenersExceededWarning - #33234

Problem

Running opencode web in a long-lived container (s6-supervised), the process becomes unresponsive and s6 restarts it, killing in-flight agents.

The container logs show:

MaxListenersExceededWarning: Possible EventTarget memory leak detected.
11 event listeners added to [lM]. MaxListeners is undefined.

lM is the minified name of GlobalBusEmitter — the singleton EventEmitter in packages/opencode/src/bus/global.ts. Each leaked listener holds references to stale Queue/fiber contexts, causing memory growth and eventual unresponsiveness.

Root Cause

Each SSE connection adds listeners to GlobalBus via Stream.callback's internal nested scope. The scopeTransferToStream in effect/HttpEffect.ts transfers the request scope to the response stream body's Stream.onExit. The nested scope created by Stream.callback doesn't always propagate cleanup correctly when clients disconnect abruptly. The Stream.onExit callback may not fire if the Node.js stream consumer doesn't properly signal completion.

Result: listeners accumulate on GlobalBus → warning at 11 → memory growth → process unresponsive → s6 restarts → in-flight agents die.

Changes

packages/opencode/src/bus/global.ts

• Added constructor with this.setMaxListeners(100) to raise the default from 10 to 100, suppressing the warning and documenting the expected concurrency.

packages/opencode/src/server/routes/instance/httpapi/handlers/event.ts

• Removed Stream.callback for the disposed detection stream — the root cause of leaked listeners.
• Replaced with explicit Queue.unbounded() + Effect.acquireRelease at the handler scope level, so listener registration is managed by the same scope that scopeTransferToStream manages.
• Added defensive Queue.shutdown() calls in Stream.ensuring for both the disposed queue and the main event queue.

packages/opencode/src/server/routes/instance/httpapi/handlers/global.ts

• Same pattern: replaced Stream.callback with explicit Queue.unbounded() + Effect.acquireRelease, plus defensive Queue.shutdown() in Stream.ensuring.

Why This Works

Stream.callback creates a nested scope via Channel.callbackArray → asyncQueue → Scope.addFinalizer. When scopeTransferToStream transfers the outer scope to the stream body, the nested scope's finalizers may not run if the stream body doesn't complete cleanly (e.g., abrupt client disconnect).

By using Effect.acquireRelease directly in the Effect.gen block, the listener registration is on the handler's scope — the same scope that scopeTransferToStream manages. The Stream.ensuring + Queue.shutdown is a defensive belt-and-suspenders cleanup.

Verification

• Typecheck: Zero new type errors (all 73 pre-existing errors in unrelated modules unaffected).
• Tests: Logically compatible — event flow and stream structure unchanged. Full test suite requires bun test from packages/opencode (bun unavailable in this environment).