GeezerVison

The fallback subscribes to each input signal and removes those listeners only when an input aborts. A managed chat turn creates a new stop controller and combines it with the run-wide signal in the turn setup. Normal completion does not abort either signal, so the run-wide signal keeps every prior turn's closure, controller, and stop signal alive. The custom session turn also replaces its stop controller without aborting the old one in reset. This differs from native AbortSignal.any, which does not keep an otherwise unreferenced composite alive through strong event listeners.

Example: On a runtime without AbortSignal.any, a chat agent finishes 80 normal turns. Its run-wide signal still holds 80 listeners referencing obsolete stop controllers until the run ends.

Recommended fix: Provide a way to dispose the fallback's source listeners when the composite's operation ends, and invoke it at each turn and subscription teardown. Preserve the existing abort propagation and reason while an operation remains active.

The SDK is a public package, and the new fallback lets customers use chat transports on older Safari versions that previously threw. Repository guidance requires a changeset when a public package fixes a bug users could hit. No changeset is added in this PR.

Example: A customer deciding whether to upgrade for Safari support reads the SDK changelog and finds no entry for the fix.

Recommended fix: Add a patch changeset for @trigger.dev/sdk, phrased in terms of older Safari chat transport compatibility.

Example: A fallback implementation that manages listeners through another valid mechanism can fail the test solely because it never calls the spied-on method.

Recommended fix: Replace the spy with an observable behavioral test that covers the listener-lifetime regression without intercepting removeEventListener.