Add PREFECT_CLIENT_EMIT_EVENTS setting to disable client-side event emission

[zionts]

Closes #21030

Summary

Adds a PREFECT_CLIENT_EMIT_EVENTS boolean setting that controls whether the client emits events to the Prefect server. Defaults to True (no behavior change).

Currently, should_emit_events() is hardcoded to return True whenever PREFECT_API_URL is set — there's no way to disable client-side event emission via configuration. This PR adds a clean opt-out for deployments that don't use event-driven features (automations, triggers).

Changes

• src/prefect/settings/models/client.py — new emit_events field on ClientSettings with env var PREFECT_CLIENT_EMIT_EVENTS
• src/prefect/events/worker.py — should_emit_events() checks the setting first, short-circuiting before API URL/key checks
• tests/events/client/test_emit_events_setting.py — 5 tests covering default behavior, override, and interaction with cloud config
• tests/test_settings.py — added to parametrized settings validation

Usage

export PREFECT_CLIENT_EMIT_EVENTS=false

Or in Python:

from prefect.settings import temporary_settings, PREFECT_CLIENT_EMIT_EVENTS

with temporary_settings(updates={PREFECT_CLIENT_EMIT_EVENTS: False}):
    # Events are not emitted in this context
    ...

Checklist

• References Add PREFECT_EMIT_EVENTS setting to disable client-side event emission #21030
• Includes tests
• No breaking changes (defaults to True)

[codspeed-hq]

Merging this PR will not alter performance

✅ 2 untouched benchmarks

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_{Comparing zionts:fix/emit-events-setting (2e5c260) with main (4fc6103)}

[desertaxle]

This is a PR that we likely won't accept because large portions of Prefect rely on events being emitted client-side. In particular, task state changes are reported via events, so there would be no task observability with events turned off.

It seems this PR is motivated by other issues you were having with event emission, so let's see if we can find a different way to address them.