fix: Add sync_mode for Sidekiq/Resque compatibility

[haacked]

Summary

• Add sync_mode option that sends events synchronously on the calling thread, bypassing the background queue entirely
• Follows the same pattern as the Python SDK: each event is sent inline via Transport#send at capture time
• Fixes event loss in forking environments (Sidekiq, Resque) where background threads are killed on fork

Usage

PostHog::Client.new(api_key: 'key', sync_mode: true)

Or with Rails:

PostHog.init do |config|
  config.api_key = 'key'
  config.sync_mode = true
end

Design

• sync_mode bypasses the queue and worker entirely — no SyncWorker class needed
• enqueue calls send_sync which creates a single-item MessageBatch and sends it immediately
• flush is a no-op in sync mode (nothing to flush)
• test_mode takes precedence over sync_mode
• Transport is initialized with 3 retries for resilience

Test plan

• New specs verify sync sends without queue/worker, error handling, serialization failures, and test_mode precedence
• Full test suite passes (326 specs, 0 failures)
• Manual testing with Sidekiq/Resque to confirm events are delivered reliably

Fixes: #10

Note

Issue #10 is a blocker for some customers to adopt our library rather than rolling their own code.

[dustinbyrne]

Seems totally reasonable to me. The Copilot comment regarding exceptions in example.call is nit-picky but seems worth considering.

[haacked]

The Copilot comment regarding exceptions in example.call is nit-picky but seems worth considering.

As I told Copilot, this is a false positive. RSpec's around hook captures test failures internally. example.call doesn't raise, so the cleanup after it always runs. This is the same pattern used across the entire test suite (e.g., send_worker_spec).

[Copilot]

Pull request overview

Adds an opt-in sync_mode to the Ruby client so event capture can send immediately on the calling thread (bypassing the queue/worker), improving reliability in forking job systems like Sidekiq/Resque.

Changes:

• Add sync_mode option to PostHog::Client that sends each event inline via Transport#send, with locking for in-flight sends and flush as a no-op (wait-only) in sync mode.
• Add Rails initializer support for config.sync_mode.
• Add worker shutdown plumbing (noop + send worker) and bump gem version to 3.6.0, plus new specs for sync-mode behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
spec/posthog/client_spec.rb	Adds specs covering sync-mode inline send, error handling, serialization failure, flush behavior, and test_mode precedence.
posthog-rails/lib/posthog/rails/railtie.rb	Exposes sync_mode configuration via Rails init config wrapper.
lib/posthog/client.rb	Implements sync_mode (inline send path, transport init, flush/shutdown coordination) and documents the new option.
lib/posthog/send_worker.rb	Adds shutdown method used by client shutdown flow.
lib/posthog/noop_worker.rb	Adds shutdown no-op to match worker interface.
lib/posthog/version.rb	Bumps version to 3.6.0.

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