[ygndotgg]

Which issue does this PR address?

Closes #3385

Rationale

Iggy lacked a native MQTT sink connector. Users could not publish Iggy stream data to MQTT brokers such as EMQX without a separate adapter service.

What changed?

This PR adds the iggy_connector_mqtt_sink plugin. It reads Iggy messages and publishes them to MQTT brokers through rumqttc and the iggy_connector_sdk C-FFI boundary.

The connector supports MQTT 3.1.1 and MQTT 5. It supports QoS 0, QoS 1, and QoS 2. It supports static, template, and dynamic MQTT topic routing.

The connector tracks MQTT acknowledgments by packet identifier. It bounds in-flight publications, reconnects after uncertain failures, and republishes only unconfirmed messages. It also supports broker authentication, TLS, mutual TLS, MQTT 5 properties, and controlled shutdown.

This PR adds sink integration tests with EMQX. The tests cover protocols, QoS levels, routing modes, MQTT 5 envelopes, broker rejection, pipelining, restart, and reconnect behavior.

Local Execution

Done

AI Usage

1. Which tools? Codex
2. Scope of usage? Generated and refined connector functions, test fixtures, integration tests, and documentation.
3. How did you verify the generated code works correctly? I reviewed the MQTT sink behavior and test coverage end to end
4. Can you explain every line of the code if asked? Yes

[github-actions]

Thanks for the PR. It is labeled S-waiting-on-review and queued for review.

Slash commands (own line, regular comment) move it around the queue:

• /ready - back to S-waiting-on-review after addressing feedback
• /author - flip to S-waiting-on-author while you finish changes
• /request-review @user-or-team - request a reviewer
• /pin - exempt the PR from the stale bot, /unpin to undo

See CONTRIBUTING.md for details.

[codecov]

Codecov Report

❌ Patch coverage is 83.83193% with 481 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.71%. Comparing base (6ce2f92) to head (3af7263).

Files with missing lines	Patch %	Lines
core/connectors/sinks/mqtt_sink/src/driver.rs	75.47%	257 Missing and 55 partials ⚠️
core/connectors/sinks/mqtt_sink/src/lib.rs	88.69%	98 Missing and 14 partials ⚠️
core/connectors/sinks/mqtt_sink/src/routing.rs	91.99%	40 Missing and 17 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4584      +/-   ##
============================================
- Coverage     90.77%   90.71%   -0.06%     
  Complexity     2989     2989              
============================================
  Files          1459     1462       +3     
  Lines        348165   351137    +2972     
  Branches     292747   295721    +2974     
============================================
+ Hits         316042   318533    +2491     
- Misses        25485    25878     +393     
- Partials       6638     6726      +88     

Components	Coverage Δ
Rust Core	92.00% <83.83%> (-0.09%)	⬇️
Java SDK	77.77% <ø> (-0.03%)	⬇️
C# SDK	83.56% <ø> (-0.19%)	⬇️
Python SDK	85.69% <ø> (ø)
PHP SDK	90.67% <ø> (ø)
Node SDK	96.44% <ø> (ø)
Go SDK	70.17% <ø> (+0.20%)	⬆️
C++ SDK	85.51% <ø> (ø)

Files with missing lines	Coverage Δ
core/connectors/sinks/mqtt_sink/src/routing.rs	91.99% <91.99%> (ø)
core/connectors/sinks/mqtt_sink/src/lib.rs	88.69% <88.69%> (ø)
core/connectors/sinks/mqtt_sink/src/driver.rs	75.47% <75.47%> (ø)

... and 41 files with indirect coverage changes

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