fix: compute payload size correctly for pg_notify

[abelanger5]

Description

Users running in Postgres-only mode will occasionally see errors like the following:

ERROR: payload string too long (SQLSTATE 22023)

We have a check for 8000 bytes, but this check was failing to account for the extra marshaling we do when sending the message through pg_notify. We wrap the message in PubSubMessage which has some overhead with additional fields and queue names, and we're also base64-encoding the raw payload a second time, which adds overhead. As a result, even ~6kb payloads could occasionally see this behavior.

This fix does a few things:

1. Removes the double base64-encoding by using json.RawMessage instead of []byte
2. Only marshals/unmarshals this message once (instead of twice, we previously did the length check with a separate call to Marshal)
3. Properly checks the size of the payload we're actually sending over the wire.

Type of change

• Bug fix (non-breaking change which fixes an issue)

[vercel]

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Project	Deployment	Review	Updated (UTC)
hatchet-docs	Ready	Preview, Comment	Jan 28, 2026 4:16pm

[Copilot]

Pull request overview

This PR fixes incorrect payload size calculations for PostgreSQL pg_notify by removing double base64-encoding, centralizing message wrapping, and enforcing the 8KB limit on the actual on-wire payload, with test coverage around the new behavior.

Changes:

• Introduces multiplexedListener.wrapMessage to wrap a queue payload into PubSubMessage using json.RawMessage, eliminating the extra base64 layer and making size calculations reflect the true JSON sent over pg_notify.
• Updates messageQueueRepository.Notify to use wrapMessage, enforce the 8000-byte limit on the wrapped payload, and fall back to database storage when exceeded; pubNonDurableMessages now delegates all size handling to Notify.
• Adds tests around wrapped message sizing and empty payload handling in multiplexer_test.go, and changes PubSubMessage.Payload to json.RawMessage to align with the new encoding approach.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
pkg/repository/multiplexer_test.go	Adds tests that exercise wrapMessage for various payload sizes and empty payload behavior, plus a helper to synthesize JSON payloads of a target size.
pkg/repository/multiplexer.go	Extracts wrapMessage to build the PubSubMessage JSON using json.RawMessage, and simplifies notify to send pre-wrapped payloads.
pkg/repository/mq.go	Changes PubSubMessage.Payload to json.RawMessage and updates Notify to use wrapMessage, enforce the 8KB pg_notify limit, and fall back to AddMessage when exceeded.
internal/msgqueue/postgres/exchange.go	Simplifies non-durable publish path to always call repo.Notify, relying on the repository’s new size-aware logic instead of performing its own 8KB check.

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[Copilot]

Changing PubSubMessage.Payload from a []byte to json.RawMessage means existing code that constructs PubSubMessage values with a []byte payload (for example in multiplexer_test.go where Payload: []byte("test-payload") is used) will no longer compile. Those call sites need to be updated to construct a json.RawMessage (or otherwise pass a value of the correct type) to keep tests and any other callers building cleanly.

Suggested change

	QueueName string `json:"queue_name"`
	Payload json.RawMessage `json:"payload"`
	QueueName string `json:"queue_name"`
	Payload []byte `json:"payload"`

[Copilot]

The comment on createJSONPayload says it "creates a JSON string of exactly the specified size", but the implementation only approximates the size (e.g. it hardcodes jsonStructureOverhead and clamps paddingSize to >= 0), so for many inputs the resulting JSON length will differ from size. Either adjust the implementation to guarantee the exact length or relax the comment to describe that it produces a payload of approximately the requested size to avoid misleading future readers and test authors.