feat(webhook): allow multiple webhook URLs per instance (fan-out)

[samuelpc7]

Description

The instance Webhook field can now hold multiple URLs. The producer delivers the
SAME event request to every address (each with its own retry). Accepted formats:
newline / comma / semicolon separated, or a JSON array. Duplicates, empty entries
and the "disabled" marker are ignored.

No schema change: the Webhook column stays a string; only
pkg/events/webhook/webhook_producer.go was touched (new splitWebhookURLs
helper). Fully backward compatible — a single URL behaves exactly as before. The
global webhook (config.WebhookUrl) keeps being sent in parallel.

Related Issue

N/A

Type of Change

• New feature (non-breaking change which adds functionality)

Testing

• Manual testing completed
• Functionality verified in development environment
• No breaking changes introduced

Screenshots (if applicable)

N/A — backend only.

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have tested my changes thoroughly
• Any dependent changes have been merged and published

Additional Notes

Single-file change. Produce now fans the same payload out to every URL returned
by splitWebhookURLs, instead of a single webhookUrl.

Summary by Sourcery

New Features:

• Allow an instance webhook configuration to specify multiple URLs, each receiving the same event payload with independent retries.

[sourcery-ai]

Reviewer's Guide

Enables fan-out of instance webhooks by parsing the existing single string field into multiple URLs (supporting several input formats) and sending the same payload concurrently to each URL while preserving existing global webhook behavior.

Sequence diagram for webhook fan-out in Produce

sequenceDiagram
    participant Producer as webhookProducer
    participant GlobalWebhook as p.url
    participant Splitter as splitWebhookURLs
    participant InstanceWebhook as webhookUrl

    Producer->>GlobalWebhook: sendWebhookWithRetry(p.url, payload, ...)
    activate GlobalWebhook
    deactivate GlobalWebhook

    Producer->>Splitter: splitWebhookURLs(webhookUrl)
    activate Splitter
    Splitter-->>Producer: []string urls
    deactivate Splitter

    loop for each url in urls
        Producer->>InstanceWebhook: sendWebhookWithRetry(url, payload, ...)
    end

Loading

File-Level Changes

Change	Details	Files
Produce now fans out instance webhooks to multiple URLs instead of a single destination.	Replaced single call to sendWebhookWithRetry for the instance webhook with a loop over parsed URLs from splitWebhookURLs. Preserved existing behavior for the global config webhook URL, which is still sent in parallel to instance webhooks. Ensured each target URL is invoked in its own goroutine while keeping retry parameters unchanged.	pkg/events/webhook/webhook_producer.go
Added splitWebhookURLs helper to parse and normalize the instance Webhook string into distinct URLs.	Introduced JSON array parsing path for webhook strings starting with '[' using encoding/json. Added fallback parsing that splits on newline, carriage return, comma, or semicolon characters. Normalized and filtered entries by trimming whitespace, ignoring empty values and the literal "disabled", and de-duplicating URLs using a map. Handled empty and "disabled"-only raw values by returning nil for no URLs.	pkg/events/webhook/webhook_producer.go

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[sourcery-ai]

Hey - I've left some high level feedback:

• Fan-out currently spawns an unbounded goroutine per URL with full retry logic; consider adding some form of concurrency limiting or a worker pool so a misconfigured instance with many URLs cannot exhaust resources.
• The special "disabled" marker is hard-coded and case-sensitive in multiple places in splitWebhookURLs; consider centralizing this into a constant and/or normalizing case so configuration is less brittle and easier to change later.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Fan-out currently spawns an unbounded goroutine per URL with full retry logic; consider adding some form of concurrency limiting or a worker pool so a misconfigured instance with many URLs cannot exhaust resources.
- The special "disabled" marker is hard-coded and case-sensitive in multiple places in splitWebhookURLs; consider centralizing this into a constant and/or normalizing case so configuration is less brittle and easier to change later.

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