Include Seer RCA in Slack and incident.io alerts

When alerts fire to Slack or incident.io, include available Seer root cause analysis so responders get RCA context in the alert itself instead of hunting it down in Sentry.

Current behavior

• Slack has Seer RCA workflows and activity notifications that can surface RCA after the fact (#117543, #118294, docs in sentry-docs#16901), but issue/metric alert payloads do not attach RCA up front.
• incident.io can receive issue alerts; metric alert routing is still open (#88159). Neither path appears to carry Seer RCA content.

Gap

Triage often starts from the Slack or incident.io alert. Without RCA in that payload, on-call has to open Sentry and locate Seer output separately, which slows first response.

Related

• Prior art for another destination: Add Root Cause to Linked Jira Tickets
• Closed (not merged) experiment to trigger RCA from an alert: #113241
• Docs follow-up for RCA in Slack GA screenshots: sentry-docs#16900

Requested by Colin Kawai via Junior.

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View Junior Session in Sentry

Start by reviewing the existing Slack Seer RCA work in #117543 and #118294, the related Jira RCA issue #92405, and incident.io metric alert routing in #88159. Trace the issue and metric alert paths for both destinations and determine where available Seer RCA is assembled. Done means Slack and incident.io alert payloads include RCA context when available, without breaking alerts that lack it.