Summary

• combine and harden the Slack extension threading fixes from fix(slack): enable thread reply reading in slack extension plugin #22216 and fix(slack): use threadId from delivery context as threadTs fallback in outbound adapter #22485
• pass includeReadThreadId: true so message read forwards threadId to Slack readMessages
• support delivery-context threadId as fallback for outbound threadTs in both sendText and sendMedia
• add extension tests for read-thread forwarding and outbound thread fallback behavior
• add an Unreleased changelog entry

Why

Slack extension behavior diverged from built-in Slack behavior in two places:

1. thread reads silently dropped threadId
2. outbound sends ignored delivery-context threadId and only used replyToId

This caused thread reads to return channel-level results and thread-bound follow-ups to leak to DM/channel root.

Validation

• pnpm test -- extensions/slack/src/channel.test.ts
• pnpm exec oxfmt --check extensions/slack/src/channel.ts extensions/slack/src/channel.test.ts CHANGELOG.md

Fixes: #22219
Fixes: #22483
Supersedes: #22216, #22485

Greptile Summary

Aligns Slack extension threading behavior with built-in Slack channel by forwarding threadId in message reads and using it as a fallback for thread_ts in outbound sends.

• Added includeReadThreadId: true flag in handleSlackMessageAction call so thread reads forward threadId to readMessages action
• Updated sendText and sendMedia to use threadId as fallback for threadTs when replyToId is not present, matching built-in Slack implementation pattern in src/channels/plugins/outbound/slack.ts:62-63
• Added test coverage for read thread forwarding and outbound thread fallback in both sendText and sendMedia

Confidence Score: 5/5

• Safe to merge with no issues found
• The changes are minimal, well-tested, and align with the existing built-in Slack implementation pattern. The fix addresses a clear behavioral gap where the extension diverged from core Slack behavior for thread handling.
• No files require special attention

_{Last reviewed commit: 991da8e}