fix(slack): decode the bot self mention in incoming message text

[privatenumber]

Problem

When a Slack message mentions the bot, the adapter resolves every mention in the text to a display name — except the bot's own. <@U_BOT> stays in message.text as raw user-ID markup while other mentions become @<DisplayName>.

Downstream consumers therefore see inconsistent text. For LLM-based consumers this is actively harmful: small models classify differently depending on whether the mention arrived as self-describing @<DisplayName> text or as cryptic <@U_BOT> markup, and there is no way for a consumer to tell a real mention from a lookalike string without re-implementing Slack's mrkdwn rules.

The reason the bot's own mention was left raw is detection coupling: Chat.detectMention matched @botUserId / <@botUserId> in the text, so resolving the markup would have hidden the mention from detection.

Changes

• resolveInlineMentions now decodes the bot's own mention like any other: <@U_BOT> resolves to @<DisplayName> (via the same users.info lookup and cache as all other mentions).
• Because resolution renders the ID markup away, detection moves to where the ID is still known: parseSlackMessage tests the raw event text for the bot's mention (labeled, unlabeled, and bare @ID forms) and sets isMention on the parsed message. Chat.detectMention remains as the fallback for username-style mentions on the rendered text.
• The skipSelfMention option is removed; the history/thread fetch paths that passed skipSelfMention: false now behave identically to live events, which also fixes an inconsistency where edited messages (parseSlackMessageSync) never resolved mentions at all.

Behavior change

message.text for a message that mentions the bot changes from <@U_BOT> hello to @Vercel Bot hello (the bot's resolved display name). Mention detection is preserved: isMention is set from the raw event text, and the labeled form is matched by the new detection patterns. Apps matching the raw <@U_BOT> markup in message.text should match the resolved display name or read message.raw instead.

Relation to #355

#355 intentionally introduced the self-mention skip: in multi-workspace installs, the request-scoped bot ID was being resolved before mention detection ran, which broke onNewMention for those workspaces. This PR preserves that guarantee without the markup coupling — the multi-workspace replay test from that scenario is updated and still asserts that a plain message event containing the bot's mention sets isMention: true and routes to onNewMention. Detection additionally covers the labeled form (<@U_BOT|Name>) that resolution now produces.

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Project	Deployment	Actions	Updated
chat	Ready	Preview, v0	Sep 3, 2026 5:34pm UTC
chat-sdk-nextjs-chat	Ready	Preview, v0	Sep 3, 2026 5:34pm UTC