Ensure handling of Discord slash commands

[PClmnt]

This PR updates the Discord Adapter to allow correctly handling of slash commands in Discord. Previously, slash commands would just be ACK'd and no response would take place. Also, Discord slash commands require defer + editing the original interaction response.

This updates the adapter so that:

• APPLICATION_COMMAND events are now dispatched to processSlashCommand.
• First slash response updates @original (PATCH /webhooks/{app_id}/{token}/messages/@original).
• Subsequent responses use followups (POST /webhooks/{app_id}/{token}).
• Works for both text and file attachments in slash responses.

There's a question open, and i've left a comment in the code about how we might want to handle nested subcommands:

Test plan

• Bot receives a Discord slash command, adapter returns deferred ACK (type 5) immediately — should succeed
• Bot posts first response via event.channel.post(...) after defer — should replace deferred “thinking…” message (PATCH @original)
• Bot posts a second response in same slash-command flow — should be sent as a follow-up message (POST webhook)
• Bot posts a slash-command response with file attachments — should succeed via interaction webhook (no channel API fallback)
• Slash command invoked inside a Discord thread — should resolve deferred response correctly in that thread context
• Regular non-slash message posting/editing/deleting/reactions continue to work as before

Video

Screen.Recording.2026-03-02.at.09.46.52.mov

Screenshots

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Resolves #131

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Additional Suggestion:

The setupDiscordFetchMock function does not handle Discord interaction webhook URLs (/webhooks/{appId}/{token}/messages/@original and /webhooks/{appId}/{token}?wait=true), causing the "should dispatch slash command handlers" test to fail with a NetworkError.

[haydenbleasel]

Hey @PClmnt! Great work on this PR 🙌 I pushed a few commits on top of yours:

• Expand subcommand path into event.command — parseSlashCommand now appends subcommand/group names to the command path (e.g. /project issue create), keeping event.text as flat values. This addresses the open question you left in the TODO comment.
• Fix initialResponseSent race condition — moved the flag set before await so concurrent post() calls don't both try to PATCH @original.
• Restore unrelated indentation change — reverted the whitespace-only diff in handleComponentInteraction to keep the PR focused.
• Extract tryPostSlashResponse helper — deduplicates the slash-context check that was repeated in postMessage and postChannelMessage.
• Fix integration test mock — added interaction webhook route handlers (editOriginal/followUp) to setupDiscordFetchMock so the slash command integration test actually works end-to-end.

Also updated docs.

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Project	Deployment	Actions	Updated (UTC)
chat	Ready	Preview, Comment, Open in v0	Mar 2, 2026 9:18pm

[PClmnt]

Hey @PClmnt! Great work on this PR 🙌 I pushed a few commits on top of yours:

• Expand subcommand path into event.command — parseSlashCommand now appends subcommand/group names to the command path (e.g. /project issue create), keeping event.text as flat values. This addresses the open question you left in the TODO comment.
• Fix initialResponseSent race condition — moved the flag set before await so concurrent post() calls don't both try to PATCH @original.
• Restore unrelated indentation change — reverted the whitespace-only diff in handleComponentInteraction to keep the PR focused.
• Extract tryPostSlashResponse helper — deduplicates the slash-context check that was repeated in postMessage and postChannelMessage.
• Fix integration test mock — added interaction webhook route handlers (editOriginal/followUp) to setupDiscordFetchMock so the slash command integration test actually works end-to-end.

Also updated docs.

Thanks so much for taking the time to sort those issues out and getting this merged though, I really appreciate it! All looks good on my side. 🚢🚢