feat: add message edit and delete tools

[JAORMX]

Summary

• Add conversations_edit_message tool — edits an existing Slack message via chat.update API
• Add conversations_delete_message tool — deletes a Slack message via chat.delete API
• Both tools are disabled by default and require explicit opt-in for safety
• Add and edit handlers share a single ConversationsWriteMessageHandler (branches on message_ts presence)

Closes #151

Details

New tools

Tool	Parameters	Description
conversations_edit_message	channel_id, message_ts, text, content_type	Edit a message. Supports text/plain and text/markdown content types.
conversations_delete_message	channel_id, message_ts	Delete a message. Returns confirmation text.

Environment variables

Both tools are gated behind dedicated env vars (disabled by default):

Variable	Values
SLACK_MCP_EDIT_MESSAGE_TOOL	true, C123,C456 (allowlist), !C123 (denylist)
SLACK_MCP_DELETE_MESSAGE_TOOL	true, C123,C456 (allowlist), !C123 (denylist)

Both tools can also be enabled via SLACK_MCP_ENABLED_TOOLS=conversations_edit_message,conversations_delete_message.

Architecture

The add and edit message tools share a single handler (ConversationsWriteMessageHandler) that branches on the presence of message_ts:

• No message_ts → add mode (posts new message via PostMessageContext)
• message_ts present → edit mode (updates existing message via UpdateMessageContext)

A shared resolveToolGate helper deduplicates env-var gating, channel ID resolution, and allowlist checking across write and delete parse functions.

Test plan

• All existing unit tests pass
• New test cases covering tool registration, ENABLED_TOOLS matrix, param validation, channel scoping, edge cases
• go build ./..., go vet ./..., go test -run "^Test[^I]" ./... -count=1 all pass

🤖 Generated with Claude Code

[korotovsky]

Hi @JAORMX, Thank you for the PR. From my experience it is very often possible to combine add and edit handlers into one handler with some additional logic. Could you try to explore this option to potentially reduce code duplication?

[JAORMX]

@korotovsky sure! I'll get to it

[JAORMX]

@korotovsky rebased and fixed the merge conflict.

[MaxGhenis]

Would love to see this merged — I'm switching to this MCP server from shouting-mcp-slack and edit/delete is the main feature gap. Happy to help test if useful.