#12199: fix(message): add threadId parameter to fetch schema for Slack thread reading

## Problem The message tool could send messages to Slack threads but couldn't read thread replies. When calling: ```javascript message(action='read', channel='slack', target='<channel>', threadId='<ts>', limit=10) ``` The tool would return channel messages instead of thread replies. ## Root Cause The `threadId` parameter was only defined in `buildSendSchema()` (for sending to threads) but not in `buildFetchSchema()` (for reading messages). The backend Slack implementation (`src/slack/actions.ts`) has always supported thread reading via the `conversations.replies` API - the parameter just wasn't exposed in the tool schema. ## Solution Added `threadId: Type.Optional(Type.String())` to `buildFetchSchema()` in `src/agents/tools/message-tool.ts`. ## Testing Direct API verification confirmed the backend implementation works correctly when the parameter is provided. ## Files Changed - `src/agents/tools/message-tool.ts` - Added threadId to buildFetchSchema() ## Impact - Enables full thread reading for Slack - Matches existing thread sending capability - No breaking changes - parameter is optional - Works with existing backend implementation <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Adds an optional `threadId` parameter to the message tool’s fetch/read schema (`src/agents/tools/message-tool.ts`) so callers can request Slack thread replies when using the existing backend support for `conversations.replies`. This change aligns the read schema with the already-supported send-to-thread behavior, without altering runtime execution logic (only schema exposure). <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk. - The change is a narrow schema-only addition (`threadId` optional) that matches existing send schema and does not affect execution flow; no conflicting properties or type issues were introduced in the modified file. - src/agents/tools/message-tool.ts <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->