#22886: fix: await onBlockReplyFlush before tool execution to preserve message ordering

## Problem When `shouldRouteToOriginating` is true (e.g., agent routing from webchat → telegram), block replies bypass the dispatcher's `sendChain` and go directly through `routeReply` → `sendMessageTelegram`. In `handleToolExecutionStart`, `onBlockReplyFlush()` was called with `void` (fire-and-forget). This meant tool-initiated sends (e.g., message tool sending a PDF) could race block replies through the async chain and reach the per-chat serializer first, causing **out-of-order delivery** on Telegram. Example: agent streams reasoning text, then sends a PDF via message tool → PDF arrives before the reasoning text. ## Fix `void` → `await` on `ctx.params.onBlockReplyFlush()` in `handleToolExecutionStart`. This ensures all pending block reply deliveries complete before tool execution proceeds. One-line change, the function is already `async`. ## Testing - Verified build compiles cleanly - Existing e2e test (`calls-onblockreplyflush-before-tool-execution-start-preserve`) still passes (mock returns void, `await undefined` is a no-op) <!-- greptile_comment --> <h3>Greptile Summary</h3> Changes `void` to `await` on `ctx.params.onBlockReplyFlush()` call in `handleToolExecutionStart` (line 141). This ensures pending block replies complete delivery before tool execution proceeds, preventing race conditions where tool-initiated sends could arrive before streamed reasoning text when routing through Telegram. - The function signature already returns `void | Promise<void>`, so awaiting is safe - Existing test passes (mock returns void, `await undefined` is a no-op) - Fixes out-of-order message delivery in agent routing scenarios (webchat → telegram) <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The change is minimal (one keyword change from `void` to `await`), the function is already async, the type signature supports both sync and async returns, and existing tests verify the behavior. The fix addresses a real race condition without introducing new complexity or breaking changes. - No files require special attention _{Last reviewed commit: e1cf374} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->