[Bugfix #584] Pace multi-line afx send messages to prevent paste detection

[waleedkadous]

Summary

Fixes #584

Root Cause

When afx send delivers a message longer than 3 lines, the entire formatted text is written to the PTY in a single session.write() call. The receiving terminal (Claude Code) classifies the rapid multi-line input as a "paste" operation, which causes the final \r (Enter) — sent 50ms later — to be swallowed. The message appears on screen but never gets submitted.

Fix

Extracted a writeMessageToSession() helper in message-write.ts that paces multi-line output:

• ≤3 lines: Single write() + 50ms delayed Enter (existing behavior, works fine)
• >3 lines: Line-by-line writes with 10ms gaps between lines, then Enter after an 80ms gap from the last line

All three delivery paths now use this helper:

1. Immediate delivery in handleSend() (tower-routes.ts)
2. Deferred delivery via deliverBufferedMessage() (tower-routes.ts)
3. Cron message delivery in tower-cron.ts

The helper also supports a delayOffset parameter and returns the end time, enabling SendBuffer.flush() to serialize multiple buffered messages without interleaving.

Test Plan

• Added 9 regression tests covering short/long messages, noEnter, delayOffset, and multi-message serialization
• Existing send-buffer tests pass (13/13)
• Full test suite passes
• TypeScript compiles cleanly

CMAP Review

• Claude: APPROVE — clean implementation, correct timing math, good test coverage
• Codex: REQUEST_CHANGES (addressed) — identified interleaving risk when multiple buffered messages flush to the same session. Fixed by adding delayOffset parameter and return value to serialize writes.
• Gemini: REQUEST_CHANGES (addressed) — identified same vulnerable pattern in tower-cron.ts and suggested extracting to shared module. Fixed by creating message-write.ts and updating tower-cron.ts.

[waleedkadous]

Architect Review

Clean fix. Good extraction of writeMessageToSession into a shared module — consolidates three separate write sites into one. The line-by-line pacing for >3 lines with serialized offsets to prevent interleaving is well thought through.

Go ahead and merge.