Complete reply-to implementation

[kwsantiago]

Current State

The --reply-to flag exists but is marked TODO in send.c:

// TODO: Handle reply_to if provided

Implementation

When --reply-to <event-id> is provided:

1. Add e tag referencing the parent event ID
2. Optionally fetch parent event to get thread root (for E tag)

NIP-10 Threading

For proper threading support:

• e tag with parent event ID (reply marker)
• Optional: E tag with root event ID (thread root)

Interface

# Reply to a specific message
whisper send --reply-to <event-id-hex> npub1... "my reply"

# Show thread context in recv
whisper recv --show-threads