Exercise 1: Why TLS Can't Begin Before the TCP Handshake Finishes — Possible Solution
====================================================================

Explanation:

Per the chapter's own handshake steps, establishing a TCP connection
requires three sequential steps -- "SYN... SYN-ACK... ACK" -- and only
"after these three steps, both sides have a working, mutually-
acknowledged connection and can begin exchanging real data." Until all
three steps complete, there is no established, reliable channel
between the client and server at all -- just a one-way SYN or a
half-acknowledged exchange in progress.

TLS's own handshake is not a separate, independent conversation --
per the chapter, "TLS's own handshake happens after, and on top of,
the TCP handshake -- two separate steps." The TLS handshake consists
of actual data being sent back and forth between client and server
(certificate exchange, key negotiation messages, and so on), and per
the chapter's own reliability section, "every byte TCP sends carries a
sequence number... [guaranteeing] data arrives... in the correct
order... and isn't duplicated." Sending that TLS handshake data
requires the exact reliable, ordered delivery mechanism the completed
TCP handshake exists to set up in the first place -- without an
established TCP connection, there is no sequencing, no
acknowledgment, and no reliable channel for the TLS handshake's own
messages to travel over at all.

In short: the TCP handshake's entire purpose is to establish the
reliable connection that ALL subsequent data -- including TLS's own
handshake messages -- depends on to be delivered correctly. TLS
messages sent before TCP's three-way handshake completed would have
no reliable connection to travel over, which is exactly why the two
handshakes must happen strictly in sequence, TCP first.

WHY THIS WORKS AS AN ANSWER
------------------------------
This explains the actual dependency (TLS handshake messages are real
data that needs TCP's reliable delivery mechanism to travel over) using
the chapter's own reliability section, rather than simply asserting
the ordering as a given rule.