TranscriptTail

The names of the product elements

The name of the type

Reads that message back, refusing one this contract did not write.

A message whose markup is empty may arrive with its newline stripped — server-sent events carry the message as lines, and a last line with nothing on it is not a line — so a count on its own is a tail that holds nothing.

The message: the row count on the first line, the markup after it.

Deliberately not JSON. This is the one message on this contract's wire that a browser reads, and reading it must cost the page nothing: measured while deciding, giving the bundle a JSON parser to read two fields took it from 12 750 bytes gzipped to 151 128 — ten times the whole bundle, and more than a whole transcript, to read a number and a string. A line and a remainder cost a indexOf.

The markup carries newlines of its own, which is why the count goes first and everything after the first newline is the markup: there is exactly one place to cut, wherever the rest wraps.

How often a followed session says something, whether or not anything has changed.

A session that only spoke when it grew would leave a page unable to tell a quiet session from a connection it has stopped hearing: both are silence. A connection can go silent while it is still open — a host frozen under the page, a proxy holding a connection nothing crosses — and nothing tells the browser, which reports a break and not a silence. So a host says "nothing changed" often enough that silence means something is wrong. That message is an ordinary tail, keeping every row the page holds and adding none.

How long a page goes on believing it is following while it hears nothing.

Long enough to survive a beat that is merely late, short enough that a reader is not left trusting a page that has stopped.