0.8.1 — partial transclusion

Migrations: none. versions.transclusions is JSON text, so the new member
below needs no schema change and every document published before this release
stays valid and unchanged.

Partial transclusion — quote a passage instead of the whole item.
Spec §16.4, decision #49. The medium had three registers of borrowing and only
two of them were writable: transclude the whole item for commentary (the stub),
or fork from a pin for a derivative. Quoting a passage as the thing you are
responding to — the common blogging norm — was the missing rung.

The grammar is adjacency. A ![[id]] directive immediately followed, with
no blank line, by a markdown blockquote is a partial transclusion, and the
blockquote is the passage:

![[7c9wk2mhq0v3xj8tn5rzfd41bg]]
> Stigmergy is what a protocol looks like from inside, and the
> reason it looks like nothing at all is the point.

Commentary begins after a blank line.

A blank line detaches it. That is deliberate and it is why there is no new
sigil: transcluding an item whole and then quoting a bit of it yourself has
been writable since 0.1, and nothing anyone has already written changes meaning.

The passage must really be in the target. At publish, the selection must be
a substring of the target snapshot's text content at the version being baked —
tags stripped, whitespace collapsed within a block, block boundaries kept as
line breaks — else a publish error, exactly like an unresolvable directive. A
quote that welds two of the source's paragraphs into one sentence is refused,
because the source has a break there and the quote does not.

In the studio. Highlight a passage in the reading view and press
quote ↗: you land in the editor with the directive and the passage already
attached, and the passage is checked while you are still choosing it rather
than at publish. Stubbing a long item now prefills an empty quote line instead
of the whole-item form — a suggestion, not a rule; delete the line and the
whole form publishes as before.

On the page, a partial quote says "excerpt of v2" where a whole
transclusion says "snapshot of v2". Without that a reader cannot tell a part
from the whole: a short quote and a short item look the same.

On the wire, the transclusions[] entry gains an OPTIONAL selector in
the W3C text-quote shape (exact, with short prefix/suffix). A reader
that ignores it entirely stays conformant — the passage is baked into
content_html like any other transclusion, the relation is still
transclusion, staleness is unchanged, and mention verification ignores it as
it ignores cited. The bake carries class="blyg-transclusion blyg-partial",
and the second class is how a reader knows this is a part.

This is a 0.3 revision, not a new protocol version: nothing a reader or a
receiver does changes. PROTOCOL_VERSION stays "0.3".

Also fixed: a thread mixing whole and partial transclusions mis-paired its
provenance lines, because the injector matched the class attribute as a literal
string. Only reachable with a partial in the thread, so no published document
is affected — but the failure mode was attributing one origin's words to
another's, which is worth naming.