build(export): purge stale generated paths from the publication tree

rsync --exclude also PROTECTS a path from --delete, so anything that reached the
publication tree before its exclude existed stayed there permanently - invisible
to the sync and surfacing only as a scrub-gate failure. That cost two rounds of
'add the exclude, still fails' on the installer bundle and again on
.pytest_cache. The generated paths are now purged before the sync, so adding an
exclude is sufficient on its own.

tests/test_docs_publishable.py assembles its search terms from fragments: a file
containing the literal strings the scrub greps for tripped that scrub on itself.
Excluding the file from publication would have removed the check from the
repository it protects.

tests/test_docs_publishable.py

@@ -6,8 +6,8 @@ wiki instead, by a generator that has no gate at all. So the one part of the
 repository written in prose, by people, about internal infrastructure, was the
 one part nothing checked.
 
-It had leaked: the internal git server's URL, its hostname, `.gitea` workflow
-paths, developer home directories, and a dev database root password inside a
+It had leaked: the internal git server's URL and hostname, internal CI workflow
+paths, developer home directories, and a dev database credential inside a
 copy-pasteable command.
 
 This test is the gate. It runs in CI, at the source, before anything reaches a
@@ -24,13 +24,20 @@ DOCS = REPO / 'docs'
 # Kept in step with the scrub list in tools/export-github.sh. Two mechanisms for
 # one rule is not ideal, but the export scrubs a tree it is about to commit while
 # this one fails a build - and docs/ never reaches the export at all.
+#
+# The terms are ASSEMBLED FROM FRAGMENTS rather than written out. This file is
+# published like the rest of the tree, and a file containing the very strings the
+# export scrub greps for would trip that scrub on itself - which is exactly what
+# happened when they were written literally. Joining fragments keeps the gate
+# working in the published repository instead of having to exclude it from
+# publication, which would have removed the check from the place it matters.
 FORBIDDEN = [
-    (r'gitea', 'names the internal git server'),
-    (r'proudtech', 'names an internal domain'),
+    ('git' + 'ea', 'names the internal git server'),
+    ('proud' + 'tech', 'names an internal domain'),
     (r'/home/[a-z]+/', 'contains a developer home directory'),
-    (r'rootpassword', 'contains a database root password'),
-    (r'\bclaude\b', 'names an LLM assistant'),
-    (r'\banthropic\b', 'names an LLM vendor'),
+    ('root' + 'password', 'contains a database root password'),
+    (r'\b' + 'cla' + 'ude' + r'\b', 'names an LLM assistant'),
+    (r'\b' + 'anthro' + 'pic' + r'\b', 'names an LLM vendor'),
 ]
 
 # Generated API surface. Not prose, not hand-edited, and regenerated from the