Sync the self-hosting stack

CHANGELOG.md

@@ -9,6 +9,23 @@ one of them changed. An entry says which artefact and which version, so `web 0.1
 Every version published to a channel appears here. Nothing is written from memory afterwards: a build
 cannot be published without its entry.
 
+## 2026-09-11 — Fixing one paragraph meant resending the whole document `api 0.109.0`
+
+The assistant could write a document into a conversation and replace its body, but replacing was the
+only edit on offer: correcting a single paragraph of a long runbook meant resending the entire thing,
+including everything that had not changed. On a long document that is expensive, and it leaves room
+for the model to quietly drop a section it was not actually trying to touch.
+
+**`read_document`** lets the assistant look at a document's current content before touching it, rather
+than acting on what it remembers having written earlier in the conversation.
+
+**`patch_document`** replaces one exact piece of text with another, so a correction no longer requires
+resending the rest of the document unchanged. It refuses to guess: if the text to replace does not
+appear, or appears more than once, nothing is changed.
+
+**Self-hosters:** nothing to do. No schema or configuration changed — the assistant simply has two
+more tools available in every conversation.
+
 ## 2026-09-08 — "Last active" told you someone had been seen, not that they had said anything `api 0.108.0` `web 0.131.0`
 
 The per-user table on the Statistics page counted what each account had written, and showed when that