Extract the glossary to a root CONTEXT.md

CLAUDE.md

@@ -214,29 +214,9 @@ env vars (see `docker-compose.yml`). `api_bootstrapper_config` builds the
 
 ## Vocabulary
 
-A term is listed only when there is a synonym to reject, or a meaning subtle
-enough that code and docs must agree on it.
-
-- **Chat** — a row in `chats`: a type (`direct` or `group`), an optional title,
-  its creator, and a pointer to its newest non-deleted message. *Avoid:*
-  conversation, room, thread.
-- **Direct chat** — a chat between exactly two users, identified by `direct_key`,
-  the canonical `min(user_id):max(user_id)` string under a unique constraint.
-  That key is what makes opening one twice an upsert instead of a read-then-race.
-  *Avoid:* DM, 1:1.
-- **Member** — the `(chat_id, user_id)` row granting access to a chat, plus that
-  user's read marker. Necessary for every read or write on a chat; not
-  sufficient for editing or deleting a message. *Avoid:* participant, subscriber.
-- **Idempotency key** — the client-supplied UUID on a send, unique per
-  `(chat_id, idempotency_key)`. Scoped to one chat, because the key identifies a
-  retry of "send this message to this chat". *Avoid:* dedupe key, request id.
-- **Unread** — a count computed at read time against one marker per member, not
-  a set of per-message receipt rows. *Avoid:* unseen, badge count.
-- **Cursor** — a message id passed as `before_id` or `after_id`. The two are
-  mutually exclusive on one request. *Avoid:* page token, offset.
-- **Read marker** — a member's `last_read_message_id`, the highest id they have
-  acknowledged. Advances only forward, via `GREATEST` inside the UPDATE. *Avoid:*
-  read receipt, watermark.
+The ubiquitous language lives in [`CONTEXT.md`](CONTEXT.md) at the repo root: a
+glossary and nothing else, listing a term only when there is a synonym to reject
+or a meaning subtle enough that code and docs must agree on it.
 
 ## Agent skills
 

CONTEXT.md

@@ -0,0 +1,50 @@
+# chat-app
+
+A chat backend: users open direct or group chats, send messages, and track what
+they have read. This file is the glossary and nothing else. The decisions taken
+live in [`docs/adr/`](docs/adr/); how the system works lives in `app/` and its
+tests.
+
+A term is listed only when there is a synonym to reject, or a meaning subtle
+enough that code and docs must agree on it. Definitions name columns and
+mechanisms where that is what makes them precise.
+
+## Language
+
+**Chat**:
+A row in `chats`: a type (`direct` or `group`), an optional title, its creator,
+and a pointer to its newest non-deleted message.
+_Avoid_: conversation, room, thread
+
+**Direct chat**:
+A chat between exactly two users, identified by `direct_key`, the canonical
+`min(user_id):max(user_id)` string under a unique constraint. That key is what
+makes opening one twice an upsert instead of a read-then-race.
+_Avoid_: DM, 1:1
+
+**Member**:
+The `(chat_id, user_id)` row granting access to a chat, plus that user's read
+marker. Necessary for every read or write on a chat; not sufficient for editing
+or deleting a message.
+_Avoid_: participant, subscriber
+
+**Idempotency key**:
+The client-supplied UUID on a send, unique per `(chat_id, idempotency_key)`.
+Scoped to one chat, because the key identifies a retry of "send this message to
+this chat".
+_Avoid_: dedupe key, request id
+
+**Unread**:
+A count computed at read time against one marker per member, not a set of
+per-message receipt rows.
+_Avoid_: unseen, badge count
+
+**Cursor**:
+A message id passed as `before_id` or `after_id`. The two are mutually exclusive
+on one request.
+_Avoid_: page token, offset
+
+**Read marker**:
+A member's `last_read_message_id`, the highest id they have acknowledged.
+Advances only forward, via `GREATEST` inside the UPDATE.
+_Avoid_: read receipt, watermark

planning/README.md

@@ -118,7 +118,7 @@ Against upstream convention 2.2.0:
    PR body.
 2. `architecture/` is removed; there is no capability-page home and no promotion
    rule. Enforceable claims are `INVARIANT:`-marked tests; the ubiquitous
-   language lives in [`../CLAUDE.md`](../CLAUDE.md)'s Vocabulary section.
+   language lives in [`../CONTEXT.md`](../CONTEXT.md).
 3. `deferred.md` is a `deferred/` directory of indexed, trigger-bearing items.
 4. Decision frontmatter drops `status` and `supersedes`. Largely subsumed by 7:
    decisions are no longer a `planning/` artifact at all.