Models know how much context they hold

A column rather than a key in capabilities_json, which is rebuilt wholesale
from the submitted checkboxes on every save and would destroy a number
living in it.

0 means unknown, and unknown has to stay tellable from small: the context
percentage and automatic compaction both refuse to act on a figure nobody
supplied. Filled in from /v1/models where the runner advertises it --
OpenRouter, vLLM and llama.cpp each spell it differently, so context_from()
reads the four spellings actually in use, accepts a quoted number but not
"8192 tokens", and rejects anything outside 256..10,000,000. Applied on
discovery only when nothing is set: a refresh must never undo a correction,
since an administrator sets this precisely because the endpoint was wrong.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/api/admin.py

@@ -14,7 +14,7 @@ from lembas.api.deps import AdminUser, Db
 from lembas.db.models import Connection, Model, User
 from lembas.services import settings_store
 from lembas.services.crypto import UNCHANGED_SENTINEL, decrypt, encrypt, mask
-from lembas.services.llm.openai_client import Endpoint, LLMError, list_models
+from lembas.services.llm.openai_client import Endpoint, LLMError, context_from, list_models
 from lembas.web.templating import render
 
 log = logging.getLogger(__name__)
@@ -198,8 +198,21 @@ async def _refresh_models(db: DBSession, connection: Connection) -> tuple[int, s
         model_id = str(entry["id"])[:300]
         seen.add(model_id)
         if model_id in existing:
+            # A context length is filled in only when nobody has one yet. A
+            # refresh must never overwrite a number an administrator typed --
+            # they are usually correcting the endpoint.
+            model = existing[model_id]
+            if not model.context_length:
+                model.context_length = context_from(entry)
             continue
-        db.add(Model(connection_id=connection.id, model_id=model_id, position=next_position))
+        db.add(
+            Model(
+                connection_id=connection.id,
+                model_id=model_id,
+                position=next_position,
+                context_length=context_from(entry),
+            )
+        )
         next_position += 1
 
     # Models that vanished upstream are dropped, so the picker never offers