Reading the answer instead of asking somebody to know it

llama-server publishes the loaded model's Jinja chat template on /props, and
that template is the very thing that rejects a reasoning effort it does not
recognise -- so the accepted set is written down, authoritatively, in a place
this application can simply read. There is a button on the model's page that
does.

The parser handles both shapes a template uses: the values inline in the test
that rejects them (Bonsai), and a named list set elsewhere with nothing near
the mention spelling them out (gpt-oss). It is deliberately conservative,
because a wrong answer here silently removes a level somebody is entitled to:
only known efforts count, an unrelated list of quoted strings is ignored, and a
single match is read as a default -- `{%- set reasoning_effort = 'medium' %}`
-- rather than as a vocabulary of one.

An endpoint with no such route says so. OpenAI and vLLM do not publish a
template, and "this cannot tell us" must not be recorded as "this model accepts
nothing".

/props sits at the server root, beside the OpenAI-compatible surface rather
than inside it, so a base URL written as .../v1 needs the suffix stripped.
Getting that wrong is a silent 404 that looks like detection simply not
working, so there is a test on it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/lembas/services/chat.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import logging
+import re
 from datetime import UTC, datetime, timedelta
 from typing import Any
 
@@ -470,6 +471,66 @@ def resolved_effort(chat) -> str:
     return value if value in EFFORTS else ""
 
 
+def efforts_from_chat_template(template: str) -> list[str]:
+    """Which efforts a model's Jinja chat template will actually accept.
+
+    The template is where the truth lives: the one on a Bonsai reads roughly
+
+        {%- if reasoning_effort not in ('xhigh', 'medium', 'low') %}
+          {{- raise_exception('Unexpected reasoning effort ' ~ reasoning_effort ...
+
+    so the accepted set is written out beside the thing that rejects everything
+    else. `llama-server` hands the whole template over on `/props`, which makes
+    this readable rather than guessable.
+
+    Deliberately conservative, because a wrong answer here silently removes a
+    level somebody is entitled to:
+
+    - only quoted literals within a short window of a `reasoning_effort`
+      mention are considered, so an unrelated list elsewhere in a four-hundred
+      line template cannot contribute;
+    - the result is intersected with `EFFORTS`, so an unknown token is dropped
+      rather than stored;
+    - fewer than two survivors is treated as "the template did not say". One
+      match is far more likely to be a default assignment
+      (`{%- set reasoning_effort = 'medium' %}`) than a vocabulary.
+
+    Returns [] when nothing can be read, which every caller treats as "ask
+    somebody" rather than as "this model accepts nothing".
+    """
+    if not template or "reasoning_effort" not in template:
+        return []
+
+    found: set[str] = set()
+
+    # Shape one: the values sit in the statement that tests them.
+    #     {%- if reasoning_effort not in ('xhigh', 'medium', 'low') %}
+    for match in re.finditer(r"reasoning_effort", template):
+        window = template[match.start() : match.start() + 400]
+        # Stop at the end of the statement that mentions it, so a later,
+        # unrelated block cannot leak in.
+        window = window.split("%}")[0] if "%}" in window else window
+        for literal in re.findall(r"""['"]([a-z]{3,8})['"]""", window):
+            if literal in EFFORTS:
+                found.add(literal)
+
+    # Shape two: the values are a named list somewhere else, and the test says
+    #     {%- if reasoning_effort not in valid_efforts %}
+    # so nothing near the mention names them. Any group of quoted literals in
+    # which *every* token is a known effort and there are at least two is taken
+    # -- that is a strong enough signal on its own, and a list of nothing but
+    # effort names that is not the effort vocabulary would be a strange thing
+    # for a chat template to contain.
+    for group in re.findall(r"[\[(]((?:\s*['\"][a-z]{3,8}['\"]\s*,?)+)[\])]", template):
+        literals = re.findall(r"""['"]([a-z]{3,8})['"]""", group)
+        if len(literals) >= 2 and all(value in EFFORTS for value in literals):
+            found.update(literals)
+
+    if len(found) < 2:
+        return []
+    return [effort for effort in EFFORTS if effort in found]
+
+
 def apply_effort(
     body: dict[str, Any], effort: str | None, supported: tuple[str, ...] | None = None
 ) -> None: