fix(llm): omit temperature for major-only Opus ids (claude-opus-5) (#5761)

The version pattern in _anthropic_rejects_temperature() required a minor
component, so major-only ids like `claude-opus-5` never matched and the
guard reported that the model accepts `temperature`. Anthropic rejects the
field outright on Opus 4.7+, so every such call returned HTTP 400 and the
stream aborted with zero tokens ("the model returned an empty response").

Make the minor optional and read a missing minor as `.0`. The major is also
capped at 1-2 digits with a no-trailing-digit lookahead, mirroring the
minor: once the minor is optional, a greedy major would swallow the date in
`claude-3-opus-20240229` and read it as version 20240229, dropping
temperature from a model that accepts it.

Fixes #5753

Co-authored-by: Alexandre Teixeira <111787685+alteixeira20@users.noreply.github.com>

src/llm_core.py

@@ -1237,15 +1237,27 @@ def _anthropic_rejects_temperature(model: str) -> bool:
         return False
     # `(?<![a-z])` anchors "opus" to a word boundary so a substring match like
     # `oct-opus`/`octopus-4-8` can't be read as Opus (it would otherwise strip
-    # temperature). Cap the minor at 1-2 digits and forbid a trailing digit so a
-    # dated id like `claude-opus-4-20250514` (Opus 4.0) parses as major-only (no
-    # minor match, kept) instead of reading the date `20250514` as a giant minor
-    # that would falsely test >= 4.7. Dated 4.7+ snapshots (`claude-opus-4-7-
-    # 20260201`) keep their explicit minor and are still matched.
-    match = re.search(r"(?<![a-z])opus[-_]?(\d+)[-_.](\d{1,2})(?!\d)", model.lower())
+    # temperature). Both version components are capped at 1-2 digits and forbid a
+    # trailing digit, so an 8-digit date can never be read as a version number:
+    # `claude-opus-4-20250514` (Opus 4.0) parses as major-only rather than reading
+    # `20250514` as a giant minor, and `claude-3-opus-20240229` (legacy Claude 3
+    # Opus, date directly after "opus-") fails to match at all rather than reading
+    # the date as a giant major. Dated 4.7+ snapshots (`claude-opus-4-7-20260201`)
+    # keep their explicit minor and are still matched.
+    #
+    # The minor is optional and a missing minor reads as `.0`, so major-only ids
+    # like `claude-opus-5` are correctly treated as >= 4.7 (issue #5753). Without
+    # this, every Opus 5 call kept `temperature` and failed with HTTP 400 — visible
+    # only on paths that pass a temperature, e.g. scheduled tasks inheriting
+    # `stream_agent_loop`'s 0.3 default, which returned empty responses.
+    match = re.search(
+        r"(?<![a-z])opus[-_]?(\d{1,2})(?!\d)(?:[-_.](\d{1,2})(?!\d))?", model.lower()
+    )
     if not match:
         return False
-    return (int(match.group(1)), int(match.group(2))) >= (4, 7)
+    major = int(match.group(1))
+    minor = int(match.group(2)) if match.group(2) else 0
+    return (major, minor) >= (4, 7)
 
 # Reasoning effort level sent to Mistral thinking-capable models. Mistral's
 # API accepts "high", "medium", "low", "none" — see