fix(chat): always think on qwen3, drop content-based classifier

Content-based gating (_should_think) was introduced in 87fcaa6 to cut
TTFT on simple prompts, but it has no way to tell that short prompts
like "create a task titled X" are going to trigger a tool call — and
qwen3:14b's tool-call template is unreliable at think=False, producing
intermittent silent generations where output tokens burn but nothing
parses into content or tool_calls.

Reverting to always-on thinking restores the pre-87fcaa6 reliability
of tool emission at the cost of TTFT latency on short conversational
prompts. This also lets us delete the silent-round retry loop (which
can no longer fire) along with its bookkeeping.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_should_think.py

@@ -1,127 +0,0 @@
-"""Tests for the `_should_think` classifier.
-
-`_should_think` decides whether qwen3-class models should engage chain-of-
-thought for a given chat turn. It is the single source of truth: frontend
-callers pass `think_requested=False` by default and defer to this function,
-while explicit `think_requested=True` acts as an override for curated
-analytical entry points.
-
-These tests lock in the content-based behavior so future tweaks don't
-silently regress the short / long / keyword boundaries.
-"""
-
-import pytest
-
-from fabledassistant.services.generation_task import (
-    _LONG_MESSAGE_CHARS,
-    _SHORT_MESSAGE_CHARS,
-    _should_think,
-)
-
-
-class TestExplicitOverride:
-    def test_override_forces_on_for_empty(self):
-        assert _should_think("", think_requested=True) is True
-
-    def test_override_forces_on_for_short_greeting(self):
-        assert _should_think("hi", think_requested=True) is True
-
-    def test_override_forces_on_for_medium_no_keyword(self):
-        text = "just checking in on the status of things for the week"
-        assert _should_think(text, think_requested=True) is True
-
-
-class TestEmptyAndWhitespace:
-    def test_empty_string_off(self):
-        assert _should_think("", think_requested=False) is False
-
-    def test_none_content_off(self):
-        # _should_think defensively handles None content from upstream callers
-        assert _should_think(None, think_requested=False) is False  # type: ignore[arg-type]
-
-    def test_whitespace_only_off(self):
-        assert _should_think("   \n\t  ", think_requested=False) is False
-
-
-class TestShortMessages:
-    def test_short_greeting_off(self):
-        assert _should_think("hi", think_requested=False) is False
-
-    def test_short_thanks_off(self):
-        assert _should_think("thanks!", think_requested=False) is False
-
-    def test_short_acknowledgement_off(self):
-        assert _should_think("ok sounds good", think_requested=False) is False
-
-    def test_just_below_short_threshold_off(self):
-        text = "a" * (_SHORT_MESSAGE_CHARS - 1)
-        assert _should_think(text, think_requested=False) is False
-
-
-class TestLongMessages:
-    def test_at_long_threshold_on(self):
-        text = "a" * _LONG_MESSAGE_CHARS
-        assert _should_think(text, think_requested=False) is True
-
-    def test_well_above_long_threshold_on(self):
-        text = "x" * (_LONG_MESSAGE_CHARS * 3)
-        assert _should_think(text, think_requested=False) is True
-
-
-class TestMediumMessages:
-    def test_medium_no_keyword_off(self):
-        # Between the short and long thresholds with no reasoning cue.
-        text = "a" * ((_SHORT_MESSAGE_CHARS + _LONG_MESSAGE_CHARS) // 2)
-        assert _should_think(text, think_requested=False) is False
-
-
-class TestKeywordTriggers:
-    @pytest.mark.parametrize(
-        "text",
-        [
-            "why is this failing",
-            "how does caching work here",
-            "how do i configure this",
-            "explain the retry logic",
-            "analyze the latency breakdown",
-            "compare gemma3 vs qwen3 for tool use",
-            "please design the schema for X",
-            "debug this error",
-            "troubleshoot the connection issue",
-            "root cause the outage",
-            "review this PR",
-            "critique my approach",
-            "walk me through the flow",
-            "step by step instructions please",
-            "pros and cons of each option",
-            "help me figure out what's wrong",
-            "discuss this article",  # covers briefing /discuss entry points
-        ],
-    )
-    def test_keyword_forces_on(self, text):
-        assert _should_think(text, think_requested=False) is True
-
-    def test_keyword_case_insensitive(self):
-        assert _should_think("WHY does this break?", think_requested=False) is True
-
-    def test_keyword_in_longer_sentence(self):
-        text = "hey quick one — can you explain what caching does for qwen3"
-        assert _should_think(text, think_requested=False) is True
-
-
-class TestNonTriggers:
-    """Messages that look chatty and should NOT trigger thinking."""
-
-    @pytest.mark.parametrize(
-        "text",
-        [
-            "hey",
-            "yep",
-            "no worries",
-            "got it, thanks",
-            "good morning",
-            "remind me later",  # no reasoning keyword, short
-        ],
-    )
-    def test_chatty_messages_off(self, text):
-        assert _should_think(text, think_requested=False) is False