[claude] Qwen3 two-model routing via task complexity classifier (#1065) v2 (#1233)

Co-authored-by: Claude (Opus 4.6) <claude@hermes.local>
Co-committed-by: Claude (Opus 4.6) <claude@hermes.local>

src/infrastructure/router/classifier.py

@@ -0,0 +1,166 @@
+"""Task complexity classifier for Qwen3 dual-model routing.
+
+Classifies incoming tasks as SIMPLE (route to Qwen3-8B for low-latency)
+or COMPLEX (route to Qwen3-14B for quality-sensitive work).
+
+Classification is fully heuristic — no LLM inference required.
+"""
+
+import re
+from enum import Enum
+
+
+class TaskComplexity(Enum):
+    """Task complexity tier for model routing."""
+
+    SIMPLE = "simple"   # Qwen3-8B Q6_K: routine, latency-sensitive
+    COMPLEX = "complex"  # Qwen3-14B Q5_K_M: quality-sensitive, multi-step
+
+
+# Keywords strongly associated with complex tasks
+_COMPLEX_KEYWORDS: frozenset[str] = frozenset(
+    [
+        "plan",
+        "review",
+        "analyze",
+        "analyse",
+        "triage",
+        "refactor",
+        "design",
+        "architecture",
+        "implement",
+        "compare",
+        "debug",
+        "explain",
+        "prioritize",
+        "prioritise",
+        "strategy",
+        "optimize",
+        "optimise",
+        "evaluate",
+        "assess",
+        "brainstorm",
+        "outline",
+        "summarize",
+        "summarise",
+        "generate code",
+        "write a",
+        "write the",
+        "code review",
+        "pull request",
+        "multi-step",
+        "multi step",
+        "step by step",
+        "backlog prioriti",
+        "issue triage",
+        "root cause",
+        "how does",
+        "why does",
+        "what are the",
+    ]
+)
+
+# Keywords strongly associated with simple/routine tasks
+_SIMPLE_KEYWORDS: frozenset[str] = frozenset(
+    [
+        "status",
+        "list ",
+        "show ",
+        "what is",
+        "how many",
+        "ping",
+        "run ",
+        "execute ",
+        "ls ",
+        "cat ",
+        "ps ",
+        "fetch ",
+        "count ",
+        "tail ",
+        "head ",
+        "grep ",
+        "find file",
+        "read file",
+        "get ",
+        "query ",
+        "check ",
+        "yes",
+        "no",
+        "ok",
+        "done",
+        "thanks",
+    ]
+)
+
+# Content longer than this is treated as complex regardless of keywords
+_COMPLEX_CHAR_THRESHOLD = 500
+
+# Short content defaults to simple
+_SIMPLE_CHAR_THRESHOLD = 150
+
+# More than this many messages suggests an ongoing complex conversation
+_COMPLEX_CONVERSATION_DEPTH = 6
+
+
+def classify_task(messages: list[dict]) -> TaskComplexity:
+    """Classify task complexity from a list of messages.
+
+    Uses heuristic rules — no LLM call required.  Errs toward COMPLEX
+    when uncertain so that quality is preserved.
+
+    Args:
+        messages: List of message dicts with ``role`` and ``content`` keys.
+
+    Returns:
+        TaskComplexity.SIMPLE or TaskComplexity.COMPLEX
+    """
+    if not messages:
+        return TaskComplexity.SIMPLE
+
+    # Concatenate all user-turn content for analysis
+    user_content = " ".join(
+        msg.get("content", "")
+        for msg in messages
+        if msg.get("role") in ("user", "human")
+        and isinstance(msg.get("content"), str)
+    ).lower().strip()
+
+    if not user_content:
+        return TaskComplexity.SIMPLE
+
+    # Complexity signals override everything -----------------------------------
+
+    # Explicit complex keywords
+    for kw in _COMPLEX_KEYWORDS:
+        if kw in user_content:
+            return TaskComplexity.COMPLEX
+
+    # Numbered / multi-step instruction list: "1. do this  2. do that"
+    if re.search(r"\b\d+\.\s+\w", user_content):
+        return TaskComplexity.COMPLEX
+
+    # Code blocks embedded in messages
+    if "```" in user_content:
+        return TaskComplexity.COMPLEX
+
+    # Long content → complex reasoning likely required
+    if len(user_content) > _COMPLEX_CHAR_THRESHOLD:
+        return TaskComplexity.COMPLEX
+
+    # Deep conversation → complex ongoing task
+    if len(messages) > _COMPLEX_CONVERSATION_DEPTH:
+        return TaskComplexity.COMPLEX
+
+    # Simplicity signals -------------------------------------------------------
+
+    # Explicit simple keywords
+    for kw in _SIMPLE_KEYWORDS:
+        if kw in user_content:
+            return TaskComplexity.SIMPLE
+
+    # Short single-sentence messages default to simple
+    if len(user_content) <= _SIMPLE_CHAR_THRESHOLD:
+        return TaskComplexity.SIMPLE
+
+    # When uncertain, prefer quality (complex model)
+    return TaskComplexity.COMPLEX