session-memory: infra-overhead + thrash signals (WP-0005 T02)

signals.py: tool_bucket helper + three tool_histogram-based extractors that the
outcome/marker signals were blind to — sig_infra_overhead (hub+task+schema share
of tool calls over threshold), sig_schema_thrash (repeated ToolSearch), and
sig_tool_thrash (one tool dominating). Thresholds in build_context. 8 new tests;
suite 88/88 green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

session_memory/detect/signals.py

@@ -91,9 +91,75 @@ def sig_error_then_recovery(digest, ctx) -> list[Signal]:
     return []
 
 
+# --- tool-mix / infrastructure-overhead signals (WP-0005 T02) ----------------
+# These read the captured ``tool_histogram`` — friction that the outcome+marker
+# signals above are blind to (sessions still "succeed", just expensively).
+
+def tool_bucket(tool: str) -> str:
+    """Group a tool name into a coarse activity bucket (flavor-agnostic)."""
+    if tool.startswith("mcp__state-hub"):
+        return "statehub_mcp"
+    if tool in ("TaskUpdate", "TaskCreate", "TaskGet", "TaskList", "TaskOutput",
+                "TaskStop", "todo_write", "update_task_status"):
+        return "task_mgmt"
+    if tool == "ToolSearch":
+        return "schema_load"
+    if tool in ("Bash", "run_terminal_command"):
+        return "shell"
+    if tool in ("Edit", "Write", "search_replace", "write", "NotebookEdit"):
+        return "edit"
+    if tool in ("Read", "read_file", "grep", "Grep", "glob", "Glob"):
+        return "read"
+    return "other"
+
+
+def _bucketed(digest) -> tuple[dict, int]:
+    buckets: dict[str, int] = {}
+    for tool, n in (digest.get("tool_histogram") or {}).items():
+        buckets[tool_bucket(tool)] = buckets.get(tool_bucket(tool), 0) + n
+    return buckets, sum(buckets.values())
+
+
+def sig_infra_overhead(digest, ctx) -> list[Signal]:
+    """Problem: a large share of tool calls is hub/task/schema plumbing, not work."""
+    buckets, total = _bucketed(digest)
+    if total < ctx.get("infra_min_calls", 20):
+        return []
+    overhead = buckets.get("statehub_mcp", 0) + buckets.get("task_mgmt", 0) + buckets.get("schema_load", 0)
+    share = overhead / total
+    if share >= ctx.get("infra_overhead_threshold", 0.30):
+        return [_base(digest, "infra_overhead", PROBLEM, "infra_overhead", round(share, 3),
+                      overhead_calls=overhead, total_calls=total,
+                      statehub=buckets.get("statehub_mcp", 0),
+                      task_mgmt=buckets.get("task_mgmt", 0),
+                      schema_load=buckets.get("schema_load", 0))]
+    return []
+
+
+def sig_schema_thrash(digest, ctx) -> list[Signal]:
+    """Problem: repeated ToolSearch — deferred-tool schemas reloaded over and over."""
+    buckets, _ = _bucketed(digest)
+    n = buckets.get("schema_load", 0)
+    if n >= ctx.get("schema_thrash_threshold", 5):
+        return [_base(digest, "schema_thrash", PROBLEM, "schema_load", float(n), tool_searches=n)]
+    return []
+
+
+def sig_tool_thrash(digest, ctx) -> list[Signal]:
+    """Problem: a single tool is hammered far more than any other — likely churn."""
+    hist = digest.get("tool_histogram") or {}
+    if not hist:
+        return []
+    tool, n = max(hist.items(), key=lambda kv: kv[1])
+    if n >= ctx.get("tool_thrash_threshold", 80):
+        return [_base(digest, "tool_thrash", PROBLEM, f"tool:{tool}", float(n), tool=tool, calls=n)]
+    return []
+
+
 EXTRACTORS: list[Callable] = [
     sig_retry_storm, sig_repeated_errors, sig_budget_overrun, sig_abandoned,
     sig_clean_pass, sig_error_then_recovery,
+    sig_infra_overhead, sig_schema_thrash, sig_tool_thrash,
 ]
 
 
@@ -104,7 +170,12 @@ def build_context(digests: list[dict]) -> dict[str, Any]:
         for d in digests
     )
     p90 = totals[int(0.9 * (len(totals) - 1))] if totals else 0
-    return {"tokens_p90": p90, "retry_storm_threshold": 3, "error_threshold": 3}
+    return {
+        "tokens_p90": p90, "retry_storm_threshold": 3, "error_threshold": 3,
+        # tool-mix / infra-overhead thresholds (WP-0005 T02)
+        "infra_min_calls": 20, "infra_overhead_threshold": 0.30,
+        "schema_thrash_threshold": 5, "tool_thrash_threshold": 80,
+    }
 
 
 def extract_signals(digests: list[dict], ctx: Optional[dict] = None) -> list[Signal]:

tests/test_detect_infra_signals.py

@@ -0,0 +1,80 @@
+"""Infra-overhead + thrash signal tests (WP-0005 T02)."""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from session_memory.detect.signals import (  # noqa: E402
+    build_context,
+    extract_signals,
+    sig_infra_overhead,
+    sig_schema_thrash,
+    sig_tool_thrash,
+    tool_bucket,
+)
+
+
+def _digest(uid="claude:a", repo="r1", tools=None):
+    return {"session_uid": uid, "flavor": "claude", "repo": repo, "outcome": "success",
+            "cost": {"input_tokens": 1, "output_tokens": 1},
+            "markers": {"errors": 0, "retries": 0, "test_runs": 0},
+            "tool_histogram": tools or {}}
+
+
+CTX = {"infra_min_calls": 20, "infra_overhead_threshold": 0.30,
+       "schema_thrash_threshold": 5, "tool_thrash_threshold": 80}
+
+
+def test_tool_bucket_mapping():
+    assert tool_bucket("mcp__state-hub__update_task_status") == "statehub_mcp"
+    assert tool_bucket("ToolSearch") == "schema_load"
+    assert tool_bucket("TaskUpdate") == "task_mgmt"
+    assert tool_bucket("Bash") == "shell"
+    assert tool_bucket("Edit") == "edit"
+
+
+def test_infra_overhead_fires_above_share():
+    # 18 statehub of 30 total = 60% overhead
+    d = _digest(tools={"mcp__state-hub__create_task": 18, "Bash": 8, "Edit": 4})
+    sig = sig_infra_overhead(d, CTX)
+    assert sig and sig[0].type == "infra_overhead"
+    assert sig[0].magnitude >= 0.30
+    assert sig[0].detail["statehub"] == 18
+
+
+def test_infra_overhead_quiet_when_mostly_work():
+    d = _digest(tools={"mcp__state-hub__create_task": 3, "Bash": 40, "Edit": 30})
+    assert sig_infra_overhead(d, CTX) == []
+
+
+def test_infra_overhead_ignores_tiny_sessions():
+    d = _digest(tools={"mcp__state-hub__create_task": 5})  # below infra_min_calls
+    assert sig_infra_overhead(d, CTX) == []
+
+
+def test_schema_thrash_fires():
+    d = _digest(tools={"ToolSearch": 9, "Bash": 5})
+    sig = sig_schema_thrash(d, CTX)
+    assert sig and sig[0].type == "schema_thrash"
+    assert sig[0].detail["tool_searches"] == 9
+
+
+def test_tool_thrash_fires_on_dominant_tool():
+    d = _digest(tools={"Bash": 120, "Edit": 5})
+    sig = sig_tool_thrash(d, CTX)
+    assert sig and sig[0].locus == "tool:Bash"
+
+
+def test_extract_signals_includes_infra():
+    d = _digest(tools={"mcp__state-hub__create_task": 18, "Bash": 8, "Edit": 4,
+                       "ToolSearch": 6})
+    types = {s.type for s in extract_signals([d])}
+    assert "infra_overhead" in types
+    assert "schema_thrash" in types
+
+
+def test_build_context_has_infra_defaults():
+    ctx = build_context([])
+    assert ctx["infra_overhead_threshold"] == 0.30
+    assert ctx["schema_thrash_threshold"] == 5

workplans/AGENTIC-WP-0005-detect-hardening.md

@@ -52,7 +52,7 @@ sessions — fixing the `abandoned` false-positive. Knobs under `[detect]` in
 
 ```task
 id: AGENTIC-WP-0005-T02
-status: todo
+status: done
 priority: high
 state_hub_task_id: "10d57b05-a731-4ece-bf45-f6a98ac77555"
 ```