refactor: unify agent history and harden runtime diagnostics

Preserve user guidance through history compression, stabilize Flash index targets, and retire withdrawn checks without applying stale verdicts.

Improve runtime diagnostics, tool responses, and history rendering. Simplify documentation and comments.

Validation: 2076 tests passed in the full suite; 381 affected tests and 26 frontend tests passed after cleanup. Ruff and the quality ratchet passed.

artemis/memory/step_memory.py

@@ -20,12 +20,13 @@ with alias resolution (tool_call_id / legacy ordinals), and status queries.
 
 What a summary *contains* (the lens semantics) lives in subclasses — the
 service only guarantees how jobs are scheduled, retried, keyed, and drained.
-Both Flash and (from M2 on) Pro profiles share this runtime.
+Flash and Pro profiles share this runtime.
 """
 
 import asyncio
 from typing import Any
 
+from artemis.data_engine.trace import detached_trace
 from artemis.utils.logger import get_logger
 
 logger = get_logger(__name__)
@@ -67,12 +68,20 @@ class StepMemoryService:
        where available; tool_call_ids (and legacy ordinals) remain queryable
        through an alias map so message-level consumers need no migration.
     5. Bounded concurrency: at most ``max_concurrency`` attempts run at once.
+    6. Detached tracing: every job runs inside
+       :func:`~artemis.data_engine.trace.detached_trace`, so a lens's model
+       calls never attach to the trace span (the operator's step) that was
+       current when the job was submitted — no lens needs to know.
 
     Subclasses implement :meth:`_attempt` (one summarization attempt for a
     payload) and may override :meth:`_on_status` to persist pending/failed
     status transitions.
     """
 
+    #: Trace node label of a lens-less subclass's jobs (``lens:<name>``); a
+    #: configured :class:`StepLens` contributes its own ``name`` instead.
+    lens_name: str | None = None
+
     def __init__(
         self,
         ctx: Any,
@@ -131,7 +140,25 @@ class StepMemoryService:
     # Scheduling core
     # ------------------------------------------------------------------
 
+    @property
+    def trace_node_name(self) -> str:
+        """Node label the job's traces and usage records carry (``lens:<name>``)."""
+        name = getattr(self._lens, "name", None) or self.lens_name or type(self).__name__.lower()
+        return f"lens:{name}"
+
     async def _run_until_ready(self, key: JobKey) -> None:
+        """Run one job to completion, detached from the submitter's trace span.
+
+        The task was created while the submitting agent's step span was
+        current and inherits that context; the whole job — every attempt,
+        retry sleeps included — runs under :func:`detached_trace` so nothing
+        a lens records (model calls, their thinking/raw_thinking children,
+        stream deltas, usage) can be attributed to the submitter's step.
+        """
+        with detached_trace(self.trace_node_name):
+            await self._run_attempts(key)
+
+    async def _run_attempts(self, key: JobKey) -> None:
         """Retry one job independently, bounded by the configured retry limit.
 
         Attempts at most ``1 + retry_limit`` times; on exhaustion the job