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Preserve user guidance through history compression, stabilize Flash index targets, and retire withdrawn checks without applying stale verdicts.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

tests/unit/agents/test_checker.py

@@ -400,7 +400,7 @@ async def test_replay_steps_result_is_a_plain_tool_message(tmp_path):
     assert tool_msg.name == "replay_steps"
     assert "- **Step 3 (Start: 9.0s)**" in tool_msg.content
     assert "[Screen]: Saved the alarm." in tool_msg.content
-    assert "[Planned Action]: Tapped 'Save' at [0.5, 0.5]" in tool_msg.content
+    assert "[Action]: Tapped 'Save' at [0.5, 0.5]" in tool_msg.content
 
 
 # --- Streamed-reasoning transcript (replay of the live Thought/Work text) -------------
@@ -647,6 +647,89 @@ def test_format_history_marks_self_described_targets_only():
     assert "target_resource_id" not in text
 
 
+def test_format_history_uses_session_offsets_and_skips_empty_steps():
+    """Rows carry the session-relative ``T+mm:ss`` clock every agent shares
+    (from the step timestamp, else from the engine's ``97.7s`` label), and a
+    step with neither summary nor action renders no row."""
+    from artemis.agents.checker.checker import _format_history
+
+    ctx = _mock_ctx()
+    ctx.data_engine.session_start_time = 1000.0
+    ctx.data_engine.get_agent_friendly_steps.return_value = [
+        {"step_number": 1, "timestamp": 1097.7, "summary": "Opened the app"},
+        {"step_number": 2, "relative_time": "12.4s", "summary": "", "action_taken": None},
+        {
+            "step_number": 3,
+            "relative_time": "130.0s",
+            "summary": None,
+            "action_taken": {"action": "click", "coordinates": [1, 2], "target_text": "Login"},
+        },
+    ]
+
+    lines = _format_history(ctx).splitlines()
+    assert len(lines) == 2
+    assert lines[0] == "- Step 1 (T+01:37): Opened the app"
+    assert lines[1].startswith("- Step 3 (T+02:10): ")
+    assert "'Login'" in lines[1]
+
+
+async def _final_check_human_text(ctx) -> str:
+    report = CheckReport(verdicts=[])
+    structured = MagicMock()
+    structured.ainvoke = AsyncMock(return_value=report)
+    llm = MagicMock()
+    llm.with_structured_output.return_value = structured
+    response = MagicMock()
+    response.tool_calls = []
+    acomplete_mock = AsyncMock(return_value=response)
+
+    with (
+        patch("artemis.agents.checker.checker.get_llm", return_value=llm),
+        patch("artemis.agents.checker.checker.acomplete", new=acomplete_mock),
+        patch(
+            "artemis.agents.checker.checker._capture_final_screen",
+            new=AsyncMock(return_value=(None, "elements")),
+        ),
+    ):
+        await run_final_check(ctx, goal="the goal", plan_text="- [x] G", ledger=[], check_items=[])
+
+    messages = acomplete_mock.await_args.args[1]
+    human = messages[-1]
+    return "\n".join(
+        block["text"] for block in human.content if isinstance(block, dict) and "text" in block
+    )
+
+
+@pytest.mark.asyncio
+async def test_final_review_lists_user_guidance_from_the_step_records():
+    """Every mid-run user instruction reaches the final review, read from the
+    step it was stamped on, so the goal is audited as amended by it."""
+    ctx = _mock_ctx()
+    ctx.data_engine.get_agent_friendly_steps.return_value = [
+        {"step_number": 1, "relative_time": "3.0s", "summary": "s1", "extra_metadata": {}},
+        {
+            "step_number": 2,
+            "relative_time": "65.0s",
+            "summary": "s2",
+            "extra_metadata": {"injected_instruction": "Skip the login"},
+        },
+    ]
+    text = await _final_check_human_text(ctx)
+    section = text.split("# User guidance received during the run\n", 1)[1].split("\n\n", 1)[0]
+    assert section == '- Step 2 (T+01:05): "Skip the login"'
+    # The system prompt audits the goal as amended by that guidance.
+    from artemis.agents.checker.checker import _load_prompts
+
+    assert "as amended by the user guidance" in _load_prompts()["final_guide"]
+
+
+@pytest.mark.asyncio
+async def test_final_review_reports_no_guidance_explicitly():
+    ctx = _mock_ctx()
+    text = await _final_check_human_text(ctx)
+    assert "# User guidance received during the run\n(none)\n" in text
+
+
 # --- tool results: status is structural, never sniffed from the words -----------------