bench: matrix v4 adds pid_roundtrip; correctness suite grows to 29 with three P&ID checks

tasks_v4.py extends v3 with one task the reader can fail on its own: the
example spec is drawn through pid_from_spec's code and read back by the
graph builder, which never sees the spec. The runner, the chart and the
doc-number gate now default to v4; --matrix v3 / v2 reproduce the earlier
sets, and tests/test_benchmark_v3.py labels its full-matrix run "v3"
explicitly now that the default has moved.

The plan's adapter check expected the two unnumbered lines to come back
with no line number; draw_line builds one from the default number_format
(bare sequence when size/service/spec/insulation are empty), so the task
asserts the two authored numbers on the two process lines and sequence-
built XDATA numbers on the other two instead.

The published A/B report still covers 26 checks; Task 21 re-runs it
against v1.5.1, which is what clears the remaining doc-number drift.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

benchmarks/render_matrix_chart.py

@@ -13,7 +13,7 @@ import json
 from pathlib import Path
 from typing import Any
 
-from benchmarks.tasks_v3 import TASKS_V3
+from benchmarks.tasks_v4 import TASKS_V4
 
 ROOT = Path(__file__).resolve().parents[1]
 DEFAULT_INPUT_DIR = ROOT / "benchmarks" / "results" / "published"
@@ -66,8 +66,8 @@ def render_chart(reports: list[dict[str, Any]], output: Path) -> None:
 
     matplotlib.rcParams["svg.hashsalt"] = "autocad-mcp-taskmatrix-v1"
 
-    task_ids = [task.task_id for task in TASKS_V3]
-    task_labels = [f"{task.task_id}  ({task.category})" for task in TASKS_V3]
+    task_ids = [task.task_id for task in TASKS_V4]
+    task_labels = [f"{task.task_id}  ({task.category})" for task in TASKS_V4]
     servers = [report["adapter"] for report in reports]
     status_by_server = {
         report["adapter"]: {item["task_id"]: item["status"] for item in report["results"]}