tools/epro2: add ProjectRelations for cross-document resolution

per-doc Relations 在大量 cross-doc 引用前是不够的：PCB 的 PAD_NET 复合
id [PAD_NET, comp, pin, pad] 里的 pad 实际是 FOOTPRINT 文档里的 pad
实例；SCH_PAGE 的 COMPONENT.partId 指向某个 SYMBOL 文档的 PART.id。

ProjectRelations 在 per-doc Relations 之上做项目级聚合，把这些跨文档
引用拼起来。

Probe 阶段（ESP-VoCat）发现的映射规则（已写入 docstring）：

1. SCH_PAGE COMPONENT.partId  ===  PART.id in some SYMBOL doc
   - 命名两种风格：'pid<hex>' (anonymous/系统 part) + '<name>.<n>' (具
     名 SKU)，但都直接相等 PART.id，**不**是不同 namespace
   - 同一 PART.id 可能出现在多个 SYMBOL 文档里（库快照），
     parts_by_id 保留全部，consumer 通常取第一个

2. PCB COMPONENT.id  →  FOOTPRINT 文档 UUID  via 单独 ATTR op:
       ATTR(parentId=<comp>, key="Footprint", value=<fp_doc_uuid>)
   COMPONENT.attrs 子 dict 只有内务字段（Unique ID / Channel ID / ...），
   **不**含 footprint 引用。这跟 schematic 的 partId 在 COMPONENT 上的
   做法不一样，是 EPRO2 流的一处不对称

3. PCB PAD_NET[comp,pin,pad] 里的 pad 是 FOOTPRINT 文档内部的 pad id；
   解析链: comp → ATTR Footprint → FOOTPRINT relations.pads[pad]

API：
  ProjectRelations.build(project) — 单遍构建
  resolve_symbol_docs(sch_uuid, comp_id) → [SYMBOL doc uuids]
  resolve_footprint_doc(pcb_uuid, comp_id) → FOOTPRINT doc uuid | None
  pad_in_footprint(fp_uuid, pad_id) → PAD payload | None
  resolve_pcb_pad_net(pcb_uuid, comp, pin, pad) → {footprint, pad} | None
  attrs_for_pcb_component(pcb_uuid, comp_id) → {key: value} 折叠

CLI 加 --project-relations，跑 ESP-VoCat:
  documents                                 278
  distinct_parts                             87
  duplicated_parts                            9
  pcb_components_with_footprint             206
  pcb_components_unresolved_footprint         0
  sch_components_with_partid                572
  sch_components_unresolved_part              0

PCB 样本验证：comp=e0 → fp=1069352d81c6 Designator='U8'，
PAD_NET pin=1 pad=e7 net=GND 跨文档解到坐标 (-37.4,-45.24)。

测试：6 个新单测覆盖 partId→symbol、comp→footprint、PAD_NET 跨文档、
attrs 折叠、unresolved 计数。parser + relations + project_relations
共 21/21 通过。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tools/epro2/__main__.py

@@ -16,6 +16,7 @@ import sys
 from collections import Counter
 from pathlib import Path
 
+from .project_relations import ProjectRelations
 from .relations import Relations
 from .replay import Project, replay_project
 
@@ -112,6 +113,59 @@ def _print_relations(proj: Project) -> None:
         )
 
 
+def _print_project_relations(proj: Project) -> None:
+    """Cross-doc resolution stats + a few sample resolutions for sanity."""
+    pr = ProjectRelations.build(proj)
+    s = pr.summary()
+    print()
+    print("=" * 72)
+    print("Project Relations (cross-doc)")
+    print("-" * 72)
+    for k, v in s.items():
+        print(f"  {k:<40s}  {v}")
+
+    # Show 3 sample SCH_PAGE component → SYMBOL resolutions
+    print()
+    print("Sample sch component → symbol resolutions:")
+    n = 0
+    for sch_uuid in pr.docs_by_type.get("SCH_PAGE", []):
+        for cid in pr.per_doc[sch_uuid].components:
+            symbols = pr.resolve_symbol_docs(sch_uuid, cid)
+            pid = pr.component_to_partid.get((sch_uuid, cid))
+            if symbols:
+                print(f"  sch={sch_uuid[:12]} comp={cid}  partId={pid!r}  →  symbol={symbols[0][:12]} (+{len(symbols)-1})")
+                n += 1
+                if n >= 3: break
+        if n >= 3: break
+
+    # Show 3 sample PCB component → FOOTPRINT resolutions, and a PAD_NET cross-doc resolution
+    print()
+    print("Sample pcb component → footprint + first PAD_NET cross-doc:")
+    n = 0
+    for pcb_uuid in pr.docs_by_type.get("PCB", []):
+        rel = pr.per_doc[pcb_uuid]
+        for cid in rel.components:
+            fp = pr.resolve_footprint_doc(pcb_uuid, cid)
+            if not fp: continue
+            attrs = pr.attrs_for_pcb_component(pcb_uuid, cid)
+            print(f"  pcb={pcb_uuid[:12]} comp={cid}  →  fp={fp[:12]}  Designator={attrs.get('Designator')!r}  Value={attrs.get('Value')!r}")
+            # Find a PAD_NET referencing this comp and try cross-doc resolve
+            for pad_id, records in rel.pad_nets_by_pad.items():
+                for rec in records:
+                    if rec["comp"] != cid: continue
+                    resolved = pr.resolve_pcb_pad_net(pcb_uuid, cid, rec["pin"], rec["pad"])
+                    if resolved:
+                        pad = resolved["pad"]
+                        print(f"    PAD_NET pin={rec['pin']} pad={rec['pad']} net={rec['net_name']}  →  pad@({pad.get('centerX')},{pad.get('centerY')})")
+                        break
+                else:
+                    continue
+                break
+            n += 1
+            if n >= 3: break
+        if n >= 3: break
+
+
 def main(argv: list[str] | None = None) -> int:
     ap = argparse.ArgumentParser(description="Replay an EPRO2 project and summarize.")
     ap.add_argument("project_dir", type=Path, help="data/raw/oshwhub/<project_uuid>/")
@@ -126,6 +180,11 @@ def main(argv: list[str] | None = None) -> int:
         action="store_true",
         help="build cross-object indices and print per-docType summary",
     )
+    ap.add_argument(
+        "--project-relations",
+        action="store_true",
+        help="build cross-document indices (partId → SYMBOL, comp → FOOTPRINT, PAD_NET cross-doc)",
+    )
     args = ap.parse_args(argv)
 
     proj = replay_project(args.project_dir)
@@ -134,6 +193,8 @@ def main(argv: list[str] | None = None) -> int:
         _dump_doc(proj, doc_id)
     if args.relations:
         _print_relations(proj)
+    if args.project_relations:
+        _print_project_relations(proj)
     return 0