tools/epro2/kicad: hierarchical export + global_label + 5-Voltage power ports

Three coupled changes so kicad-cli sch erc runs at the project level
(across all sheets of one schematic) instead of single-sheet:

1. (label) → (global_label (shape passive)). EPRO2 nets are
   project-global by construction (named rails span every page in the
   SCH and physically wire across PCBs); KiCad's local label is sheet-
   scoped and triggers `label_dangling` for any name not duplicated on
   the same page.

2. New root_sch_writer that groups SCH_PAGE docs by their parent SCH
   (META.schematic), emits one root .kicad_sch per group with one
   (sheet ...) entry per child, and threads the root-assigned uuid back
   into each child's (sheet_instances) so KiCad can bind them.
   --all-sch now defaults to this; --flat falls back to one-file-per-page.

3. EPRO2's "5-Voltage" placeholder COMPONENT (partId
   pid8a0e77bacb214e, 365 instances on ESP-VoCat) is the editor's power
   port. The rail name lives in the placement's `Global Net Name` ATTR,
   not in the PART. We now emit a (global_label "<rail>") at the
   placement coords whenever that attr is set (101/365 of them on
   ESP-VoCat — the rest are unconfigured drafts).

ESP-VoCat 5 hierarchical roots: 2325 → 2265 violations. Modest because
5 of 6 SCHs are single-page (no cross-sheet nets to resolve), and the
one 4-page schematic (CoreBoard) shares only a handful of names across
sheets — most net names are de-facto sheet-local. The remaining ~190
pin_not_connected are dominated by 0402-style passives whose pin tip
lies on a wire's interior, not at an endpoint; KiCad needs an explicit
(junction) at those points and we don't yet emit one. Marked as the
next follow-up in log.md.

47 → 52 unit tests pass.

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

tools/epro2/tests/test_root_sch_writer.py

@@ -0,0 +1,68 @@
+"""Root sheet writer regression: hierarchical parent .kicad_sch."""
+
+from tools.epro2.kicad._sexpr_reader import parse
+from tools.epro2.kicad.root_sch_writer import ChildSheet, write_root_sheet
+
+
+def _block(parsed, name):
+    return [c for c in parsed if isinstance(c, list) and c and c[0] == name]
+
+
+def test_root_emits_one_sheet_block_per_child():
+    children = [
+        ChildSheet("Overview.kicad_sch", "Overview", "uuid-1"),
+        ChildSheet("MCU.kicad_sch", "MCU", "uuid-2"),
+        ChildSheet("Codec.kicad_sch", "Codec", "uuid-3"),
+    ]
+    parsed = parse(write_root_sheet("CoreBoard", children))
+    sheets = _block(parsed, "sheet")
+    assert len(sheets) == 3
+    # Each sheet block carries the assigned uuid + Sheetname + Sheetfile
+    titles = []
+    files = []
+    uuids = []
+    for sh in sheets:
+        uuids.append(next(c for c in sh if isinstance(c, list) and c[0] == "uuid")[1])
+        for c in sh:
+            if isinstance(c, list) and c[0] == "property":
+                if c[1] == "Sheetname":
+                    titles.append(c[2])
+                elif c[1] == "Sheetfile":
+                    files.append(c[2])
+    assert titles == ["Overview", "MCU", "Codec"]
+    assert files == ["Overview.kicad_sch", "MCU.kicad_sch", "Codec.kicad_sch"]
+    assert uuids == ["uuid-1", "uuid-2", "uuid-3"]
+
+
+def test_root_assigns_sequential_page_numbers_starting_at_2():
+    """Root itself is page 1 of the hierarchy; children start at page 2 so
+    that a child's (sheet_instances (page "<n>")) lines up with the root's
+    (instances ... (page "<n>"))."""
+    children = [
+        ChildSheet("a.kicad_sch", "A", "u-a"),
+        ChildSheet("b.kicad_sch", "B", "u-b"),
+    ]
+    parsed = parse(write_root_sheet("Project", children))
+    sheets = _block(parsed, "sheet")
+    page_nums = []
+    for sh in sheets:
+        inst = next(c for c in sh if isinstance(c, list) and c[0] == "instances")
+        proj = next(c for c in inst if isinstance(c, list) and c[0] == "project")
+        path = next(c for c in proj if isinstance(c, list) and c[0] == "path")
+        page = next(c for c in path if isinstance(c, list) and c[0] == "page")
+        page_nums.append(page[1])
+    assert page_nums == ["2", "3"]
+    # And the root's own page is 1
+    root_inst = _block(parsed, "sheet_instances")[0]
+    root_path = next(c for c in root_inst if isinstance(c, list) and c[0] == "path")
+    root_page = next(c for c in root_path if isinstance(c, list) and c[0] == "page")
+    assert root_page[1] == "1"
+
+
+def test_root_handles_zero_children():
+    """Empty schematic: still emit a valid kicad_sch with no (sheet) blocks."""
+    parsed = parse(write_root_sheet("Empty", []))
+    assert parsed[0] == "kicad_sch"
+    assert _block(parsed, "sheet") == []
+    # sheet_instances still required (KiCad demands at least one path)
+    assert _block(parsed, "sheet_instances")