feat(task-8): SECTION 25 grid and symbols - arch_grid, arch_symbol

engineering/arch/symbols.py is pure: grid_prims() draws each structural axis on
the grid role - its CENTER linetype comes from the A-GRID-E-N row, no primitive
sets one - with a 5 mm (paper) bubble and its label touching both ends, on the
symbol role so the circle does not print dashed. Numbers run along x and
letters along y (A..Z, AA, ... none skipped) unless labels names them;
positions are sorted, duplicates and label-count mismatches refused by path.

symbol_prims() draws the four plan symbols: the north arrow (a circle, an
arrow turned CCW from +Y, the vocab(lang) north letter upright beyond the tip),
the section mark (the cut line, a labelled bubble past each end and a viewing
arrow at each end, p1/p2 relative to the origin), the level mark (the triangle,
its line and the value formatted +3.00 / ±0.00, with a decimal comma in
Turkish) and the elevation mark (a circle whose pointers are the tangents from
r*sqrt(2) touching it at +/-45 degrees). An unknown kind is refused with the
list, a parameter the kind does not take with the ones it does. Every size is
a declared paper-mm drafting choice times the plot scale, not a standards value.

arch_grid and arch_symbol draw through draw_prims with ARCH_ROLE_LAYER; alias
records (COLUMNGRIDADD, English and Turkish synonyms), a regenerated inventory,
the README snapshot at 233 tools and the branch-local group snapshot
(entity_creation 21) complete the registration.

Beyond the plan: grid_axes refuses a labels value that is not a dict and a
labels.x / labels.y that is not a list (a string was split into one label per
character, a number raised a bare TypeError). No new ActiveX member: a live run
on AutoCAD 2026 (scratch document, closed after) drew the grid and all four
symbols through draw_prims - A-GRID-E-N created with CENTER, bubbles, texts and
symbols on A-SYMB-T-N, the Turkish north letter K and the level "+3,00".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

tests/test_tool_registry.py

@@ -495,7 +495,7 @@ async def test_tool_groups_is_byte_identical_to_the_source_declared_grouping():
 
 
 async def test_tool_group_sizes_are_unchanged():
-    """Frozen snapshot of the surface (231 tools, 25 groups).
+    """Frozen snapshot of the surface (233 tools, 25 groups).
 
     Taken before @cad_tool landed at 131 tools; `batch` moved 2 -> 3 when
     v1.5.0's `cad_batch` joined `entity_batch_create`/`entity_batch_modify`, and
@@ -589,6 +589,10 @@ async def test_tool_group_sizes_are_unchanged():
     tags: `entity_query` 9 -> 10, `entity_creation` 18 -> 19. This snapshot is
     branch-local: the track F merge task recomputes it once the walls, rooms
     and catalogue branches have landed.
+
+    Group C's second task added the structural grid and the plan symbols
+    (`arch_grid` / `arch_symbol`), both tagged `arch` and `create`:
+    `entity_creation` 19 -> 21, for the same branch-local reason.
     """
     sizes = {label: len(names) for label, names in (await server._tool_groups()).items()}
     assert sizes == {
@@ -599,7 +603,7 @@ async def test_tool_group_sizes_are_unchanged():
         "dimensions": 5,
         "drawing": 11,
         "engineering": 10,
-        "entity_creation": 19,
+        "entity_creation": 21,
         "entity_modification": 16,
         "entity_query": 10,
         "environment": 22,
@@ -618,4 +622,4 @@ async def test_tool_group_sizes_are_unchanged():
         "validation": 1,
         "view": 4,
     }
-    assert sum(sizes.values()) == 231
+    assert sum(sizes.values()) == 233