release: v1.5.0 — discovery layer, honesty debt closed, Wave A

Tool count 131 -> 154; 474 -> 1242 collected tests.

The release exists for two measured reasons. A 149-tool catalog costs a client
~40,300 tokens before it has asked for anything, and a drafter searching the way
drafters think -- FILLET, BPOLY, QSELECT, WBLOCK -- scored df=0 against the stock
index, because those words were simply not in the data.

Discovery and batching
- DISCOVERY_MODE=search replaces the catalog with search_tools + call_tool,
  ranked over an AutoCAD command and synonym corpus (discovery/aliases.py) on
  top of fastmcp's BM25 index. Measured: 40,305 -> 356 tokens advertised.
- cad_batch runs a step list in one round trip; fields= projects result-heavy
  responses. The `core` profile is gone -- discovery replaced it.

Honesty debt (Tier 0)
- OCS/ECS: `extrusion` appeared nowhere in this codebase, so mirrored and
  rotated geometry reported coordinates that were quietly wrong. backends/ocs.py
  translates at the backend boundary; every tool coordinate is WCS on both
  engines, and a tilted plane refuses rather than answering with a number that
  looks fine.
- drawing_save_as(fmt="dwg") wrote DXF bytes to a .dwg path. drawing_audit never
  repaired. analysis_measure_area shoelaced points the caller typed in.
- ezdxf calls gained a per-call timeout, so one hung call can no longer wedge a
  server whose document lock is a single asyncio.Lock.

Architecture
- The 1854-line backend ABC is 19 contract modules; @capability(key, reason=)
  makes optional methods declarative and a gate fails on undeclared holes.
- 8 layout/viewport tools, CHSPACE, CAD_PROGID escape hatch.
- Wave A: selection filters, boundary tracing, hatch depth, annotation objects,
  measurement -- 13 tools of a planned 39. The REGION and 2D-boolean family was
  cut on evidence: add_region() yields zero ACIS bytes and the greiner_hormann
  substitute loses 28.2% of the area on a square with one semicircular edge.

Verified against a live AutoCAD 2026, which found four COM defects no amount of
reading would have caught -- AcadPViewport has no ViewCenter, and the line that
set it had been swallowed by a bare except since v1.4.

Benchmark v3 (15 tasks) and what it caught
- v2 scored this server 10/10, which carried no information: every task in it
  exercised something the server was built around. Five tasks were added because
  they can fail, and three did while being written -- a hatch could not be
  measured though the refusal listed HATCH as measurable, the boundary tools and
  the measure tool disagreed about the same shape (139.2177 vs 139.2699), and a
  circle stored as two bulged vertices measured 0.0.
- Competitor reports are NOT re-scored. They are pinned v1.4 runs against v2 and
  were never asked these five questions; the chart shows those rows `not run`.
- Correctness A/B: 21/24 -> 24/24, zero regressions.

Performance, stated plainly
The published v1.4 perf report was recorded on CPython 3.14 and the new one on
3.11.15, so the apparent 2-6x speedup is the interpreter, not this release.
Re-measured on one interpreter, v1.5.0 is 28% slower creating entities and 22%
slower on the 10k roundtrip. Fully attributed: EZDXF_CALL_TIMEOUT=0 restores
v1.4.0's exact numbers. That is the deadlock fix being paid for, the knob is
documented, and winning it back is on the 1.6 roadmap.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backends/capability.py

@@ -0,0 +1,134 @@
+"""Optional contract methods: declared once, refused loudly, gated by a test.
+
+The backend contract is large (112 abstract methods before this file existed,
+and the plan adds ~39 more). Every one of them is an `@abstractmethod`, which
+means adding a single method to the contract makes **both** backends fail at
+instantiation until both are written — and two test modules construct
+`ComBackend` at import time, so the whole suite goes red on a half-finished
+edit. That is a real cost paid on every contract change.
+
+The obvious fix is to give new methods a default body. The obvious default is
+wrong: returning ``{"ok": False, "capability": ...}`` from a method nobody
+implemented produces exactly the quiet "this didn't work and nothing told you"
+that the v1.5.0 honesty pass spent a milestone deleting. A default that lies
+quietly is worse than a build break.
+
+So `@capability` gives a default that **raises**
+`UnsupportedCapabilityError` — the same typed refusal the deliberate
+boundaries raise, carrying the same `capability` key, surfaced by the same
+`CapabilityRefusalMiddleware`, and indistinguishable to a client from a
+hand-written refusal. Three properties follow:
+
+* An unimplemented method refuses instead of pretending. It cannot silently
+  succeed and it cannot silently do nothing.
+* The refusal is *declared*: `test_capability.py` fails if a key used here is
+  missing from either backend's `CapabilityMap`, so `system_capabilities` can
+  never disagree with what a call actually does. This is the part that keeps
+  the escape hatch honest — without it, `@capability` would just be a way to
+  ship undeclared holes.
+* Overriding is ordinary subclassing. A backend that implements the method
+  simply defines it; nothing needs to be un-registered.
+
+`@abstractmethod` remains the default for anything both backends must have.
+Reach for `@capability` only when a method is genuinely optional — an engine
+boundary (no ACIS kernel headlessly) rather than an unfinished chore.
+"""
+
+from __future__ import annotations
+
+import functools
+from collections.abc import Callable
+from typing import Any
+
+__all__ = [
+    "UnsupportedCapabilityError",
+    "capability",
+    "capability_keys",
+    "is_capability_default",
+]
+
+
+# ---------------------------------------------------------------------------
+# The refusal vocabulary
+#
+# This lives here rather than in ``backends.base`` because the contracts import
+# the decorator and ``base`` imports the contracts — putting the exception in
+# ``base`` makes that a cycle. ``backends.base`` re-exports both names, so
+# ``from backends.base import UnsupportedCapabilityError`` is unchanged for the
+# rest of the repo.
+#
+# There is exactly one authoring rule: a backend that cannot do a thing RAISES
+# ``UnsupportedCapabilityError(capability, message)``, where ``capability`` is a
+# key of ``capabilities().features`` so a client can pre-check the same boundary
+# through ``system_capabilities`` instead of parsing English. Tools never catch
+# it and never hand-build refusal payloads — one middleware turns it into the
+# wire payload, and ``cad_batch`` turns it into a step row. One class object,
+# defined once: two look-alike types would silently break every ``isinstance``
+# classifier.
+#
+# The ``{"ok": False, "error": ...}`` returned-dict shape stays legal only for
+# soft failures that are not capability boundaries ("Layout not found", "No
+# active transaction").
+# ---------------------------------------------------------------------------
+
+
+def _unsupported(error: str, capability_key: str) -> dict:
+    """Build a backend's machine-readable "this backend can't" payload."""
+    return {"ok": False, "error": error, "capability": capability_key}
+
+
+class UnsupportedCapabilityError(RuntimeError):
+    """Raised when a call needs a capability this backend does not have.
+
+    Stays a plain ``RuntimeError``: rebasing it on ``FastMCPError`` was measured
+    and changes nothing a client can observe, because the refusal is carried by
+    ``ToolResult(structured_content=..., is_error=True)`` rather than by the
+    exception class. ``to_dict()`` keeps the ``{ok, error, capability}`` payload
+    attached to the raise so the boundary survives the ``__cause__`` chain.
+    """
+
+    def __init__(self, capability: str, error: str):
+        super().__init__(error)
+        self.capability = capability
+
+    def to_dict(self) -> dict:
+        return _unsupported(str(self), self.capability)
+
+
+#: ``{capability_key: (method_name, ...)}`` for every method declared optional.
+#: Populated at import by the decorator and read by the parity gate.
+_REGISTRY: dict[str, set[str]] = {}
+
+
+def capability(key: str, *, reason: str = "") -> Callable[[Callable], Callable]:
+    """Mark a contract method optional, defaulting to a typed refusal.
+
+    Args:
+        key: capability name; must appear in **both** backends' capability maps.
+        reason: appended to the refusal message. Say what the caller can do
+            instead, not merely that they cannot do this.
+    """
+
+    def decorate(func: Callable) -> Callable:
+        @functools.wraps(func)
+        async def default(self, *args: Any, **kwargs: Any):
+            message = f"{func.__name__}: not supported by the {self.name} backend"
+            raise UnsupportedCapabilityError(key, f"{message}. {reason}".rstrip())
+
+        default.__capability__ = key
+        default.__is_capability_default__ = True
+        _REGISTRY.setdefault(key, set()).add(func.__name__)
+        return default
+
+    return decorate
+
+
+def capability_keys() -> dict[str, set[str]]:
+    """Every optional-capability key and the methods declared under it."""
+    return {key: set(names) for key, names in _REGISTRY.items()}
+
+
+def is_capability_default(owner: type, method_name: str) -> bool:
+    """True when ``owner`` inherited the refusing default rather than implementing it."""
+    attribute = getattr(owner, method_name, None)
+    return bool(getattr(attribute, "__is_capability_default__", False))