chore(harnessx-removal): delete HarnessX code and packaging (task 6)

Deletes harness_ext.py and hunter_harness.py with their HarnessX-only
tests (the judge path, verify_judge.py, went in task 5). The harnessx
extra, its mypy override and its uv.lock entries are removed (uv lock
drops only packages; no remaining version changes). The conftest
fixture becomes assert_cold_import; test_gate's two never-import checks
become one allow-list (stdlib, openultrasast, yaml) over the governance
planes' module-level imports, and the skipped live-extra tolerance test
is deleted. Audit rows for the two modules are removed, stage_processors
is reworded, and the module-audit manifest is regenerated (no orphan).

test_removed_plane_references implements Req 2.4 over src, tests and
pyproject.toml: a match must carry a `retired 2026-..` tag (the spec's
own slug is not counted). The README part is a strict xfail until task 8
rewrites the README's plane sections.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

pyproject.toml

@@ -11,15 +11,6 @@ requires-python = ">=3.11"
 dependencies = ["pyyaml>=6.0"]
 
 [project.optional-dependencies]
-# HarnessX is the optional agentic plane (LLM hunter/verifier + self-improvement).
-# SHA-pinned for reproducibility; the heavy transitive footprint (see
-# .kiro/specs/harnessx-self-improving-rulesets/dependency-audit.md) lands ONLY when
-# this extra is installed. The core install declares only PyYAML (plane manifests) and every HarnessX
-# import is guarded by openultrasast.harness_ext (lazy). pip does not pull the
-# recipe/verl_harnessX submodule (it is outside the packaged harnessx* modules).
-harnessx = [
-    "harnessx @ git+https://github.com/Darwin-Agent/HarnessX.git@274c512eea67c64701f992d3b6fe06f0fd590ef0",
-]
 # The plane's memory store on MinIO (OUSAST_MEMORY=minio://<bucket>, plane/memory.py). Imported lazily; the
 # core install and the file store need nothing beyond PyYAML.
 minio = [
@@ -69,12 +60,6 @@ warn_redundant_casts = true
 warn_return_any = true
 warn_unused_configs = true
 
-# HarnessX is an optional extra, absent in the type-check environment; its lazy
-# imports inside guarded functions must not fail mypy.
-[[tool.mypy.overrides]]
-module = "harnessx.*"
-ignore_missing_imports = true
-
 [[tool.mypy.overrides]]
 module = "tree_sitter"
 ignore_missing_imports = true