docs(harnessx-removal): the plane replaces HarnessX in README, docs and specs (task 8)

README: "Configuring the HarnessX agentic plane" becomes "The agentic
plane (ax)" (ousast plane run|status|doctor|remember, per-task Model,
budget and egress, pointer to ops/ax/README.md, one tagged retirement
line); "The HarnessX self-improving cycle" becomes "The self-improving
cycle", and its MetaAgent paragraph is replaced by the memory proposer
(`ousast improve --memory`, provenance, train-on-test guard). The fusion
panel_model/decider_model lines and the [harnessx] spend caps are gone.
The README reference test now passes without its strict xfail.

docs/examples.md section 6 runs the plane; docs/threat-model.md describes
the per-task EgressPolicy, the usd/calls budgets and the start-request
credential path. RELEASE_NOTES.md gets an Unreleased entry: HarnessX
removed, the retired keys and their errors, the silent loss of the
second hunter for users who set [models] hunter, and the plane as the
agentic path.

Dated retirement notes (2026-09-30) head the requirements, design and
brief of harnessx-self-improving-rulesets, learning-harness,
three-stage-scan and openrouter-sast-harness, and follow the spec table
in steering/overview.md; history is unchanged. All tasks are checked, so
spec.json moves to implementation-complete.

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

tests/test_removed_plane_references.py

@@ -11,8 +11,6 @@ from __future__ import annotations
 import re
 from pathlib import Path
 
-import pytest
-
 ROOT = Path(__file__).resolve().parents[1]
 _NAME = "harness" + "x"
 _PATTERN = re.compile(_NAME, re.IGNORECASE)
@@ -48,7 +46,6 @@ def test_the_retirement_notes_exist() -> None:
     assert _PATTERN.search(config) and _TAG.search(config)
 
 
-@pytest.mark.xfail(strict=True, reason="the README's plane sections are rewritten in task 8; drop this mark there")
 def test_the_readme_names_the_removed_plane_only_in_its_retirement_note() -> None:
     offenders = _untagged([ROOT / "README.md"])
     assert offenders == [], "\n".join(offenders)