chore(taxonomy): move ANCHOR.a2ml to .machine_readable/6a2/anchor/ + add 6a2 metadata (batch 8/8)

.machine_readable/6a2/0-AI-MANIFEST.a2ml

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+# AI Manifest for 6a2 Directory
+
+## Purpose
+
+This manifest declares the AI-assistant context for the 6a2 machine-readable metadata directory.
+
+## Canonical Locations
+
+The 6 core A2ML files MUST exist in this directory:
+1. AGENTIC.a2ml
+2. ECOSYSTEM.a2ml
+3. META.a2ml
+4. NEUROSYM.a2ml
+5. PLAYBOOK.a2ml
+6. STATE.a2ml
+
+## Invariants
+
+- No duplicate files in root directory
+- Single source of truth: this directory is authoritative
+- No stale metadata
+
+## Protocol
+
+When multiple agents may write to A2ML files concurrently:
+1. Read file and record git-sha-at-read in [provenance] section
+2. Lock by creating .lock-<FILENAME>
+3. Write updated file with new [provenance] metadata
+4. Release by removing lock file
+5. On conflict: re-read and retry if git-sha-at-read does not match HEAD
+

.machine_readable/6a2/README.adoc

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+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+# A2ML 6a2 Directory
+
+This directory contains the 6 core A2ML machine-readable metadata files for this repository.
+
+## Files
+
+- `AGENTIC.a2ml` - AI agent operational gating, safety controls
+- `ECOSYSTEM.a2ml` - Project ecosystem position, relationships, explicit boundaries
+- `META.a2ml` - Architecture decisions (ADRs), development practices, design rationale
+- `NEUROSYM.a2ml` - Symbolic semantics, composition algebra
+- `PLAYBOOK.a2ml` - Executable plans, operational runbooks
+- `STATE.a2ml` - Project state, phase, milestones, session history
+
+## Standards Compliance
+
+These files follow the A2ML Format Family specification from:
+https://github.com/hyperpolymath/standards/tree/main/a2ml
+
+## Generation
+
+These files may be generated from .scm source files using transpilation tools.
+Source .scm files should be removed after successful transpilation.
+
+## See Also
+
+- [A2ML Repository Template](https://github.com/hyperpolymath/standards/blob/main/A2ML-REPO-TEMPLATE.adoc)
+- [6A2 Format Family](https://github.com/hyperpolymath/standards#a2ml-format-family-7-formats)
+