PR#2: Geometry Layer v0 — Instrumentation (gate.py emission hook)

[LalaSkye]

Geometry Layer v0 -- PR#2: Instrumentation

Artefact ref: MORPHEUS_PR2_GEOMETRY_INSTRUMENTATION_stop-machine_fb5b267
Scope: NON_EXEC (no runtime semantic change)
Spec ref: docs/geometry_export_spec_v0.1.md

What this adds

Adds optional GEOMETRY_LOG_PATH JSONL emission; off by default; best-effort; deterministic; no semantic change.

• Three private helper functions: _sha256_bytes, _canonical_json, _emit_geometry_event
• Single hook point at end of evaluate() in gate.py
• Enabled only via GEOMETRY_LOG_PATH env var
• Emission failure silently returns (never throws, never blocks)
• Canonical JSON with sorted keys, SHA-256 hashes
• Stdlib-only imports (hashlib, json, os)
• No new external dependencies

What this does NOT change

• Zero changes to ALLOW/HOLD/DENY/SILENCE semantics
• No imports from analysis/, docs/, artifacts/, examples/
• No wall-clock timestamps
• No CI changes
• No new shared utility modules

Build sequence

This is PR#2 of 4:

• PR#1 (Docs only): Merged
• PR#2 (this): Instrumentation (gate.py emission hook)
• PR#3: CI (geometry-analysis job + drift alarm)
• PR#4: Tests (adversarial fixtures + determinism proxy)