diff --git a/primitives/envelope-gate/gate.py b/primitives/envelope-gate/gate.py
index 75198bc..1c2c800 100644
--- a/primitives/envelope-gate/gate.py
+++ b/primitives/envelope-gate/gate.py
@@ -5,10 +5,10 @@
     - FIRST_FAIL: halt on first violation (default, frozen at msg-0003).
     - ACCUMULATE_ALL: collect all violations (available for diagnostics).
 
-Decision mapping:
+    Decision mapping:
     - No violations      -> ALLOW
     - Structural violation  -> DENY
-    - Policy violation      -> HOLD
+    - Policy violation     -> HOLD
     - Not addressed to gate -> SILENCE
 
 Deterministic. No side effects. No network calls.
@@ -16,12 +16,16 @@
 
 from __future__ import annotations
 
+import hashlib
 import importlib.util
+import json
+import os
 import sys
 from dataclasses import dataclass, field
 from pathlib import Path
 from typing import List
 
+
 # ---------------------------------------------------------------------------
 # Robust local imports via importlib (avoids sibling gate.py collision)
 # ---------------------------------------------------------------------------
@@ -50,6 +54,7 @@ def _load_local(module_name: str):
 @dataclass(frozen=True)
 class GateResult:
     """Outcome of running an envelope through the conformance gate."""
+
     msg_id: str
     exit: str  # ALLOW | HOLD | DENY | SILENCE
     violations: List[Violation] = field(default_factory=list)
@@ -65,14 +70,44 @@ def _classify_exit(violations: List[Violation]) -> str:
     """Map a list of violations to a gate exit decision."""
     if not violations:
         return Exit.ALLOW.value
+
     # Any R0 structural failure -> DENY (envelope is malformed)
     for v in violations:
         if v.code.startswith("R0_"):
             return Exit.DENY.value
+
     # Everything else -> HOLD (policy or enum issue, fixable)
     return Exit.HOLD.value
 
 
+# ---------------------------------------------------------------------------
+# Geometry Layer v0 -- optional JSONL emission (best-effort, off by default)
+# ---------------------------------------------------------------------------
+
+
+def _sha256_bytes(b: bytes) -> str:
+    """Return hex SHA-256 digest of *b*."""
+    return hashlib.sha256(b).hexdigest()
+
+
+def _canonical_json(obj: dict) -> str:
+    """Canonical JSON: sorted keys, compact separators, no ASCII escaping."""
+    return json.dumps(obj, sort_keys=True, separators=(",", ":"), ensure_ascii=False)
+
+
+def _emit_geometry_event(event: dict) -> None:
+    """Append one JSONL line to GEOMETRY_LOG_PATH if set; silently no-op otherwise."""
+    path = os.environ.get("GEOMETRY_LOG_PATH")
+    if not path:
+        return
+    try:
+        line = _canonical_json(event) + "\n"
+        with open(path, "a", encoding="utf-8") as fh:
+            fh.write(line)
+    except Exception:
+        return
+
+
 def evaluate(
     envelope: Envelope,
     policy: str = "FIRST_FAIL",
@@ -81,7 +116,7 @@ def evaluate(
 
     Args:
         envelope: A parsed Envelope object.
-        policy: "FIRST_FAIL" (default) or "ACCUMULATE_ALL".
+        policy:   "FIRST_FAIL" (default) or "ACCUMULATE_ALL".
 
     Returns:
         GateResult with exit decision and any violations found.
@@ -97,9 +132,26 @@ def evaluate(
             if policy == "FIRST_FAIL":
                 break
 
+    exit_decision = _classify_exit(violations)
+    violation_codes = sorted([v.code for v in violations])
+
+    # -- Geometry Layer v0: optional emission (never throws, never blocks) --
+    _emit_geometry_event({
+        "schema_version": "0.1",
+        "primitive": "envelope-gate",
+        "event": "gate_evaluated",
+        "envelope_id": envelope.msg_id or None,
+        "exit": exit_decision,
+        "violations": violation_codes,
+        "input_hash": _sha256_bytes(envelope.raw.encode("utf-8")),
+        "result_hash": _sha256_bytes(
+            _canonical_json({"exit": exit_decision, "violations": violation_codes}).encode("utf-8")
+        ),
+    })
+
     return GateResult(
         msg_id=envelope.msg_id or "(unknown)",
-        exit=_classify_exit(violations),
+        exit=exit_decision,
         violations=violations,
         rules_checked=rules_checked,
         rules_total=len(ALL_RULES),