From 6defe7eb6c462bb784d1f27f5afe7ca4b627fc70 Mon Sep 17 00:00:00 2001
From: Gille <4317663+helix4u@users.noreply.github.com>
Date: Wed, 26 Aug 2026 13:55:19 -0600
Subject: [PATCH] fix(config): preserve lossy decimal values as strings

---
 hermes_cli/config.py                         | 13 ++++++++++++-
 tests/hermes_cli/test_config_set_coercion.py | 12 ++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/hermes_cli/config.py b/hermes_cli/config.py
index 32d6cbf936..e563d137fc 100644
--- a/hermes_cli/config.py
+++ b/hermes_cli/config.py
@@ -15,6 +15,7 @@ This module provides:
 """
 
 import copy
+from decimal import Decimal, InvalidOperation
 from hermes_cli.cli_output import line_input
 import json
 import logging
@@ -5434,7 +5435,12 @@ def _coerce_int(value: str):
 
 
 def _coerce_float(value: str):
-    """Return float(value) for a clean float literal, else None."""
+    """Return ``float(value)`` when conversion preserves its decimal value.
+
+    Decimal-looking identifiers can be much more precise than a binary float.
+    Silently rounding one here corrupts it before it reaches ``config.yaml``,
+    so values that do not round-trip through ``float`` remain strings.
+    """
     try:
         f = float(value)
     except (TypeError, ValueError):
@@ -5443,6 +5449,11 @@ def _coerce_float(value: str):
     # and round-trip confusingly through YAML.
     if f != f or f in (float("inf"), float("-inf")):
         return None
+    try:
+        if Decimal(value) != Decimal(str(f)):
+            return None
+    except InvalidOperation:
+        return None
     return f
 
 
diff --git a/tests/hermes_cli/test_config_set_coercion.py b/tests/hermes_cli/test_config_set_coercion.py
index 821d3c7d4e..53518a5910 100644
--- a/tests/hermes_cli/test_config_set_coercion.py
+++ b/tests/hermes_cli/test_config_set_coercion.py
@@ -42,6 +42,18 @@ class TestNumericCoercion:
         v = _read(tmp_path, "agent", "max_turns")
         assert v == -2.5 and isinstance(v, float)
 
+    def test_lossy_decimal_identifier_stays_string(self, tmp_path, monkeypatch):
+        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+        client_id = "123456789012.98765432109876"
+
+        cfg.set_config_value("mcp_servers.example.oauth.client_id", client_id)
+
+        saved = _read(
+            tmp_path, "mcp_servers", "example", "oauth", "client_id"
+        )
+        assert saved == client_id
+        assert isinstance(saved, str)
+
 
 class TestNullCoercion:
     @pytest.mark.parametrize("token", ["null", "none", "None", "~"])