fix(telemetry): persist first accounted fallback route

hermes_state.py

@@ -2579,6 +2579,33 @@ class SessionDB:
         )
 
         def _do(conn):
+            row = conn.execute(
+                "SELECT model, billing_provider, api_call_count FROM sessions WHERE id = ?",
+                (session_id,),
+            ).fetchone()
+            existing_model = row["model"] if row is not None else None
+            existing_provider = row["billing_provider"] if row is not None else None
+            existing_api_calls = int((row["api_call_count"] if row is not None else 0) or 0)
+
+            # Session creation records the requested primary route before any API
+            # call. If it fails and fallback succeeds, the first accounted usage
+            # event is the first authoritative route. After that, preserve the
+            # legacy row: one row cannot represent mixed-provider usage.
+            first_accounted_route = (
+                existing_api_calls == 0
+                and bool(model)
+                and bool(billing_provider)
+                and (existing_model != model or existing_provider != billing_provider)
+            )
+            if first_accounted_route:
+                conn.execute(
+                    """UPDATE sessions
+                       SET model = ?, billing_provider = ?,
+                           billing_base_url = COALESCE(?, billing_base_url),
+                           billing_mode = COALESCE(?, billing_mode)
+                       WHERE id = ?""",
+                    (model, billing_provider, billing_base_url, billing_mode, session_id),
+                )
             conn.execute(sql, params)
             if record_model_usage:
                 self._record_model_usage(

tests/test_hermes_state.py

@@ -272,6 +272,43 @@ class TestSessionLifecycle:
         session = db.get_session("s1")
         assert session["model"] == "openai/gpt-5.4"
 
+    def test_first_accounted_fallback_replaces_requested_primary_route(self, db):
+        """First successful fallback usage must persist one coherent route pair."""
+        db.create_session(session_id="s1", source="cli", model="gpt-5.6-sol")
+
+        db.update_token_counts(
+            "s1",
+            input_tokens=10,
+            output_tokens=5,
+            model="glm-5.2",
+            billing_provider="custom:zai",
+            billing_base_url="https://api.z.ai/api/coding/paas/v4/",
+            api_call_count=1,
+        )
+
+        session = db.get_session("s1")
+        assert session["model"] == "glm-5.2"
+        assert session["billing_provider"] == "custom:zai"
+        assert session["billing_base_url"] == "https://api.z.ai/api/coding/paas/v4/"
+        assert session["api_call_count"] == 1
+
+    def test_accounted_primary_route_is_not_rewritten_by_later_fallback(self, db):
+        """A mixed-provider session keeps its first accounted route in the legacy row."""
+        db.create_session(session_id="s1", source="cli", model="gpt-5.6-sol")
+        db.update_token_counts(
+            "s1", input_tokens=10, output_tokens=5, model="gpt-5.6-sol",
+            billing_provider="openai-codex", api_call_count=1,
+        )
+        db.update_token_counts(
+            "s1", input_tokens=10, output_tokens=5, model="glm-5.2",
+            billing_provider="custom:zai", api_call_count=1,
+        )
+
+        session = db.get_session("s1")
+        assert session["model"] == "gpt-5.6-sol"
+        assert session["billing_provider"] == "openai-codex"
+        assert session["api_call_count"] == 2
+
     def test_update_token_counts_preserves_existing_model(self, db):
         db.create_session(session_id="s1", source="cli", model="anthropic/claude-opus-4.6")
         db.update_token_counts("s1", input_tokens=10, output_tokens=5, model="openai/gpt-5.4")