Inject Solar throttle gap derived from queue maximum_concurrency

Terraform computes SOLAR_MIN_REQUEST_INTERVAL_SECONDS = N / (0.8 * 600 / 60)
from var.maximum_concurrency (=4.0s at N=32) so the fleet width has one source
of truth and the per-container Solar pacing tracks it automatically.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

deployment/terraform/lambda/modelling_e2e/main.tf

@@ -13,6 +13,17 @@ data "aws_secretsmanager_secret_version" "db_credentials" {
 
 locals {
   db_credentials = jsondecode(data.aws_secretsmanager_secret_version.db_credentials.secret_string)
+
+  # Per-container minimum gap (seconds) between Google Solar API calls. The Solar
+  # API caps the whole GCP project at a hard 600 QPM shared across Building
+  # Insights + Data Layers. Each of the up-to-`maximum_concurrency` containers
+  # loops its ~50-property batch sequentially, so pacing each one to
+  # 0.8 (safety headroom) × 600 QPM ÷ 60 ÷ N keeps the fleet sum under the
+  # ceiling — eliminating the sustained 429 storm that per-process backoff alone
+  # can't ride out. Derived from `maximum_concurrency` so N has one source of
+  # truth. At N=32 → 4.0s. Consumed by the handler's throttle (see
+  # infrastructure/solar/google_solar_api_client.py).
+  solar_min_request_interval_seconds = var.maximum_concurrency / (0.8 * 600 / 60)
 }
 
 module "lambda" {
@@ -42,6 +53,8 @@ module "lambda" {
     OPEN_EPC_API_TOKEN   = var.open_epc_api_token
     GOOGLE_SOLAR_API_KEY = var.google_solar_api_key
     DATA_BUCKET          = "retrofit-data-${var.stage}"
+
+    SOLAR_MIN_REQUEST_INTERVAL_SECONDS = tostring(local.solar_min_request_interval_seconds)
   }
 }