fix(validate-inputs): surface errors in logs, annotation, and step summary (#299)

Introduce error() helper to:
- write to stderr for log visibility
- emit a titled ::error:: annotation for Checks
- append to GITHUB_STEP_SUMMARY for run summary

Replace ad-hoc echo+exit paths with error() across all validation
branches.

Author: jerop

scripts/validate-inputs.sh

@@ -1,6 +1,24 @@
 #!/bin/bash
 set -euo pipefail
 
+# Emit a clear error in three places:
+# - STDERR (visible in step logs)
+# - GitHub annotation with a title (more visible in Checks)
+# - Step summary (always shown in the job summary)
+error() {
+  local msg="$1"
+  echo "ERROR: ${msg}" >&2
+  echo "::error title=Input validation failed::${msg}"
+  if [[ -n "${GITHUB_STEP_SUMMARY:-}" ]]; then
+    {
+      echo "### Input validation failed"
+      echo
+      echo "- ${msg}"
+    } >> "${GITHUB_STEP_SUMMARY}"
+  fi
+  exit 1
+}
+
 # Auth inputs (as boolean presence flags)
 gemini_api_key_present="${INPUT_GEMINI_API_KEY_PRESENT:-false}"
 google_api_key_present="${INPUT_GOOGLE_API_KEY_PRESENT:-false}"
@@ -19,47 +37,39 @@ if [[ "${google_api_key_present}" == "true" ]]; then ((auth_methods++)); fi
 if [[ "${gcp_workload_identity_provider_present}" == "true" ]]; then ((auth_methods++)); fi
 
 if [[ ${auth_methods} -eq 0 ]]; then
-  echo "::error::No authentication method provided. Please provide one of 'gemini_api_key', 'google_api_key', or 'gcp_workload_identity_provider'."
-  exit 1
+  error "No authentication method provided. Please provide one of 'gemini_api_key', 'google_api_key', or 'gcp_workload_identity_provider'."
 fi
 
 if [[ ${auth_methods} -gt 1 ]]; then
-  echo "::error::Multiple authentication methods provided. Please use only one of 'gemini_api_key', 'google_api_key', or 'gcp_workload_identity_provider'."
-  exit 1
+  error "Multiple authentication methods provided. Please use only one of 'gemini_api_key', 'google_api_key', or 'gcp_workload_identity_provider'."
 fi
 
 # WIF validation
 if [[ "${gcp_workload_identity_provider_present}" == "true" ]]; then
   if [[ "${gcp_project_id_present}" != "true" || "${gcp_service_account_present}" != "true" ]]; then
-    echo "::error::When using Workload Identity Federation ('gcp_workload_identity_provider'), you must also provide 'gcp_project_id' and 'gcp_service_account'."
-    exit 1
+    error "When using Workload Identity Federation ('gcp_workload_identity_provider'), you must also provide 'gcp_project_id' and 'gcp_service_account'."
   fi
   if [[ "${use_vertex_ai}" != "true" && "${use_gemini_code_assist}" != "true" ]]; then
-    echo "::error::When using Workload Identity Federation, you must set either 'use_vertex_ai' or 'use_gemini_code_assist' to 'true'. Both are set to 'false', please choose one."
-    exit 1
+    error "When using Workload Identity Federation, you must set either 'use_vertex_ai' or 'use_gemini_code_assist' to 'true'. Both are set to 'false', please choose one."
   fi
   if [[ "${use_vertex_ai}" == "true" && "${use_gemini_code_assist}" == "true" ]]; then
-    echo "::error::When using Workload Identity Federation, 'use_vertex_ai' and 'use_gemini_code_assist' cannot both be 'true'. Both are set to 'true', please choose one."
-    exit 1
+    error "When using Workload Identity Federation, 'use_vertex_ai' and 'use_gemini_code_assist' cannot both be 'true'. Both are set to 'true', please choose one."
   fi
 fi
 
 # Vertex AI API Key validation
 if [[ "${google_api_key_present}" == "true" ]]; then
   if [[ "${use_vertex_ai}" != "true" ]]; then
-    echo "::error::When using 'google_api_key', you must set 'use_vertex_ai' to 'true'."
-    exit 1
+    error "When using 'google_api_key', you must set 'use_vertex_ai' to 'true'."
   fi
   if [[ "${use_gemini_code_assist}" == "true" ]]; then
-    echo "::error::When using 'google_api_key', 'use_gemini_code_assist' cannot be 'true'."
-    exit 1
+    error "When using 'google_api_key', 'use_gemini_code_assist' cannot be 'true'."
   fi
 fi
 
 # Gemini API Key validation
 if [[ "${gemini_api_key_present}" == "true" ]]; then
   if [[ "${use_vertex_ai}" == "true" || "${use_gemini_code_assist}" == "true" ]]; then
-    echo "::error::When using 'gemini_api_key', both 'use_vertex_ai' and 'use_gemini_code_assist' must be 'false'."
-    exit 1
+    error "When using 'gemini_api_key', both 'use_vertex_ai' and 'use_gemini_code_assist' must be 'false'."
   fi
 fi