[Bug] gemini-stage-0 creates the corpus GCS bucket but never grants the Discovery Engine service agent storage.objectViewer on it — gem4gov datastore import then fails every document with PERMISSION_DENIED #145

Bug Description

In gemini-stage-0, discovery-engine.tf creates a GCS bucket (google_storage_bucket.gemini_enterprise_gcs_bucket) for the document corpus when create_bucket = true, and cmek.tf grants the project's Discovery Engine service agent roles/cloudkms.cryptoKeyEncrypterDecrypter on the CMEK key. But nothing grants that service agent (service-<PROJECT_NUMBER>@gcp-sa-discoveryengine.iam.gserviceaccount.com) roles/storage.objectViewer (or objectUser) on the bucket it just created — iam.tf only binds project-level roles to the admin/user GROUPS, and there is no google_storage_bucket_iam_member for the DE service agent anywhere in the stage. As a result, when the operator later runs gem4gov datastore import --source-type=gcs --gcs-bucket=<that bucket>, the ImportDocuments long-running operation completes done: true / error: null but with failureCount == totalCount: every document fails with code 7 PERMISSION_DENIED — "Permission denied while checking the GCS content of gs://<bucket>/<file>". The data store indexes zero documents. Because gem4gov's import does not poll or surface the per-document result (the counts live only in the operation metadata / response.errorSamples), this looks like a silent success.

Environment and Deployment Context

• Stellar Engine Version/Commit: main (gemini-stage-0/discovery-engine.tf + iam.tf + cmek.tf; gem4gov-cli/data_stores.py import_gcs_documents)
• Deployment Type:
  • US Region Restricted (e.g., Access Policy constraint)
  • FedRAMP Medium
  • FedRAMP High
  • DoD IL4
  • DoD IL5
  • Stand-alone / Custom
• Affected Component: blueprints/fedramp-high/gemini-enterprise/gemini-stage-0/iam.tf (no bucket-scoped grant for the Discovery Engine service agent) + discovery-engine.tf (google_storage_bucket.gemini_enterprise_gcs_bucket).

Steps to Reproduce

1. Run gemini-stage-0 with a GCS data store and create_bucket = true so the stage creates …-<display-name>-data.
2. Copy documents into that bucket.
3. Run gem4gov datastore import --project-id <proj> --source-type=gcs --data-store-id <id> --gcs-bucket <that bucket> and press Enter for the root path.
4. Poll the import operation: metadata.failureCount == metadata.totalCount, response.errorSamples[*].code == 7, message "Permission denied while checking the GCS content of gs://<bucket>/<file>". The data store's documents list is empty.

Expected Behavior

gemini-stage-0 should grant the Discovery Engine service agent read on the corpus bucket it creates, e.g. a google_storage_bucket_iam_member binding roles/storage.objectViewer (or roles/storage.objectUser) for serviceAccount:service-<num>@gcp-sa-discoveryengine.iam.gserviceaccount.com on google_storage_bucket.gemini_enterprise_gcs_bucket — mirroring the CMEK grant it already makes for the same agent. Then a corpus import from that bucket succeeds without a manual IAM step.

Actual Behavior

The stage creates the bucket and the CMEK grant but not the storage grant, so every subsequent document import fails PERMISSION_DENIED and the data store indexes nothing — with no error surfaced by the CLI.

Additional Context

The KMS grant for the same agent is already present (google_kms_crypto_key_iam_member.discoveryengine_sa_kms_access), so the missing piece is a single parallel storage binding. Related: gem4gov's import is fire-and-forget with no polling/validation, which is what makes this failure silent — worth its own hardening (surface failureCount/errorSamples, or poll the LRO).