diff --git a/AGENTS.md b/AGENTS.md
index ab10b79..50dfdf1 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -1,5 +1,11 @@
 # GovOPlaN Campaign Codex Guide
 
+## Documentation Contract
+
+- Treat documentation as part of every behavior change. Update this module's manifest-driven `DocumentationTopic` contributions for affected user and administrator behavior.
+- Keep feature content here; `govoplan-docs` projects it without importing Campaign internals.
+- Maintain a static user/admin baseline and run `/mnt/DATA/git/govoplan/tools/checks/check-manifest-shapes.py` after behavior or manifest changes.
+
 ## Scope
 
 This repository owns the `campaigns` module: campaign authoring, validation, message building, attachment resolution, queue/review/send control, reports, campaign module manifest, and `@govoplan/campaign-webui`.
diff --git a/README.md b/README.md
index eca70a7..c93b179 100644
--- a/README.md
+++ b/README.md
@@ -23,6 +23,13 @@ primitives, CSRF/API helpers, shell layout, and route rendering. Tenancy is an
 optional platform module for tenant administration and tenant resolver behavior.
 Files and mail own their respective storage and transport capabilities.
 
+Generated EML is durable execution material, not a node-local runtime cache.
+Campaign stores it through Core's shared object-storage contract under opaque
+Campaign-owned keys; database job rows retain the expected size, digest, and
+Message-ID. Workers resolve and verify the object before delivery. Build
+failure compensates objects written before database commit, and retention keeps
+the database reference when object deletion fails so cleanup can be retried.
+
 ## Dependencies
 
 The module has one required runtime dependency:
diff --git a/docs/CAMPAIGN_DELIVERY_RUNBOOK.md b/docs/CAMPAIGN_DELIVERY_RUNBOOK.md
index 7ad8d8a..c2c3bd5 100644
--- a/docs/CAMPAIGN_DELIVERY_RUNBOOK.md
+++ b/docs/CAMPAIGN_DELIVERY_RUNBOOK.md
@@ -134,6 +134,29 @@ production process manager. Repeat the worker-loss drill under the selected
 systemd, container, Kubernetes, or other production supervisor and the target
 Redis/SMTP infrastructure before deployment approval.
 
+## Shared Build Artifacts
+
+Generated EML is stored through Core's configured object-storage backend under
+opaque Campaign-owned keys. The job records expected byte size, SHA-256 digest,
+and Message-ID. A worker on another node must retrieve and verify those values
+before attempting delivery.
+
+- Do not expose object keys to ordinary campaign users or copy them into
+  business fields.
+- A build failure deletes objects written before the database transaction can
+  commit.
+- Retention clears metadata only after object deletion succeeds; an unavailable
+  backend leaves the reference in place for a later retry.
+- A hard process loss between object creation and metadata commit can leave an
+  orphan object. Reconcile only within the Campaign build prefix and verify that
+  no job references the object before deleting it.
+- Restore Campaign rows, object storage, and the encryption key to one
+  coordinated recovery point before resuming workers.
+
+For a scaled-runtime drill, build on one API replica, consume from another
+worker, compare the stored evidence, and inject storage failures during build
+and retention.
+
 ## Reporting Checks
 
 - Partial delivery must show accepted, failed, and unknown counts separately.
diff --git a/src/govoplan_campaign/backend/manifest.py b/src/govoplan_campaign/backend/manifest.py
index 7da2b71..bac4181 100644
--- a/src/govoplan_campaign/backend/manifest.py
+++ b/src/govoplan_campaign/backend/manifest.py
@@ -28,6 +28,7 @@ from govoplan_core.core.modules import (
     RoleTemplate,
 )
 from govoplan_core.core.operations import OperationalCheckProviderRegistration
+from govoplan_core.core.provider_governance import declared_module_architecture
 from govoplan_core.core.views import ViewSurface
 from govoplan_core.db.base import Base
 from govoplan_core.core.postbox import (
@@ -718,6 +719,37 @@ manifest = ModuleManifest(
                 ],
             },
         ),
+        DocumentationTopic(
+            id="campaigns.reference.shared-build-artifacts",
+            title="Operate Campaign build artifacts across workers",
+            summary="Generated messages use shared object storage and are verified before delivery.",
+            body="Campaign stores generated EML under opaque shared object keys and records expected size, SHA-256 digest, and Message-ID in each job. A worker may run on another node and verifies that evidence before delivery. Failed builds compensate newly written objects; retention retains metadata when deletion fails. Never copy or edit runtime object keys as business data.",
+            layer="evidence",
+            documentation_types=("admin",),
+            audience=("campaign_operator", "platform_operator", "release_reviewer"),
+            order=53,
+            conditions=(
+                DocumentationCondition(
+                    required_modules=("campaigns",),
+                    any_scopes=("campaigns:diagnostic:read", "system:settings:read"),
+                ),
+            ),
+            links=(
+                DocumentationLink(label="Campaign operator queue", href="/campaigns/queue", kind="runtime"),
+                DocumentationLink(label="Campaign delivery runbook", href="govoplan-campaign/docs/CAMPAIGN_DELIVERY_RUNBOOK.md", kind="repository"),
+            ),
+            related_modules=("files", "ops", "mail"),
+            metadata={
+                "kind": "reference",
+                "route": "/campaigns/queue",
+                "screen": "Campaign operator queue",
+                "verification": "Build on one replica, deliver from another, verify object digest/size evidence, and exercise storage failure during build and retention.",
+                "limitations": [
+                    "A hard process loss between object creation and database commit can leave an orphan object until an inventory reconciler removes it.",
+                    "Database, object storage, and encryption keys require a coordinated deployment backup and restore procedure.",
+                ],
+            },
+        ),
     ),
     documentation_providers=(documentation_topics,),
     ownership_providers=(
@@ -762,6 +794,19 @@ manifest = ModuleManifest(
             cache_seconds=60,
         ),
     ),
+    architecture=declared_module_architecture(
+        layer="communication_participation",
+        kind="domain",
+        maturity="vertical_slice",
+        documentation_ref="docs/CAMPAIGN_HANDBOOK.md",
+        test_ref="tests/test_execution_snapshot_integrity.py",
+        known_limits=("Target-environment recovery and accessibility evidence is incomplete for reference-ready maturity.",),
+        owned_concepts=("campaign", "campaign version", "recipient snapshot", "delivery job", "delivery report"),
+        non_owned_concepts=("mail transport", "postbox", "durable address directory", "file storage"),
+        recovery_docs=("docs/CAMPAIGN_DELIVERY_RUNBOOK.md",),
+        security_docs=("docs/ACCESS_EXPLANATION_COVERAGE.md",),
+        operations_docs=("docs/CAMPAIGN_DELIVERY_RUNBOOK.md",),
+    ),
 )
 
 
diff --git a/src/govoplan_campaign/backend/operational_checks.py b/src/govoplan_campaign/backend/operational_checks.py
index 906827b..c3e5bc4 100644
--- a/src/govoplan_campaign/backend/operational_checks.py
+++ b/src/govoplan_campaign/backend/operational_checks.py
@@ -1,55 +1,56 @@
 from __future__ import annotations
 
-import os
 import secrets
-from pathlib import Path
 
+from govoplan_core.core.object_storage import (
+    StorageBackendError,
+    configured_storage_backend,
+)
 from govoplan_core.core.operations import OperationalCheck
-from govoplan_campaign.backend.persistence.campaigns import BUILD_OUTPUT_DIR
+from govoplan_core.settings import settings as core_settings
+from govoplan_campaign.backend.runtime import get_settings
 
 
 def generated_eml_storage_check() -> OperationalCheck:
-    """Verify the current EML evidence path and report its node-local boundary."""
+    """Verify Campaign evidence against the deployment object-store boundary."""
 
-    root = Path(BUILD_OUTPUT_DIR)
-    probe = root / ".govoplan-health" / f"{secrets.token_hex(16)}.probe"
+    storage = configured_storage_backend(get_settings() or core_settings)
+    probe = f"campaign-artifacts/.health/{secrets.token_hex(16)}.probe"
     payload = secrets.token_bytes(64)
     try:
-        probe.parent.mkdir(parents=True, mode=0o700, exist_ok=True)
-        with probe.open("xb") as handle:
-            handle.write(payload)
-            handle.flush()
-            os.fsync(handle.fileno())
-        if probe.read_bytes() != payload:
+        storage.put_bytes(probe, payload, content_type="application/octet-stream")
+        if storage.get_bytes(probe) != payload:
             raise OSError("generated EML persistence returned different bytes")
-    except OSError as exc:
+    except (OSError, StorageBackendError) as exc:
         return OperationalCheck(
             id="campaign.generated_eml_storage",
             label="Generated Campaign EML evidence",
             state="error",
             detail=(
-                "The generated EML evidence path failed a bounded durable-write probe "
+                "The generated EML object store failed a bounded write/read probe "
                 f"({type(exc).__name__})."
             ),
             readiness_critical=True,
-            metrics={"backend": "node_local_filesystem"},
+            metrics={"backend": storage.name},
         )
     finally:
         try:
-            probe.unlink(missing_ok=True)
-            probe.parent.rmdir()
-        except OSError:
+            storage.delete(probe)
+        except StorageBackendError:
             pass
 
+    node_local = storage.name == "local"
     return OperationalCheck(
         id="campaign.generated_eml_storage",
         label="Generated Campaign EML evidence",
-        state="warning",
+        state="warning" if node_local else "ok",
         detail=(
-            "Generated EML passed a local write/fsync/read probe, but remains node-local. "
-            "Use one shared runtime volume and include it in coordinated backups until "
-            "Campaign evidence is migrated to managed object storage."
+            "Generated EML passed the object-store write/read/delete probe. "
+            + (
+                "The configured backend is node-local and is suitable only for a single-node profile."
+                if node_local
+                else "The configured backend is shared across application and worker nodes."
+            )
         ),
-        metrics={"backend": "node_local_filesystem"},
+        metrics={"backend": storage.name},
     )
-
diff --git a/src/govoplan_campaign/backend/persistence/campaigns.py b/src/govoplan_campaign/backend/persistence/campaigns.py
index a0a9ee7..ceef032 100644
--- a/src/govoplan_campaign/backend/persistence/campaigns.py
+++ b/src/govoplan_campaign/backend/persistence/campaigns.py
@@ -2,18 +2,24 @@ from __future__ import annotations
 
 import copy
 import hashlib
-import json
-import os
+from dataclasses import dataclass
 from datetime import UTC, datetime
 from email import policy
 from email.parser import BytesParser
 from pathlib import Path
+from tempfile import TemporaryDirectory
 from typing import Any
 from uuid import uuid4
 
 from sqlalchemy import func
 from sqlalchemy.orm import Session
 
+from govoplan_core.core.object_storage import (
+    StorageBackend,
+    StorageBackendError,
+    configured_storage_backend,
+)
+from govoplan_core.settings import settings as core_settings
 from govoplan_campaign.backend.db.models import (
     Campaign,
     CampaignIssue,
@@ -52,20 +58,19 @@ from govoplan_campaign.backend.integrations import (
     postbox_integration,
 )
 from govoplan_campaign.backend.path_security import assert_server_safe_campaign_paths
-
-RUNTIME_DIR = Path(__file__).resolve().parents[3] / "runtime"
-CAMPAIGN_SNAPSHOT_DIR = RUNTIME_DIR / "campaign_snapshots"
-BUILD_OUTPUT_DIR = RUNTIME_DIR / "generated_eml"
+from govoplan_campaign.backend.runtime import get_settings
 
 
 class CampaignPersistenceError(RuntimeError):
     pass
 
 
-def _ensure_dirs() -> None:
-    for directory in (CAMPAIGN_SNAPSHOT_DIR, BUILD_OUTPUT_DIR):
-        directory.mkdir(parents=True, mode=0o700, exist_ok=True)
-        directory.chmod(0o700)
+@dataclass(frozen=True, slots=True)
+class _StoredEmlArtifact:
+    storage_key: str
+    size_bytes: int
+    sha256: str
+    message_id_header: str | None
 
 
 
@@ -107,22 +112,82 @@ def load_campaign_config_from_json(
     return CampaignConfig.model_validate(materialized)
 
 
-def _write_campaign_snapshot(version: CampaignVersion) -> Path:
-    _ensure_dirs()
-    path = CAMPAIGN_SNAPSHOT_DIR / f"{version.id}.json"
-    flags = os.O_WRONLY | os.O_CREAT | os.O_TRUNC
-    if hasattr(os, "O_NOFOLLOW"):
-        flags |= os.O_NOFOLLOW
-    descriptor = os.open(path, flags, 0o600)
+def _campaign_reference_path(version: CampaignVersion) -> Path:
+    """Return a path anchor without persisting a second configuration copy."""
+
+    source_base_path = str(version.source_base_path or "").strip()
+    base = Path(source_base_path).expanduser().resolve() if source_base_path else Path.cwd()
+    return base / "campaign.json"
+
+
+def _object_storage() -> StorageBackend:
+    return configured_storage_backend(get_settings() or core_settings)
+
+
+def _persist_built_eml_artifacts(
+    *,
+    storage: StorageBackend,
+    tenant_id: str,
+    campaign_id: str,
+    version_id: str,
+    build_id: str,
+    built_messages: list[Any],
+) -> dict[int, _StoredEmlArtifact]:
+    artifacts: dict[int, _StoredEmlArtifact] = {}
     try:
-        os.fchmod(descriptor, 0o600)
-        with os.fdopen(descriptor, "w", encoding="utf-8") as stream:
-            descriptor = -1
-            json.dump(version.raw_json, stream, ensure_ascii=False, indent=2)
-    finally:
-        if descriptor >= 0:
-            os.close(descriptor)
-    return path
+        for built in built_messages:
+            message = built.draft
+            if not message.eml_path:
+                continue
+            path = Path(message.eml_path)
+            if not path.is_file():
+                raise CampaignPersistenceError(
+                    "Generated EML evidence is missing for entry "
+                    f"{message.entry_index}"
+                )
+            payload = path.read_bytes()
+            digest = hashlib.sha256(payload).hexdigest()
+            parsed = BytesParser(policy=policy.default).parsebytes(payload)
+            message_id = parsed.get("Message-ID")
+            storage_key = (
+                f"campaign-artifacts/{tenant_id}/{campaign_id}/{version_id}/"
+                f"{build_id}/{message.entry_index:08d}-{digest}.eml"
+            )
+            try:
+                storage.put_bytes(
+                    storage_key,
+                    payload,
+                    content_type="message/rfc822",
+                )
+            except StorageBackendError as exc:
+                raise CampaignPersistenceError(
+                    f"Generated EML evidence could not be persisted: {exc}"
+                ) from exc
+            artifacts[message.entry_index] = _StoredEmlArtifact(
+                storage_key=storage_key,
+                size_bytes=len(payload),
+                sha256=digest,
+                message_id_header=str(message_id) if message_id else None,
+            )
+            message.eml_path = None
+            message.eml_size_bytes = len(payload)
+    except Exception:
+        _delete_storage_keys(
+            storage,
+            [artifact.storage_key for artifact in artifacts.values()],
+        )
+        raise
+    return artifacts
+
+
+def _delete_storage_keys(storage: StorageBackend, keys: list[str]) -> None:
+    for key in keys:
+        try:
+            storage.delete(key)
+        except StorageBackendError:
+            # A committed build remains authoritative. Reconciliation can
+            # remove an orphaned superseded object later.
+            continue
 
 
 def _next_version_number(session: Session, campaign_id: str) -> int:
@@ -143,11 +208,11 @@ def normalize_campaign_paths(raw_json: dict[str, Any], source_base_path: str | P
     """Resolve paths for an explicitly trusted, file-oriented import.
 
     The CLI naturally resolves relative paths against the campaign.json file.
-    Once the campaign is stored in the database, the JSON snapshot lives in
-    app/mailer/runtime/campaign_snapshots. To keep existing file-based
-    campaigns working, relative file paths are normalized to absolute paths at
-    import time when a source_base_path is known. HTTP/API callers are rejected
-    by ``assert_server_safe_campaign_paths`` before they can reach this helper.
+    Once the campaign is stored in the database, its JSON is authoritative.
+    To keep existing file-based campaigns working, relative file paths are
+    normalized to absolute paths at import time when a source_base_path is
+    known. HTTP/API callers are rejected by
+    ``assert_server_safe_campaign_paths`` before they can reach this helper.
     """
     base = Path(source_base_path).expanduser().resolve() if source_base_path else None
     data = copy.deepcopy(raw_json)
@@ -232,7 +297,6 @@ def create_campaign_version_from_json(
     campaign.current_version_id = version.id
     session.add(campaign)
     if commit:
-        _write_campaign_snapshot(version)
         session.commit()
     else:
         session.flush()
@@ -299,7 +363,7 @@ def load_version_config(session: Session, version_id: str):
         raw_json,
         managed_files_available=files_integration().available,
     )
-    path = _write_campaign_snapshot(version)
+    path = _campaign_reference_path(version)
     return version, path, load_campaign_config_from_json(session, tenant_id=campaign.tenant_id, raw_json=raw_json, campaign_id=campaign.id)
 
 
@@ -391,8 +455,6 @@ def validate_campaign_version(
         version.workflow_state = CampaignVersionWorkflowState.APPROVED.value
         version.is_complete = True
         if lock_on_success and version.locked_at is None:
-            from datetime import UTC, datetime
-
             version.locked_at = datetime.now(UTC)
             version.locked_by_user_id = user_id
     else:
@@ -426,9 +488,13 @@ def _job_from_message(
     version_id: str,
     message: MessageDraft,
     resolved_postbox_targets: list[dict[str, Any]] | None = None,
+    stored_eml: _StoredEmlArtifact | None = None,
 ) -> CampaignJob:
     recipient_email = message.to[0].email if message.to else None
     eml_sha256, message_id_header = _eml_evidence(message.eml_path)
+    if stored_eml is not None:
+        eml_sha256 = stored_eml.sha256
+        message_id_header = stored_eml.message_id_header
     return CampaignJob(
         tenant_id=tenant_id,
         campaign_id=campaign_id,
@@ -438,8 +504,9 @@ def _job_from_message(
         recipient_email=recipient_email,
         subject=message.subject,
         message_id_header=message_id_header,
-        eml_local_path=message.eml_path,
-        eml_size_bytes=message.eml_size_bytes,
+        eml_storage_key=stored_eml.storage_key if stored_eml else None,
+        eml_local_path=message.eml_path if stored_eml is None else None,
+        eml_size_bytes=stored_eml.size_bytes if stored_eml else message.eml_size_bytes,
         eml_sha256=eml_sha256,
         build_status=message.build_status.value if hasattr(message.build_status, "value") else str(message.build_status),
         validation_status=_job_validation_status(message.validation_status.value),
@@ -531,7 +598,18 @@ def _replace_version_jobs(
     version_id: str,
     built_messages: list[Any],
     postbox_targets_by_index: dict[int, list[dict[str, Any]]],
-) -> list[tuple[CampaignJob, MessageDraft]]:
+    stored_eml_by_index: dict[int, _StoredEmlArtifact],
+) -> tuple[list[tuple[CampaignJob, MessageDraft]], list[str]]:
+    old_storage_keys = [
+        str(key)
+        for (key,) in session.query(CampaignJob.eml_storage_key)
+        .filter(
+            CampaignJob.campaign_version_id == version_id,
+            CampaignJob.eml_storage_key.is_not(None),
+        )
+        .all()
+        if key
+    ]
     session.query(CampaignIssue).filter(
         CampaignIssue.campaign_version_id == version_id,
         CampaignIssue.job_id.is_not(None),
@@ -547,11 +625,12 @@ def _replace_version_jobs(
             version_id=version_id,
             message=built.draft,
             resolved_postbox_targets=postbox_targets_by_index.get(built.draft.entry_index, []),
+            stored_eml=stored_eml_by_index.get(built.draft.entry_index),
         )
         session.add(job)
         pairs.append((job, built.draft))
     session.flush()
-    return pairs
+    return pairs, old_storage_keys
 
 
 def _mail_execution_profile(
@@ -664,71 +743,112 @@ def build_campaign_version(
         raise CampaignPersistenceError("Campaign version must be successfully validated before messages are built")
     _ensure_version_validated_and_locked(version)
 
-    output_dir = BUILD_OUTPUT_DIR / campaign.id / version.id
     files = files_integration()
-    with files.prepared_campaign_snapshot(
-        session,
-        tenant_id=tenant_id,
-        campaign_id=campaign.id,
-        raw_json=version.raw_json if isinstance(version.raw_json, dict) else {},
-        include_bytes=True,
-        prefix="govoplan-managed-build-",
-    ) as prepared:
-        managed_raw = load_campaign_json(prepared.path)
-        managed_config = load_campaign_config_from_json(session, tenant_id=tenant_id, raw_json=managed_raw, campaign_id=campaign.id)
-        result = build_campaign_messages(managed_config, campaign_file=prepared.path, output_dir=output_dir, write_eml=write_eml)
-        files.annotate_built_messages_with_managed_files(result.built_messages, prepared.managed_files_by_local_path)
-        entries_by_index = {
-            index: entry
-            for index, entry in enumerate(
-                load_campaign_entries(
-                    managed_config,
-                    campaign_file=prepared.path,
-                ),
-                start=1,
-            )
-        }
-        resolved_postbox_targets_by_index = _resolve_built_postbox_targets(
+    storage = _object_storage()
+    build_id = uuid4().hex
+    with TemporaryDirectory(prefix="govoplan-campaign-build-") as output_directory:
+        with files.prepared_campaign_snapshot(
             session,
             tenant_id=tenant_id,
-            config=managed_config,
+            campaign_id=campaign.id,
+            raw_json=version.raw_json if isinstance(version.raw_json, dict) else {},
+            include_bytes=True,
+            prefix="govoplan-managed-build-",
+        ) as prepared:
+            managed_raw = load_campaign_json(prepared.path)
+            managed_config = load_campaign_config_from_json(
+                session,
+                tenant_id=tenant_id,
+                raw_json=managed_raw,
+                campaign_id=campaign.id,
+            )
+            result = build_campaign_messages(
+                managed_config,
+                campaign_file=prepared.path,
+                output_dir=Path(output_directory),
+                write_eml=write_eml,
+            )
+            files.annotate_built_messages_with_managed_files(
+                result.built_messages,
+                prepared.managed_files_by_local_path,
+            )
+            entries_by_index = {
+                index: entry
+                for index, entry in enumerate(
+                    load_campaign_entries(
+                        managed_config,
+                        campaign_file=prepared.path,
+                    ),
+                    start=1,
+                )
+            }
+            resolved_postbox_targets_by_index = _resolve_built_postbox_targets(
+                session,
+                tenant_id=tenant_id,
+                config=managed_config,
+                built_messages=result.built_messages,
+                entries_by_index=entries_by_index,
+            )
+        stored_eml_by_index = _persist_built_eml_artifacts(
+            storage=storage,
+            tenant_id=tenant_id,
+            campaign_id=campaign.id,
+            version_id=version.id,
+            build_id=build_id,
             built_messages=result.built_messages,
-            entries_by_index=entries_by_index,
         )
-    report_json = _campaign_build_report(result, files)
-    report_json["built_by_user_id"] = user_id
-    version.build_summary = report_json
-    editor_state = copy.deepcopy(version.editor_state or {})
-    editor_state.pop("review_send", None)
-    version.editor_state = editor_state
+    new_storage_keys = [item.storage_key for item in stored_eml_by_index.values()]
+    try:
+        report_json = _campaign_build_report(result, files)
+        report_json["built_by_user_id"] = user_id
+        version.build_summary = report_json
+        editor_state = copy.deepcopy(version.editor_state or {})
+        editor_state.pop("review_send", None)
+        version.editor_state = editor_state
 
-    job_build_pairs = _replace_version_jobs(
-        session,
-        tenant_id=tenant_id,
-        campaign_id=campaign.id,
-        version_id=version.id,
-        built_messages=result.built_messages,
-        postbox_targets_by_index=resolved_postbox_targets_by_index,
-    )
-    jobs = [job for job, _message in job_build_pairs]
-    files.record_campaign_attachment_uses_for_jobs(session, jobs, stage="built")
-    _store_execution_snapshot(session, version=version, config=managed_config, jobs=jobs, build_summary=report_json)
-    _store_job_issues(
-        session,
-        tenant_id=tenant_id,
-        campaign_id=campaign.id,
-        version_id=version.id,
-        job_build_pairs=job_build_pairs,
-    )
-    _apply_campaign_build_state(
-        campaign,
-        version,
-        needs_review_count=result.report.needs_review_count,
-        blocked_count=result.report.blocked_count,
-        queueable_count=result.report.queueable_count,
-    )
+        job_build_pairs, old_storage_keys = _replace_version_jobs(
+            session,
+            tenant_id=tenant_id,
+            campaign_id=campaign.id,
+            version_id=version.id,
+            built_messages=result.built_messages,
+            postbox_targets_by_index=resolved_postbox_targets_by_index,
+            stored_eml_by_index=stored_eml_by_index,
+        )
+        jobs = [job for job, _message in job_build_pairs]
+        files.record_campaign_attachment_uses_for_jobs(
+            session,
+            jobs,
+            stage="built",
+        )
+        _store_execution_snapshot(
+            session,
+            version=version,
+            config=managed_config,
+            jobs=jobs,
+            build_summary=report_json,
+        )
+        _store_job_issues(
+            session,
+            tenant_id=tenant_id,
+            campaign_id=campaign.id,
+            version_id=version.id,
+            job_build_pairs=job_build_pairs,
+        )
+        _apply_campaign_build_state(
+            campaign,
+            version,
+            needs_review_count=result.report.needs_review_count,
+            blocked_count=result.report.blocked_count,
+            queueable_count=result.report.queueable_count,
+        )
 
-    session.add(version)
-    session.add(campaign)
-    session.commit()
+        session.add(version)
+        session.add(campaign)
+        session.commit()
+    except Exception:
+        session.rollback()
+        _delete_storage_keys(storage, new_storage_keys)
+        raise
+    _delete_storage_keys(storage, old_storage_keys)
     return report_json
diff --git a/src/govoplan_campaign/backend/persistence/versions.py b/src/govoplan_campaign/backend/persistence/versions.py
index a7aed2c..b857228 100644
--- a/src/govoplan_campaign/backend/persistence/versions.py
+++ b/src/govoplan_campaign/backend/persistence/versions.py
@@ -38,7 +38,6 @@ from govoplan_campaign.backend.integrations import files_integration, mail_integ
 from govoplan_campaign.backend.persistence.campaigns import (
     CampaignPersistenceError,
     _next_version_number,
-    _write_campaign_snapshot,
     normalize_campaign_paths,
 )
 from govoplan_campaign.backend.path_security import assert_server_safe_campaign_paths
@@ -250,7 +249,6 @@ def create_minimal_campaign(
     campaign.current_version_id = version.id
     session.add(campaign)
     if commit:
-        _write_campaign_snapshot(version)
         session.commit()
     else:
         session.flush()
@@ -435,7 +433,6 @@ def _persist_forked_version(
     campaign.status = CampaignStatus.DRAFT.value
     session.add(campaign)
     if commit:
-        _write_campaign_snapshot(version)
         session.commit()
     else:
         session.flush()
@@ -705,7 +702,6 @@ def _persist_updated_version(
     session.add(campaign)
     session.flush()
     if commit:
-        _write_campaign_snapshot(version)
         session.commit()
     else:
         session.flush()
diff --git a/src/govoplan_campaign/backend/retention.py b/src/govoplan_campaign/backend/retention.py
index d35b576..c3c13dd 100644
--- a/src/govoplan_campaign/backend/retention.py
+++ b/src/govoplan_campaign/backend/retention.py
@@ -9,7 +9,15 @@ from typing import Any, Callable
 
 from sqlalchemy.orm import Session
 
+from govoplan_core.core.object_storage import (
+    StorageBackend,
+    StorageBackendError,
+    StorageObjectMissing,
+    configured_storage_backend,
+)
+from govoplan_core.settings import settings as core_settings
 from govoplan_campaign.backend.db.models import CampaignJob, CampaignVersion, JobImapStatus, JobQueueStatus
+from govoplan_campaign.backend.runtime import get_settings
 
 FINAL_VERSION_STATES = {
     "completed",
@@ -111,8 +119,16 @@ def _apply_eml_retention(
     dry_run: bool,
     now: datetime,
     policy_for_campaign_id: Callable[[str | None], object],
+    storage: StorageBackend | None = None,
 ) -> dict[str, int]:
-    result = {"eligible": 0, "metadata_cleared": 0, "files_deleted": 0, "files_missing": 0, "skipped_not_final": 0}
+    result = {
+        "eligible": 0,
+        "metadata_cleared": 0,
+        "files_deleted": 0,
+        "files_missing": 0,
+        "delete_failed": 0,
+        "skipped_not_final": 0,
+    }
     jobs = (
         session.query(CampaignJob)
         .filter((CampaignJob.eml_local_path.is_not(None)) | (CampaignJob.eml_storage_key.is_not(None)))
@@ -137,6 +153,21 @@ def _apply_eml_retention(
         result["eligible"] += 1
         if dry_run:
             continue
+        if job.eml_storage_key:
+            active_storage = storage or configured_storage_backend(
+                get_settings() or core_settings
+            )
+            try:
+                if active_storage.exists(job.eml_storage_key):
+                    active_storage.delete(job.eml_storage_key)
+                    result["files_deleted"] += 1
+                else:
+                    result["files_missing"] += 1
+            except StorageObjectMissing:
+                result["files_missing"] += 1
+            except StorageBackendError:
+                result["delete_failed"] += 1
+                continue
         if job.eml_local_path:
             path = Path(job.eml_local_path)
             if path.exists():
diff --git a/src/govoplan_campaign/backend/route_support.py b/src/govoplan_campaign/backend/route_support.py
index cd633ec..1c45bcd 100644
--- a/src/govoplan_campaign/backend/route_support.py
+++ b/src/govoplan_campaign/backend/route_support.py
@@ -645,17 +645,9 @@ def _clear_current_version_mail_profile_for_owner_transfer(
 
 
 def _write_current_version_snapshot_if_available(version: CampaignVersion) -> None:
-    try:
-        from govoplan_campaign.backend.persistence.campaigns import (
-            _write_campaign_snapshot,
-        )
-
-        _write_campaign_snapshot(version)
-    except Exception:
-        # The database state is authoritative for the WebUI. Snapshot writing is
-        # best-effort here because ownership changes should not fail due to an
-        # unavailable local runtime directory.
-        return
+    # Kept as a compatibility no-op for callers outside this package. Campaign
+    # JSON is database-authoritative and no longer mirrored onto an API node.
+    del version
 
 
 def bounded_query_rows(query, *, limit: int, label: str):
diff --git a/src/govoplan_campaign/backend/sending/jobs.py b/src/govoplan_campaign/backend/sending/jobs.py
index ffc68c6..f53531f 100644
--- a/src/govoplan_campaign/backend/sending/jobs.py
+++ b/src/govoplan_campaign/backend/sending/jobs.py
@@ -16,6 +16,10 @@ from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm import Session
 
 from govoplan_core.core.notifications import NotificationDispatchRequest, notification_dispatch_provider
+from govoplan_core.core.object_storage import (
+    StorageBackendError,
+    configured_storage_backend,
+)
 from govoplan_core.audit.logging import audit_event
 from govoplan_core.security.redaction import redact_secret_values
 from govoplan_core.settings import settings as core_settings
@@ -53,7 +57,7 @@ from govoplan_campaign.backend.sending.postbox_delivery import (
     PostboxChannelOutcome,
     deliver_campaign_job_to_postboxes,
 )
-from govoplan_campaign.backend.runtime import get_registry
+from govoplan_campaign.backend.runtime import get_registry, get_settings
 from govoplan_campaign.backend.integrations import (
     ImapAppendError,
     ImapConfigurationError,
@@ -2389,6 +2393,17 @@ def _verify_eml_evidence(job: CampaignJob, payload: bytes) -> None:
 
 
 def _load_eml_bytes_for_job(job: CampaignJob) -> bytes:
+    if job.eml_storage_key:
+        try:
+            payload = configured_storage_backend(
+                get_settings() or core_settings
+            ).get_bytes(job.eml_storage_key)
+        except StorageBackendError as exc:
+            raise SendJobError(
+                f"Generated EML object could not be read for job {job.id}: {exc}"
+            ) from exc
+        _verify_eml_evidence(job, payload)
+        return payload
     if job.eml_local_path:
         path = Path(job.eml_local_path)
         if not path.exists():
@@ -2396,7 +2411,7 @@ def _load_eml_bytes_for_job(job: CampaignJob) -> bytes:
         payload = path.read_bytes()
         _verify_eml_evidence(job, payload)
         return payload
-    raise SendJobError("Only local EML paths are supported for sending in this implementation step")
+    raise SendJobError("Generated EML evidence is not available for this job")
 
 
 def _load_eml_for_job(job: CampaignJob):
diff --git a/tests/test_campaign_optimistic_concurrency.py b/tests/test_campaign_optimistic_concurrency.py
index 7353ec1..e69d73d 100644
--- a/tests/test_campaign_optimistic_concurrency.py
+++ b/tests/test_campaign_optimistic_concurrency.py
@@ -92,9 +92,6 @@ class CampaignOptimisticConcurrencyTests(unittest.TestCase):
                 "govoplan_campaign.backend.persistence.versions._updated_runtime_json",
                 side_effect=lambda _session, **kwargs: kwargs["raw_json"],
             ),
-            patch(
-                "govoplan_campaign.backend.persistence.versions._write_campaign_snapshot"
-            ),
         ):
             return update_campaign_version(
                 session,
diff --git a/tests/test_operational_checks.py b/tests/test_operational_checks.py
index cfe4041..482840d 100644
--- a/tests/test_operational_checks.py
+++ b/tests/test_operational_checks.py
@@ -2,17 +2,17 @@ from __future__ import annotations
 
 from unittest.mock import patch
 
+from govoplan_core.core.object_storage import LocalFilesystemStorageBackend
 from govoplan_campaign.backend.operational_checks import generated_eml_storage_check
 
 
 def test_generated_eml_probe_reports_node_local_boundary(tmp_path) -> None:
     with patch(
-        "govoplan_campaign.backend.operational_checks.BUILD_OUTPUT_DIR",
-        tmp_path,
+        "govoplan_campaign.backend.operational_checks.configured_storage_backend",
+        return_value=LocalFilesystemStorageBackend(tmp_path),
     ):
         result = generated_eml_storage_check()
 
     assert result.state == "warning"
     assert "node-local" in result.detail
     assert list(tmp_path.rglob("*.probe")) == []
-
diff --git a/tests/test_response_security.py b/tests/test_response_security.py
index 564b655..929c54f 100644
--- a/tests/test_response_security.py
+++ b/tests/test_response_security.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import stat
 import unittest
 from datetime import UTC, datetime
 from types import SimpleNamespace
@@ -307,20 +306,18 @@ def test_diagnostics_permission_is_operator_only_by_default() -> None:
     assert "campaigns:diagnostic:read" not in role_permissions["campaign_reviewer"]
 
 
-def test_campaign_snapshot_with_inline_credentials_is_owner_only(tmp_path, monkeypatch) -> None:
+def test_database_campaign_config_is_not_mirrored_to_node_local_disk(tmp_path) -> None:
     from govoplan_campaign.backend.persistence import campaigns as persistence
 
-    snapshots = tmp_path / "snapshots"
-    output = tmp_path / "generated"
-    monkeypatch.setattr(persistence, "CAMPAIGN_SNAPSHOT_DIR", snapshots)
-    monkeypatch.setattr(persistence, "BUILD_OUTPUT_DIR", output)
-    path = persistence._write_campaign_snapshot(  # type: ignore[arg-type]
-        SimpleNamespace(id="version-secret", raw_json={"server": {"smtp": {"password": "secret"}}})
+    path = persistence._campaign_reference_path(  # type: ignore[arg-type]
+        SimpleNamespace(
+            source_base_path=str(tmp_path),
+            raw_json={"server": {"smtp": {"password": "secret"}}},
+        )
     )
 
-    assert stat.S_IMODE(path.stat().st_mode) == 0o600
-    assert stat.S_IMODE(snapshots.stat().st_mode) == 0o700
-    assert stat.S_IMODE(output.stat().st_mode) == 0o700
+    assert path == tmp_path / "campaign.json"
+    assert list(tmp_path.iterdir()) == []
 
 
 class ResponseSecurityTests(unittest.TestCase):
diff --git a/tests/test_server_path_security.py b/tests/test_server_path_security.py
index 135dc9f..8ebdd65 100644
--- a/tests/test_server_path_security.py
+++ b/tests/test_server_path_security.py
@@ -79,13 +79,13 @@ class ServerCampaignPathSecurityTests(unittest.TestCase):
                 "govoplan_campaign.backend.persistence.campaigns.files_integration",
                 return_value=SimpleNamespace(available=True),
             ),
-            patch("govoplan_campaign.backend.persistence.campaigns._write_campaign_snapshot") as write_snapshot,
+            patch("govoplan_campaign.backend.persistence.campaigns._campaign_reference_path") as reference_path,
             patch("govoplan_campaign.backend.persistence.campaigns.load_campaign_config_from_json") as load_config,
         ):
             with self.assertRaisesRegex(CampaignPathSecurityError, "template source paths"):
                 load_version_config(session, "version-1")  # type: ignore[arg-type]
 
-        write_snapshot.assert_not_called()
+        reference_path.assert_not_called()
         load_config.assert_not_called()
 
     def test_source_base_symlink_escape_is_rejected(self) -> None:
diff --git a/tests/test_shared_artifact_storage.py b/tests/test_shared_artifact_storage.py
new file mode 100644
index 0000000..3c8b935
--- /dev/null
+++ b/tests/test_shared_artifact_storage.py
@@ -0,0 +1,129 @@
+from __future__ import annotations
+
+import hashlib
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+from types import SimpleNamespace
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from govoplan_core.core.object_storage import (
+    LocalFilesystemStorageBackend,
+    StorageBackendError,
+)
+from govoplan_campaign.backend.persistence.campaigns import (
+    CampaignPersistenceError,
+    _persist_built_eml_artifacts,
+)
+from govoplan_campaign.backend.retention import _apply_eml_retention
+from govoplan_campaign.backend.sending.jobs import _load_eml_bytes_for_job
+
+
+class _FailingStorage:
+    name = "test"
+
+    def __init__(self) -> None:
+        self.objects: dict[str, bytes] = {}
+        self.deleted: list[str] = []
+
+    def put_bytes(self, key: str, data: bytes, **_kwargs) -> None:
+        if self.objects:
+            raise StorageBackendError("object service unavailable")
+        self.objects[key] = data
+
+    def delete(self, key: str) -> None:
+        self.deleted.append(key)
+        self.objects.pop(key, None)
+
+
+def test_partial_campaign_artifact_write_is_compensated(tmp_path: Path) -> None:
+    first = tmp_path / "first.eml"
+    second = tmp_path / "second.eml"
+    first.write_bytes(b"Message-ID: <first@example.test>\r\n\r\nfirst")
+    second.write_bytes(b"Message-ID: <second@example.test>\r\n\r\nsecond")
+    messages = [
+        SimpleNamespace(
+            draft=SimpleNamespace(
+                entry_index=1,
+                eml_path=str(first),
+                eml_size_bytes=None,
+            )
+        ),
+        SimpleNamespace(
+            draft=SimpleNamespace(
+                entry_index=2,
+                eml_path=str(second),
+                eml_size_bytes=None,
+            )
+        ),
+    ]
+    storage = _FailingStorage()
+
+    with pytest.raises(CampaignPersistenceError, match="could not be persisted"):
+        _persist_built_eml_artifacts(
+            storage=storage,  # type: ignore[arg-type]
+            tenant_id="tenant-1",
+            campaign_id="campaign-1",
+            version_id="version-1",
+            build_id="build-1",
+            built_messages=messages,
+        )
+
+    assert storage.objects == {}
+    assert len(storage.deleted) == 1
+
+
+def test_worker_loads_and_verifies_campaign_eml_from_object_storage(
+    tmp_path: Path,
+) -> None:
+    payload = b"Message-ID: <message@example.test>\r\n\r\nbody"
+    storage = LocalFilesystemStorageBackend(tmp_path)
+    storage.put_bytes("campaign-artifacts/message.eml", payload)
+    job = SimpleNamespace(
+        id="job-1",
+        eml_storage_key="campaign-artifacts/message.eml",
+        eml_local_path=None,
+        eml_size_bytes=len(payload),
+        eml_sha256=hashlib.sha256(payload).hexdigest(),
+        message_id_header="<message@example.test>",
+    )
+
+    with patch(
+        "govoplan_campaign.backend.sending.jobs.configured_storage_backend",
+        return_value=storage,
+    ):
+        assert _load_eml_bytes_for_job(job) == payload
+
+
+def test_retention_preserves_reference_when_object_store_is_unavailable() -> None:
+    job = SimpleNamespace(
+        campaign_id="campaign-1",
+        updated_at=datetime.now(timezone.utc) - timedelta(days=10),
+        queue_status="draft",
+        send_status="smtp_accepted",
+        imap_status="appended",
+        eml_local_path=None,
+        eml_storage_key="campaign-artifacts/message.eml",
+    )
+    session = MagicMock()
+    session.query.return_value.filter.return_value.order_by.return_value.all.return_value = [
+        job
+    ]
+    storage = MagicMock()
+    storage.exists.side_effect = StorageBackendError("object service unavailable")
+
+    result = _apply_eml_retention(
+        session,
+        dry_run=False,
+        now=datetime.now(timezone.utc),
+        policy_for_campaign_id=lambda _campaign_id: SimpleNamespace(
+            generated_eml_retention_days=1
+        ),
+        storage=storage,
+    )
+
+    assert result["delete_failed"] == 1
+    assert result["metadata_cleared"] == 0
+    assert job.eml_storage_key == "campaign-artifacts/message.eml"
+    session.add.assert_not_called()