feat: harden shared platform contracts

2026-07-30 14:26:36 +02:00
parent 6970bf7457
commit 9b88ae388b
24 changed files with 2034 additions and 57 deletions
--- a/docs/COMPATIBILITY_INVENTORY.md
+++ b/docs/COMPATIBILITY_INVENTORY.md
@@ -0,0 +1,43 @@
+# GovOPlaN Compatibility Inventory
+
+This inventory classifies compatibility paths covered by
+`COMPATIBILITY_POLICY.md`. It is intentionally limited to behavior that changes
+accepted data, imports, permissions, or migration state. Operational fallbacks
+such as Redis degradation and language fallback are not compatibility paths.
+
+## Database Bridges
+
+| Path | Purpose | Retention | Removal |
+| --- | --- | --- | --- |
+| `govoplan_core.db.migrations.reconcile_legacy_create_all_schema` | Reconciles databases created before Alembic ownership was recorded. | At least one major release after runtime aliases are removed. | Review after `1.0`; keep release-baseline tests. |
+| Migration table/column aliases in `govoplan_core.db.migrations` | Detect and reconcile pre-split table ownership and migration tracks. | All tagged `0.1.x` upgrade origins plus one major release cycle. | Remove only after the corresponding baseline leaves support. |
+| Access and module migration backfills for legacy permission names | Converts persisted role assignments without dropping authority. | Same as the database upgrade origin that contains the old role. | Keep migrations immutable; remove only runtime expansion at `0.2`. |
+
+## Portable-Schema Readers
+
+| Path | Purpose | Retention | Removal |
+| --- | --- | --- | --- |
+| `govoplan_core.mail.config.normalize_split_transport_credentials` | Reads pre-split SMTP/IMAP credentials and emits the split representation. | Current and previous two configuration schema versions. | Version-gate once Mail writes an explicit current schema version; reject inputs older than the two-version window. |
+| `ImapServerConfig.discard_legacy_enabled` | Reads the former nested IMAP `enabled` field without writing it. | Current and previous two configuration schema versions. | Remove with the oldest accepted Mail configuration schema. |
+| `govoplan_core.core.configuration_packages` readers | Reads explicitly versioned configuration-package manifests. | Current and previous two schema versions. | Retire individual readers as their version leaves the window. |
+
+## Runtime And API Aliases
+
+| Path | Purpose | Retention | Removal |
+| --- | --- | --- | --- |
+| `govoplan_core.security.scope_aliases.LEGACY_SCOPE_ALIASES` | Expands pre-granular permission names. | Tagged `0.1.x` runtime/API window. | Remove at `0.2` after role backfills and migration notes are verified. |
+| `govoplan_core.security.module_permissions.LEGACY_TO_MODULE_SCOPES` | Maps pre-module-split scopes to canonical owning-module scopes. | Tagged `0.1.x` runtime/API window. | Remove at `0.2`; keep database migration evidence for one major cycle. |
+| `govoplan_core.privacy.retention` | Stable import facade delegating policy-owned behavior through a capability. | Tagged `0.1.x` import window. | Remove at `0.2` after all in-tree callers use the policy contract and release notes name the replacement. |
+| Legacy tenant aliases in API response schemas | Preserves active-tenant response fields used by `0.1.x` clients. | Tagged `0.1.x` API window. | Remove at `0.2` with response-schema migration notes. |
+| Optional fields in Poll response references | Accepts providers built against the earlier Poll contract. | Tagged `0.1.x` runtime contract window. | Remove or require a new interface version at `0.2`. |
+| Legacy single-tenant summary providers | Allows modules without the batch provider introduced in `0.1.x`. | Tagged `0.1.x` module contract window. | Remove at `0.2` after manifests advertise the batch provider contract. |
+
+## Removed Paths
+
+| Path | Reason | Removed |
+| --- | --- | --- |
+| `govoplan_core.core.module_installer._run_restart_command_legacy` | Private wrapper had no callers and never represented a persisted or published contract. | Current development line |
+| Retired `govoplan_core.api.admin` and pre-split core model imports | In-tree callers and module packages use their owning modules; regression tests prohibit reintroduction. | Before `0.1.10` |
+
+Every new compatibility path must be added here with its classification,
+diagnostic, test owner, and planned removal release.
--- a/docs/MODULE_ARCHITECTURE.md
+++ b/docs/MODULE_ARCHITECTURE.md
@@ -277,6 +277,23 @@ unsafe methods.
 This avoids retransmitting unchanged snapshots. It does not identify which row
 changed inside a collection.

+### Mutation Preconditions
+
+Weak response ETags are cache validators only. Mutable aggregates expose a
+separate positive, monotonic revision and an opaque strong ETag generated by
+`govoplan_core.core.concurrency.strong_resource_etag`. HTTP mutations send that
+strong ETag in `If-Match`; capability and worker calls carry the equivalent
+typed `expected_revision`.
+
+Core's compare-and-set primitive advances the revision in the same transaction
+as the domain mutation. A missing HTTP precondition is `428 Precondition
+Required`, a stale HTTP precondition is `412 Precondition Failed`, and a
+domain/reconciliation conflict is `409 Conflict`. Conflict responses contain
+bounded resource and revision metadata rather than the complete current
+object. Modules may opt into the conservative three-way merge helper, but must
+declare protected workflow, delivery, ownership, lock, evidence, signature,
+and cryptographic paths that can never be merged automatically.
+
 ### Delta Collections

 Collection endpoints that can expose row-level changes should use the shared
--- a/src/govoplan_core/celery_app.py
+++ b/src/govoplan_core/celery_app.py
@@ -20,6 +20,7 @@ from govoplan_core.core.events import (
    publish_platform_event,
 )
 from govoplan_core.core.module_management import load_startup_enabled_modules, startup_candidate_module_ids
+from govoplan_core.core.mail import CAPABILITY_MAIL_DELIVERY_OUTBOX, MailDeliveryOutboxProvider
 from govoplan_core.core.modules import ModuleContext
 from govoplan_core.core.notifications import CAPABILITY_NOTIFICATIONS_DISPATCH, NotificationDispatchProvider
 from govoplan_core.core.postbox import (
@@ -51,6 +52,8 @@ celery.conf.update(
        "govoplan.campaigns.append_sent": {"queue": "append_sent"},
        "govoplan.notifications.deliver": {"queue": "notifications"},
        "govoplan.notifications.deliver_pending": {"queue": "notifications"},
+        "govoplan.mail.dispatch_outbox": {"queue": "mail"},
+        "govoplan.mail.purge_outbox": {"queue": "mail"},
        "govoplan.calendar.dispatch_outbox": {"queue": "calendar"},
        "govoplan.dataflow.dispatch_runs": {"queue": "dataflow"},
        "govoplan.dataflow.purge_runs": {"queue": "dataflow"},
@@ -69,6 +72,16 @@ celery.conf.update(
            "schedule": 60.0,
            "args": (None, 100),
        },
+        "mail-outbox-every-five-seconds": {
+            "task": "govoplan.mail.dispatch_outbox",
+            "schedule": 5.0,
+            "args": (None, 25),
+        },
+        "mail-outbox-retention-daily": {
+            "task": "govoplan.mail.purge_outbox",
+            "schedule": 24 * 60 * 60.0,
+            "args": (250,),
+        },
        "dataflow-triggers-every-minute": {
            "task": "govoplan.dataflow.dispatch_triggers",
            "schedule": 60.0,
@@ -151,6 +164,16 @@ def _calendar_outbox() -> CalendarOutboxProvider | None:
    return capability


+def _mail_delivery_outbox() -> MailDeliveryOutboxProvider | None:
+    registry = _platform_registry()
+    if not registry.has_capability(CAPABILITY_MAIL_DELIVERY_OUTBOX):
+        return None
+    capability = registry.require_capability(CAPABILITY_MAIL_DELIVERY_OUTBOX)
+    if not isinstance(capability, MailDeliveryOutboxProvider):
+        raise RuntimeError("Mail delivery outbox capability is invalid")
+    return capability
+
+
 def _dataflow_trigger_dispatcher(
    registry: PlatformRegistry | None = None,
 ) -> DataflowTriggerDispatcher | None:
@@ -265,6 +288,51 @@ def deliver_pending_notifications(self, tenant_id: str | None = None, limit: int
        return result


+@celery.task(name="govoplan.mail.dispatch_outbox", bind=True, max_retries=0)
+def dispatch_mail_outbox(
+    self,
+    tenant_id: str | None = None,
+    limit: int = 25,
+):
+    """Drain durable Mail commands; retry and reconciliation live in Mail."""
+
+    from govoplan_core.db.session import get_database
+
+    with get_database().SessionLocal() as session:
+        provider = _mail_delivery_outbox()
+        if provider is None:
+            return {
+                "selected": 0,
+                "accepted": 0,
+                "partially_refused": 0,
+                "retrying": 0,
+                "failed": 0,
+                "outcome_unknown": 0,
+                "command_ids": [],
+            }
+        return dict(
+            provider.dispatch_due(
+                session,
+                tenant_id=tenant_id,
+                limit=limit,
+                worker_id=getattr(self.request, "hostname", None),
+            )
+        )
+
+
+@celery.task(name="govoplan.mail.purge_outbox", bind=True, max_retries=0)
+def purge_mail_outbox(self, limit: int = 250):
+    """Minimize expired Mail payloads while retaining delivery evidence."""
+
+    from govoplan_core.db.session import get_database
+
+    with get_database().SessionLocal() as session:
+        provider = _mail_delivery_outbox()
+        if provider is None:
+            return {"purged": 0}
+        return dict(provider.purge_expired(session, limit=limit))
+
+
@celery.task(name="govoplan.calendar.dispatch_outbox", bind=True, max_retries=0)
 def dispatch_calendar_outbox(self, tenant_id: str | None = None, limit: int = 50):
    """Drain durable Calendar operations; retry timing lives in the database."""
--- a/src/govoplan_core/core/concurrency.py
+++ b/src/govoplan_core/core/concurrency.py
@@ -0,0 +1,559 @@
+from __future__ import annotations
+
+import copy
+import hashlib
+import json
+from dataclasses import dataclass, field
+from typing import Any, Callable, Iterable, Mapping, Sequence
+
+from sqlalchemy.orm import Session
+
+
+class ConcurrencyError(RuntimeError):
+    """Base class for mutation precondition and compare-and-set failures."""
+
+
+class MissingPreconditionError(ConcurrencyError):
+    def __init__(self, *, resource_type: str, resource_id: str) -> None:
+        self.resource_type = resource_type
+        self.resource_id = resource_id
+        super().__init__("A strong If-Match precondition is required for this mutation.")
+
+    def as_dict(self) -> dict[str, Any]:
+        return {
+            "code": "precondition_required",
+            "resource": {
+                "type": self.resource_type,
+                "id": self.resource_id,
+            },
+            "retryable": True,
+        }
+
+
+class RevisionConflictError(ConcurrencyError):
+    def __init__(
+        self,
+        *,
+        resource_type: str,
+        resource_id: str,
+        current_revision: int,
+        submitted_base_revision: int,
+        refresh_path: str | None = None,
+        conflicts: Sequence["MergeConflict"] = (),
+        merge_candidate: Any = None,
+        current_etag: str | None = None,
+    ) -> None:
+        self.resource_type = resource_type
+        self.resource_id = resource_id
+        self.current_revision = int(current_revision)
+        self.submitted_base_revision = int(submitted_base_revision)
+        self.refresh_path = refresh_path
+        self.conflicts = tuple(conflicts)
+        self.merge_candidate = merge_candidate
+        self.current_etag = current_etag
+        super().__init__(
+            f"{resource_type} {resource_id} changed from revision "
+            f"{submitted_base_revision} to {current_revision}"
+        )
+
+    @property
+    def safe_merge_available(self) -> bool:
+        return self.merge_candidate is not None and not self.conflicts
+
+    def as_dict(
+        self,
+        *,
+        include_values: bool = False,
+        include_merge_candidate: bool = False,
+    ) -> dict[str, Any]:
+        result: dict[str, Any] = {
+            "code": "revision_conflict",
+            "resource": {
+                "type": self.resource_type,
+                "id": self.resource_id,
+            },
+            "current_revision": self.current_revision,
+            "submitted_base_revision": self.submitted_base_revision,
+            "retryable": True,
+            "safe_merge_available": self.safe_merge_available,
+            "conflicts": [
+                conflict.as_dict(include_values=include_values)
+                for conflict in self.conflicts[:100]
+            ],
+        }
+        if self.refresh_path:
+            result["refresh_path"] = self.refresh_path
+        if self.current_etag:
+            result["current_etag"] = self.current_etag
+        if include_merge_candidate and self.safe_merge_available:
+            result["merge_candidate"] = copy.deepcopy(self.merge_candidate)
+        return result
+
+
+@dataclass(frozen=True, slots=True)
+class MergeConflict:
+    path: str
+    kind: str
+    base_value: Any = None
+    local_value: Any = None
+    current_value: Any = None
+
+    def as_dict(self, *, include_values: bool = False) -> dict[str, Any]:
+        result: dict[str, Any] = {
+            "path": self.path or "/",
+            "kind": self.kind,
+        }
+        if include_values:
+            result.update(
+                {
+                    "base_value": _bounded_json_value(self.base_value),
+                    "local_value": _bounded_json_value(self.local_value),
+                    "current_value": _bounded_json_value(self.current_value),
+                }
+            )
+        return result
+
+
+@dataclass(slots=True)
+class ThreeWayMergeResult:
+    value: Any
+    conflicts: list[MergeConflict] = field(default_factory=list)
+    applied_paths: list[str] = field(default_factory=list)
+
+    @property
+    def merged(self) -> bool:
+        return not self.conflicts
+
+
+ProtectedPath = str | Callable[[str], bool]
+
+
+def strong_resource_etag(
+    resource_type: str,
+    resource_id: str,
+    revision: int,
+) -> str:
+    """Return an opaque strong ETag for one mutable aggregate revision."""
+
+    normalized_revision = int(revision)
+    if normalized_revision < 1:
+        raise ValueError("Resource revisions must be positive integers")
+    digest = hashlib.sha256(
+        "\x00".join(
+            (
+                "govoplan-strong-revision-v1",
+                str(resource_type),
+                str(resource_id),
+                str(normalized_revision),
+            )
+        ).encode("utf-8")
+    ).hexdigest()
+    return f'"sha256-{digest}"'
+
+
+def if_match_matches(header_value: str | None, expected_etag: str) -> bool:
+    """Apply strong comparison semantics to an If-Match header."""
+
+    if not header_value:
+        return False
+    for raw_candidate in header_value.split(","):
+        candidate = raw_candidate.strip()
+        if candidate == "*":
+            return True
+        if candidate.startswith("W/"):
+            continue
+        if candidate == expected_etag:
+            return True
+    return False
+
+
+def assert_revision_precondition(
+    if_match: str | None,
+    *,
+    resource_type: str,
+    resource_id: str,
+    submitted_base_revision: int,
+) -> None:
+    if not if_match:
+        raise MissingPreconditionError(
+            resource_type=resource_type,
+            resource_id=resource_id,
+        )
+    submitted_etag = strong_resource_etag(
+        resource_type,
+        resource_id,
+        submitted_base_revision,
+    )
+    if not if_match_matches(if_match, submitted_etag):
+        raise ConcurrencyError(
+            "If-Match does not identify the submitted base revision."
+        )
+
+
+def claim_revision(
+    session: Session,
+    *,
+    model: type[Any],
+    filters: Iterable[Any],
+    revision_attribute: str,
+    expected_revision: int,
+    resource_type: str,
+    resource_id: str,
+    refresh_path: str | None = None,
+) -> int:
+    """Atomically claim the next revision in the caller's transaction."""
+
+    revision_column = getattr(model, revision_attribute)
+    expected = int(expected_revision)
+    normalized_filters = tuple(filters)
+    query = session.query(model).filter(*normalized_filters)
+    updated = query.filter(revision_column == expected).update(
+        {revision_column: revision_column + 1},
+        synchronize_session=False,
+    )
+    if updated == 1:
+        session.flush()
+        return expected + 1
+
+    current = (
+        session.query(revision_column)
+        .filter(*normalized_filters)
+        .scalar()
+    )
+    if current is None:
+        raise LookupError(f"{resource_type} {resource_id} was not found")
+    raise RevisionConflictError(
+        resource_type=resource_type,
+        resource_id=resource_id,
+        current_revision=int(current),
+        submitted_base_revision=expected,
+        refresh_path=refresh_path,
+        current_etag=strong_resource_etag(
+            resource_type,
+            resource_id,
+            int(current),
+        ),
+    )
+
+
+def three_way_merge(
+    base: Any,
+    local: Any,
+    current: Any,
+    *,
+    protected_paths: Sequence[ProtectedPath] = (),
+    stable_id_fields: Sequence[str] = ("id",),
+) -> ThreeWayMergeResult:
+    """Conservatively merge local changes onto a concurrently changed value."""
+
+    return _merge_value(
+        copy.deepcopy(base),
+        copy.deepcopy(local),
+        copy.deepcopy(current),
+        path="",
+        protected_paths=tuple(protected_paths),
+        stable_id_fields=tuple(stable_id_fields),
+    )
+
+
+def _merge_value(
+    base: Any,
+    local: Any,
+    current: Any,
+    *,
+    path: str,
+    protected_paths: Sequence[ProtectedPath],
+    stable_id_fields: Sequence[str],
+) -> ThreeWayMergeResult:
+    local_changed = local != base
+    current_changed = current != base
+    if not local_changed:
+        return ThreeWayMergeResult(value=current)
+    if local == current:
+        return ThreeWayMergeResult(value=current)
+    if _is_protected(path, protected_paths):
+        return _conflict(path, "protected_path", base, local, current)
+    if not current_changed:
+        return ThreeWayMergeResult(
+            value=local,
+            applied_paths=[path or "/"],
+        )
+    if isinstance(base, Mapping) and isinstance(local, Mapping) and isinstance(current, Mapping):
+        return _merge_mapping(
+            base,
+            local,
+            current,
+            path=path,
+            protected_paths=protected_paths,
+            stable_id_fields=stable_id_fields,
+        )
+    if isinstance(base, list) and isinstance(local, list) and isinstance(current, list):
+        return _merge_list(
+            base,
+            local,
+            current,
+            path=path,
+            protected_paths=protected_paths,
+            stable_id_fields=stable_id_fields,
+        )
+    return _conflict(path, "same_path_changed", base, local, current)
+
+
+def _merge_mapping(
+    base: Mapping[str, Any],
+    local: Mapping[str, Any],
+    current: Mapping[str, Any],
+    *,
+    path: str,
+    protected_paths: Sequence[ProtectedPath],
+    stable_id_fields: Sequence[str],
+) -> ThreeWayMergeResult:
+    missing = object()
+    result: dict[str, Any] = {}
+    conflicts: list[MergeConflict] = []
+    applied_paths: list[str] = []
+    keys = list(dict.fromkeys((*current.keys(), *local.keys(), *base.keys())))
+    for key in keys:
+        child_path = _join_path(path, str(key))
+        base_value = base.get(key, missing)
+        local_value = local.get(key, missing)
+        current_value = current.get(key, missing)
+        merged = _merge_presence(
+            base_value,
+            local_value,
+            current_value,
+            missing=missing,
+            path=child_path,
+            protected_paths=protected_paths,
+            stable_id_fields=stable_id_fields,
+        )
+        conflicts.extend(merged.conflicts)
+        applied_paths.extend(merged.applied_paths)
+        if merged.value is not missing:
+            result[str(key)] = merged.value
+    return ThreeWayMergeResult(
+        value=result,
+        conflicts=conflicts,
+        applied_paths=applied_paths,
+    )
+
+
+def _merge_presence(
+    base: Any,
+    local: Any,
+    current: Any,
+    *,
+    missing: object,
+    path: str,
+    protected_paths: Sequence[ProtectedPath],
+    stable_id_fields: Sequence[str],
+) -> ThreeWayMergeResult:
+    if local is missing and current is missing:
+        return ThreeWayMergeResult(value=missing)
+    if base is missing:
+        if local is missing:
+            return ThreeWayMergeResult(value=current)
+        if current is missing:
+            if _is_protected(path, protected_paths):
+                return _conflict(path, "protected_path", None, local, None)
+            return ThreeWayMergeResult(value=local, applied_paths=[path])
+        if local == current:
+            return ThreeWayMergeResult(value=current)
+        return _conflict(path, "concurrent_add", None, local, current)
+    if local is missing:
+        if current == base:
+            if _is_protected(path, protected_paths):
+                return _conflict(path, "protected_path", base, None, current)
+            return ThreeWayMergeResult(value=missing, applied_paths=[path])
+        return _conflict(path, "delete_vs_edit", base, None, current)
+    if current is missing:
+        if local == base:
+            return ThreeWayMergeResult(value=missing)
+        return _conflict(path, "edit_vs_delete", base, local, None)
+    return _merge_value(
+        base,
+        local,
+        current,
+        path=path,
+        protected_paths=protected_paths,
+        stable_id_fields=stable_id_fields,
+    )
+
+
+def _merge_list(
+    base: list[Any],
+    local: list[Any],
+    current: list[Any],
+    *,
+    path: str,
+    protected_paths: Sequence[ProtectedPath],
+    stable_id_fields: Sequence[str],
+) -> ThreeWayMergeResult:
+    identity_field = _stable_identity_field(
+        (base, local, current),
+        stable_id_fields,
+    )
+    if identity_field is None:
+        return _conflict(path, "unkeyed_collection", base, local, current)
+
+    base_by_id = {str(item[identity_field]): item for item in base}
+    local_by_id = {str(item[identity_field]): item for item in local}
+    current_by_id = {str(item[identity_field]): item for item in current}
+    base_order = list(base_by_id)
+    local_order = list(local_by_id)
+    current_order = list(current_by_id)
+
+    local_reordered = _common_order(local_order, base_order) != _common_order(
+        base_order,
+        local_order,
+    )
+    current_reordered = _common_order(current_order, base_order) != _common_order(
+        base_order,
+        current_order,
+    )
+    if local_reordered and current_reordered and local_order != current_order:
+        return _conflict(path, "collection_reorder", base_order, local_order, current_order)
+
+    result_by_id: dict[str, Any] = {}
+    conflicts: list[MergeConflict] = []
+    applied_paths: list[str] = []
+    identities = list(dict.fromkeys((*current_order, *local_order, *base_order)))
+    missing = object()
+    for identity in identities:
+        item_path = _join_path(path, f"{identity_field}={identity}")
+        merged = _merge_presence(
+            base_by_id.get(identity, missing),
+            local_by_id.get(identity, missing),
+            current_by_id.get(identity, missing),
+            missing=missing,
+            path=item_path,
+            protected_paths=protected_paths,
+            stable_id_fields=stable_id_fields,
+        )
+        conflicts.extend(merged.conflicts)
+        applied_paths.extend(merged.applied_paths)
+        if merged.value is not missing:
+            result_by_id[identity] = merged.value
+
+    order_source = local_order if local_reordered and not current_reordered else current_order
+    merged_order = [identity for identity in order_source if identity in result_by_id]
+    for identity in identities:
+        if identity in result_by_id and identity not in merged_order:
+            merged_order.append(identity)
+    return ThreeWayMergeResult(
+        value=[result_by_id[identity] for identity in merged_order],
+        conflicts=conflicts,
+        applied_paths=applied_paths,
+    )
+
+
+def _stable_identity_field(
+    values: Sequence[list[Any]],
+    candidates: Sequence[str],
+) -> str | None:
+    all_items = [item for value in values for item in value]
+    if not all_items or not all(isinstance(item, Mapping) for item in all_items):
+        return None
+    for candidate in candidates:
+        valid = True
+        for value in values:
+            identities = [
+                str(item.get(candidate, "")).strip()
+                for item in value
+                if isinstance(item, Mapping)
+            ]
+            if any(not identity for identity in identities) or len(identities) != len(
+                set(identities)
+            ):
+                valid = False
+                break
+        if valid:
+            return candidate
+    return None
+
+
+def _common_order(left: Sequence[str], right: Sequence[str]) -> list[str]:
+    right_set = set(right)
+    return [item for item in left if item in right_set]
+
+
+def _is_protected(path: str, protected_paths: Sequence[ProtectedPath]) -> bool:
+    normalized = path or "/"
+    for protected in protected_paths:
+        if callable(protected):
+            if protected(normalized):
+                return True
+            continue
+        prefix = protected.rstrip("/") or "/"
+        if normalized == prefix or normalized.startswith(f"{prefix}/"):
+            return True
+    return False
+
+
+def _join_path(parent: str, segment: str) -> str:
+    escaped = segment.replace("~", "~0").replace("/", "~1")
+    return f"{parent}/{escaped}" if parent else f"/{escaped}"
+
+
+def _conflict(
+    path: str,
+    kind: str,
+    base: Any,
+    local: Any,
+    current: Any,
+) -> ThreeWayMergeResult:
+    return ThreeWayMergeResult(
+        value=current,
+        conflicts=[
+            MergeConflict(
+                path=path or "/",
+                kind=kind,
+                base_value=base,
+                local_value=local,
+                current_value=current,
+            )
+        ],
+    )
+
+
+def _bounded_json_value(value: Any, *, depth: int = 0) -> Any:
+    if depth >= 4:
+        return {"summary": type(value).__name__}
+    if value is None or isinstance(value, (bool, int, float)):
+        return value
+    if isinstance(value, str):
+        return value[:500]
+    if isinstance(value, Mapping):
+        result = {
+            str(key)[:100]: _bounded_json_value(item, depth=depth + 1)
+            for key, item in list(value.items())[:20]
+        }
+        if len(value) > 20:
+            result["_truncated_items"] = len(value) - 20
+        return result
+    if isinstance(value, Sequence) and not isinstance(value, (bytes, bytearray)):
+        result = [
+            _bounded_json_value(item, depth=depth + 1)
+            for item in list(value)[:20]
+        ]
+        if len(value) > 20:
+            result.append({"_truncated_items": len(value) - 20})
+        return result
+    try:
+        return json.loads(json.dumps(value))
+    except (TypeError, ValueError):
+        return {"summary": type(value).__name__}
+
+
+__all__ = [
+    "ConcurrencyError",
+    "MergeConflict",
+    "MissingPreconditionError",
+    "RevisionConflictError",
+    "ThreeWayMergeResult",
+    "assert_revision_precondition",
+    "claim_revision",
+    "if_match_matches",
+    "strong_resource_etag",
+    "three_way_merge",
+]
--- a/src/govoplan_core/core/mail.py
+++ b/src/govoplan_core/core/mail.py
@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+from collections.abc import Mapping
+from typing import Protocol, runtime_checkable
+
+
+CAPABILITY_MAIL_DELIVERY_OUTBOX = "mail.delivery_outbox"
+
+
+@runtime_checkable
+class MailDeliveryOutboxProvider(Protocol):
+    """Stable worker boundary for Mail-owned external delivery effects."""
+
+    def dispatch_due(
+        self,
+        session: object,
+        *,
+        tenant_id: str | None = None,
+        limit: int = 25,
+        worker_id: str | None = None,
+    ) -> Mapping[str, object]:
+        ...
+
+    def purge_expired(
+        self,
+        session: object,
+        *,
+        limit: int = 250,
+    ) -> Mapping[str, object]:
+        ...
--- a/src/govoplan_core/core/module_installer.py
+++ b/src/govoplan_core/core/module_installer.py
@@ -3328,12 +3328,6 @@ def _wait_for_health_urls(urls: Iterable[str], *, timeout_seconds: float, interv
    return payload


-def _run_restart_command_legacy(command: str | None) -> dict[str, object] | None:
-    if not command:
-        return None
-    return _run_restart_command(command)
-
-
 def _planned_python_install_packages(record: Mapping[str, object]) -> tuple[str, ...]:
    raw_plan = record.get("plan")
    if not isinstance(raw_plan, list):
--- a/src/govoplan_core/core/modules.py
+++ b/src/govoplan_core/core/modules.py
@@ -215,6 +215,17 @@ class ModuleContext:
 DocumentationLayer = Literal["always", "configured", "available", "evidence"]
 DocumentationLinkKind = Literal["runtime", "api", "repository", "wiki", "public"]
 DocumentationType = Literal["admin", "user"]
+DocumentationConfigurationState = Literal["enabled", "disabled", "inherited", "unavailable"]
+DocumentationSourceKind = Literal[
+    "manifest",
+    "route",
+    "capability",
+    "policy",
+    "configuration_package",
+    "wiki",
+    "repository",
+]
+DocumentationSourceState = Literal["configured", "disabled", "unavailable"]


@dataclass(frozen=True, slots=True)
@@ -296,6 +307,40 @@ class DocumentationContext:
    data: Mapping[str, Any] = field(default_factory=dict)


+@dataclass(frozen=True, slots=True)
+class DocumentationConfigurationDecision:
+    key: str
+    state: DocumentationConfigurationState
+    source: str | None = None
+    reason: str | None = None
+
+
+DocumentationConfigurationResolver = Callable[
+    [DocumentationContext, tuple[str, ...]],
+    Mapping[str, DocumentationConfigurationDecision],
+]
+
+
+@dataclass(frozen=True, slots=True)
+class DocumentationConfigurationProviderRegistration:
+    keys: tuple[str, ...]
+    resolve: DocumentationConfigurationResolver
+
+
+@dataclass(frozen=True, slots=True)
+class DocumentationSourceDefinition:
+    id: str
+    kind: DocumentationSourceKind
+    label: str
+    documentation_types: tuple[DocumentationType, ...] = ("admin",)
+    condition: DocumentationCondition = field(default_factory=DocumentationCondition)
+    state: DocumentationSourceState = "configured"
+    provenance: Mapping[str, Any] = field(default_factory=dict)
+    inspection: Mapping[str, Any] = field(default_factory=dict)
+    link: DocumentationLink | None = None
+    configuration_key: str | None = None
+
+
 class ResourceAclProvider(Protocol):
    resource_type: str

@@ -372,3 +417,8 @@ class ModuleManifest:
    on_deactivate: LifecycleHook | None = None
    documentation: tuple[DocumentationTopic, ...] = ()
    documentation_providers: tuple[DocumentationProvider, ...] = ()
+    documentation_configuration_providers: tuple[
+        DocumentationConfigurationProviderRegistration,
+        ...,
+    ] = ()
+    documentation_sources: tuple[DocumentationSourceDefinition, ...] = ()
--- a/src/govoplan_core/core/postbox.py
+++ b/src/govoplan_core/core/postbox.py
@@ -16,6 +16,7 @@ CAPABILITY_POSTBOX_ROUTING = "postbox.routing"

 PostboxAction = Literal["discover", "read", "send", "acknowledge", "administer"]
 PostboxMessageListState = Literal["all", "unread", "read", "acknowledged"]
+PostboxMessageAvailability = Literal["available", "withdrawn", "expired"]


@dataclass(frozen=True, slots=True)
@@ -140,6 +141,7 @@ class PostboxMessageRef:
    subject: str
    body_text: str | None
    status: str
+    availability: PostboxMessageAvailability
    classification: str
    sender_label: str | None
    delivered_at: datetime
@@ -159,6 +161,29 @@ class PostboxMessageRef:
    metadata: Mapping[str, object] = field(default_factory=dict)


+@dataclass(frozen=True, slots=True)
+class PostboxDeliveryReceiptSummaryRef:
+    delivery_id: str
+    message_id: str
+    postbox_id: str
+    delivery_status: str
+    accepted_at: datetime
+    current_holder_count: int = 0
+    currently_readable: bool = False
+    message_count: int = 1
+    routed_message_count: int = 0
+    readable_message_count: int = 0
+    read_receipt_count: int = 0
+    acknowledged_receipt_count: int = 0
+    withdrawn_message_count: int = 0
+    expired_message_count: int = 0
+    first_read_at: datetime | None = None
+    last_read_at: datetime | None = None
+    first_acknowledged_at: datetime | None = None
+    last_acknowledged_at: datetime | None = None
+    route_status_counts: Mapping[str, int] = field(default_factory=dict)
+
+
@dataclass(frozen=True, slots=True)
 class PostboxDeliveryRequest:
    tenant_id: str
@@ -317,6 +342,16 @@ class PostboxEvidenceProvider(Protocol):
    ) -> PostboxMessageRef:
        ...

+    def delivery_receipt_summaries(
+        self,
+        session: object,
+        *,
+        tenant_id: str,
+        producer_module: str,
+        delivery_ids: Sequence[str],
+    ) -> Mapping[str, PostboxDeliveryReceiptSummaryRef]:
+        ...
+

@runtime_checkable
 class PostboxRoutingProvider(Protocol):
--- a/src/govoplan_core/core/registry.py
+++ b/src/govoplan_core/core/registry.py
@@ -564,6 +564,43 @@ def _validate_manifest_shape(manifest: ModuleManifest) -> None:
            raise RegistryError(
                f"Module {manifest.id!r} documentation topic {topic.id!r}: {issue}"
            )
+    _validate_documentation_extensions(manifest)
+
+
+def _validate_documentation_extensions(manifest: ModuleManifest) -> None:
+    provider_keys: set[str] = set()
+    for registration in manifest.documentation_configuration_providers:
+        if not registration.keys:
+            raise RegistryError(
+                f"Module {manifest.id!r} documentation configuration provider must declare keys"
+            )
+        for raw_key in registration.keys:
+            key = raw_key.strip()
+            if not key:
+                raise RegistryError(
+                    f"Module {manifest.id!r} documentation configuration provider declares an empty key"
+                )
+            if key in provider_keys:
+                raise RegistryError(
+                    f"Module {manifest.id!r} declares duplicate documentation configuration key {key!r}"
+                )
+            provider_keys.add(key)
+
+    source_ids: set[str] = set()
+    for source in manifest.documentation_sources:
+        if not _INTERFACE_NAME_RE.match(source.id):
+            raise RegistryError(
+                f"Module {manifest.id!r} documentation source id must be namespaced: {source.id!r}"
+            )
+        if source.id in source_ids:
+            raise RegistryError(
+                f"Module {manifest.id!r} declares duplicate documentation source {source.id!r}"
+            )
+        source_ids.add(source.id)
+        if not source.label.strip():
+            raise RegistryError(
+                f"Module {manifest.id!r} documentation source {source.id!r} must have a label"
+            )


 def _validate_manifest_identity(manifest: ModuleManifest) -> None:
--- a/src/govoplan_core/security/redaction.py
+++ b/src/govoplan_core/security/redaction.py
@@ -30,18 +30,21 @@ def redact_secret_values(value: object, *, placeholder: str = "<redacted>") -> o
        return result
    if isinstance(value, list):
        return [redact_secret_values(item, placeholder=placeholder) for item in value]
+    if isinstance(value, tuple):
+        return tuple(redact_secret_values(item, placeholder=placeholder) for item in value)
    return value


 def contains_plain_secret(value: object) -> bool:
-    if not isinstance(value, Mapping):
-        return False
-    for key, item in value.items():
-        normalized_key = str(key).strip().casefold().replace("-", "_")
-        if normalized_key in {"credential_ref", "secret_ref", "secret_reference"}:
-            continue
-        if is_sensitive_key(key) and item not in (None, "", {"secret_ref": ""}):  # nosec B105 - empty redaction sentinels.
-            return True
-        if isinstance(item, Mapping) and contains_plain_secret(item):
-            return True
+    if isinstance(value, Mapping):
+        for key, item in value.items():
+            normalized_key = str(key).strip().casefold().replace("-", "_")
+            if normalized_key in {"credential_ref", "secret_ref", "secret_reference"}:
+                continue
+            if is_sensitive_key(key) and item not in (None, "", {"secret_ref": ""}):  # nosec B105 - empty redaction sentinels.
+                return True
+            if contains_plain_secret(item):
+                return True
+    elif isinstance(value, (list, tuple)):
+        return any(contains_plain_secret(item) for item in value)
    return False
--- a/tests/test_api_smoke.py
+++ b/tests/test_api_smoke.py
@@ -132,6 +132,24 @@ class ApiSmokeTests(unittest.TestCase):
        self.assertEqual(response.status_code, 201, response.text)
        return str(response.json()["id"])

+    def _campaign_version_precondition(
+        self,
+        headers: dict[str, str],
+        campaign_id: str,
+        version_id: str,
+    ) -> tuple[dict[str, str], int]:
+        response = self.client.get(
+            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}",
+            headers=headers,
+        )
+        self.assertEqual(response.status_code, 200, response.text)
+        etag = response.headers.get("etag")
+        self.assertIsNotNone(etag)
+        return (
+            {**headers, "If-Match": str(etag)},
+            int(response.json()["edit_revision"]),
+        )
+
    def test_recipient_import_mapping_profiles_are_db_backed(self) -> None:
        headers, _ = self._login()
        payload = {
@@ -950,6 +968,33 @@ class ApiSmokeTests(unittest.TestCase):
        user_always = {item["id"]: item for item in user_docs_payload["layers"]["always"]["documentation"]}
        self.assertEqual(user_always["docs.configured-system-documentation"]["translation_locale"], "de")

+        sources = self.client.get("/api/v1/docs/sources", headers=headers)
+        self.assertEqual(sources.status_code, 200, sources.text)
+        source_payload = sources.json()
+        self.assertEqual(source_payload["total"], len(source_payload["items"]))
+        manifest_source = next(
+            item
+            for item in source_payload["items"]
+            if item["id"] == "docs.manifest"
+        )
+        self.assertEqual(manifest_source["kind"], "manifest")
+        self.assertNotIn("inspection", manifest_source)
+
+        inspected_source = self.client.get(
+            manifest_source["inspection_url"],
+            headers=headers,
+        )
+        self.assertEqual(inspected_source.status_code, 200, inspected_source.text)
+        self.assertEqual(
+            inspected_source.json()["inspection"]["module_id"],
+            "docs",
+        )
+        unknown_source = self.client.get(
+            "/api/v1/docs/sources/docs.unknown",
+            headers=headers,
+        )
+        self.assertEqual(unknown_source.status_code, 404, unknown_source.text)
+
        platform_status = self.client.get("/api/v1/platform/status", headers=headers)
        self.assertEqual(platform_status.status_code, 200, platform_status.text)
        i18n_status = platform_status.json()["i18n"]
@@ -2747,7 +2792,10 @@ class ApiSmokeTests(unittest.TestCase):
            archive.writestr("reports/february.txt", "February report")
        payload.seek(0)

-        with patch("govoplan_files.backend.router._read_limited_upload", side_effect=AssertionError("ZIP upload should not be fully buffered")):
+        with patch(
+            "govoplan_files.backend.routes.uploads._read_limited_upload",
+            side_effect=AssertionError("ZIP upload should not be fully buffered"),
+        ):
            response = self.client.post(
                "/api/v1/files/upload-zip",
                headers=headers,
@@ -2890,10 +2938,18 @@ class ApiSmokeTests(unittest.TestCase):
        self.assertTrue(full_payload["full"])
        self.assertEqual(full_payload["current_version"]["id"], version_id)

+        mutation_headers, base_revision = self._campaign_version_precondition(
+            headers,
+            campaign_id,
+            version_id,
+        )
        autosaved = self.client.post(
            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}/autosave",
-            headers=headers,
-            json={"current_step": "fields"},
+            headers=mutation_headers,
+            json={
+                "current_step": "fields",
+                "base_revision": base_revision,
+            },
        )
        self.assertEqual(autosaved.status_code, 200, autosaved.text)
        self.assertEqual(autosaved.json()["current_step"], "fields")
@@ -3038,10 +3094,18 @@ class ApiSmokeTests(unittest.TestCase):
        self.assertEqual(temporary.json()["user_lock_state"], "temporary")
        self.assertTrue(temporary.json()["user_locked_at"])

+        mutation_headers, base_revision = self._campaign_version_precondition(
+            headers,
+            campaign_id,
+            version_id,
+        )
        blocked_update = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}",
-            headers=headers,
-            json={"current_step": "fields"},
+            headers=mutation_headers,
+            json={
+                "current_step": "fields",
+                "base_revision": base_revision,
+            },
        )
        self.assertEqual(blocked_update.status_code, 409, blocked_update.text)

@@ -3052,10 +3116,18 @@ class ApiSmokeTests(unittest.TestCase):
        self.assertEqual(unlocked.status_code, 200, unlocked.text)
        self.assertIsNone(unlocked.json()["user_lock_state"])

+        mutation_headers, base_revision = self._campaign_version_precondition(
+            headers,
+            campaign_id,
+            version_id,
+        )
        updated = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}",
-            headers=headers,
-            json={"current_step": "fields"},
+            headers=mutation_headers,
+            json={
+                "current_step": "fields",
+                "base_revision": base_revision,
+            },
        )
        self.assertEqual(updated.status_code, 200, updated.text)
        self.assertEqual(updated.json()["current_step"], "fields")
@@ -3116,18 +3188,34 @@ class ApiSmokeTests(unittest.TestCase):
        self.assertNotEqual(second_version_id, first_version_id)
        self.assertEqual(copied.json()["campaign"]["current_version_id"], second_version_id)

+        mutation_headers, base_revision = self._campaign_version_precondition(
+            headers,
+            campaign_id,
+            first_version_id,
+        )
        historical_update = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{first_version_id}",
-            headers=headers,
-            json={"current_step": "fields"},
+            headers=mutation_headers,
+            json={
+                "current_step": "fields",
+                "base_revision": base_revision,
+            },
        )
        self.assertEqual(historical_update.status_code, 409, historical_update.text)
        self.assertIn("Historical campaign versions are read-only", historical_update.text)

+        mutation_headers, base_revision = self._campaign_version_precondition(
+            headers,
+            campaign_id,
+            second_version_id,
+        )
        second_update = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{second_version_id}",
-            headers=headers,
-            json={"current_step": "fields"},
+            headers=mutation_headers,
+            json={
+                "current_step": "fields",
+                "base_revision": base_revision,
+            },
        )
        self.assertEqual(second_update.status_code, 200, second_update.text)

@@ -4613,8 +4701,14 @@ class ApiSmokeTests(unittest.TestCase):
        )
        updated = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{second_version_id}",
-            headers=headers,
-            json={"campaign_json": campaign_json},
+            headers={
+                **headers,
+                "If-Match": str(version_response.headers["etag"]),
+            },
+            json={
+                "campaign_json": campaign_json,
+                "base_revision": version_response.json()["edit_revision"],
+            },
        )
        self.assertEqual(updated.status_code, 200, updated.text)
        validated = self.client.post(
@@ -5883,10 +5977,18 @@ class ApiSmokeTests(unittest.TestCase):
        self.assertEqual(allowed_write.status_code, 200, allowed_write.text)
        changed_config = version_detail.json()["raw_json"]
        changed_config["entries"]["inline"][0]["to"][0]["email"] = "changed@example.org"
+        mutation_headers, base_revision = self._campaign_version_precondition(
+            reader_headers,
+            campaign_id,
+            version_id,
+        )
        denied_recipient_edit = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}",
-            headers=reader_headers,
-            json={"campaign_json": changed_config},
+            headers=mutation_headers,
+            json={
+                "campaign_json": changed_config,
+                "base_revision": base_revision,
+            },
        )
        self.assertEqual(denied_recipient_edit.status_code, 403, denied_recipient_edit.text)
        self.assertEqual(self.client.get(f"/api/v1/campaigns/{campaign_id}", headers=other_headers).status_code, 403)
@@ -6030,18 +6132,29 @@ class ApiSmokeTests(unittest.TestCase):
        }
        blocked_inline = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}",
-            headers=headers,
-            json={"campaign_json": inline_json},
+            headers={**headers, "If-Match": str(detail.headers["etag"])},
+            json={
+                "campaign_json": inline_json,
+                "base_revision": detail.json()["edit_revision"],
+            },
        )
        self.assertEqual(blocked_inline.status_code, 422, blocked_inline.text)
        self.assertIn("may only reference", blocked_inline.json()["detail"])

        reusable_json = detail.json()["raw_json"]
        reusable_json["server"] = {"mail_profile_id": tenant_profile_id}
+        mutation_headers, base_revision = self._campaign_version_precondition(
+            headers,
+            campaign_id,
+            version_id,
+        )
        allowed_reusable = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}",
-            headers=headers,
-            json={"campaign_json": reusable_json},
+            headers=mutation_headers,
+            json={
+                "campaign_json": reusable_json,
+                "base_revision": base_revision,
+            },
        )
        self.assertEqual(allowed_reusable.status_code, 200, allowed_reusable.text)

@@ -6080,8 +6193,11 @@ class ApiSmokeTests(unittest.TestCase):
        raw_json["server"] = {"mail_profile_id": profile_id}
        denied_update = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}",
-            headers=headers,
-            json={"campaign_json": raw_json},
+            headers={**headers, "If-Match": str(detail.headers["etag"])},
+            json={
+                "campaign_json": raw_json,
+                "base_revision": detail.json()["edit_revision"],
+            },
        )
        self.assertEqual(denied_update.status_code, 422, denied_update.text)

@@ -6091,10 +6207,18 @@ class ApiSmokeTests(unittest.TestCase):
            json={"policy": {"allowed_profile_ids": [profile_id]}},
        )
        self.assertEqual(allowed_policy.status_code, 200, allowed_policy.text)
+        mutation_headers, base_revision = self._campaign_version_precondition(
+            headers,
+            campaign_id,
+            version_id,
+        )
        allowed_update = self.client.put(
            f"/api/v1/campaigns/{campaign_id}/versions/{version_id}",
-            headers=headers,
-            json={"campaign_json": raw_json},
+            headers=mutation_headers,
+            json={
+                "campaign_json": raw_json,
+                "base_revision": base_revision,
+            },
        )
        self.assertEqual(allowed_update.status_code, 200, allowed_update.text)

--- a/tests/test_core_events.py
+++ b/tests/test_core_events.py
@@ -250,6 +250,38 @@ class CoreEventTests(unittest.TestCase):
        self.assertIn("frame-ancestors 'none'", response.headers["Content-Security-Policy"])
        self.assertEqual("max-age=86400", response.headers["Strict-Transport-Security"])

+    def test_slow_request_log_excludes_query_headers_and_cookies(self) -> None:
+        router = APIRouter()
+
+        @router.get("/slow")
+        def slow() -> dict[str, bool]:
+            return {"ok": True}
+
+        with patch("govoplan_core.server.fastapi._slow_request_threshold_ms", return_value=0.0001):
+            app = create_govoplan_app(
+                title="request log redaction test",
+                version="test",
+                registry=PlatformRegistry(),
+                api_router=router,
+            )
+
+        with self.assertLogs("govoplan.request", level="WARNING") as captured:
+            with TestClient(app) as client:
+                response = client.get(
+                    "/slow?token=query-secret",
+                    headers={
+                        "Authorization": "Bearer header-secret",
+                        "Cookie": "govoplan_session=cookie-secret",
+                    },
+                )
+
+        self.assertEqual(200, response.status_code, response.text)
+        rendered = "\n".join(captured.output)
+        self.assertIn("path=/slow", rendered)
+        self.assertNotIn("query-secret", rendered)
+        self.assertNotIn("header-secret", rendered)
+        self.assertNotIn("cookie-secret", rendered)
+
    def test_production_app_startup_rejects_an_unvalidated_environment(self) -> None:
        with patch.dict("os.environ", {"APP_ENV": "production"}, clear=True), self.assertRaisesRegex(
            RuntimeError,
--- a/tests/test_documentation_topic_contract.py
+++ b/tests/test_documentation_topic_contract.py
@@ -3,7 +3,10 @@ from __future__ import annotations
 import unittest

 from govoplan_core.core.modules import (
+    DocumentationConfigurationDecision,
+    DocumentationConfigurationProviderRegistration,
    DocumentationCondition,
+    DocumentationSourceDefinition,
    DocumentationTopic,
    ModuleManifest,
    user_workflow_scope_condition_issues,
@@ -67,6 +70,52 @@ class DocumentationTopicContractTests(unittest.TestCase):
        self.assertEqual(user_workflow_scope_condition_issues(user_reference), ())
        registry_for(scoped, admin_workflow, user_reference).validate()

+    def test_documentation_configuration_and_source_extensions_are_validated(self) -> None:
+        resolver = lambda _context, keys: {  # noqa: E731
+            key: DocumentationConfigurationDecision(key=key, state="enabled")
+            for key in keys
+        }
+        registry = PlatformRegistry()
+        registry.register(ModuleManifest(
+            id="example",
+            name="Example",
+            version="1.0.0",
+            documentation_configuration_providers=(
+                DocumentationConfigurationProviderRegistration(
+                    keys=("example.feature",),
+                    resolve=resolver,
+                ),
+            ),
+            documentation_sources=(
+                DocumentationSourceDefinition(
+                    id="example.handbook",
+                    kind="repository",
+                    label="Example handbook",
+                ),
+            ),
+        ))
+
+        registry.validate()
+
+        duplicate = PlatformRegistry()
+        duplicate.register(ModuleManifest(
+            id="example",
+            name="Example",
+            version="1.0.0",
+            documentation_configuration_providers=(
+                DocumentationConfigurationProviderRegistration(
+                    keys=("example.feature",),
+                    resolve=resolver,
+                ),
+                DocumentationConfigurationProviderRegistration(
+                    keys=("example.feature",),
+                    resolve=resolver,
+                ),
+            ),
+        ))
+        with self.assertRaisesRegex(RegistryError, "duplicate documentation configuration key"):
+            duplicate.validate()
+

 def registry_for(*topics: DocumentationTopic) -> PlatformRegistry:
    registry = PlatformRegistry()
--- a/tests/test_mail_delivery_worker.py
+++ b/tests/test_mail_delivery_worker.py
@@ -0,0 +1,85 @@
+from __future__ import annotations
+
+import unittest
+from contextlib import contextmanager
+from types import SimpleNamespace
+from unittest.mock import patch
+
+from govoplan_core.celery_app import (
+    celery,
+    dispatch_mail_outbox,
+    purge_mail_outbox,
+)
+
+
+class _Provider:
+    def dispatch_due(self, session, **kwargs):
+        return {"session": session, **kwargs}
+
+    def purge_expired(self, session, **kwargs):
+        return {"session": session, **kwargs}
+
+
+class MailDeliveryWorkerTests(unittest.TestCase):
+    def test_dispatch_uses_optional_provider_boundary(self) -> None:
+        session = object()
+
+        @contextmanager
+        def session_scope():
+            yield session
+
+        database = SimpleNamespace(SessionLocal=session_scope)
+        with (
+            patch("govoplan_core.db.session.get_database", return_value=database),
+            patch(
+                "govoplan_core.celery_app._mail_delivery_outbox",
+                return_value=_Provider(),
+            ),
+        ):
+            result = dispatch_mail_outbox.run("tenant-1", 7)
+
+        self.assertIs(result["session"], session)
+        self.assertEqual(result["tenant_id"], "tenant-1")
+        self.assertEqual(result["limit"], 7)
+
+    def test_purge_uses_optional_provider_boundary(self) -> None:
+        session = object()
+
+        @contextmanager
+        def session_scope():
+            yield session
+
+        database = SimpleNamespace(SessionLocal=session_scope)
+        with (
+            patch("govoplan_core.db.session.get_database", return_value=database),
+            patch(
+                "govoplan_core.celery_app._mail_delivery_outbox",
+                return_value=_Provider(),
+            ),
+        ):
+            result = purge_mail_outbox.run(19)
+
+        self.assertIs(result["session"], session)
+        self.assertEqual(result["limit"], 19)
+
+    def test_worker_routes_and_schedules_are_declared(self) -> None:
+        self.assertEqual(
+            celery.conf.task_routes["govoplan.mail.dispatch_outbox"],
+            {"queue": "mail"},
+        )
+        self.assertEqual(
+            celery.conf.task_routes["govoplan.mail.purge_outbox"],
+            {"queue": "mail"},
+        )
+        self.assertEqual(
+            celery.conf.beat_schedule["mail-outbox-every-five-seconds"]["task"],
+            "govoplan.mail.dispatch_outbox",
+        )
+        self.assertEqual(
+            celery.conf.beat_schedule["mail-outbox-retention-daily"]["task"],
+            "govoplan.mail.purge_outbox",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()
--- a/tests/test_optimistic_concurrency.py
+++ b/tests/test_optimistic_concurrency.py
@@ -0,0 +1,175 @@
+from __future__ import annotations
+
+import unittest
+
+from sqlalchemy import Integer, String, create_engine
+from sqlalchemy.orm import Mapped, Session, mapped_column, sessionmaker
+from sqlalchemy.pool import StaticPool
+
+from govoplan_core.core.concurrency import (
+    MissingPreconditionError,
+    RevisionConflictError,
+    assert_revision_precondition,
+    claim_revision,
+    if_match_matches,
+    strong_resource_etag,
+    three_way_merge,
+)
+from govoplan_core.db.base import Base
+
+
+class _RevisionFixture(Base):
+    __tablename__ = "test_revision_fixture"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True)
+    edit_revision: Mapped[int] = mapped_column(Integer, default=1, nullable=False)
+    value: Mapped[str] = mapped_column(String(100), nullable=False)
+
+
+class OptimisticConcurrencyTests(unittest.TestCase):
+    def test_strong_etags_and_if_match_use_strong_comparison(self) -> None:
+        etag = strong_resource_etag("campaign_version", "version-1", 3)
+
+        self.assertTrue(if_match_matches(etag, etag))
+        self.assertTrue(if_match_matches(f'"other", {etag}', etag))
+        self.assertFalse(if_match_matches(f"W/{etag}", etag))
+        self.assertNotEqual(
+            etag,
+            strong_resource_etag("campaign_version", "version-1", 4),
+        )
+        with self.assertRaises(MissingPreconditionError):
+            assert_revision_precondition(
+                None,
+                resource_type="campaign_version",
+                resource_id="version-1",
+                submitted_base_revision=3,
+            )
+
+    def test_compare_and_set_allows_only_one_writer_for_a_revision(self) -> None:
+        engine = create_engine(
+            "sqlite+pysqlite://",
+            connect_args={"check_same_thread": False},
+            poolclass=StaticPool,
+        )
+        _RevisionFixture.__table__.create(engine)
+        session_factory = sessionmaker(bind=engine, class_=Session)
+        with session_factory() as session:
+            session.add(_RevisionFixture(id="resource-1", value="base"))
+            session.commit()
+            next_revision = claim_revision(
+                session,
+                model=_RevisionFixture,
+                filters=(_RevisionFixture.id == "resource-1",),
+                revision_attribute="edit_revision",
+                expected_revision=1,
+                resource_type="fixture",
+                resource_id="resource-1",
+            )
+            session.commit()
+            self.assertEqual(next_revision, 2)
+
+            with self.assertRaises(RevisionConflictError) as raised:
+                claim_revision(
+                    session,
+                    model=_RevisionFixture,
+                    filters=(_RevisionFixture.id == "resource-1",),
+                    revision_attribute="edit_revision",
+                    expected_revision=1,
+                    resource_type="fixture",
+                    resource_id="resource-1",
+                )
+            self.assertEqual(raised.exception.current_revision, 2)
+        engine.dispose()
+
+    def test_disjoint_map_and_stable_id_collection_changes_merge(self) -> None:
+        base = {
+            "campaign": {"name": "Original", "description": "Base"},
+            "entries": {
+                "inline": [
+                    {"id": "one", "name": "One", "active": True},
+                    {"id": "two", "name": "Two", "active": True},
+                ]
+            },
+        }
+        local = {
+            **base,
+            "campaign": {"name": "Local", "description": "Base"},
+            "entries": {
+                "inline": [
+                    {"id": "one", "name": "One", "active": False},
+                    {"id": "two", "name": "Two", "active": True},
+                ]
+            },
+        }
+        current = {
+            **base,
+            "campaign": {"name": "Original", "description": "Remote"},
+            "entries": {
+                "inline": [
+                    {"id": "one", "name": "One", "active": True},
+                    {"id": "two", "name": "Remote Two", "active": True},
+                ]
+            },
+        }
+
+        result = three_way_merge(base, local, current)
+
+        self.assertTrue(result.merged)
+        self.assertEqual(result.value["campaign"], {"name": "Local", "description": "Remote"})
+        self.assertEqual(result.value["entries"]["inline"][0]["active"], False)
+        self.assertEqual(result.value["entries"]["inline"][1]["name"], "Remote Two")
+
+    def test_same_path_unkeyed_collection_and_protected_edits_conflict(self) -> None:
+        same_path = three_way_merge(
+            {"name": "Base"},
+            {"name": "Local"},
+            {"name": "Remote"},
+        )
+        self.assertEqual(same_path.conflicts[0].kind, "same_path_changed")
+
+        unkeyed = three_way_merge(
+            {"values": ["a"]},
+            {"values": ["a", "local"]},
+            {"values": ["a", "remote"]},
+        )
+        self.assertEqual(unkeyed.conflicts[0].kind, "unkeyed_collection")
+
+        protected = three_way_merge(
+            {"workflow_state": "draft", "name": "Base"},
+            {"workflow_state": "ready", "name": "Base"},
+            {"workflow_state": "draft", "name": "Remote"},
+            protected_paths=("/workflow_state",),
+        )
+        self.assertEqual(protected.conflicts[0].kind, "protected_path")
+
+    def test_delete_versus_edit_and_conflicting_reorder_remain_explicit(self) -> None:
+        base = [{"id": "one", "value": "1"}, {"id": "two", "value": "2"}]
+        delete_vs_edit = three_way_merge(
+            base,
+            [{"id": "two", "value": "2"}],
+            [{"id": "one", "value": "remote"}, {"id": "two", "value": "2"}],
+        )
+        self.assertEqual(delete_vs_edit.conflicts[0].kind, "delete_vs_edit")
+
+        reordered = three_way_merge(
+            [
+                {"id": "one"},
+                {"id": "two"},
+                {"id": "three"},
+            ],
+            [
+                {"id": "two"},
+                {"id": "one"},
+                {"id": "three"},
+            ],
+            [
+                {"id": "one"},
+                {"id": "three"},
+                {"id": "two"},
+            ],
+        )
+        self.assertEqual(reordered.conflicts[0].kind, "collection_reorder")
+
+
+if __name__ == "__main__":
+    unittest.main()
--- a/tests/test_postbox_contract.py
+++ b/tests/test_postbox_contract.py
@@ -1,6 +1,7 @@
 from __future__ import annotations

 import unittest
+from datetime import datetime, timezone

 from govoplan_core.core.modules import ModuleContext, ModuleManifest
 from govoplan_core.core.postbox import (
@@ -11,6 +12,7 @@ from govoplan_core.core.postbox import (
    CAPABILITY_POSTBOX_MESSAGES,
    PostboxAccessProvider,
    PostboxDeliveryProvider,
+    PostboxDeliveryReceiptSummaryRef,
    PostboxDirectoryProvider,
    PostboxEvidenceProvider,
    PostboxMessagesProvider,
@@ -69,6 +71,17 @@ class _PostboxProvider:
        del session, tenant_id, message_id, attachment
        return None

+    def delivery_receipt_summaries(
+        self,
+        session,
+        *,
+        tenant_id,
+        producer_module,
+        delivery_ids,
+    ):
+        del session, tenant_id, producer_module, delivery_ids
+        return {}
+

 class PostboxContractTests(unittest.TestCase):
    def test_protocols_and_registry_helpers_resolve_without_module_imports(self) -> None:
@@ -78,6 +91,16 @@ class PostboxContractTests(unittest.TestCase):
        self.assertIsInstance(provider, PostboxMessagesProvider)
        self.assertIsInstance(provider, PostboxDeliveryProvider)
        self.assertIsInstance(provider, PostboxEvidenceProvider)
+        self.assertEqual(
+            "delivery-1",
+            PostboxDeliveryReceiptSummaryRef(
+                delivery_id="delivery-1",
+                message_id="message-1",
+                postbox_id="postbox-1",
+                delivery_status="accepted",
+                accepted_at=datetime.now(timezone.utc),
+            ).delivery_id,
+        )

        registry = PlatformRegistry()
        registry.register(
--- a/tests/test_security_redaction.py
+++ b/tests/test_security_redaction.py
@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+import unittest
+
+from govoplan_core.security.redaction import contains_plain_secret, redact_secret_values
+
+
+class SecurityRedactionTests(unittest.TestCase):
+    def test_structured_payload_redaction_covers_nested_container_shapes(self) -> None:
+        payload = {
+            "request": {
+                "Authorization": "Bearer must-not-leak",
+                "headers": [{"x-api-key": "must-not-leak"}],
+            },
+            "records": (
+                {"clientSecret": "must-not-leak", "status": "ok"},
+                {"credential_ref": "credential-1"},
+            ),
+        }
+
+        redacted = redact_secret_values(payload)
+
+        self.assertEqual("<redacted>", redacted["request"]["Authorization"])  # type: ignore[index]
+        self.assertEqual("<redacted>", redacted["request"]["headers"][0]["x-api-key"])  # type: ignore[index]
+        self.assertEqual("<redacted>", redacted["records"][0]["clientSecret"])  # type: ignore[index]
+        self.assertEqual("<redacted>", redacted["records"][1]["credential_ref"])  # type: ignore[index]
+        self.assertNotIn("must-not-leak", repr(redacted))
+
+    def test_plain_secret_detection_descends_into_lists_and_tuples(self) -> None:
+        self.assertTrue(contains_plain_secret([{"metadata": ({"private-key": "secret"},)}]))
+        self.assertFalse(contains_plain_secret([{"credential_ref": "credential-1"}]))
+
+
+if __name__ == "__main__":
+    unittest.main()
--- a/webui/scripts/test-dialog-focus-structure.mjs
+++ b/webui/scripts/test-dialog-focus-structure.mjs
@@ -10,6 +10,8 @@ const stackSource = readFileSync("src/components/dialogStack.ts", "utf8");
 assert(source.includes("ref={panelRef}"), "Dialog wires its panel ref to the focus boundary");
 assert(source.includes("tabIndex={-1}"), "Dialog exposes a programmatically focusable fallback");
 assert(source.includes("return registerDialog({"), "Dialog registers with the shared modal stack");
+assert(source.includes("createPortal(dialog, document.body)"), "Dialog supports opt-in body portals without replacing the shared stack");
+assert(source.includes("panelStyle"), "Dialog accepts bounded custom panel positioning");
 assert(!source.includes('window.addEventListener("keydown"'), "Dialog instances do not install competing keyboard listeners");
 assert(stackSource.includes('window.addEventListener("keydown", handleWindowKeyDown)'), "the modal stack owns one keyboard listener");
 assert(stackSource.includes("handleTopDialogKeyDown(event, currentActiveElement())"), "the keyboard listener delegates only to the topmost dialog");
--- a/webui/src/api/concurrency.ts
+++ b/webui/src/api/concurrency.ts
@@ -0,0 +1,376 @@
+import { isApiError } from "./client";
+
+export type RevisionConflictDetail = {
+  code: "revision_conflict";
+  resource: {
+    type: string;
+    id: string;
+  };
+  current_revision: number;
+  submitted_base_revision: number;
+  retryable: boolean;
+  refresh_path?: string;
+  current_etag?: string;
+};
+
+export type MergeConflict = {
+  path: string;
+  kind: string;
+  baseValue: unknown;
+  localValue: unknown;
+  currentValue: unknown;
+};
+
+export type ThreeWayMergeResult<T = unknown> = {
+  value: T;
+  conflicts: MergeConflict[];
+  appliedPaths: string[];
+};
+
+export type ConflictChoice = "current" | "local";
+
+type MissingValue = { readonly missing: true };
+const MISSING: MissingValue = Object.freeze({ missing: true });
+
+export function revisionConflictFromError(error: unknown): RevisionConflictDetail | null {
+  if (!isApiError(error, 409, 412)) return null;
+  try {
+    const parsed = JSON.parse(error.body) as { detail?: unknown };
+    const detail = asRecord(parsed.detail);
+    const resource = asRecord(detail.resource);
+    if (
+      detail.code !== "revision_conflict"
+      || typeof resource.type !== "string"
+      || typeof resource.id !== "string"
+      || !Number.isInteger(detail.current_revision)
+      || !Number.isInteger(detail.submitted_base_revision)
+    ) return null;
+    return {
+      code: "revision_conflict",
+      resource: {
+        type: resource.type,
+        id: resource.id
+      },
+      current_revision: Number(detail.current_revision),
+      submitted_base_revision: Number(detail.submitted_base_revision),
+      retryable: detail.retryable !== false,
+      refresh_path: typeof detail.refresh_path === "string" ? detail.refresh_path : undefined,
+      current_etag: typeof detail.current_etag === "string" ? detail.current_etag : undefined
+    };
+  } catch {
+    return null;
+  }
+}
+
+export function threeWayMerge<T>(
+  base: T,
+  local: T,
+  current: T,
+  options: {
+    protectedPaths?: readonly string[];
+    stableIdFields?: readonly string[];
+  } = {}
+): ThreeWayMergeResult<T> {
+  return mergeValue(
+    cloneValue(base),
+    cloneValue(local),
+    cloneValue(current),
+    "",
+    options.protectedPaths ?? [],
+    options.stableIdFields ?? ["id"]
+  ) as ThreeWayMergeResult<T>;
+}
+
+export function applyConflictChoices<T>(
+  merge: ThreeWayMergeResult<T>,
+  choices: Readonly<Record<string, ConflictChoice>>
+): T {
+  let result: unknown = cloneValue(merge.value);
+  for (const conflict of merge.conflicts) {
+    if ((choices[conflict.path] ?? "current") !== "local") continue;
+    result = writePath(result, conflict.path, cloneValue(conflict.localValue));
+  }
+  return result as T;
+}
+
+function mergeValue(
+  base: unknown,
+  local: unknown,
+  current: unknown,
+  path: string,
+  protectedPaths: readonly string[],
+  stableIdFields: readonly string[]
+): ThreeWayMergeResult {
+  const localChanged = !deepEqual(local, base);
+  const currentChanged = !deepEqual(current, base);
+  if (!localChanged) return result(current);
+  if (deepEqual(local, current)) return result(current);
+  if (isProtected(path, protectedPaths)) {
+    return conflictResult(path, "protected_path", base, local, current);
+  }
+  if (!currentChanged) return result(local, [], [path || "/"]);
+  if (isRecord(base) && isRecord(local) && isRecord(current)) {
+    return mergeRecord(base, local, current, path, protectedPaths, stableIdFields);
+  }
+  if (Array.isArray(base) && Array.isArray(local) && Array.isArray(current)) {
+    return mergeList(base, local, current, path, protectedPaths, stableIdFields);
+  }
+  return conflictResult(path, "same_path_changed", base, local, current);
+}
+
+function mergeRecord(
+  base: Record<string, unknown>,
+  local: Record<string, unknown>,
+  current: Record<string, unknown>,
+  path: string,
+  protectedPaths: readonly string[],
+  stableIdFields: readonly string[]
+): ThreeWayMergeResult<Record<string, unknown>> {
+  const value: Record<string, unknown> = {};
+  const conflicts: MergeConflict[] = [];
+  const appliedPaths: string[] = [];
+  const keys = [...new Set([...Object.keys(current), ...Object.keys(local), ...Object.keys(base)])];
+  for (const key of keys) {
+    const childPath = joinPath(path, key);
+    const merged = mergePresence(
+      hasOwn(base, key) ? base[key] : MISSING,
+      hasOwn(local, key) ? local[key] : MISSING,
+      hasOwn(current, key) ? current[key] : MISSING,
+      childPath,
+      protectedPaths,
+      stableIdFields
+    );
+    conflicts.push(...merged.conflicts);
+    appliedPaths.push(...merged.appliedPaths);
+    if (!isMissing(merged.value)) value[key] = merged.value;
+  }
+  return result(value, conflicts, appliedPaths);
+}
+
+function mergePresence(
+  base: unknown | MissingValue,
+  local: unknown | MissingValue,
+  current: unknown | MissingValue,
+  path: string,
+  protectedPaths: readonly string[],
+  stableIdFields: readonly string[]
+): ThreeWayMergeResult {
+  if (isMissing(local) && isMissing(current)) return result(MISSING);
+  if (isMissing(base)) {
+    if (isMissing(local)) return result(current);
+    if (isMissing(current)) {
+      if (isProtected(path, protectedPaths)) {
+        return conflictResult(path, "protected_path", undefined, local, undefined);
+      }
+      return result(local, [], [path]);
+    }
+    if (deepEqual(local, current)) return result(current);
+    return conflictResult(path, "concurrent_add", undefined, local, current);
+  }
+  if (isMissing(local)) {
+    if (deepEqual(current, base)) {
+      if (isProtected(path, protectedPaths)) {
+        return conflictResult(path, "protected_path", base, undefined, current);
+      }
+      return result(MISSING, [], [path]);
+    }
+    return conflictResult(path, "delete_vs_edit", base, undefined, current);
+  }
+  if (isMissing(current)) {
+    if (deepEqual(local, base)) return result(MISSING);
+    return conflictResult(path, "edit_vs_delete", base, local, undefined);
+  }
+  return mergeValue(base, local, current, path, protectedPaths, stableIdFields);
+}
+
+function mergeList(
+  base: unknown[],
+  local: unknown[],
+  current: unknown[],
+  path: string,
+  protectedPaths: readonly string[],
+  stableIdFields: readonly string[]
+): ThreeWayMergeResult<unknown[]> {
+  const identityField = stableIdentityField([base, local, current], stableIdFields);
+  if (!identityField) {
+    return conflictResult(path, "unkeyed_collection", base, local, current);
+  }
+  const byId = (items: unknown[]) => new Map(
+    items.map((item) => [String((item as Record<string, unknown>)[identityField]), item])
+  );
+  const baseById = byId(base);
+  const localById = byId(local);
+  const currentById = byId(current);
+  const baseOrder = [...baseById.keys()];
+  const localOrder = [...localById.keys()];
+  const currentOrder = [...currentById.keys()];
+  const localReordered = !deepEqual(commonOrder(localOrder, baseOrder), commonOrder(baseOrder, localOrder));
+  const currentReordered = !deepEqual(commonOrder(currentOrder, baseOrder), commonOrder(baseOrder, currentOrder));
+  if (localReordered && currentReordered && !deepEqual(localOrder, currentOrder)) {
+    return conflictResult(path, "collection_reorder", baseOrder, localOrder, currentOrder);
+  }
+
+  const mergedById = new Map<string, unknown>();
+  const conflicts: MergeConflict[] = [];
+  const appliedPaths: string[] = [];
+  const identities = [...new Set([...currentOrder, ...localOrder, ...baseOrder])];
+  for (const identity of identities) {
+    const merged = mergePresence(
+      baseById.has(identity) ? baseById.get(identity) : MISSING,
+      localById.has(identity) ? localById.get(identity) : MISSING,
+      currentById.has(identity) ? currentById.get(identity) : MISSING,
+      joinPath(path, `${identityField}=${identity}`),
+      protectedPaths,
+      stableIdFields
+    );
+    conflicts.push(...merged.conflicts);
+    appliedPaths.push(...merged.appliedPaths);
+    if (!isMissing(merged.value)) mergedById.set(identity, merged.value);
+  }
+
+  const orderSource = localReordered && !currentReordered ? localOrder : currentOrder;
+  const mergedOrder = orderSource.filter((identity) => mergedById.has(identity));
+  for (const identity of identities) {
+    if (mergedById.has(identity) && !mergedOrder.includes(identity)) mergedOrder.push(identity);
+  }
+  return result(
+    mergedOrder.map((identity) => mergedById.get(identity)),
+    conflicts,
+    appliedPaths
+  );
+}
+
+function writePath(root: unknown, path: string, value: unknown): unknown {
+  if (!path || path === "/") return value;
+  const segments = path.slice(1).split("/").map(decodePointerSegment);
+  const cloned = cloneValue(root);
+  let target: unknown = cloned;
+  for (let index = 0; index < segments.length - 1; index += 1) {
+    target = descend(target, segments[index]);
+  }
+  const finalSegment = segments[segments.length - 1];
+  if (Array.isArray(target)) {
+    const itemIndex = arraySegmentIndex(target, finalSegment);
+    if (itemIndex < 0) return cloned;
+    if (value === undefined) target.splice(itemIndex, 1);
+    else target[itemIndex] = value;
+  } else if (isRecord(target)) {
+    if (value === undefined) delete target[finalSegment];
+    else target[finalSegment] = value;
+  }
+  return cloned;
+}
+
+function descend(target: unknown, segment: string): unknown {
+  if (Array.isArray(target)) {
+    const index = arraySegmentIndex(target, segment);
+    return index >= 0 ? target[index] : undefined;
+  }
+  return isRecord(target) ? target[segment] : undefined;
+}
+
+function arraySegmentIndex(items: unknown[], segment: string): number {
+  const separator = segment.indexOf("=");
+  if (separator > 0) {
+    const key = segment.slice(0, separator);
+    const value = segment.slice(separator + 1);
+    return items.findIndex((item) => isRecord(item) && String(item[key]) === value);
+  }
+  const index = Number(segment);
+  return Number.isInteger(index) ? index : -1;
+}
+
+function stableIdentityField(values: unknown[][], candidates: readonly string[]): string | null {
+  const allItems = values.flat();
+  if (allItems.length === 0 || !allItems.every(isRecord)) return null;
+  for (const candidate of candidates) {
+    const valid = values.every((items) => {
+      const identities = items.map((item) => String((item as Record<string, unknown>)[candidate] ?? "").trim());
+      return identities.every(Boolean) && new Set(identities).size === identities.length;
+    });
+    if (valid) return candidate;
+  }
+  return null;
+}
+
+function commonOrder(left: string[], right: string[]): string[] {
+  const rightSet = new Set(right);
+  return left.filter((item) => rightSet.has(item));
+}
+
+function isProtected(path: string, protectedPaths: readonly string[]): boolean {
+  const normalized = path || "/";
+  return protectedPaths.some((rawPrefix) => {
+    const prefix = rawPrefix.replace(/\/+$/, "") || "/";
+    return normalized === prefix || normalized.startsWith(`${prefix}/`);
+  });
+}
+
+function conflictResult<T>(
+  path: string,
+  kind: string,
+  baseValue: unknown,
+  localValue: unknown,
+  currentValue: T
+): ThreeWayMergeResult<T> {
+  return result(currentValue, [{
+    path: path || "/",
+    kind,
+    baseValue,
+    localValue,
+    currentValue
+  }]);
+}
+
+function result<T>(
+  value: T,
+  conflicts: MergeConflict[] = [],
+  appliedPaths: string[] = []
+): ThreeWayMergeResult<T> {
+  return { value, conflicts, appliedPaths };
+}
+
+function joinPath(parent: string, segment: string): string {
+  const escaped = segment.replace(/~/g, "~0").replace(/\//g, "~1");
+  return parent ? `${parent}/${escaped}` : `/${escaped}`;
+}
+
+function decodePointerSegment(segment: string): string {
+  return segment.replace(/~1/g, "/").replace(/~0/g, "~");
+}
+
+function isMissing(value: unknown): value is MissingValue {
+  return value === MISSING;
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return Boolean(value) && typeof value === "object" && !Array.isArray(value);
+}
+
+function asRecord(value: unknown): Record<string, unknown> {
+  return isRecord(value) ? value : {};
+}
+
+function cloneValue<T>(value: T): T {
+  if (value === undefined || value === null || typeof value !== "object") return value;
+  if (typeof structuredClone === "function") return structuredClone(value);
+  return JSON.parse(JSON.stringify(value)) as T;
+}
+
+function deepEqual(left: unknown, right: unknown): boolean {
+  if (Object.is(left, right)) return true;
+  if (Array.isArray(left) && Array.isArray(right)) {
+    return left.length === right.length && left.every((item, index) => deepEqual(item, right[index]));
+  }
+  if (isRecord(left) && isRecord(right)) {
+    const leftKeys = Object.keys(left);
+    const rightKeys = Object.keys(right);
+    return leftKeys.length === rightKeys.length
+      && leftKeys.every((key) => hasOwn(right, key) && deepEqual(left[key], right[key]));
+  }
+  return false;
+}
+
+function hasOwn(value: object, key: PropertyKey): boolean {
+  return Object.prototype.hasOwnProperty.call(value, key);
+}
--- a/webui/src/components/ConcurrencyConflictDialog.tsx
+++ b/webui/src/components/ConcurrencyConflictDialog.tsx
@@ -0,0 +1,203 @@
+import {
+  createContext,
+  useCallback,
+  useContext,
+  useMemo,
+  useRef,
+  useState,
+  type ReactNode
+} from "react";
+import {
+  applyConflictChoices,
+  type ConflictChoice,
+  type ThreeWayMergeResult
+} from "../api/concurrency";
+import { usePlatformLanguage } from "../i18n/LanguageContext";
+import Button from "./Button";
+import Dialog from "./Dialog";
+import SegmentedControl from "./SegmentedControl";
+
+export type ConcurrencyResolution<T = unknown> =
+  | { action: "apply"; value: T; resolvedPaths: string[] }
+  | { action: "reload" }
+  | { action: "cancel" };
+
+export type ConcurrencyResolutionRequest<T = unknown> = {
+  resourceLabel: string;
+  merge: ThreeWayMergeResult<T>;
+};
+
+type Resolver = <T>(
+  request: ConcurrencyResolutionRequest<T>
+) => Promise<ConcurrencyResolution<T>>;
+
+type PendingResolution = {
+  request: ConcurrencyResolutionRequest;
+  resolve: (resolution: ConcurrencyResolution) => void;
+};
+
+const ConcurrencyResolverContext = createContext<Resolver | null>(null);
+
+export function ConcurrencyConflictProvider({ children }: { children: ReactNode }) {
+  const [pending, setPending] = useState<PendingResolution | null>(null);
+  const pendingRef = useRef<PendingResolution | null>(null);
+
+  const requestResolution = useCallback<Resolver>((request) => {
+    pendingRef.current?.resolve({ action: "cancel" });
+    return new Promise((resolve) => {
+      const next: PendingResolution = {
+        request: request as ConcurrencyResolutionRequest,
+        resolve: resolve as (resolution: ConcurrencyResolution) => void
+      };
+      pendingRef.current = next;
+      setPending(next);
+    });
+  }, []);
+
+  const finish = useCallback((resolution: ConcurrencyResolution) => {
+    const active = pendingRef.current;
+    pendingRef.current = null;
+    setPending(null);
+    active?.resolve(resolution);
+  }, []);
+
+  return (
+    <ConcurrencyResolverContext.Provider value={requestResolution}>
+      {children}
+      <ConcurrencyConflictDialog
+        request={pending?.request ?? null}
+        onResolve={finish}
+      />
+    </ConcurrencyResolverContext.Provider>
+  );
+}
+
+export function useConcurrencyConflictResolver(): Resolver {
+  const resolver = useContext(ConcurrencyResolverContext);
+  if (!resolver) {
+    throw new Error(
+      "useConcurrencyConflictResolver must be used inside ConcurrencyConflictProvider"
+    );
+  }
+  return resolver;
+}
+
+function ConcurrencyConflictDialog({
+  request,
+  onResolve
+}: {
+  request: ConcurrencyResolutionRequest | null;
+  onResolve: (resolution: ConcurrencyResolution) => void;
+}) {
+  const { translateText } = usePlatformLanguage();
+  const [choices, setChoices] = useState<Record<string, ConflictChoice>>({});
+  const requestKey = request
+    ? request.merge.conflicts.map((conflict) => `${conflict.path}:${conflict.kind}`).join("|")
+    : "";
+  const effectiveChoices = useMemo(
+    () => Object.fromEntries(
+      (request?.merge.conflicts ?? []).map((conflict) => [
+        conflict.path,
+        choices[conflict.path] ?? "current"
+      ])
+    ),
+    [choices, request, requestKey]
+  );
+
+  function applyResolution() {
+    if (!request) return;
+    onResolve({
+      action: "apply",
+      value: applyConflictChoices(request.merge, effectiveChoices),
+      resolvedPaths: request.merge.conflicts.map((conflict) => conflict.path)
+    });
+    setChoices({});
+  }
+
+  function finish(action: "reload" | "cancel") {
+    onResolve({ action });
+    setChoices({});
+  }
+
+  return (
+    <Dialog
+      open={Boolean(request)}
+      title="Concurrent changes"
+      role="alertdialog"
+      className="concurrency-conflict-dialog"
+      footerClassName="button-row compact-actions"
+      onClose={() => finish("cancel")}
+      footer={
+        <>
+          <Button type="button" onClick={() => finish("cancel")}>
+            {translateText("i18n:govoplan-core.cancel.77dfd213")}
+          </Button>
+          <Button type="button" onClick={() => finish("reload")}>
+            {translateText("i18n:govoplan-core.reload.cce71553")}
+          </Button>
+          <Button type="button" variant="primary" onClick={applyResolution}>
+            Apply resolution
+          </Button>
+        </>
+      }
+    >
+      <p>
+        {request?.resourceLabel ?? "This item"} changed after you loaded it.
+        Review each overlapping change before saving.
+      </p>
+      <div className="concurrency-conflict-list">
+        {(request?.merge.conflicts ?? []).map((conflict) => (
+          <section className="concurrency-conflict-item" key={`${requestKey}:${conflict.path}`}>
+            <div className="concurrency-conflict-heading">
+              <code>{conflict.path}</code>
+              <span>{conflictKindLabel(conflict.kind)}</span>
+            </div>
+            <div className="concurrency-conflict-values">
+              <ConflictValue label="Current" value={conflict.currentValue} />
+              <ConflictValue label="Your change" value={conflict.localValue} />
+            </div>
+            <SegmentedControl
+              value={effectiveChoices[conflict.path] ?? "current"}
+              options={[
+                { id: "current", label: "Keep current" },
+                { id: "local", label: "Use my change" }
+              ]}
+              onChange={(value) => setChoices((current) => ({
+                ...current,
+                [conflict.path]: value as ConflictChoice
+              }))}
+            />
+          </section>
+        ))}
+      </div>
+    </Dialog>
+  );
+}
+
+function ConflictValue({ label, value }: { label: string; value: unknown }) {
+  return (
+    <div>
+      <strong>{label}</strong>
+      <pre>{previewValue(value)}</pre>
+    </div>
+  );
+}
+
+function previewValue(value: unknown): string {
+  if (value === undefined) return "(removed)";
+  if (typeof value === "string") return value.slice(0, 500);
+  try {
+    const serialized = JSON.stringify(value, null, 2);
+    return serialized.length > 1000
+      ? `${serialized.slice(0, 1000)}\n...`
+      : serialized;
+  } catch {
+    return String(value);
+  }
+}
+
+function conflictKindLabel(kind: string): string {
+  return kind.replace(/_/g, " ");
+}
+
+export default ConcurrencyConflictDialog;
--- a/webui/src/components/Dialog.tsx
+++ b/webui/src/components/Dialog.tsx
@@ -1,4 +1,5 @@
-import { useEffect, useId, useRef, type ReactNode } from "react";
+import { useEffect, useId, useRef, type CSSProperties, type ReactNode } from "react";
+import { createPortal } from "react-dom";
 import { translateReactNode, usePlatformLanguage } from "../i18n/LanguageContext";
 import { shouldCloseDialogOnBackdrop } from "./dialogInteractions";
 import {
@@ -26,6 +27,9 @@ export type DialogProps = {
  titleClassName?: string;
  bodyClassName?: string;
  footerClassName?: string;
+  portal?: boolean;
+  panelStyle?: CSSProperties;
+  backdropStyle?: CSSProperties;
 };

 function joinClasses(...classes: Array<string | undefined | false>) {
@@ -49,7 +53,10 @@ export default function Dialog({
  headerClassName = "",
  titleClassName = "",
  bodyClassName = "",
-  footerClassName = ""
+  footerClassName = "",
+  portal = false,
+  panelStyle,
+  backdropStyle
 }: DialogProps) {
  const titleId = useId();
  const canClose = Boolean(onClose) && !closeDisabled;
@@ -107,9 +114,10 @@ export default function Dialog({

  if (!open) return null;

-  return (
+  const dialog = (
    <div
      className={joinClasses("dialog-backdrop", backdropClassName)}
+      style={backdropStyle}
      role="presentation"
      onMouseDown={(event) => {
        if (
@@ -122,6 +130,7 @@ export default function Dialog({
        ref={panelRef}
        tabIndex={-1}
        className={joinClasses("dialog-panel", className)}
+        style={panelStyle}
        role={role}
        aria-modal="true"
        data-dialog-stack-state="topmost"
@@ -147,4 +156,8 @@ export default function Dialog({
      </section>
    </div>
  );
+
+  return portal && typeof document !== "undefined"
+    ? createPortal(dialog, document.body)
+    : dialog;
 }
--- a/webui/src/components/PageScrollViewport.tsx
+++ b/webui/src/components/PageScrollViewport.tsx
@@ -1,4 +1,4 @@
-import type { HTMLAttributes, ReactNode } from "react";
+import { forwardRef, type HTMLAttributes, type ReactNode } from "react";

 export type PageScrollViewportProps = Omit<
  HTMLAttributes<HTMLDivElement>,
@@ -7,17 +7,22 @@ export type PageScrollViewportProps = Omit<
  children: ReactNode;
 };

-export default function PageScrollViewport({
-  children,
-  className = "",
-  ...props
-}: PageScrollViewportProps) {
-  return (
-    <div
-      {...props}
-      className={["page-scroll-viewport", className].filter(Boolean).join(" ")}
-    >
-      {children}
-    </div>
-  );
-}
+const PageScrollViewport = forwardRef<HTMLDivElement, PageScrollViewportProps>(
+  function PageScrollViewport({
+    children,
+    className = "",
+    ...props
+  }, ref) {
+    return (
+      <div
+        {...props}
+        ref={ref}
+        className={["page-scroll-viewport", className].filter(Boolean).join(" ")}
+      >
+        {children}
+      </div>
+    );
+  }
+);
+
+export default PageScrollViewport;
--- a/webui/src/index.ts
+++ b/webui/src/index.ts
@@ -1,6 +1,7 @@
 export * from "./types";

 export * from "./api/client";
+export * from "./api/concurrency";
 export * from "./api/auth";
 export * from "./api/platform";
 export * from "./api/notificationSummary";
@@ -55,6 +56,15 @@ export { default as Button } from "./components/Button";
 export type { ButtonProps } from "./components/Button";
 export { default as Card } from "./components/Card";
 export { default as ConfirmDialog } from "./components/ConfirmDialog";
+export {
+  default as ConcurrencyConflictDialog,
+  ConcurrencyConflictProvider,
+  useConcurrencyConflictResolver
+} from "./components/ConcurrencyConflictDialog";
+export type {
+  ConcurrencyResolution,
+  ConcurrencyResolutionRequest
+} from "./components/ConcurrencyConflictDialog";
 export { default as ConnectionTree } from "./components/ConnectionTree";
 export type { ConnectionTreeColumn, ConnectionTreeProps } from "./components/ConnectionTree";
 export { default as ColorPickerField } from "./components/ColorPickerField";
--- a/webui/src/styles/layout.css
+++ b/webui/src/styles/layout.css
@@ -132,6 +132,14 @@
 .step-intro h2 { margin: 0; color: var(--text-strong); }
 .step-intro p { margin-top: 6px; color: var(--muted); }
 .button-row { display: flex; gap: 10px; margin: 16px 0; flex-wrap: wrap; }
+.concurrency-conflict-dialog { width: min(860px, calc(100vw - 32px)); }
+.concurrency-conflict-list { display: grid; gap: 12px; max-height: min(58vh, 620px); overflow: auto; }
+.concurrency-conflict-item { border: var(--border-line); border-radius: var(--radius-sm); padding: 12px; }
+.concurrency-conflict-heading { display: flex; justify-content: space-between; gap: 12px; align-items: baseline; margin-bottom: 10px; }
+.concurrency-conflict-heading span { color: var(--muted); font-size: 12px; text-transform: capitalize; }
+.concurrency-conflict-values { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; margin-bottom: 10px; }
+.concurrency-conflict-values strong { display: block; margin-bottom: 4px; font-size: 12px; }
+.concurrency-conflict-values pre { min-height: 54px; max-height: 160px; margin: 0; padding: 8px; overflow: auto; background: var(--panel-soft); border: var(--border-line); white-space: pre-wrap; overflow-wrap: anywhere; }
 .alert { padding: 14px 16px; border-radius: var(--radius-sm); margin-bottom: 16px; }
 .alert.success { background: var(--success-bg); color: var(--success-text); }
 .alert.info { background: var(--info-bg); color: var(--info-text); }
@@ -149,6 +157,7 @@
  .section-sidebar { display: none; }
  .wizard-card { grid-template-columns: 1fr; }
  .metric-grid, .dashboard-grid, .settings-grid { grid-template-columns: 1fr; }
+  .concurrency-conflict-values { grid-template-columns: 1fr; }
 }