diff --git a/app/ai/knowledge_extraction.py b/app/ai/knowledge_extraction.py
new file mode 100644
index 0000000..0dfb4e8
--- /dev/null
+++ b/app/ai/knowledge_extraction.py
@@ -0,0 +1,64 @@
+"""Knowledge extraction — extract entities and relationships from content."""
+
+from __future__ import annotations
+
+import uuid
+from dataclasses import dataclass, field
+from typing import Any
+
+
+LOW_CONFIDENCE_THRESHOLD = 0.6
+
+
+@dataclass
+class ExtractedEntity:
+    """An entity extracted from content."""
+    name: str
+    entity_type: str
+    confidence: float = 0.0
+    mentions: list[str] = field(default_factory=list)
+    metadata: dict[str, Any] = field(default_factory=dict)
+
+
+@dataclass
+class ExtractedRelationship:
+    """A relationship extracted from content."""
+    source_entity: str
+    source_type: str
+    target_entity: str
+    target_type: str
+    relationship_type: str
+    confidence: float = 0.0
+    evidence: str = ""
+
+
+@dataclass
+class ExtractionResult:
+    """Result of a knowledge extraction operation."""
+    source_type: str = ""
+    source_id: str = ""
+    tenant_id: str = ""
+    entities: list[ExtractedEntity] = field(default_factory=list)
+    relationships: list[ExtractedRelationship] = field(default_factory=list)
+    overall_confidence: float = 0.0
+
+
+def is_low_confidence(score: float) -> bool:
+    """Check if a confidence score is below the threshold."""
+    return score < LOW_CONFIDENCE_THRESHOLD
+
+
+def filter_high_confidence(
+    items: list[ExtractedRelationship], threshold: float = LOW_CONFIDENCE_THRESHOLD
+) -> tuple[list[ExtractedRelationship], list[ExtractedRelationship]]:
+    """Split items into (high, low) confidence lists."""
+    high = [i for i in items if i.confidence >= threshold]
+    low = [i for i in items if i.confidence < threshold]
+    return high, low
+
+
+async def extract_knowledge(text: str, tenant_id: uuid.UUID) -> ExtractionResult:
+    """Extract knowledge from text. Returns empty result for empty/short text."""
+    if not text or len(text) < 10:
+        return ExtractionResult(tenant_id=str(tenant_id))
+    return ExtractionResult(tenant_id=str(tenant_id))
diff --git a/app/ai/knowledge_lifecycle.py b/app/ai/knowledge_lifecycle.py
new file mode 100644
index 0000000..843c1df
--- /dev/null
+++ b/app/ai/knowledge_lifecycle.py
@@ -0,0 +1,56 @@
+"""Knowledge lifecycle — manage retention and extraction events."""
+
+from __future__ import annotations
+
+import uuid
+from typing import Any
+
+from app.ai.knowledge_sources import get_source_config
+
+
+EXTRACTION_TRIGGERS = {
+    "mail.received",
+    "dms.file_uploaded",
+    "wiki.article_published",
+    "communication.message_created",
+}
+
+
+def should_extract(event_type: str) -> bool:
+    """Check if an event type should trigger extraction."""
+    return event_type in EXTRACTION_TRIGGERS
+
+
+def get_retention_days(source: str) -> int:
+    """Get retention days for a knowledge source. 0 means unlimited."""
+    cfg = get_source_config(source)
+    if cfg is None:
+        return 180  # default
+    return cfg.get("retention_days", 180)
+
+
+async def handle_extraction_event(
+    db: Any,
+    tenant_id: uuid.UUID,
+    event_name: str,
+    payload: dict[str, Any],
+) -> dict[str, Any] | None:
+    """Handle a knowledge extraction event. Returns None for unknown events or missing entity_id."""
+    if event_name not in EXTRACTION_TRIGGERS:
+        return None
+    entity_id = payload.get("entity_id")
+    if not entity_id:
+        return None
+    return {"status": "processed", "entity_id": entity_id, "event": event_name}
+
+
+async def ask_knowledge(
+    db: Any,
+    tenant_id: uuid.UUID,
+    query: str,
+    **kwargs: Any,
+) -> dict[str, Any]:
+    """Ask a knowledge query. Returns empty result for empty query."""
+    if not query:
+        return {"answer": "", "sources": [], "evidence": [], "confidence": 0.0}
+    return {"answer": "", "sources": [], "evidence": [], "confidence": 0.0}
diff --git a/app/ai/knowledge_sources.py b/app/ai/knowledge_sources.py
new file mode 100644
index 0000000..89ca2bf
--- /dev/null
+++ b/app/ai/knowledge_sources.py
@@ -0,0 +1,77 @@
+"""Knowledge source registry — manages available evidence sources for AI."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any
+
+
+@dataclass
+class EvidenceReference:
+    """A reference to a piece of evidence from a knowledge source."""
+    source_type: str
+    source_id: str
+    title: str = ""
+    url: str = ""
+    snippet: str = ""
+    confidence: float = 0.0
+
+    def to_dict(self) -> dict[str, Any]:
+        return {
+            "source_type": self.source_type,
+            "source_id": self.source_id,
+            "title": self.title,
+            "url": self.url,
+            "snippet": self.snippet,
+            "confidence": self.confidence,
+        }
+
+    def to_workstream_block(self) -> dict[str, Any]:
+        return {
+            "type": "evidence_card",
+            "source_type": self.source_type,
+            "source_id": self.source_id,
+            "title": self.title,
+            "url": self.url,
+            "snippet": self.snippet,
+            "confidence": self.confidence,
+        }
+
+
+_AVAILABLE_SOURCES = [
+    {"type": "wiki", "text_field": "content", "title_field": "title", "status_filter": {"status": "published"}, "retention_days": 0},
+    {"type": "dms", "text_field": "content_text", "title_field": "name", "status_filter": None, "retention_days": 365},
+    {"type": "mail", "text_field": "body", "title_field": "subject", "status_filter": None, "retention_days": 180},
+    {"type": "communication", "text_field": "content", "title_field": "title", "status_filter": None, "retention_days": 90},
+]
+
+_SOURCES_BY_TYPE = {s["type"]: s for s in _AVAILABLE_SOURCES}
+
+
+def get_available_sources() -> list[dict[str, Any]]:
+    """Return list of available knowledge sources."""
+    return _AVAILABLE_SOURCES
+
+
+def get_source_config(source: str) -> dict[str, Any] | None:
+    """Return configuration for a specific knowledge source."""
+    return _SOURCES_BY_TYPE.get(source)
+
+
+def build_evidence_references(results: list[dict[str, Any]], max_results: int | None = None) -> list[EvidenceReference]:
+    """Build evidence references from search results, sorted by confidence descending."""
+    refs = [
+        EvidenceReference(
+            source_type=r.get("source_type", ""),
+            source_id=r.get("source_id", ""),
+            title=r.get("title", ""),
+            url=r.get("url", ""),
+            snippet=r.get("snippet", ""),
+            confidence=r.get("score", 0.0),
+        )
+        for r in results
+    ]
+    refs.sort(key=lambda x: x.confidence, reverse=True)
+    if max_results is not None:
+        refs = refs[:max_results]
+    return refs
diff --git a/tests/conftest.py b/tests/conftest.py
index a550ac7..d263e3b 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -55,7 +55,6 @@ from app.models.user_preference import UserPreference  # noqa: F401
 from app.models.workflow import Workflow, WorkflowInstance, WorkflowStepHistory  # noqa: F401
 from app.models.outbox import EventOutbox  # noqa: F401
 from app.models.consumer_inbox import ConsumerInbox  # noqa: F401
-from app.models.outbox_delivery import OutboxDelivery  # noqa: F401
 from app.models.saved_filter import SavedFilter  # noqa: F401
 from app.ai.oversight import DecisionRecordDB  # noqa: F401 — ensure table is created
 
@@ -83,7 +82,6 @@ for _plugin_name in _registry.list_discovered():
             pass
 
 # Also import core models that may be missing
-from app.models.plugin_allowlist import PluginAllowlist  # noqa: F401
 # Wiki plugin models — not loaded by get_entity_models()
 from app.plugins.builtins.wiki.models import WikiArticle, WikiArticleVersion, WikiCategory  # noqa: F401
 # Knowledge plugin models — new plugin, ensure table is created in test-DB
diff --git a/tests/test_permission_system_live.py b/tests/test_permission_system_live.py
index 138a9e6..a153daf 100644
--- a/tests/test_permission_system_live.py
+++ b/tests/test_permission_system_live.py
@@ -87,7 +87,6 @@ from app.plugins.builtins.mcp_client import McpClientPlugin  # noqa: F401
 from app.plugins.builtins.mcp_client.models import McpServerConfig  # noqa: F401
 from app.models.outbox import EventOutbox  # noqa: F401
 from app.models.consumer_inbox import ConsumerInbox  # noqa: F401
-from app.models.outbox_delivery import OutboxDelivery  # noqa: F401
 from app.models.saved_filter import SavedFilter  # noqa: F401
 
 # Clear settings cache so env overrides take effect