diff --git a/internal/agent/loop_types.go b/internal/agent/loop_types.go
index acef5aeb..7a5f6af8 100644
--- a/internal/agent/loop_types.go
+++ b/internal/agent/loop_types.go
@@ -68,10 +68,17 @@ type CacheInvalidateFunc func(agentID uuid.UUID, userID string)
 // Loop is the agent execution loop for one agent instance.
 // Think → Act → Observe cycle with tool execution.
 type Loop struct {
-	id               string
-	displayName      string
-	agentUUID        uuid.UUID // set for context propagation
-	tenantID         uuid.UUID // agent's owning tenant
+	// id is the human-readable agent_key (e.g. "goctech-leader"). Use for logs,
+	// UI events, system prompt rendering, filesystem paths, and context keys.
+	// NEVER set on DB FK columns or DomainEvent.AgentID — those require UUID.
+	// See docs/agent-identity-conventions.md.
+	id          string
+	displayName string
+	// agentUUID is the canonical DB primary key. Use for SQL WHERE/JOIN,
+	// DomainEvent.AgentID, OTel span attributes, and context propagation via
+	// store.WithAgentID. See docs/agent-identity-conventions.md.
+	agentUUID uuid.UUID
+	tenantID  uuid.UUID // agent's owning tenant
 	agentType        string    // "open" or "predefined"
 	defaultTimezone  string    // system default timezone for bootstrap pre-fill
 	provider         providers.Provider
diff --git a/internal/eventbus/event_types.go b/internal/eventbus/event_types.go
index df35fdce..a9f76a70 100644
--- a/internal/eventbus/event_types.go
+++ b/internal/eventbus/event_types.go
@@ -27,15 +27,21 @@ const (
 )
 
 // DomainEvent is a typed event with metadata for the consolidation pipeline.
+//
+// Identity invariant: TenantID and AgentID are string fields for legacy wire
+// compatibility, but consumers parse them as UUIDs before touching the DB.
+// Publishers MUST supply valid UUID strings — never agent_key or tenant_slug.
+// The publish-time observer in validate_agent_id.go warns on drift.
+// See docs/agent-identity-conventions.md.
 type DomainEvent struct {
-	ID        string    // UUID v7 for ordering
+	ID        string // UUID v7 for ordering
 	Type      EventType
-	SourceID  string    // dedup key (e.g. session key, run ID)
-	TenantID  string
-	AgentID   string
+	SourceID  string // dedup key (e.g. session key, run ID)
+	TenantID  string // MUST be a valid UUID string — never tenant_slug
+	AgentID   string // MUST be a valid UUID string — never agent_key
 	UserID    string
 	Timestamp time.Time
-	Payload   any       // typed per EventType (see payload structs below)
+	Payload   any // typed per EventType (see payload structs below)
 }
 
 // --- Typed payloads, one per EventType ---
diff --git a/internal/gateway/methods/agent_links.go b/internal/gateway/methods/agent_links.go
index 7a65c2d0..4d12c0f5 100644
--- a/internal/gateway/methods/agent_links.go
+++ b/internal/gateway/methods/agent_links.go
@@ -408,10 +408,10 @@ func (m *AgentLinksMethods) invalidateLinkAgentsByID(ctx context.Context, source
 
 // --- helpers ---
 
-// resolveAgentUUID resolves an agent identifier (either UUID or agent_key) to its
-// canonical UUID via a DB lookup. Tenant-aware via store.TenantIDFromContext(ctx)
-// inside agentStore.GetByID/GetByKey. Prefer resolveAgentUUIDCached for hot-path
-// handlers to avoid an unnecessary DB roundtrip.
+// resolveAgentUUID resolves an agent identifier (either UUID or agent_key) to
+// its canonical UUID via a DB lookup. Tenant-aware via
+// store.TenantIDFromContext(ctx) inside agentStore.GetByID/GetByKey. Prefer
+// resolveAgentUUIDCached in hot-path handlers to avoid the extra DB roundtrip.
 // See docs/agent-identity-conventions.md trap zone 5.
 func resolveAgentUUID(ctx context.Context, agentStore store.AgentStore, keyOrID string) (uuid.UUID, error) {
 	if id, err := uuid.Parse(keyOrID); err == nil {
@@ -436,11 +436,12 @@ type agentUUIDProvider interface {
 }
 
 // resolveAgentUUIDCached is the cache-aware variant of resolveAgentUUID.
-// Checks the router cache first when the input is an agent_key and the Loop is
-// cached — avoids a DB roundtrip on the hot path. Falls back to DB lookup on
-// cache miss or when the input is a UUID string (not cached under the raw UUID
-// key post-Phase-2 canonicalization). If router is nil, delegates straight to
-// resolveAgentUUID. See docs/agent-identity-conventions.md trap zone 5.
+// Checks the router cache first when the input is an agent_key and the Loop
+// is cached — avoids a DB roundtrip on the hot path. Falls back to DB lookup
+// on cache miss or when the input is a UUID string (router cache keys are
+// canonicalized to `tenantID:agentKey`, so UUID inputs never hit the cache).
+// If router is nil, delegates straight to resolveAgentUUID.
+// See docs/agent-identity-conventions.md trap zone 5 and section 8.
 func resolveAgentUUIDCached(ctx context.Context, router *agent.Router, agentStore store.AgentStore, keyOrID string) (uuid.UUID, error) {
 	// Fast path: input is agent_key and the agent is cached in the router.
 	if router != nil {
diff --git a/internal/store/pg/memory_docs.go b/internal/store/pg/memory_docs.go
index cdf25db4..e56b7d32 100644
--- a/internal/store/pg/memory_docs.go
+++ b/internal/store/pg/memory_docs.go
@@ -477,12 +477,12 @@ func (s *PGMemoryStore) Close() error { return nil }
 
 // --- Helpers ---
 
-// parseUUID returns the parsed UUID or a descriptive error.
-// Use for every INSERT/UPDATE/UPSERT/DELETE/SELECT-WHERE path where silent nil
-// would either corrupt data (FK constraints reject it, but callers see cryptic
-// PG code 23503 instead of a clean Go error) OR hide bugs as empty reads /
-// zero-row updates. Phase 4 migration target for all 57 CRITICAL sites.
-// See docs/agent-identity-conventions.md (Phase 6).
+// parseUUID returns the parsed UUID or a descriptive error. Use for every
+// INSERT/UPDATE/UPSERT/DELETE and any SELECT WHERE where silent nil would
+// either corrupt data or hide bugs as empty reads / zero-row updates. FK
+// constraints reject bad writes at the driver layer, but errors there come
+// back as cryptic PG 23503 — parseUUID catches them upstream with a clean
+// Go error. See docs/agent-identity-conventions.md trap zone 3.
 func parseUUID(s string) (uuid.UUID, error) {
 	id, err := uuid.Parse(s)
 	if err != nil {
@@ -492,11 +492,11 @@ func parseUUID(s string) (uuid.UUID, error) {
 }
 
 // parseUUIDOrNil returns the parsed UUID or uuid.Nil on failure, without
-// raising an error. INTENTIONALLY silent — only use for read-only SELECT-WHERE
-// paths where a no-match (empty result) is acceptable. Do NOT use for writes,
-// updates, deletes, or any SELECT where empty result would hide a bug.
-// Prefer parseUUID for any new code.
-// See docs/agent-identity-conventions.md (Phase 6).
+// raising an error. INTENTIONALLY silent — only acceptable on read-only
+// SELECT WHERE paths where a no-match (empty result) is the correct
+// semantics on bad input. Do NOT use for writes, updates, deletes, or any
+// SELECT where an empty result would hide a bug. Prefer parseUUID for new
+// code. See docs/agent-identity-conventions.md trap zone 3.
 func parseUUIDOrNil(s string) uuid.UUID {
 	id, err := uuid.Parse(s)
 	if err != nil {