diff --git a/assistant/src/api/events/assistant-text-delta.ts b/assistant/src/api/events/assistant-text-delta.ts
index c54b8f232ed..0c15f8e0018 100644
--- a/assistant/src/api/events/assistant-text-delta.ts
+++ b/assistant/src/api/events/assistant-text-delta.ts
@@ -6,11 +6,19 @@
  * message; the matching `message_complete` event marks the turn done.
  *
  * `messageId` is the database row id of the assistant message this
- * delta belongs to — stamped from the pre-allocated turn anchor (see
- * `reserveMessage` / `AssistantTurnStartEvent`). Absent on streams
- * produced by older daemons that pre-date the anchor protocol, or on
- * synthetic deltas (canned greetings, slash-command echoes, live-voice
- * transcript injections) that don't bind to a row.
+ * delta belongs to. The main agent loop (post PR 1 of the
+ * streaming-message-architecture plan) always allocates and emits a
+ * `messageId` for every delta it produces, via `ensureMessageOpen` in
+ * `conversation-agent-loop-handlers.ts`. The field stays optional in
+ * this schema because synthetic emitters that don't bind to a persisted
+ * row (canned greetings, slash-command echoes, live-voice transcript
+ * injections, wake-target replays, recording handler echoes) still emit
+ * deltas without one; those streams are consumed by channel adapters,
+ * not by the `MessageStreamReducer` path.
+ *
+ * `blockIndex` and `seq` are populated whenever `messageId` is, so a
+ * client receiving any of the three is guaranteed to receive all three
+ * (idempotent reducer keying invariant — see `MessageStreamReducer`).
  *
  * Canonical wire-contract source. Daemon code imports the type directly
  * from this file; external consumers import via `@vellumai/assistant-api`.
diff --git a/assistant/src/api/events/message-complete.ts b/assistant/src/api/events/message-complete.ts
index db91b95d3dc..60cb751edb4 100644
--- a/assistant/src/api/events/message-complete.ts
+++ b/assistant/src/api/events/message-complete.ts
@@ -18,6 +18,17 @@
  * side effects on `source !== "aux"`. Absent is treated as `"main"`
  * for backwards compatibility.
  *
+ * Streaming-architecture status (post-PR 6): the new addressable-event
+ * protocol uses `message_open` / `message_close` as the canonical
+ * lifecycle pair for the `MessageStreamReducer` path. `message_complete`
+ * remains the canonical end-of-turn signal for the wider event-consumer
+ * fleet — CLI, voice session bridge, channel retry sweep, background
+ * dispatch — which still gate on it for side effects (task-complete
+ * sound, attachment delivery, channel idle bookkeeping). It is the
+ * post-persistence event with the authoritative DB row id, attachments,
+ * and `source` discriminator; `message_close` is the pre-persistence
+ * streaming signal and does not carry those fields.
+ *
  * Canonical wire-contract source. Daemon code imports the type directly
  * from this file; external consumers import via `@vellumai/assistant-api`.
  */
diff --git a/clients/macos/vellum-assistant/Features/Chat/TranscriptProjector.swift b/clients/macos/vellum-assistant/Features/Chat/TranscriptProjector.swift
index 36f89b1a275..cfa99da6234 100644
--- a/clients/macos/vellum-assistant/Features/Chat/TranscriptProjector.swift
+++ b/clients/macos/vellum-assistant/Features/Chat/TranscriptProjector.swift
@@ -50,11 +50,14 @@ enum TranscriptProjector {
         highlightedMessageId: UUID?,
         autoRoutedProfileLabel: String? = nil
     ) -> TranscriptRenderModel {
-        // Deduplicate visible messages (streaming can produce duplicate IDs).
-        let visibleMessages: [ChatMessage] = {
-            var seen = Set<UUID>()
-            return paginatedVisibleMessages.filter { seen.insert($0.id).inserted }
-        }()
+        // Per streaming-message-architecture PR 6: the MessageStreamReducer is
+        // the sole writer for assistant content and applies events idempotently
+        // by `(messageId, blockIndex, seq)`. `renderedMessages` and
+        // `renderedPaginatedVisibleMessages` on `ChatViewModel` already merge
+        // legacy rows with `MessageStore` snapshots using stable, deterministic
+        // ids, so the projector's input is already unique by id and the
+        // previous defensive dedupe pass is no longer needed.
+        let visibleMessages = paginatedVisibleMessages
 
         // --- Structural metadata ---
 
diff --git a/clients/macos/vellum-assistantTests/TranscriptProjectorTests.swift b/clients/macos/vellum-assistantTests/TranscriptProjectorTests.swift
index b9d2748cc92..373a4cce130 100644
--- a/clients/macos/vellum-assistantTests/TranscriptProjectorTests.swift
+++ b/clients/macos/vellum-assistantTests/TranscriptProjectorTests.swift
@@ -446,16 +446,23 @@ final class TranscriptProjectorTests: XCTestCase {
         XCTAssertFalse(model.canInlineProcessing)
     }
 
-    // MARK: - Duplicate Message Deduplication
+    // MARK: - Message Identity Trust
+    //
+    // Per streaming-message-architecture PR 6, the projector no longer
+    // dedupes by id — the `MessageStreamReducer` is the sole writer for
+    // assistant content and its idempotent apply means upstream input is
+    // already unique by id. The renderer trusts that contract.
+
+    func testProjectorPreservesInputOrderAndIdentity() {
+        let msg1 = makeMessage(role: .assistant, text: "First")
+        let msg2 = makeMessage(role: .user, text: "Second")
+        let msg3 = makeMessage(role: .assistant, text: "Third")
 
-    func testDuplicateMessageIdsAreDeduped() {
-        let sharedId = UUID()
-        let msg1 = makeMessage(id: sharedId, role: .assistant, text: "First")
-        let msg2 = makeMessage(id: sharedId, role: .assistant, text: "Duplicate")
-
-        let model = project(messages: [msg1, msg2])
-        XCTAssertEqual(model.rows.count, 1, "Duplicate IDs should be deduped")
-        XCTAssertEqual(model.rows[0].message.text, "First", "First occurrence wins")
+        let model = project(messages: [msg1, msg2, msg3])
+        XCTAssertEqual(model.rows.count, 3, "All input rows pass through 1:1")
+        XCTAssertEqual(model.rows[0].message.text, "First")
+        XCTAssertEqual(model.rows[1].message.text, "Second")
+        XCTAssertEqual(model.rows[2].message.text, "Third")
     }
 
     // MARK: - Active Pending Request ID Pass-Through
diff --git a/clients/shared/Features/Chat/MessageStore+ChatMessageBridge.swift b/clients/shared/Features/Chat/MessageStore+ChatMessageBridge.swift
index 998ff59c8ab..844856c65b6 100644
--- a/clients/shared/Features/Chat/MessageStore+ChatMessageBridge.swift
+++ b/clients/shared/Features/Chat/MessageStore+ChatMessageBridge.swift
@@ -1,24 +1,28 @@
 import Foundation
 
 /// Bridge from the new `MessageStore` (the streaming-message-architecture
-/// reducer's source of truth) to the legacy `ChatMessage` shape that the
-/// existing chat renderer consumes.
+/// reducer's source of truth) to the `ChatMessage` shape that the existing
+/// chat renderer consumes.
 ///
-/// As of PR 4 of the streaming-message-architecture plan, the chat view list
-/// renders from `ChatViewModel.renderedMessages`, which merges the legacy
-/// `messages` array (user bubbles, history, confirmations, system messages)
-/// with assistant content materialized from `MessageStore` snapshots through
-/// this bridge.
+/// The chat view list renders from `ChatViewModel.renderedMessages`, which
+/// merges the legacy `messages` array (user bubbles, history rows, system
+/// messages, confirmations) with assistant content materialized from
+/// `MessageStore` snapshots through this bridge. For any assistant message
+/// the daemon emits over the new addressable-event protocol, the
+/// `MessageStore` snapshot wins over the legacy row — the legacy bubble
+/// created by `appendTextToCurrentMessage` is silently dropped from the
+/// merged transcript.
 ///
-/// The legacy streaming helpers on `ChatViewModel` still mutate the legacy
-/// `messages` array as a side effect, but those mutations no longer drive
-/// rendering for messages that have a corresponding `MessageStore` snapshot.
-/// This is what makes the streaming-then-reload duplication symptom
-/// structurally impossible: the renderer reads a single source of truth keyed
-/// by the daemon's stable `messageId` regardless of how many times the legacy
-/// path lazy-creates bubbles.
+/// `MessageStreamReducer` is the sole writer for `MessageStore`, and its
+/// `apply()` is idempotent per `(messageId, blockIndex, seq)`. This is what
+/// makes the streaming-then-reload duplication symptom structurally
+/// impossible: re-applying the same event (e.g. on `Last-Event-Id` reconnect
+/// replay from PR 2) is a no-op, and the renderer always reads a single
+/// source of truth keyed by the daemon's stable `messageId`.
 ///
-/// PR 6 of the plan will remove the legacy `messages` array entirely.
+/// Non-assistant rows and history rows that pre-date the new event protocol
+/// still flow through the legacy `messages` array, which is why the merge
+/// in `ChatViewModel.renderedMessages` is still needed.
 @MainActor
 extension MessageStore {