fix: duplicate user message on first send in a new tabdev

When a draft is promoted to a real conversation, send() appends the
user message as a provisional chunk (optimistic echo). But load()
also fires syncTail, which fetches the CR-6 persisted user message
as a committed chunk — showing the message twice until turn seal.

Fix: applyHistory now removes provisional chunks that duplicate the
last committed chunk (matching role + text content) when new committed
chunks arrive during generation. The optimistic echo is dropped once
the authoritative committed version arrives.

684 tests green.

1 files changed, 20 insertions, 0 deletions

diff --git a/src/core/chunks/reducer.test.ts b/src/core/chunks/reducer.test.ts
index a346545..883461e 100644
--- a/src/core/chunks/reducer.test.ts
+++ b/src/core/chunks/reducer.test.ts
@@ -551,6 +551,26 @@ describe("applyHistory", () => {
 		expect(s.committed).toHaveLength(2);
 		expect(s.committed.map((c) => c.seq)).toEqual([1, 2]);
 	});
+
+	it("removes provisional duplicate when committed user message arrives during generation", () => {
+		// Simulate: send() appends provisional user message, then syncTail
+		// fetches the same message as committed (CR-6: persisted at turn start).
+		let s = initialState();
+		s = appendUserMessage(s, "hello");
+		s = foldEvent(s, turnStart("t1"));
+		expect(s.provisional).toHaveLength(1);
+		expect(s.provisional[0]?.role).toBe("user");
+		expect(s.generating).toBe(true);
+
+		// syncTail fetches the persisted user message as committed
+		s = applyHistory(s, [storedChunk(1, "user", { type: "text", text: "hello" })]);
+
+		// The provisional duplicate is removed — no double render
+		expect(s.provisional).toEqual([]);
+		expect(s.committed).toHaveLength(1);
+		expect(s.committed[0]?.role).toBe("user");
+		expect(s.committed[0]?.chunk).toEqual({ type: "text", text: "hello" });
+	});
 });
 
 describe("selectChunks", () => {