3 files changed, 96 insertions, 0 deletions

diff --git a/src/core/chunks/reducer.test.ts b/src/core/chunks/reducer.test.ts
index a346545..c479488 100644
--- a/src/core/chunks/reducer.test.ts
+++ b/src/core/chunks/reducer.test.ts
@@ -551,6 +551,86 @@ describe("applyHistory", () => {
 		expect(s.committed).toHaveLength(2);
 		expect(s.committed.map((c) => c.seq)).toEqual([1, 2]);
 	});
+
+	it("clears provisional when new committed chunks arrive during generation (CR-6)", () => {
+		let s = initialState();
+		s = foldEvent(s, turnStart("t1"));
+		s = foldEvent(s, textDelta("t1", "hello"));
+		s = foldEvent(s, toolCall("t1", "tc1", "run_shell", {}));
+		s = foldEvent(s, toolResult("t1", "tc1", "run_shell", "output"));
+		expect(s.generating).toBe(true);
+		expect(s.provisional.length).toBeGreaterThan(0);
+
+		s = applyHistory(s, [
+			storedChunk(1, "assistant", { type: "text", text: "hello" }),
+			storedChunk(2, "assistant", {
+				type: "tool-call",
+				toolCallId: "tc1",
+				toolName: "run_shell",
+				input: {},
+				stepId: "s0" as StepId,
+			}),
+			storedChunk(3, "tool", {
+				type: "tool-result",
+				toolCallId: "tc1",
+				toolName: "run_shell",
+				content: "output",
+				isError: false,
+				stepId: "s0" as StepId,
+			}),
+		]);
+
+		expect(s.provisional).toEqual([]);
+		expect(s.generating).toBe(true);
+		expect(s.committed).toHaveLength(3);
+	});
+
+	it("keeps provisional when no new committed chunks arrive during generation", () => {
+		let s = initialState();
+		s = applyHistory(s, [storedChunk(1, "user", { type: "text", text: "q" })]);
+		s = foldEvent(s, turnStart("t1"));
+		s = foldEvent(s, textDelta("t1", "hello"));
+		s = foldEvent(s, toolCall("t1", "tc1", "run_shell", {}));
+		// At this point: provisional has [text "hello", tool-call]
+		expect(s.provisional.length).toBeGreaterThan(0);
+
+		// applyHistory with chunks already in committed — no new additions
+		s = applyHistory(s, [storedChunk(1, "user", { type: "text", text: "q" })]);
+
+		expect(s.provisional.length).toBeGreaterThan(0);
+	});
+
+	it("keeps accumulating when clearing provisional during generation (CR-6)", () => {
+		let s = initialState();
+		s = applyHistory(s, [storedChunk(1, "user", { type: "text", text: "q" })]);
+		s = foldEvent(s, turnStart("t1"));
+		s = foldEvent(s, toolCall("t1", "tc1", "run_shell", {}));
+		s = foldEvent(s, toolResult("t1", "tc1", "run_shell", "output"));
+		// Start accumulating text for the NEXT step
+		s = foldEvent(s, textDelta("t1", "streaming..."));
+		expect(s.accumulating).not.toBeNull();
+
+		s = applyHistory(s, [
+			storedChunk(2, "assistant", {
+				type: "tool-call",
+				toolCallId: "tc1",
+				toolName: "run_shell",
+				input: {},
+				stepId: "s0" as StepId,
+			}),
+			storedChunk(3, "tool", {
+				type: "tool-result",
+				toolCallId: "tc1",
+				toolName: "run_shell",
+				content: "output",
+				isError: false,
+				stepId: "s0" as StepId,
+			}),
+		]);
+
+		expect(s.provisional).toEqual([]);
+		expect(s.accumulating).not.toBeNull();
+	});
 });
 
 describe("selectChunks", () => {
diff --git a/src/core/chunks/reducer.ts b/src/core/chunks/reducer.ts
index 035846c..37f0164 100644
--- a/src/core/chunks/reducer.ts
+++ b/src/core/chunks/reducer.ts
@@ -54,8 +54,10 @@ export function applyHistory(
 ): TranscriptState {
 	const seqMap = new Map<number, StoredChunk>();
 	for (const c of state.committed) seqMap.set(c.seq, c);
+	let addedNew = false;
 	for (const c of chunks) {
 		if (c.seq < state.hiddenBeforeSeq) continue;
+		if (!seqMap.has(c.seq)) addedNew = true;
 		seqMap.set(c.seq, c);
 	}
 	const committed = Array.from(seqMap.values()).sort((a, b) => a.seq - b.seq);
@@ -70,6 +72,15 @@ export function applyHistory(
 		};
 	}
 
+	// During generation: if new committed chunks arrived (CR-6 — backend
+	// persists at step boundaries), clear provisional chunks. They're
+	// duplicates — the same content was folded from live events but is now
+	// persisted with seq. Keep the accumulating chunk (current in-progress
+	// step, not yet persisted).
+	if (addedNew && state.generating) {
+		return { ...state, committed, provisional: [], accumulating: state.accumulating };
+	}
+
 	return { ...state, committed };
 }
 
diff --git a/src/features/chat/store.svelte.ts b/src/features/chat/store.svelte.ts
index 9beabfc..f6c23fc 100644
--- a/src/features/chat/store.svelte.ts
+++ b/src/features/chat/store.svelte.ts
@@ -284,6 +284,11 @@ export function createChatStore(deps: ChatStoreDependencies): ChatStore {
 			if (transcript.sealedTurnId !== null) {
 				void syncTail();
 				void syncMetrics();
+			} else if (msg.event.type === "step-complete") {
+				// CR-6: backend persists chunks at step boundaries. Fetch them
+				// as committed so trimTranscript can unload oldest chunks
+				// uniformly — no unbounded provisional growth during long turns.
+				void syncTail();
 			}
 		},