diff --git a/apps/mobile/src/features/review/reviewModel.ts b/apps/mobile/src/features/review/reviewModel.ts
index bc0e23b336582..1b2131c73e0c1 100644
--- a/apps/mobile/src/features/review/reviewModel.ts
+++ b/apps/mobile/src/features/review/reviewModel.ts
@@ -1,6 +1,9 @@
 import { parsePatchFiles } from "@pierre/diffs/utils/parsePatchFiles";
 import type { ChangeTypes, FileDiffMetadata } from "@pierre/diffs/types";
-import type { ThreadCheckpointSummary } from "@t3tools/client-runtime/state/thread-checkpoints";
+import {
+  checkpointFileTotals,
+  type ThreadCheckpointSummary,
+} from "@t3tools/client-runtime/state/thread-checkpoints";
 import type { ReviewDiffPreviewSource } from "@t3tools/contracts";
 import { quoteGitPatchPath } from "@t3tools/shared/gitPatchPath";
 import * as Arr from "effect/Array";
@@ -107,7 +110,7 @@ function checkpointTitle(checkpoint: ThreadCheckpointSummary): string {
 }
 
 function checkpointSubtitle(checkpoint: ThreadCheckpointSummary): string {
-  const fileCount = checkpoint.files.length;
+  const fileCount = checkpointFileTotals(checkpoint).count;
   if (checkpoint.status !== "ready") {
     return `Diff ${checkpoint.status}`;
   }
diff --git a/apps/server/src/orchestration-v2/ThreadStream.ts b/apps/server/src/orchestration-v2/ThreadStream.ts
index 3c4baab80ef07..80ee5c32d6152 100644
--- a/apps/server/src/orchestration-v2/ThreadStream.ts
+++ b/apps/server/src/orchestration-v2/ThreadStream.ts
@@ -10,7 +10,10 @@ import {
   buildBoundedThreadProjection,
   type BoundedProjectionResult,
 } from "./threadHistoryPaging.ts";
-import { projectThreadProjectionForWire } from "./WireProjection.ts";
+import {
+  capProjectionCheckpointFilesForWire,
+  projectThreadProjectionForWire,
+} from "./WireProjection.ts";
 
 export const THREAD_RESUME_MAX_REPLAY_EVENTS = 128;
 
@@ -44,10 +47,9 @@ export function boundedSnapshotResponseFields(input: {
   readonly compactIds: boolean;
 }) {
   const { bounded } = input;
+  const capped = capProjectionCheckpointFilesForWire(bounded.projection);
   // Dedupe keeps shared items one object, which the compaction's identity check needs.
-  const projection = input.dedupeBodies
-    ? dedupeSnapshotBodies(bounded.projection)
-    : bounded.projection;
+  const projection = input.dedupeBodies ? dedupeSnapshotBodies(capped) : capped;
   const compactProjection = input.compactTurnItems ? omitLocalVisibleTurnItems(projection) : null;
   return {
     projection: compactProjection ?? projection,
diff --git a/apps/server/src/orchestration-v2/WireProjection.test.ts b/apps/server/src/orchestration-v2/WireProjection.test.ts
index d449aeb933dbf..0d63d832f0ca9 100644
--- a/apps/server/src/orchestration-v2/WireProjection.test.ts
+++ b/apps/server/src/orchestration-v2/WireProjection.test.ts
@@ -1,4 +1,7 @@
 import {
+  CheckpointId,
+  CheckpointRef,
+  CheckpointScopeId,
   MessageId,
   ContextHandoffId,
   ProviderThreadId,
@@ -381,6 +384,46 @@ describe("live body deduper", () => {
     ]);
   });
 
+  it("caps a large checkpoint's files for the wire and still dedupes its item", () => {
+    const files = Array.from({ length: 250 }, (_, index) => ({
+      path: `vendor/file-${index}.ts`,
+      kind: "modified",
+      additions: 2,
+      deletions: 1,
+    }));
+    const checkpointId = CheckpointId.make("checkpoint-large");
+    const scopeId = CheckpointScopeId.make("scope-large");
+    const captured = event(1, {
+      type: "checkpoint.captured",
+      payload: {
+        id: checkpointId,
+        threadId: base.threadId,
+        scopeId,
+        runId: null,
+        nodeId: NodeId.make("node-large"),
+        parentCheckpointId: null,
+        ordinalWithinScope: 1,
+        appRunOrdinal: null,
+        ref: CheckpointRef.make("refs/t3/checkpoints/large"),
+        status: "ready",
+        files,
+        capturedAt: at,
+      },
+    });
+    const item = event(2, {
+      type: "turn-item.updated",
+      payload: { ...base, type: "checkpoint", checkpointId, scopeId, files },
+    });
+    const dedupe = makeLiveBodyDeduper();
+    const [record, card] = [captured, item].map((streamed) =>
+      dedupe({ ...streamed, event: projectDomainEventForWire(streamed.event) }),
+    );
+
+    const filesTotal = { count: 250, additions: 500, deletions: 250 };
+    expect(payloadOf(record!)).toMatchObject({ files: files.slice(0, 200), filesTotal });
+    expect(payloadOf(card!)).toMatchObject({ files: [], filesOmitted: true, filesTotal });
+  });
+
   it("ships a reply whole when its message arrives after it", () => {
     const first = reply(1, "a");
     expect([first, message(2, "a")].map(makeLiveBodyDeduper())[0]).toBe(first);
diff --git a/apps/server/src/orchestration-v2/WireProjection.ts b/apps/server/src/orchestration-v2/WireProjection.ts
index 6b66f1b91f204..2181b7feec5fa 100644
--- a/apps/server/src/orchestration-v2/WireProjection.ts
+++ b/apps/server/src/orchestration-v2/WireProjection.ts
@@ -21,6 +21,8 @@ import {
   toolOutputIndicatesFailure,
 } from "@t3tools/shared/toolOutput";
 
+// A checkpoint over vendored or generated trees can list 15k+ files; the card needs a prefix.
+const MAX_WIRE_CHECKPOINT_FILES = 200;
 const MAX_DETAIL_STRING_BYTES = 32_768;
 const MAX_DYNAMIC_VALUE_BYTES = 16_384;
 const MAX_ON_DEMAND_BYTES = 256 * 1024;
@@ -96,8 +98,59 @@ function summarizeDynamicValue(value: unknown): unknown {
   };
 }
 
+type CheckpointFiles = Pick<OrchestrationV2Checkpoint, "files" | "filesTotal">;
+
+// Same input, same output object: snapshot compaction relies on shared item identity.
+const cappedCheckpointFiles = new WeakMap<object, object>();
+
+function capCheckpointFiles<T extends CheckpointFiles>(value: T): T {
+  if (value.files.length <= MAX_WIRE_CHECKPOINT_FILES || value.filesTotal !== undefined) {
+    return value;
+  }
+  const cached = cappedCheckpointFiles.get(value);
+  if (cached !== undefined) return cached as T;
+  let additions = 0;
+  let deletions = 0;
+  for (const file of value.files) {
+    additions += file.additions;
+    deletions += file.deletions;
+  }
+  const capped = {
+    ...value,
+    files: value.files.slice(0, MAX_WIRE_CHECKPOINT_FILES),
+    filesTotal: { count: value.files.length, additions, deletions },
+  };
+  cappedCheckpointFiles.set(value, capped);
+  return capped;
+}
+
+/** Idempotent; bounded snapshots that skip `projectThreadProjectionForWire` still need it. */
+export function capProjectionCheckpointFilesForWire(
+  projection: OrchestrationV2ThreadProjection,
+): OrchestrationV2ThreadProjection {
+  const checkpoints = projection.checkpoints.map(capCheckpointFiles);
+  const turnItems = projection.turnItems.map(capCheckpointItemFiles);
+  const visibleTurnItems = projection.visibleTurnItems.map((row) => {
+    const item = capCheckpointItemFiles(row.item);
+    return item === row.item ? row : { ...row, item };
+  });
+  const unchanged = (next: ReadonlyArray<unknown>, previous: ReadonlyArray<unknown>) =>
+    next.every((value, index) => value === previous[index]);
+  return unchanged(checkpoints, projection.checkpoints) &&
+    unchanged(turnItems, projection.turnItems) &&
+    unchanged(visibleTurnItems, projection.visibleTurnItems)
+    ? projection
+    : { ...projection, checkpoints, turnItems, visibleTurnItems };
+}
+
+function capCheckpointItemFiles(item: OrchestrationV2TurnItem): OrchestrationV2TurnItem {
+  return item.type === "checkpoint" ? capCheckpointFiles(item) : item;
+}
+
 export function projectTurnItemForWire(item: OrchestrationV2TurnItem): OrchestrationV2TurnItem {
   switch (item.type) {
+    case "checkpoint":
+      return capCheckpointFiles(item);
     case "handoff": {
       const { summary: _summary, ...projected } = item;
       return projected;
@@ -241,6 +294,7 @@ export function projectThreadProjectionForWire(
   };
   return {
     ...projection,
+    checkpoints: projection.checkpoints.map(capCheckpointFiles),
     contextHandoffs: projection.contextHandoffs.map(projectContextHandoffForWire),
     turnItems: projection.turnItems.map(project),
     visibleTurnItems: projection.visibleTurnItems.map((row) => ({
@@ -257,7 +311,9 @@ export function projectDomainEventForWire(
     ? { ...event, payload: projectTurnItemForWire(event.payload) }
     : event.type === "context-handoff.updated"
       ? { ...event, payload: projectContextHandoffForWire(event.payload) }
-      : event;
+      : event.type === "checkpoint.captured"
+        ? { ...event, payload: capCheckpointFiles(event.payload) }
+        : event;
 }
 
 const LIVE_DEDUPE_MEMORY = 32;
diff --git a/apps/web/src/components/ChatView.logic.ts b/apps/web/src/components/ChatView.logic.ts
index c7c0f77bc97fb..bef8f7ab405f1 100644
--- a/apps/web/src/components/ChatView.logic.ts
+++ b/apps/web/src/components/ChatView.logic.ts
@@ -3,6 +3,7 @@ import {
   deriveLatestThreadRun,
   deriveThreadRuntime,
 } from "@t3tools/client-runtime/state/thread-execution";
+import { checkpointFileTotals } from "@t3tools/client-runtime/state/thread-checkpoints";
 import { derivePendingBackgroundWork } from "@t3tools/shared/orchestrationV2PendingBackgroundWork";
 import {
   latestUnheldRun,
@@ -218,7 +219,7 @@ export function shouldOpenProactiveTurnDiff(input: {
 }
 
 export function resolveProactiveTurnDiffAction(input: {
-  checkpoint: Pick<TurnDiffSummary, "status" | "files"> | undefined;
+  checkpoint: Pick<TurnDiffSummary, "status" | "files" | "filesTotal"> | undefined;
   isGitRepo: boolean | undefined;
 }): "defer" | "ignore" | "open" {
   if (input.checkpoint === undefined || input.checkpoint.status === "missing") return "defer";
@@ -230,11 +231,8 @@ export function resolveProactiveTurnDiffAction(input: {
   ) {
     return "ignore";
   }
-  const changedLines = input.checkpoint.files.reduce(
-    (total, file) => total + file.additions + file.deletions,
-    0,
-  );
-  return input.checkpoint.files.length >= 3 || changedLines >= 50 ? "open" : "ignore";
+  const totals = checkpointFileTotals(input.checkpoint);
+  return totals.count >= 3 || totals.additions + totals.deletions >= 50 ? "open" : "ignore";
 }
 
 /** Mark reactivated Diff tabs to preserve review scope. Already-active tabs must not leave a marker for
diff --git a/apps/web/src/components/chat/ChangedFilesTree.tsx b/apps/web/src/components/chat/ChangedFilesTree.tsx
index 0b569cbc0c563..868484f37b474 100644
--- a/apps/web/src/components/chat/ChangedFilesTree.tsx
+++ b/apps/web/src/components/chat/ChangedFilesTree.tsx
@@ -1,11 +1,7 @@
-import { type RunId } from "@t3tools/contracts";
+import { type OrchestrationV2CheckpointFileTotals, type RunId } from "@t3tools/contracts";
 import { type MouseEvent, type ReactNode, memo, useLayoutEffect, useRef, useState } from "react";
 import { type TurnDiffFileChange } from "../../types";
-import {
-  buildTurnDiffTree,
-  summarizeTurnDiffStats,
-  type TurnDiffTreeNode,
-} from "../../lib/turnDiffTree";
+import { buildTurnDiffTree, type TurnDiffTreeNode } from "../../lib/turnDiffTree";
 import { ChevronRightIcon, FileDiffIcon } from "lucide-react";
 import { ChevronsDownUp, ChevronsUpDown, Folder, FolderClosed } from "lucide";
 import { cn } from "~/lib/utils";
@@ -30,7 +26,9 @@ type ChangedFileContextMenuHandler = (filePath: string, event: MouseEvent) => vo
 
 export const ChangedFilesCard = memo(function ChangedFilesCard(props: {
   runId: RunId;
+  /** May be a prefix of the changed files; `totals` covers all of them. */
   files: ReadonlyArray<TurnDiffFileChange>;
+  totals: OrchestrationV2CheckpointFileTotals;
   allDirectoriesExpanded: boolean;
   resolvedTheme: "light" | "dark";
   onToggleAllDirectories: () => void;
@@ -40,13 +38,14 @@ export const ChangedFilesCard = memo(function ChangedFilesCard(props: {
   const {
     runId,
     files,
+    totals,
     allDirectoriesExpanded,
     resolvedTheme,
     onToggleAllDirectories,
     onOpenTurnDiff,
     onFileContextMenu,
   } = props;
-  const summaryStat = summarizeTurnDiffStats(files);
+  const hiddenFileCount = totals.count - files.length;
   const hasDirectories = files.some((file) => /[/\\]/.test(file.path));
 
   return (
@@ -60,12 +59,12 @@ export const ChangedFilesCard = memo(function ChangedFilesCard(props: {
       >
         <div className="flex min-w-0 flex-wrap items-center gap-x-3 gap-y-1 text-xs font-medium text-foreground">
           <span>
-            {files.length} changed file{files.length === 1 ? "" : "s"}
+            {totals.count.toLocaleString()} changed file{totals.count === 1 ? "" : "s"}
           </span>
-          {hasNonZeroStat(summaryStat) && (
+          {hasNonZeroStat(totals) && (
             <DiffStatLabel
-              additions={summaryStat.additions}
-              deletions={summaryStat.deletions}
+              additions={totals.additions}
+              deletions={totals.deletions}
               layout="inline"
               className="text-xs leading-4"
             />
@@ -126,6 +125,19 @@ export const ChangedFilesCard = memo(function ChangedFilesCard(props: {
         onOpenTurnDiff={onOpenTurnDiff}
         onFileContextMenu={onFileContextMenu}
       />
+      {hiddenFileCount > 0 && (
+        <div className="px-3 pb-2">
+          <Button
+            type="button"
+            size="xs"
+            variant="ghost-muted"
+            onClick={() => onOpenTurnDiff(runId, files[0]?.path)}
+          >
+            {hiddenFileCount.toLocaleString()} more file{hiddenFileCount === 1 ? "" : "s"} in the
+            full diff
+          </Button>
+        </div>
+      )}
     </div>
   );
 });
diff --git a/apps/web/src/components/chat/TimelineAssistantRows.tsx b/apps/web/src/components/chat/TimelineAssistantRows.tsx
index 89b52ae5c5cba..228eb6f79b9c3 100644
--- a/apps/web/src/components/chat/TimelineAssistantRows.tsx
+++ b/apps/web/src/components/chat/TimelineAssistantRows.tsx
@@ -9,6 +9,7 @@ import { Button } from "../ui/button";
 import { ProposedPlanCard } from "./ProposedPlanCard";
 import { HtmlRenderFrame } from "./HtmlRenderFrame";
 import { McpAppFrame } from "./McpAppFrame";
+import { checkpointFileTotals } from "@t3tools/client-runtime/state/thread-checkpoints";
 import { ChangedFilesCard } from "./ChangedFilesTree";
 import { useFileContextMenuHandler } from "../../fileContextMenu";
 import { useProject, useThreadShell } from "../../state/entities";
@@ -347,6 +348,7 @@ function AssistantChangedFilesSectionInner({
     <ChangedFilesCard
       runId={turnSummary.runId}
       files={checkpointFiles}
+      totals={checkpointFileTotals(turnSummary)}
       allDirectoriesExpanded={allDirectoriesExpanded}
       resolvedTheme={resolvedTheme}
       onToggleAllDirectories={() =>
diff --git a/apps/web/src/lib/turnDiffTree.ts b/apps/web/src/lib/turnDiffTree.ts
index 810a04755e895..e841e18ce24d2 100644
--- a/apps/web/src/lib/turnDiffTree.ts
+++ b/apps/web/src/lib/turnDiffTree.ts
@@ -98,20 +98,6 @@ function toTreeNodes(directory: MutableDirectoryNode): TurnDiffTreeNode[] {
   return [...subdirectories, ...files];
 }
 
-export function summarizeTurnDiffStats(files: ReadonlyArray<TurnDiffFileChange>): TurnDiffStat {
-  return files.reduce(
-    (acc, file) => {
-      const stat = readStat(file);
-      if (!stat) return acc;
-      return {
-        additions: acc.additions + stat.additions,
-        deletions: acc.deletions + stat.deletions,
-      };
-    },
-    { additions: 0, deletions: 0 },
-  );
-}
-
 export function buildTurnDiffTree(files: ReadonlyArray<TurnDiffFileChange>): TurnDiffTreeNode[] {
   const root: MutableDirectoryNode = {
     name: "",
diff --git a/packages/client-runtime/src/state/threadCheckpoints.ts b/packages/client-runtime/src/state/threadCheckpoints.ts
index 4501007e20053..ee2fe45d9c756 100644
--- a/packages/client-runtime/src/state/threadCheckpoints.ts
+++ b/packages/client-runtime/src/state/threadCheckpoints.ts
@@ -3,6 +3,7 @@ import type {
   CheckpointRef,
   CheckpointScopeId,
   MessageId,
+  OrchestrationV2CheckpointFileTotals,
   OrchestrationV2ThreadProjection,
   RunId,
 } from "@t3tools/contracts";
@@ -15,12 +16,14 @@ export interface ThreadCheckpointSummary {
   readonly checkpointTurnCount: number;
   readonly checkpointRef: CheckpointRef;
   readonly status: "ready" | "missing" | "error" | "stale";
+  /** A prefix of the changed files when `filesTotal` is set; see `checkpointFileTotals`. */
   readonly files: ReadonlyArray<{
     readonly path: string;
     readonly kind: string;
     readonly additions: number;
     readonly deletions: number;
   }>;
+  readonly filesTotal?: OrchestrationV2CheckpointFileTotals;
   readonly assistantMessageId: MessageId | null;
   readonly completedAt: string;
 }
@@ -43,9 +46,23 @@ export function deriveThreadCheckpointSummaries(
         checkpointRef: checkpoint.ref,
         status: checkpoint.status,
         files: checkpoint.files,
+        ...(checkpoint.filesTotal === undefined ? {} : { filesTotal: checkpoint.filesTotal }),
         assistantMessageId,
         completedAt: DateTime.formatIso(checkpoint.capturedAt),
       },
     ];
   });
 }
+
+export function checkpointFileTotals(
+  checkpoint: Pick<ThreadCheckpointSummary, "files" | "filesTotal">,
+): OrchestrationV2CheckpointFileTotals {
+  if (checkpoint.filesTotal !== undefined) return checkpoint.filesTotal;
+  let additions = 0;
+  let deletions = 0;
+  for (const file of checkpoint.files) {
+    additions += file.additions;
+    deletions += file.deletions;
+  }
+  return { count: checkpoint.files.length, additions, deletions };
+}
diff --git a/packages/contracts/src/orchestrationV2.ts b/packages/contracts/src/orchestrationV2.ts
index 747d05e7ce4eb..026e74831233d 100644
--- a/packages/contracts/src/orchestrationV2.ts
+++ b/packages/contracts/src/orchestrationV2.ts
@@ -1349,6 +1349,14 @@ export const OrchestrationV2CheckpointFileSummary = Schema.Struct({
 });
 export type OrchestrationV2CheckpointFileSummary = typeof OrchestrationV2CheckpointFileSummary.Type;
 
+/** Sent only when the wire carries a prefix of `files`; the totals cover the full list. */
+export const OrchestrationV2CheckpointFileTotals = Schema.Struct({
+  count: NonNegativeInt,
+  additions: NonNegativeInt,
+  deletions: NonNegativeInt,
+});
+export type OrchestrationV2CheckpointFileTotals = typeof OrchestrationV2CheckpointFileTotals.Type;
+
 export const OrchestrationV2Checkpoint = Schema.Struct({
   id: CheckpointId,
   threadId: ThreadId,
@@ -1361,6 +1369,7 @@ export const OrchestrationV2Checkpoint = Schema.Struct({
   ref: CheckpointRef,
   status: Schema.Literals(["ready", "missing", "error", "stale"]),
   files: Schema.Array(OrchestrationV2CheckpointFileSummary),
+  filesTotal: Schema.optionalKey(OrchestrationV2CheckpointFileTotals),
   capturedAt: Schema.DateTimeUtc,
 });
 export type OrchestrationV2Checkpoint = typeof OrchestrationV2Checkpoint.Type;
@@ -1659,6 +1668,7 @@ export const OrchestrationV2TurnItem = Schema.Union([
     checkpointId: CheckpointId,
     scopeId: CheckpointScopeId,
     files: Schema.Array(OrchestrationV2CheckpointFileSummary),
+    filesTotal: Schema.optionalKey(OrchestrationV2CheckpointFileTotals),
     /** Same as the files of checkpoint `checkpointId`. */
     filesOmitted: DedupedBodyMarker,
   }),