diff --git a/site/src/pages/AgentsPage/AgentChatInput.tsx b/site/src/pages/AgentsPage/AgentChatInput.tsx
index 8e7e6588b8..c21db17eb4 100644
--- a/site/src/pages/AgentsPage/AgentChatInput.tsx
+++ b/site/src/pages/AgentsPage/AgentChatInput.tsx
@@ -1,4 +1,4 @@
-import type { ChatQueuedMessage } from "api/typesGenerated";
+import type { ChatMessagePart, ChatQueuedMessage } from "api/typesGenerated";
 import {
 	ModelSelector,
 	type ModelSelectorOption,
@@ -94,11 +94,7 @@ interface AgentChatInputProps {
 	onStartQueueEdit?: (
 		id: number,
 		text: string,
-		fileBlocks: readonly {
-			mediaType: string;
-			data?: string;
-			fileId?: string;
-		}[],
+		fileBlocks: readonly ChatMessagePart[],
 	) => void;
 	onCancelQueueEdit?: () => void;
 	// History editing state, owned by the parent.
diff --git a/site/src/pages/AgentsPage/AgentDetail.tsx b/site/src/pages/AgentsPage/AgentDetail.tsx
index bb2badf4a6..be0201bb3f 100644
--- a/site/src/pages/AgentsPage/AgentDetail.tsx
+++ b/site/src/pages/AgentsPage/AgentDetail.tsx
@@ -15,6 +15,7 @@ import {
 import { deploymentSSHConfig } from "api/queries/deployment";
 import { workspaceById, workspaceByIdKey } from "api/queries/workspaces";
 import type * as TypesGen from "api/typesGenerated";
+import type { ChatMessagePart } from "api/typesGenerated";
 import { useProxy } from "contexts/ProxyContext";
 import {
 	getTerminalHref,
@@ -102,18 +103,14 @@ export function useConversationEditingState(deps: {
 		string | null
 	>(null);
 	const [editingFileBlocks, setEditingFileBlocks] = useState<
-		readonly { mediaType: string; data?: string; fileId?: string }[]
+		readonly ChatMessagePart[]
 	>([]);
 
 	const handleEditUserMessage = useCallback(
 		(
 			messageId: number,
 			text: string,
-			fileBlocks?: readonly {
-				mediaType: string;
-				data?: string;
-				fileId?: string;
-			}[],
+			fileBlocks?: readonly ChatMessagePart[],
 		) => {
 			setDraftBeforeHistoryEdit((prev) =>
 				editingMessageId !== null ? prev : inputValueRef.current,
@@ -143,15 +140,7 @@ export function useConversationEditingState(deps: {
 	>(null);
 
 	const handleStartQueueEdit = useCallback(
-		(
-			id: number,
-			text: string,
-			fileBlocks: readonly {
-				mediaType: string;
-				data?: string;
-				fileId?: string;
-			}[],
-		) => {
+		(id: number, text: string, fileBlocks: readonly ChatMessagePart[]) => {
 			setDraftBeforeQueueEdit((prev) =>
 				editingQueuedMessageID === null ? inputValueRef.current : prev,
 			);
diff --git a/site/src/pages/AgentsPage/AgentDetail/ConversationTimeline.tsx b/site/src/pages/AgentsPage/AgentDetail/ConversationTimeline.tsx
index bb879f5e55..1d5449299d 100644
--- a/site/src/pages/AgentsPage/AgentDetail/ConversationTimeline.tsx
+++ b/site/src/pages/AgentsPage/AgentDetail/ConversationTimeline.tsx
@@ -246,10 +246,10 @@ function renderBlockList({
 					);
 				}
 				case "file":
-					if (block.mediaType.startsWith("image/")) {
-						const src = block.fileId
-							? `/api/experimental/chats/files/${block.fileId}`
-							: `data:${block.mediaType};base64,${block.data}`;
+					if (block.media_type.startsWith("image/")) {
+						const src = block.file_id
+							? `/api/experimental/chats/files/${block.file_id}`
+							: `data:${block.media_type};base64,${block.data}`;
 						return (
 							<button
 								key={`${keyPrefix}-file-${index}`}
@@ -291,7 +291,7 @@ const ChatMessageItem = memo<{
 	onEditUserMessage?: (
 		messageId: number,
 		text: string,
-		fileBlocks?: Array<{ mediaType: string; data?: string; fileId?: string }>,
+		fileBlocks?: readonly TypesGen.ChatMessagePart[],
 	) => void;
 	editingMessageId?: number | null;
 	savingMessageId?: number | null;
@@ -381,7 +381,7 @@ const ChatMessageItem = memo<{
 												const fileBlocks = parsed.blocks.filter(
 													(b): b is Extract<RenderBlock, { type: "file" }> =>
 														b.type === "file" &&
-														b.mediaType.startsWith("image/"),
+														b.media_type.startsWith("image/"),
 												);
 												onEditUserMessage(
 													message.id,
@@ -408,15 +408,15 @@ const ChatMessageItem = memo<{
 									{(() => {
 										const imageBlocks = parsed.blocks.filter(
 											(b): b is Extract<RenderBlock, { type: "file" }> =>
-												b.type === "file" && b.mediaType.startsWith("image/"),
+												b.type === "file" && b.media_type.startsWith("image/"),
 										);
 										if (imageBlocks.length === 0) return null;
 										return (
 											<div className="mt-2 flex flex-wrap gap-2">
 												{imageBlocks.map((block, i) => {
-													const src = block.fileId
-														? `/api/experimental/chats/files/${block.fileId}`
-														: `data:${block.mediaType};base64,${block.data}`;
+													const src = block.file_id
+														? `/api/experimental/chats/files/${block.file_id}`
+														: `data:${block.media_type};base64,${block.data}`;
 													return (
 														<button
 															key={`user-file-${i}`}
@@ -612,7 +612,7 @@ const StickyUserMessage: FC<{
 	onEditUserMessage?: (
 		messageId: number,
 		text: string,
-		fileBlocks?: Array<{ mediaType: string; data?: string; fileId?: string }>,
+		fileBlocks?: readonly TypesGen.ChatMessagePart[],
 	) => void;
 	editingMessageId?: number | null;
 	savingMessageId?: number | null;
@@ -751,11 +751,7 @@ const StickyUserMessage: FC<{
 		? (
 				messageId: number,
 				text: string,
-				fileBlocks?: Array<{
-					mediaType: string;
-					data?: string;
-					fileId?: string;
-				}>,
+				fileBlocks?: readonly TypesGen.ChatMessagePart[],
 			) => {
 				onEditUserMessage(messageId, text, fileBlocks);
 				requestAnimationFrame(() => {
@@ -873,7 +869,7 @@ interface ConversationTimelineProps {
 	onEditUserMessage?: (
 		messageId: number,
 		text: string,
-		fileBlocks?: Array<{ mediaType: string; data?: string; fileId?: string }>,
+		fileBlocks?: readonly TypesGen.ChatMessagePart[],
 	) => void;
 	editingMessageId?: number | null;
 	savingMessageId?: number | null;
diff --git a/site/src/pages/AgentsPage/AgentDetail/messageParsing.test.ts b/site/src/pages/AgentsPage/AgentDetail/messageParsing.test.ts
index 30c3b90a3c..0a5023bb07 100644
--- a/site/src/pages/AgentsPage/AgentDetail/messageParsing.test.ts
+++ b/site/src/pages/AgentsPage/AgentDetail/messageParsing.test.ts
@@ -258,9 +258,9 @@ describe("parseMessageContent", () => {
 		expect(result.blocks).toHaveLength(1);
 		expect(result.blocks[0]).toEqual({
 			type: "file",
-			mediaType: "image/png",
+			media_type: "image/png",
 			data: undefined,
-			fileId: "abc-123-def",
+			file_id: "abc-123-def",
 		});
 	});
 
@@ -275,9 +275,9 @@ describe("parseMessageContent", () => {
 		expect(result.blocks).toHaveLength(1);
 		expect(result.blocks[0]).toEqual({
 			type: "file",
-			mediaType: "image/png",
+			media_type: "image/png",
 			data: "iVBORw0KGgo=",
-			fileId: undefined,
+			file_id: undefined,
 		});
 	});
 
diff --git a/site/src/pages/AgentsPage/AgentDetail/messageParsing.ts b/site/src/pages/AgentsPage/AgentDetail/messageParsing.ts
index 8e29b5b686..8dbe78e3eb 100644
--- a/site/src/pages/AgentsPage/AgentDetail/messageParsing.ts
+++ b/site/src/pages/AgentsPage/AgentDetail/messageParsing.ts
@@ -244,23 +244,17 @@ export const parseMessageContent = (content: unknown): ParsedMessageContent => {
 					parsed.blocks = ensureToolBlock(parsed.blocks, id);
 					break;
 				}
-				case "file": {
-					const mediaType = asString(typedBlock.media_type);
-					const data = asString(typedBlock.data);
-					const fileId = asString(typedBlock.file_id);
-					if (mediaType && (data || fileId)) {
+				case "file":
+					if (
+						typedBlock.media_type &&
+						(typedBlock.data || typedBlock.file_id)
+					) {
 						parsed.blocks = [
 							...parsed.blocks,
-							{
-								type: "file",
-								mediaType,
-								data: data || undefined,
-								fileId: fileId || undefined,
-							},
+							typedBlock as Extract<RenderBlock, { type: "file" }>,
 						];
 					}
 					break;
-				}
 				case "source": {
 					const url = asString(typedBlock.url);
 					const title = asString(typedBlock.title);
diff --git a/site/src/pages/AgentsPage/AgentDetail/streamState.ts b/site/src/pages/AgentsPage/AgentDetail/streamState.ts
index 29b3af2318..8ddba6477d 100644
--- a/site/src/pages/AgentsPage/AgentDetail/streamState.ts
+++ b/site/src/pages/AgentsPage/AgentDetail/streamState.ts
@@ -141,26 +141,17 @@ export const applyMessagePartToStreamState = (
 				},
 			};
 		}
-		case "file": {
-			const mediaType = asString(part.media_type);
-			const data = asString(part.data);
-			const fileId = asString(part.file_id);
-			if (!mediaType || (!data && !fileId)) {
+		case "file":
+			if (!part.media_type || (!part.data && !part.file_id)) {
 				return prev;
 			}
 			return {
 				...nextState,
 				blocks: [
 					...nextState.blocks,
-					{
-						type: "file",
-						mediaType,
-						data: data || undefined,
-						fileId: fileId || undefined,
-					},
+					part as Extract<RenderBlock, { type: "file" }>,
 				],
 			};
-		}
 		case "source": {
 			const url = asString(part.url);
 			const title = asString(part.title);
diff --git a/site/src/pages/AgentsPage/AgentDetail/types.ts b/site/src/pages/AgentsPage/AgentDetail/types.ts
index ffbbcc2cda..8a1c5aee68 100644
--- a/site/src/pages/AgentsPage/AgentDetail/types.ts
+++ b/site/src/pages/AgentsPage/AgentDetail/types.ts
@@ -38,9 +38,9 @@ export type RenderBlock =
 	  }
 	| {
 			type: "file";
-			mediaType: string;
+			media_type: string;
 			data?: string; // base64, absent when file_id is available
-			fileId?: string;
+			file_id?: string;
 	  }
 	| {
 			type: "file-reference";
diff --git a/site/src/pages/AgentsPage/AgentDetailContent.tsx b/site/src/pages/AgentsPage/AgentDetailContent.tsx
index b6685562a5..b80a7fb7d7 100644
--- a/site/src/pages/AgentsPage/AgentDetailContent.tsx
+++ b/site/src/pages/AgentsPage/AgentDetailContent.tsx
@@ -48,7 +48,7 @@ interface AgentDetailTimelineProps {
 	onEditUserMessage?: (
 		messageId: number,
 		text: string,
-		fileBlocks?: readonly { mediaType: string; data?: string }[],
+		fileBlocks?: readonly TypesGen.ChatMessagePart[],
 	) => void;
 	editingMessageId?: number | null;
 	savingMessageId?: number | null;
@@ -169,22 +169,14 @@ interface AgentDetailInputProps {
 	onStartQueueEdit: (
 		id: number,
 		text: string,
-		fileBlocks: readonly {
-			mediaType: string;
-			data?: string;
-			fileId?: string;
-		}[],
+		fileBlocks: readonly TypesGen.ChatMessagePart[],
 	) => void;
 	onCancelQueueEdit: () => void;
 	isEditingHistoryMessage: boolean;
 	onCancelHistoryEdit: () => void;
-	// File blocks from the message being edited, converted to
+	// File parts from the message being edited, converted to
 	// File objects and pre-populated into attachments.
-	editingFileBlocks?: readonly {
-		mediaType: string;
-		data?: string;
-		fileId?: string;
-	}[];
+	editingFileBlocks?: readonly TypesGen.ChatMessagePart[];
 }
 
 export const AgentDetailInput: FC<AgentDetailInputProps> = ({
@@ -258,29 +250,28 @@ export const AgentDetailInput: FC<AgentDetailInputProps> = ({
 			return;
 		}
 		const files = editingFileBlocks.map((block, i) => {
-			const ext = block.mediaType.split("/")[1] ?? "png";
+			const mt = block.media_type ?? "application/octet-stream";
+			const ext = mt.split("/")[1] ?? "png";
 			// Empty File used as a Map key only, its content is never
-			// read because the existing fileId is reused at send time.
-			return new File([], `attachment-${i}.${ext}`, {
-				type: block.mediaType,
-			});
+			// read because the existing file_id is reused at send time.
+			return new File([], `attachment-${i}.${ext}`, { type: mt });
 		});
 		setAttachments(files);
 		setPreviewUrls(
 			new Map(
 				files.map((f, i) => [
 					f,
-					`/api/experimental/chats/files/${editingFileBlocks[i].fileId}`,
+					`/api/experimental/chats/files/${editingFileBlocks[i].file_id}`,
 				]),
 			),
 		);
 		const newUploadStates = new Map<File, UploadState>();
 		for (const [i, file] of files.entries()) {
 			const block = editingFileBlocks[i];
-			if (block.fileId) {
+			if (block.file_id) {
 				newUploadStates.set(file, {
 					status: "uploaded",
-					fileId: block.fileId,
+					fileId: block.file_id,
 				});
 			}
 		}
diff --git a/site/src/pages/AgentsPage/AgentDetailView.stories.tsx b/site/src/pages/AgentsPage/AgentDetailView.stories.tsx
index 771a25a2be..6479031856 100644
--- a/site/src/pages/AgentsPage/AgentDetailView.stories.tsx
+++ b/site/src/pages/AgentsPage/AgentDetailView.stories.tsx
@@ -3,7 +3,7 @@ import { withAuthProvider, withDashboardProvider } from "testHelpers/storybook";
 import type { Meta, StoryObj } from "@storybook/react-vite";
 import { API } from "api/api";
 import type * as TypesGen from "api/typesGenerated";
-import type { ChatDiffStatus } from "api/typesGenerated";
+import type { ChatDiffStatus, ChatMessagePart } from "api/typesGenerated";
 import type { ModelSelectorOption } from "components/ai-elements";
 import { fn, spyOn } from "storybook/test";
 import { reactRouterParameters } from "storybook-addon-remix-react-router";
@@ -47,11 +47,7 @@ const defaultEditing = {
 	chatInputRef: { current: null },
 	editorInitialValue: "",
 	editingMessageId: null,
-	editingFileBlocks: [] as readonly {
-		mediaType: string;
-		data?: string;
-		fileId?: string;
-	}[],
+	editingFileBlocks: [] as readonly ChatMessagePart[],
 	handleEditUserMessage: fn(),
 	handleCancelHistoryEdit: fn(),
 	editingQueuedMessageID: null,
diff --git a/site/src/pages/AgentsPage/AgentDetailView.tsx b/site/src/pages/AgentsPage/AgentDetailView.tsx
index 1093afb650..17f47dc07e 100644
--- a/site/src/pages/AgentsPage/AgentDetailView.tsx
+++ b/site/src/pages/AgentsPage/AgentDetailView.tsx
@@ -1,5 +1,5 @@
 import type * as TypesGen from "api/typesGenerated";
-import type { ChatDiffStatus } from "api/typesGenerated";
+import type { ChatDiffStatus, ChatMessagePart } from "api/typesGenerated";
 import type { ModelSelectorOption } from "components/ai-elements";
 import { ArchiveIcon } from "lucide-react";
 import { type FC, type RefObject, useEffect, useRef, useState } from "react";
@@ -31,30 +31,18 @@ interface EditingState {
 	chatInputRef: RefObject<ChatMessageInputRef | null>;
 	editorInitialValue: string;
 	editingMessageId: number | null;
-	editingFileBlocks: readonly {
-		mediaType: string;
-		data?: string;
-		fileId?: string;
-	}[];
+	editingFileBlocks: readonly ChatMessagePart[];
 	handleEditUserMessage: (
 		messageId: number,
 		text: string,
-		fileBlocks?: readonly {
-			mediaType: string;
-			data?: string;
-			fileId?: string;
-		}[],
+		fileBlocks?: readonly ChatMessagePart[],
 	) => void;
 	handleCancelHistoryEdit: () => void;
 	editingQueuedMessageID: number | null;
 	handleStartQueueEdit: (
 		id: number,
 		text: string,
-		fileBlocks: readonly {
-			mediaType: string;
-			data?: string;
-			fileId?: string;
-		}[],
+		fileBlocks: readonly ChatMessagePart[],
 	) => void;
 	handleCancelQueueEdit: () => void;
 	handleSendFromInput: (message: string, fileIds?: string[]) => void;
diff --git a/site/src/pages/AgentsPage/QueuedMessagesList.stories.tsx b/site/src/pages/AgentsPage/QueuedMessagesList.stories.tsx
index d2854813e8..edbc1e4280 100644
--- a/site/src/pages/AgentsPage/QueuedMessagesList.stories.tsx
+++ b/site/src/pages/AgentsPage/QueuedMessagesList.stories.tsx
@@ -163,7 +163,7 @@ export const EditPassesFileBlocks: Story = {
 		const editButton = canvas.getByRole("button", { name: "Edit" });
 		await userEvent.click(editButton);
 		expect(args.onEdit).toHaveBeenCalledWith(1, "Check this screenshot", [
-			{ mediaType: "image/png", fileId: "abc-123" },
+			{ type: "file", file_id: "abc-123", media_type: "image/png" },
 		]);
 	},
 };
@@ -184,8 +184,8 @@ export const EditAttachmentOnlyMessage: Story = {
 		const editButton = canvas.getByRole("button", { name: "Edit" });
 		await userEvent.click(editButton);
 		expect(args.onEdit).toHaveBeenCalledWith(1, "", [
-			{ mediaType: "image/png", fileId: "img-1" },
-			{ mediaType: "image/jpeg", fileId: "img-2" },
+			{ type: "file", file_id: "img-1", media_type: "image/png" },
+			{ type: "file", file_id: "img-2", media_type: "image/jpeg" },
 		]);
 	},
 };
diff --git a/site/src/pages/AgentsPage/QueuedMessagesList.test.ts b/site/src/pages/AgentsPage/QueuedMessagesList.test.ts
index 1695f44925..d451b7a14a 100644
--- a/site/src/pages/AgentsPage/QueuedMessagesList.test.ts
+++ b/site/src/pages/AgentsPage/QueuedMessagesList.test.ts
@@ -38,21 +38,21 @@ describe("getQueuedMessageInfo", () => {
 
 	it("returns attachment label for a single file", () => {
 		const result = getQueuedMessageInfo(
-			makeMessage([{ type: "file", file_id: "a" }]),
+			makeMessage([{ type: "file", file_id: "a", media_type: "image/png" }]),
 		);
 		expect(result).toEqual({
 			displayText: "[Queued message]",
 			rawText: "",
 			attachmentCount: 1,
-			fileBlocks: [{ mediaType: "application/octet-stream", fileId: "a" }],
+			fileBlocks: [{ type: "file", file_id: "a", media_type: "image/png" }],
 		});
 	});
 
 	it("returns attachment label for multiple files", () => {
 		const result = getQueuedMessageInfo(
 			makeMessage([
-				{ type: "file", file_id: "a" },
-				{ type: "file", file_id: "b" },
+				{ type: "file", file_id: "a", media_type: "image/png" },
+				{ type: "file", file_id: "b", media_type: "image/png" },
 			]),
 		);
 		expect(result).toEqual({
@@ -60,8 +60,8 @@ describe("getQueuedMessageInfo", () => {
 			rawText: "",
 			attachmentCount: 2,
 			fileBlocks: [
-				{ mediaType: "application/octet-stream", fileId: "a" },
-				{ mediaType: "application/octet-stream", fileId: "b" },
+				{ type: "file", file_id: "a", media_type: "image/png" },
+				{ type: "file", file_id: "b", media_type: "image/png" },
 			],
 		});
 	});
@@ -70,14 +70,14 @@ describe("getQueuedMessageInfo", () => {
 		const result = getQueuedMessageInfo(
 			makeMessage([
 				{ type: "text", text: "look" },
-				{ type: "file", file_id: "a" },
+				{ type: "file", file_id: "a", media_type: "image/png" },
 			]),
 		);
 		expect(result).toEqual({
 			displayText: "look",
 			rawText: "look",
 			attachmentCount: 1,
-			fileBlocks: [{ mediaType: "application/octet-stream", fileId: "a" }],
+			fileBlocks: [{ type: "file", file_id: "a", media_type: "image/png" }],
 		});
 	});
 
@@ -107,14 +107,14 @@ describe("getQueuedMessageInfo", () => {
 		const result = getQueuedMessageInfo(
 			makeMessage([
 				{ type: "text", text: " " },
-				{ type: "file", file_id: "a" },
+				{ type: "file", file_id: "a", media_type: "image/png" },
 			]),
 		);
 		expect(result).toEqual({
 			displayText: "[Queued message]",
 			rawText: "",
 			attachmentCount: 1,
-			fileBlocks: [{ mediaType: "application/octet-stream", fileId: "a" }],
+			fileBlocks: [{ type: "file", file_id: "a", media_type: "image/png" }],
 		});
 	});
 
@@ -146,8 +146,8 @@ describe("getQueuedMessageInfo", () => {
 			rawText: "check this",
 			attachmentCount: 2,
 			fileBlocks: [
-				{ mediaType: "image/png", fileId: "img-1" },
-				{ mediaType: "application/pdf", fileId: "doc-2" },
+				{ type: "file", file_id: "img-1", media_type: "image/png" },
+				{ type: "file", file_id: "doc-2", media_type: "application/pdf" },
 			],
 		});
 	});
diff --git a/site/src/pages/AgentsPage/QueuedMessagesList.tsx b/site/src/pages/AgentsPage/QueuedMessagesList.tsx
index a6da3fabc9..1f9d48d00d 100644
--- a/site/src/pages/AgentsPage/QueuedMessagesList.tsx
+++ b/site/src/pages/AgentsPage/QueuedMessagesList.tsx
@@ -1,4 +1,4 @@
-import type { ChatQueuedMessage } from "api/typesGenerated";
+import type { ChatMessagePart, ChatQueuedMessage } from "api/typesGenerated";
 import { Button } from "components/Button/Button";
 import { Spinner } from "components/Spinner/Spinner";
 import {
@@ -16,17 +16,15 @@ import {
 import { type FC, useCallback, useEffect, useMemo, useState } from "react";
 import { cn } from "utils/cn";
 
-interface FileBlock {
-	mediaType: string;
-	data?: string;
-	fileId?: string;
-}
-
 interface QueuedMessagesListProps {
 	messages: readonly ChatQueuedMessage[];
 	onDelete: (id: number) => Promise<void> | void;
 	onPromote: (id: number) => Promise<void> | void;
-	onEdit?: (id: number, text: string, fileBlocks: readonly FileBlock[]) => void;
+	onEdit?: (
+		id: number,
+		text: string,
+		fileBlocks: readonly ChatMessagePart[],
+	) => void;
 	editingMessageID?: number | null;
 	className?: string;
 }
@@ -35,20 +33,14 @@ interface QueuedMessageInfo {
 	displayText: string;
 	rawText: string;
 	attachmentCount: number;
-	fileBlocks: readonly FileBlock[];
+	fileBlocks: readonly ChatMessagePart[];
 }
 
 export const getQueuedMessageInfo = (
 	message: ChatQueuedMessage,
 ): QueuedMessageInfo => {
 	const { content } = message;
-	const fileBlocks: FileBlock[] = content
-		.filter((p) => p.type === "file")
-		.map((p) => ({
-			mediaType: p.media_type ?? "application/octet-stream",
-			fileId: p.file_id,
-			data: p.data,
-		}));
+	const fileBlocks = content.filter((p) => p.type === "file");
 	const rawText = content
 		.filter((p) => p.type === "text")
 		.map((p) => p.text)