Add model selection and file creation diffs

ARCHITECTURE.md

@@ -102,6 +102,10 @@ remain in Eve's events instead of becoming parallel Convex records. Token usage
 recorded for future product decisions but does not enforce a product quota; Eve's
 per-session safety limits still apply.
 
+The selected model is transient browser state sent with each turn. The Eve channel
+validates it into current request attributes, and the agent resolves it at turn scope
+with the shared default as fallback. Convex does not persist model selection.
+
 ## Coding harness
 
 Eve's built-ins are the base. The local additions are deliberately narrow:
@@ -113,7 +117,7 @@ Eve's built-ins are the base. The local additions are deliberately narrow:
 - **`clone_repository`** validates a public GitHub repository, clones it into the
   current workspace, and returns its root entries in the repository activity.
 - **`write_file`** preserves Eve's create/overwrite contract and read-before-write
-  protection, adding a bounded diff for complete replacements.
+  protection, adding a bounded diff for new files and complete replacements.
 - **`edit_file`** applies batched, exact, unique, non-overlapping replacements to one
   snapshot and stores a context-limited unified diff.
 - **`start_dev`** starts the model-selected server command, exposes its port, verifies
@@ -174,8 +178,9 @@ Here `sessionId` is Eve's durable session ID, not the app's public session ID.
   Its header shows the selected GitHub repository when the workspace has one.
   The read-only workspace contains breadcrumbs, a keyboard-accessible tree, and a
   highlighted source viewer. File tool activity can open the corresponding file.
-- **Composer** composes text input, the self-contained Chat Voice Input package, and
-  submit as independent controls. Audio is never recorded or persisted.
+- **Composer** composes text input, a turn-scoped model selector, the self-contained
+  Chat Voice Input package, and submit as independent controls. Audio is never
+  recorded or persisted.
 - **Activity** projects Eve events into reasoning, tool calls, live Bash output,
   file diffs, and elapsed time.
 - **Session management** includes responsive sidebar navigation, rename, and delete.

agent/agent.ts

@@ -1,7 +1,18 @@
-import { defineAgent } from "eve";
+import { defineAgent, defineDynamic } from "eve";
+
+import { DEFAULT_MODEL_ID, isModelId } from "@/lib/models";
 
 export default defineAgent({
-  model: "anthropic/claude-haiku-4.5",
+  model: defineDynamic({
+    fallback: DEFAULT_MODEL_ID,
+    events: {
+      "turn.started": (_event, ctx) => {
+        const model = ctx.session.auth.current?.attributes.model;
+        if (!isModelId(model)) return null;
+        return model;
+      },
+    },
+  }),
   limits: {
     maxInputTokensPerSession: 2_000_000,
     maxOutputTokensPerSession: 100_000,

agent/channels/eve.ts

@@ -2,6 +2,7 @@ import { ForbiddenError, localDev, none, vercelOidc } from "eve/channels/auth";
 import { defaultEveAuth, eveChannel } from "eve/channels/eve";
 
 import { isPublicId, SESSION_ID_ATTRIBUTE, SESSION_ID_HEADER } from "@/lib/identity";
+import { isModelId, MODEL_HEADER } from "@/lib/models";
 
 export default eveChannel({
   auth: [vercelOidc(), localDev(), none()],
@@ -10,18 +11,20 @@ export default eveChannel({
     if (!auth) return { auth };
 
     const sessionId = ctx.eve.request.headers.get(SESSION_ID_HEADER);
-    if (sessionId === null) return { auth };
-    if (!isPublicId(sessionId)) {
+    if (sessionId !== null && !isPublicId(sessionId)) {
       throw new ForbiddenError({
         code: "invalid_session_id",
         message: "The session id header is invalid.",
       });
     }
 
-    const attributes = {
+    const attributes: Record<string, string | readonly string[]> = {
       ...auth.attributes,
-      [SESSION_ID_ATTRIBUTE]: sessionId,
     };
+    if (sessionId !== null) attributes[SESSION_ID_ATTRIBUTE] = sessionId;
+    const model = ctx.eve.request.headers.get(MODEL_HEADER);
+    if (isModelId(model)) attributes.model = model;
+
     return { auth: { ...auth, attributes } };
   },
 });

agent/tools/edit_file.ts

@@ -11,7 +11,7 @@ const editSchema = z.object({
 
 export default defineTool({
   description:
-    "Replace one or more exact, unique, non-overlapping text ranges in an existing file. Every oldText is matched against the original file, so use one call for multiple changes to the same file.",
+    "Replace one or more exact, unique, non-overlapping text ranges in an existing file. Copy each oldText verbatim from the latest file read. Every oldText is matched against the same original snapshot. If any edit fails, no changes are applied; read the file again and retry the call.",
   inputSchema: z.object({
     edits: z.array(editSchema).min(1).max(50),
     filePath: z.string().min(1).max(4_096),

agent/tools/write_file.ts

@@ -22,7 +22,6 @@ export default defineTool({
       const fileDiff = computeFileDiff(input.filePath, original, input.content);
       ctx.abortSignal.throwIfAborted();
       const result = writeFileOutputSchema.parse(await writeFile.execute(input, ctx));
-      if (!result.existed) return result;
       if (!fileDiff) return result;
       return { ...result, ...fileDiff };
     });

app/home-page.tsx

@@ -4,13 +4,15 @@ import { href, useNavigate } from "react-router";
 import { AppHeader } from "@/components/app-header";
 import { SessionStart } from "@/components/session/session-start";
 import { api } from "@/convex/_generated/api";
+import { useComposerStore } from "@/lib/composer-store";
 import type { GitRepository } from "@/lib/github";
 import { createPublicId } from "@/lib/identity";
 import { sendTurn } from "@/lib/session-runtime";
 
 export function HomePage() {
   const createSession = useConvexMutation(api.sessions.create);
   const navigate = useNavigate();
+  const selectedModel = useComposerStore((state) => state.selectedModel);
 
   function openSession(sessionId: string): void {
     void navigate(href("/s/:sessionId", { sessionId }));
@@ -23,6 +25,7 @@ export function HomePage() {
       { clientContext, message },
       {
         beforeSend: createSession({ message, sessionId }),
+        modelId: selectedModel,
       },
     );
     openSession(sessionId);

components/chat/composer.tsx

@@ -1,8 +1,9 @@
 import { ArrowUp, Square } from "lucide-react";
 import { type KeyboardEvent, type SubmitEvent, useEffect, useRef } from "react";
 
+import { ModelSelector } from "@/components/chat/model-selector";
 import { Button } from "@/components/ui/button";
-import ChatVoiceInput from "@/lib/chat-voice-input";
+import ChatVoiceInput, { useChatVoiceInput } from "@/lib/chat-voice-input";
 import { useComposerStore } from "@/lib/composer-store";
 
 type ComposerProps = {
@@ -20,6 +21,12 @@ type TextInputProps = {
 
 type SubmitButtonProps = Pick<ComposerProps, "disabled" | "isGenerating" | "onStop">;
 
+function SecondaryControls({ disabled }: { readonly disabled: boolean }) {
+  const { status } = useChatVoiceInput();
+  if (status === "recording") return null;
+  return <ModelSelector disabled={disabled} />;
+}
+
 function handleKeyDown(event: KeyboardEvent<HTMLTextAreaElement>): void {
   if (event.key !== "Enter" || event.shiftKey || event.nativeEvent.isComposing) return;
 
@@ -105,8 +112,20 @@ export function Composer({ disabled, isGenerating, onSend, onStop }: ComposerPro
     >
       <TextInput disabled={disabled} onValueChange={onValueChange} value={value} />
       <div className="flex min-w-0 items-center justify-end gap-1 pt-1">
-        <ChatVoiceInput disabled={audioDisabled} onValueChange={onValueChange} value={value} />
-        <SubmitButton disabled={submitDisabled} isGenerating={isGenerating} onStop={onStop} />
+        <ChatVoiceInput.Provider
+          disabled={audioDisabled}
+          onValueChange={onValueChange}
+          value={value}
+        >
+          <ChatVoiceInput.Error />
+          <ChatVoiceInput.Waveform />
+          <ChatVoiceInput.Timer />
+          <SecondaryControls disabled={disabled} />
+          <div className="flex gap-1.5">
+            <ChatVoiceInput.Button />
+            <SubmitButton disabled={submitDisabled} isGenerating={isGenerating} onStop={onStop} />
+          </div>
+        </ChatVoiceInput.Provider>
       </div>
     </form>
   );

components/chat/message.tsx

@@ -80,13 +80,9 @@ export function UserMessage({ actions, children, messageId }: MessageProps) {
 }
 
 export function AssistantMessage({ actions, children, messageId }: MessageProps) {
-  const className = actions
-    ? "group/message relative pt-3 pb-12"
-    : "group/message relative pt-3 pb-5";
-
   return (
     <ThreadMessage messageId={messageId}>
-      <article aria-label="Assistant" className={className}>
+      <article aria-label="Assistant" className="group/message relative pt-3 pb-12">
         <div>{children}</div>
         {actions && <div className="absolute bottom-5 left-0">{actions}</div>}
       </article>

components/chat/model-selector.tsx

@@ -0,0 +1,51 @@
+import { ChevronDown } from "lucide-react";
+
+import { Button } from "@/components/ui/button";
+import { getMenuAnchorStyle, MenuContent, MenuItem } from "@/components/ui/menu";
+import { useComposerStore } from "@/lib/composer-store";
+import { MODEL_OPTIONS } from "@/lib/models";
+
+type ModelSelectorProps = {
+  readonly disabled: boolean;
+  readonly hidden?: boolean;
+};
+
+export function ModelSelector({ disabled, hidden }: ModelSelectorProps) {
+  const selectedModel = useComposerStore((state) => state.selectedModel);
+  const setSelectedModel = useComposerStore((state) => state.setSelectedModel);
+  const model = MODEL_OPTIONS.find((option) => option.value === selectedModel) ?? MODEL_OPTIONS[0];
+  const menuId = "composer-model-menu";
+
+  return (
+    <>
+      <Button
+        aria-label="Select model"
+        className="gap-1 px-2 font-normal"
+        disabled={disabled}
+        hidden={hidden}
+        popoverTarget={menuId}
+        style={getMenuAnchorStyle(menuId)}
+        variant="ghost"
+      >
+        <span>{model.label}</span>
+        <ChevronDown aria-hidden="true" className="ml-0.5 size-3.5 text-muted-foreground" />
+      </Button>
+      <MenuContent
+        className="w-36 [position-area:top_span-right] [position-try-fallbacks:flip-block]"
+        id={menuId}
+        side="top"
+      >
+        {MODEL_OPTIONS.map((option) => (
+          <MenuItem
+            className="text-sm"
+            key={option.value}
+            onClick={() => setSelectedModel(option.value)}
+            popoverTarget={menuId}
+          >
+            {option.label}
+          </MenuItem>
+        ))}
+      </MenuContent>
+    </>
+  );
+}

components/session/tool-activity.tsx

@@ -103,11 +103,16 @@ function isSettled(part: EveDynamicToolPart): boolean {
   );
 }
 
+function DeletedLines({ count }: { readonly count: number }) {
+  if (count === 0) return null;
+  return <span className="text-destructive">-{count}</span>;
+}
+
 function FileDiffStats({ diff }: { readonly diff: FileDiff }) {
   const { additions, deletions } = useMemo(() => getFileDiffStats(diff.diff), [diff.diff]);
   return (
     <span className="flex shrink-0 gap-1 font-mono text-sm">
-      <span className="text-destructive">-{deletions}</span>
+      <DeletedLines count={deletions} />
       <span className="text-success">+{additions}</span>
     </span>
   );

components/session/use-session.ts

@@ -4,6 +4,7 @@ import type { EveMessage, EveMessagePart, SendTurnPayload, SessionState } from "
 import { useEffect, useMemo } from "react";
 
 import { api } from "@/convex/_generated/api";
+import { useComposerStore } from "@/lib/composer-store";
 import { projectActivityTimings, projectEveMessages, type StoredEveEvent } from "@/lib/eve-events";
 import { findPendingInput, isSessionLimitRequest } from "@/lib/pending-input";
 import {
@@ -112,6 +113,7 @@ export function isSessionGenerating(
 }
 
 export function useSession({ checkpointEvents, session, sessionId }: UseSessionOptions) {
+  const selectedModel = useComposerStore((state) => state.selectedModel);
   const connectionCount = useConvexConnectionState().connectionCount;
   const status = session?.status;
   const eveSessionId = session?.eveSessionId;
@@ -168,6 +170,7 @@ export function useSession({ checkpointEvents, session, sessionId }: UseSessionO
         ? () => recordInputResponses({ inputResponses, sessionId, streamIndex: cursor })
         : undefined,
       beforeSend: prepareTurn({ sessionId, streamIndex: cursor }),
+      modelId: selectedModel,
       sessionState: toSessionState(session),
     });
   }

lib/composer-store.ts

@@ -1,11 +1,17 @@
 import { create } from "zustand";
 
+import { DEFAULT_MODEL_ID, type ModelId } from "@/lib/models";
+
 type ComposerStore = {
   readonly draft: string;
+  readonly selectedModel: ModelId;
   readonly setDraft: (value: string) => void;
+  readonly setSelectedModel: (model: ModelId) => void;
 };
 
 export const useComposerStore = create<ComposerStore>()((set) => ({
   draft: "",
+  selectedModel: DEFAULT_MODEL_ID,
   setDraft: (draft) => set({ draft }),
+  setSelectedModel: (selectedModel) => set({ selectedModel }),
 }));

lib/file-diff.ts

@@ -13,14 +13,15 @@ export function computeFileDiff(
   original: string | null,
   edited: string,
 ): FileDiff | undefined {
-  if (original === null || original === edited) return;
+  const previous = original ?? "";
+  if (previous === edited) return;
   if (
-    Buffer.byteLength(original, "utf8") > fileBytesMax ||
+    Buffer.byteLength(previous, "utf8") > fileBytesMax ||
     Buffer.byteLength(edited, "utf8") > fileBytesMax
   ) {
     return;
   }
-  const diff = createPatch(path, original, edited, undefined, undefined, {
+  const diff = createPatch(path, previous, edited, undefined, undefined, {
     context: 4,
     timeout: 2_000,
   });

lib/models.ts

@@ -0,0 +1,18 @@
+export const MODEL_OPTIONS = [
+  { label: "GPT 5.6 Terra", value: "openai/gpt-5.6-terra" },
+  { label: "GPT 5.6 Luna", value: "openai/gpt-5.6-luna" },
+  { label: "Claude Sonnet 5", value: "anthropic/claude-sonnet-5" },
+  { label: "Claude Opus 5", value: "anthropic/claude-opus-5" },
+  { label: "Gemini 3.6 Flash", value: "google/gemini-3.6-flash" },
+  { label: "Deepseek V4 Flash", value: "deepseek/deepseek-v4-flash" },
+  { label: "Kimi 2.7", value: "moonshotai/kimi-k2.7-code" },
+] as const;
+
+export type ModelId = (typeof MODEL_OPTIONS)[number]["value"];
+
+export const DEFAULT_MODEL_ID: ModelId = MODEL_OPTIONS[0].value;
+export const MODEL_HEADER = "x-eve-model";
+
+export function isModelId(value: unknown): value is ModelId {
+  return MODEL_OPTIONS.some((model) => model.value === value);
+}