Add /model slash command

.claude/CLAUDE.md

@@ -49,7 +49,7 @@ Do NOT invoke git-commit until steps 1-3 are done.
 ## Current State
 
 Branch: `main`
-In-progress: None. Audit centralisation complete and tested.
+In-progress: None. `/model` command complete and tested (#81).
 
 ## Architecture
 

.claude/sessions/2026-03-15.md

@@ -1,3 +1,10 @@
+### 01:50 — feature/#81 /model slash command
+
+- Did: Added `/model [haiku|sonnet|opus]` command — sets a process-local model override for the current session; `/model` with no arg clears it and reverts to config. Override survives config hot reload (`updateConfig()` leaves `sessionModelOverride` untouched). Status line shows amber `model: sonnet*` indicator when override is active.
+- Files: `src/session.ts`, `src/ClaudeCli.ts`, `src/terminal.ts`
+- Decisions: Named the session-level field `sessionModelOverride` to avoid confusion with the existing `modelOverride` parameter on `send()` (used for compact model). Override priority chain in `send()`: per-call param (`compactModel`) → `sessionModelOverride` → `this.model` (config). `Terminal.modelOverride` holds the short name (e.g. `sonnet`) for display; `session.sessionModelOverride` holds the full model ID. Pre-existing biome formatting fix applied to `.claude/settings.local.json` (unrelated, caught by CI).
+- Next: Nothing — all scenarios tested and passing.
+
 ### 00:55 — audit/centralise
 
 - Did: Centralised audit storage from per-project `.claude/audit.jsonl` to `~/.claude/audit/<session-id>.jsonl`. Fixed timing bug where `setSessionId` was called after all messages had already been processed (moved call to `init` message handler in `onMessage`). Fixed `/session <id>` switch missing `audit.setSessionId()` call.

src/ClaudeCli.ts

@@ -9,6 +9,7 @@ import { CommandMode } from './CommandMode.js';
 import { CONFIG_PATH, LOCAL_CONFIG_PATH } from './cli-config/consts.js';
 import { diffConfig } from './cli-config/diffConfig.js';
 import { loadCliConfig } from './cli-config/loadCliConfig.js';
+import type { BaseModel } from './cli-config/schema.js';
 import type { ResolvedCliConfig } from './cli-config/types.js';
 import { validateRawConfig } from './cli-config/validateRawConfig.js';
 import { readClipboardImage, readClipboardText, truncateText } from './clipboard.js';
@@ -143,6 +144,12 @@ export class ClaudeCli {
     this.term.log(`${' '.repeat(indent)}session: $${this.usage.sessionCost.toFixed(4)}`);
   }
 
+  private static readonly MODEL_ALIASES: Record<string, BaseModel> = {
+    haiku: 'claude-haiku-4-5-20251001',
+    sonnet: 'claude-sonnet-4-6',
+    opus: 'claude-opus-4-6',
+  };
+
   private async handleCommand(text: string): Promise<boolean> {
     const trimmed = text.trim();
     if (trimmed === '/quit' || trimmed === '/exit') {
@@ -193,6 +200,26 @@ export class ClaudeCli {
       this.submit('/compact');
       return true;
     }
+    if (trimmed === '/model' || trimmed.startsWith('/model ')) {
+      const arg = trimmed.slice('/model'.length).trim();
+      if (!arg) {
+        this.session.clearSessionModelOverride();
+        this.term.modelOverride = undefined;
+        this.term.info(`Model override cleared — using config: ${this.session.activeModel}`);
+      } else {
+        const resolved = ClaudeCli.MODEL_ALIASES[arg];
+        if (!resolved) {
+          const valid = Object.keys(ClaudeCli.MODEL_ALIASES).join(', ');
+          this.term.error(`Unknown model: ${arg}. Valid: ${valid}`);
+        } else {
+          this.session.setSessionModelOverride(resolved);
+          this.term.modelOverride = arg;
+          this.term.info(`Model override set: ${arg} (${resolved})`);
+        }
+      }
+      this.redraw();
+      return true;
+    }
     if (trimmed === '/add-dir' || trimmed.startsWith('/add-dir ')) {
       const arg = trimmed.slice('/add-dir'.length).trim();
       if (!arg) {
@@ -835,7 +862,7 @@ export class ClaudeCli {
       this.term.info('Starting new session');
     }
     this.term.info('Enter = newline, Ctrl+Enter = send, Ctrl+C = quit');
-    this.term.info('Commands: /help, /version, /quit, /exit, /session [id], /compact-at <uuid>, /add-dir <path>');
+    this.term.info('Commands: /help, /version, /quit, /exit, /session [id], /compact-at <uuid>, /add-dir <path>, /model [haiku|sonnet|opus]');
     this.term.info('---');
 
     if (process.stdin.isTTY) {

src/cli-config/schema.ts

@@ -28,8 +28,9 @@ const BASE_MODELS = [
   'claude-3-haiku-20240307',
 ] as const satisfies readonly string[];
 
-type BaseModel = (typeof BASE_MODELS)[number];
-type ExtendedModel = `${BaseModel}[1m]`;
+export type BaseModel = (typeof BASE_MODELS)[number];
+export type ExtendedModel = `${BaseModel}[1m]`;
+export type ClaudeModel = BaseModel | ExtendedModel;
 
 const claudeModelSchema = z.enum([...BASE_MODELS, ...BASE_MODELS.map((m) => `${m}[1m]` as ExtendedModel)] as [BaseModel | ExtendedModel, ...(BaseModel | ExtendedModel)[]]);
 

src/session.ts

@@ -3,6 +3,7 @@ import { appendFileSync } from 'node:fs';
 import { type CanUseTool, type Options, type Query, query, type SDKMessage, type SDKUserMessage } from '@anthropic-ai/claude-agent-sdk';
 import type { ImageBlockParam, TextBlockParam } from '@anthropic-ai/sdk/resources/messages/messages';
 import type { Attachment } from './AttachmentStore.js';
+import type { ClaudeModel } from './cli-config/schema.js';
 import type { ThinkingEffort } from './cli-config/types.js';
 import { READ_ONLY_TOOLS } from './config.js';
 
@@ -18,25 +19,43 @@ export class QuerySession extends EventEmitter<SessionEvents> {
   private activeQuery: Query | undefined;
   private aborted = false;
   private additionalDirs: string[] = [];
+  private sessionModelOverride: ClaudeModel | undefined;
   public canUseTool: CanUseTool | undefined;
   public systemPromptAppend: string | undefined;
   public disableTools = false;
   public removeTools = false;
 
   public constructor(
-    private model: string,
+    private model: ClaudeModel,
     private maxTurns: number,
     private thinking: boolean,
     private thinkingEffort: ThinkingEffort,
   ) {
     super();
   }
 
-  public updateConfig(model: string, maxTurns: number, thinking: boolean, thinkingEffort: ThinkingEffort): void {
+  public updateConfig(model: ClaudeModel, maxTurns: number, thinking: boolean, thinkingEffort: ThinkingEffort): void {
     this.model = model;
     this.maxTurns = maxTurns;
     this.thinking = thinking;
     this.thinkingEffort = thinkingEffort;
+    // sessionModelOverride intentionally not cleared — it must survive config hot reload
+  }
+
+  public get activeModel(): ClaudeModel {
+    return this.sessionModelOverride ?? this.model;
+  }
+
+  public get hasSessionModelOverride(): boolean {
+    return this.sessionModelOverride !== undefined;
+  }
+
+  public setSessionModelOverride(model: ClaudeModel): void {
+    this.sessionModelOverride = model;
+  }
+
+  public clearSessionModelOverride(): void {
+    this.sessionModelOverride = undefined;
   }
 
   public get isActive(): boolean {
@@ -106,13 +125,13 @@ export class QuerySession extends EventEmitter<SessionEvents> {
     return generateMessages();
   }
 
-  public async send(input: string, onMessage: (msg: SDKMessage) => void, attachments?: readonly Attachment[], modelOverride?: string): Promise<void> {
+  public async send(input: string, onMessage: (msg: SDKMessage) => void, attachments?: readonly Attachment[], modelOverride?: ClaudeModel): Promise<void> {
     this.aborted = false;
     const abort = new AbortController();
     this.abort = abort;
 
     const options: Options = {
-      model: modelOverride ?? this.model,
+      model: modelOverride ?? this.sessionModelOverride ?? this.model,
       thinking: {
         type: this.thinking ? 'adaptive' : 'disabled',
       },

src/terminal.ts

@@ -31,6 +31,7 @@ export class Terminal {
   private pauseBuffer: string[] = [];
   private questionLines: string[] = [];
   public sessionId: string | undefined;
+  public modelOverride: string | undefined;
 
   public constructor(
     private readonly appState: AppState,
@@ -117,6 +118,9 @@ export class Terminal {
           return null;
         }
         b.emoji('⚡');
+        if (this.modelOverride) {
+          b.text(` \x1b[33mmodel: ${this.modelOverride}*\x1b[0m`);
+        }
         break;
       case 'sending': {
         const elapsed = this.appState.elapsedSeconds ?? 0;