fix(copilot): a model value must start with a letter or digit

Like resumeSessionId, model follows a flag, so --model --yolo made --yolo its own flag and bypassed the allowAll clamp. New model-plain token pattern, the same rule in the create schema, and golden and schema tests.

src/config/cli-registry/patterns.ts

@@ -20,6 +20,7 @@
 export type TokenPattern =
   | 'model'
   | 'model-claude'
+  | 'model-plain'
   | 'model-pi'
   | 'id'
   | 'id-dotted'
@@ -43,6 +44,9 @@ const PATTERNS: Record<TokenPattern, RegExp> = {
   model: /^[a-zA-Z0-9._\-/]+$/,
   // buildSpawnCommand's claude branch — `[` and `]` for bracketed model aliases
   'model-claude': /^[a-zA-Z0-9._\-[\]]+$/,
+  // copilot --model. Same characters as `model`, but a leading alphanumeric: the value follows a
+  // flag, so `--yolo` must not pass as a model id and become its own flag (the allowAll clamp bypass).
+  'model-plain': /^[a-zA-Z0-9][a-zA-Z0-9._\-/]*$/,
   // buildPiCommand — `:` for a thinking suffix (`sonnet:high`), `/` for `provider/id`
   'model-pi': /^[a-zA-Z0-9._\-/:]+$/,
   // opencode --session, codex resume

src/config/cli-registry/stock.ts

@@ -1691,7 +1691,8 @@ const COPILOT: CliEntry = {
   launch: {
     params: {
       allowAll: { type: 'bool' },
-      model: { type: 'token', pattern: 'model' },
+      // `model-plain`, not `model`: the leading alphanumeric keeps a flag-shaped value out.
+      model: { type: 'token', pattern: 'model-plain' },
       // `path-segment`, not `id-dotted`: the leading alphanumeric keeps a flag-shaped value out.
       resumeId: { type: 'token', pattern: 'path-segment' },
       continueSession: { type: 'bool' },

src/web/schemas.ts

@@ -441,10 +441,12 @@ const GrokConfigSchema = z
 
 const CopilotConfigSchema = z
   .object({
+    // A leading alphanumeric, like resumeSessionId below: a value like `--yolo` would otherwise be read
+    // as its own flag after `--model` (bypassing the allowAll clamp). `/` stays for provider/id.
     model: z
       .string()
       .max(100)
-      .regex(/^[a-zA-Z0-9._\-/]+$/)
+      .regex(/^[a-zA-Z0-9][a-zA-Z0-9._\-/]*$/)
       .optional(),
     allowAll: z.boolean().optional(),
     continueSession: z.boolean().optional(),

test/cli-registry-spawn-golden.test.ts

@@ -372,6 +372,17 @@ describe('copilot', () => {
     expect(cp({ resumeSessionId: 'my-feature' })).toBe('copilot --resume my-feature');
   });
 
+  // `--model --yolo` would make `--yolo` its own flag and get around the allowAll clamp, so a model id
+  // starts with an alphanumeric too. A provider/id value (the `/`) is still accepted.
+  it('drops a model value that would be read as a flag', () => {
+    for (const model of ['--yolo', '-n', '--allow-all-tools', '.', '/etc/passwd']) {
+      expect(cp({ model })).toBe('copilot');
+      expect(cp({ allowAll: false, model })).toBe('copilot');
+    }
+    expect(cp({ model: 'claude-sonnet-5.5' })).toBe('copilot --model claude-sonnet-5.5');
+    expect(cp({ model: 'openai/gpt-5' })).toBe('copilot --model openai/gpt-5');
+  });
+
   it('never puts a credential on the command line', () => {
     const cmd = cp({ allowAll: true, model: 'auto' }) ?? '';
     expect(cmd).not.toContain('token');

test/copilot-config-schema.test.ts

@@ -0,0 +1,25 @@
+/**
+ * @fileoverview copilotConfig on the session create body: `model` and `resumeSessionId` follow a flag
+ * (`--model`, `--resume`), so a value that starts with `-` would be read as its own flag and get
+ * around the allowAll clamp. Both need a leading letter or digit.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { CreateSessionSchema } from '../src/web/schemas.js';
+
+const parse = (copilotConfig: unknown) =>
+  CreateSessionSchema.safeParse({ workingDir: '/tmp', mode: 'copilot', copilotConfig });
+
+describe('copilotConfig schema', () => {
+  it.each(['--yolo', '-n', '--allow-all-tools', '.hidden', '/etc/passwd'])('rejects model %s', (model) => {
+    expect(parse({ model }).success).toBe(false);
+  });
+
+  it.each(['--yolo', '-n', '--allow-all-tools'])('rejects resumeSessionId %s', (resumeSessionId) => {
+    expect(parse({ resumeSessionId }).success).toBe(false);
+  });
+
+  it.each(['auto', 'claude-sonnet-5.5', 'openai/gpt-5'])('accepts model %s', (model) => {
+    expect(parse({ model }).success).toBe(true);
+  });
+});