fix(custom-model): pre-approve the injected API key in the isolated Claude config dir

The CLAUDE_CONFIG_DIR isolation from the previous commit fixed the cosmetic
auth warning but introduced a real regression: an otherwise-empty config
directory has none of a real profile's prior custom-API-key approvals, so
Claude Code stops at an interactive 'Detected a custom API key - use it?'
prompt on every single launch. Confirmed live. With nobody at a TTY to
answer, the prompt's own default ('No') silently refuses the very key this
feature just injected, which looks like the endpoint being ignored.

Adds apiKeyTrustFile to the env-kind customModelInjection capability shape
({relPath, shape: 'claude-api-key-responses'}), set on claude's entry to
{relPath: '.claude.json', shape: 'claude-api-key-responses'}. The apply step
merges customApiKeyResponses.approved: [apiKey] into
<isolatedConfigDir>/.claude.json - the exact field a real answered prompt
itself writes to (confirmed against a real ~/.claude.json after answering by
hand once), so this answers the prompt in advance rather than bypassing it.
Merges onto whatever the CLI already wrote into that file on an earlier
launch in the same isolated directory rather than overwriting it; a missing
or corrupt file is treated as empty rather than failing the apply.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RqZeHrRS6DYcGcGX2p9EwG

src/custom-model-injection-apply.ts

@@ -10,7 +10,7 @@
  * cli-registry changes" requirement it was written against.
  */
 
-import { chmodSync, existsSync, mkdirSync, writeFileSync, rmSync, symlinkSync } from 'node:fs';
+import { chmodSync, existsSync, mkdirSync, readFileSync, writeFileSync, rmSync, symlinkSync } from 'node:fs';
 import { homedir, platform } from 'node:os';
 import { join, dirname } from 'node:path';
 import { dataPath } from './config/instance.js';
@@ -79,6 +79,45 @@ function linkSharedProjectsDir(isolatedDir: string): void {
   }
 }
 
+/**
+ * Pre-approves the injected API key in an isolated config directory's trust-dialog state
+ * (`customModelInjection.apiKeyTrustFile`), so an otherwise-empty directory doesn't make the
+ * CLI stop at an interactive "Detected a custom API key — use it?" prompt on every single
+ * launch. Confirmed live: with nobody at the TTY to answer, that prompt's own default
+ * ("No") silently refuses the very key this feature just injected — this isn't bypassing
+ * the check, it's answering it the same field a real answered prompt itself writes to
+ * (verified against a real `~/.claude.json` after answering by hand once).
+ *
+ * Merges rather than overwrites: the file may already carry fields the CLI itself wrote on
+ * an earlier launch in this same isolated directory (machineID, userID, other approved
+ * keys), and a corrupt or partially-written file (a crash mid-write) is treated as absent
+ * rather than failing the whole apply over a nice-to-have.
+ */
+function seedApiKeyTrustFile(
+  configDir: string,
+  trustFile: { relPath: string; shape: 'claude-api-key-responses' },
+  apiKey: string
+): void {
+  const filePath = join(configDir, trustFile.relPath);
+  let existing: Record<string, unknown> = {};
+  try {
+    existing = JSON.parse(readFileSync(filePath, 'utf8')) as Record<string, unknown>;
+  } catch {
+    existing = {};
+  }
+  const responses = (existing.customApiKeyResponses ?? {}) as { approved?: unknown; rejected?: unknown };
+  const approved = new Set(Array.isArray(responses.approved) ? (responses.approved as string[]) : []);
+  approved.add(apiKey);
+  const rejected = Array.isArray(responses.rejected) ? responses.rejected : [];
+  existing.customApiKeyResponses = { approved: [...approved], rejected };
+  try {
+    writeFileSync(filePath, JSON.stringify(existing, null, 2), { encoding: 'utf8', mode: 0o600 });
+    chmodSync(filePath, 0o600);
+  } catch {
+    // best-effort only — the interactive prompt returns instead of a hard failure here
+  }
+}
+
 /** Best-effort recursive removal of a previously-written configDir. Never throws. */
 export function removeConfigDir(dir: string | undefined): void {
   if (!dir) return;
@@ -128,6 +167,9 @@ export function applyCustomModelInjection(
       configDir = customModelConfigDir(sessionId);
       mkdirSync(configDir, { recursive: true, mode: 0o700 });
       linkSharedProjectsDir(configDir);
+      if (injection.apiKeyTrustFile && injection.apiKey) {
+        seedApiKeyTrustFile(configDir, injection.apiKeyTrustFile, injection.apiKey);
+      }
       envOverrides = { ...envOverrides, [injection.configDirVar]: configDir };
     }
     return {