fix: block update command for 3P providers, align thinking block handling

1. cli/update.ts: Block the update command for third-party providers.
   The update mechanism downloads from Anthropic's GCS bucket, which
   would silently replace the OpenClaude build (with the OpenAI shim)
   with the upstream Claude Code binary (without it). Now shows an
   actionable message directing users to rebuild from source.

2. codexShim.ts: Filter thinking blocks from assistant history, matching
   the openaiShim behavior. Without this, thinking blocks were included
   as plain text in assistant messages for the Codex transport but
   excluded for the OpenAI transport — causing inconsistent history
   when switching providers mid-session.

src/cli/update.ts

@@ -1,4 +1,5 @@
 import chalk from 'chalk'
+import { getAPIProvider } from 'src/utils/model/providers.js'
 import { logEvent } from 'src/services/analytics/index.js'
 import {
   getLatestVersion,
@@ -28,6 +29,19 @@ import { gte } from 'src/utils/semver.js'
 import { getInitialSettings } from 'src/utils/settings/settings.js'
 
 export async function update() {
+  // Block updates for third-party providers. The update mechanism downloads
+  // from Anthropic's distribution bucket, which would silently replace the
+  // OpenClaude build (with the OpenAI shim) with the upstream Claude Code
+  // binary (without it).
+  if (getAPIProvider() !== 'firstParty') {
+    writeToStdout(
+      chalk.yellow('Auto-update is not available for third-party provider builds.\n') +
+      'To update, pull the latest source from the repository and rebuild:\n' +
+      '  git pull && bun install && bun run build\n',
+    )
+    return
+  }
+
   logEvent('tengu_update_check', {})
   writeToStdout(`Current version: ${MACRO.VERSION}\n`)