#9739: #9291 fix(models): preserve existing models in models.json when merging providers

When auth profiles are temporarily inaccessible (e.g., macOS keychain locked), the implicit providers don't include qwen-portal. If explicit config has qwen-portal without models array, the previous code replaced the existing provider entirely, losing vision-model. Now uses mergeProviders() instead of simple spread when merging with existing models.json, which properly merges models at provider level. Fixes #9291 <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR changes `ensureOpenClawModelsJson()` to use a provider-level merge (`mergeProviders`) when combining newly-resolved providers with an existing `models.json`, with the intent of preserving previously persisted models when the incoming provider config omits a `models` array (e.g. when auth profiles/keychain are temporarily inaccessible). It also adds a Vitest regression test file covering the qwen-portal scenario. In the broader codebase, `ensureOpenClawModelsJson()` is called by model listing, gateway/profile flows, and media tooling to keep `~/.openclaw/agents/*/models.json` up to date; merge-mode behavior directly impacts whether users retain or lose provider model catalogs across intermittent auth/profile failures. <h3>Confidence Score: 3/5</h3> - This PR is close to mergeable but has a likely merge-logic bug and a regression test that may not exercise the intended scenario. - Switching to `mergeProviders()` is directionally correct, but `mergeProviderModels()` can still drop an existing provider's `models` array when the incoming provider omits `models` and the existing provider has no `models` field. The newly added test appears to create auth profiles, which may cause implicit providers to include qwen-portal and mask the problematic path. - src/agents/models-config.ts; src/agents/models-config.preserves-existing-models-when-new-provider-has-none.test.ts <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->