* fix: preserve stored provider in resolveSessionModelRef for vendor-prefixed models
When an OpenRouter model with a vendor prefix (e.g. "anthropic/claude-haiku-4.5")
was successfully used and persisted to the session entry, the next call to
resolveSessionModelRef would re-parse the model string through parseModelRef,
which splits on the first slash and incorrectly extracts "anthropic" as the
provider — discarding the stored "openrouter" provider entirely. This caused
subsequent requests to attempt direct Anthropic API calls with an OpenRouter
API key, producing "credit balance too low" billing errors.
The fix trusts the explicitly stored modelProvider on the session entry and
skips parseModelRef re-parsing when a provider is already recorded. parseModelRef
is still used as a fallback when no provider is stored on the entry.
Co-authored-by: Cursor <cursoragent@cursor.com>
* Changelog: add OpenRouter note for #22753
---------
Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Vincent Koc <vincentkoc@ieee.org>
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