fix(dims): handle prefixed model IDs on openai-compatible path (#2325) (#3309)

OpenRouter (and potentially other proxy providers) expose OpenAI's
text-embedding-3 models with a provider prefix in the model ID, e.g.
`openai/text-embedding-3-large` rather than bare `text-embedding-3-large`.

`dimsProviderOptions()` checks `modelId.startsWith('text-embedding-3')`
which fails for the prefixed form, so the `dimensions` parameter is never
sent. The upstream provider returns its native dimensionality (3072 for
-large) instead of the configured value (e.g. 1536), causing an immediate
"dim mismatch" error on first embed.

The default OpenRouter embedding (`text-embedding-3-small` at 1536d)
masked this because its native size happens to match the default config.
The bug surfaces when using `-large`, or `-small` with a non-1536 dim
(512, 768, 1024 — all listed in the recipe's `dims_options`).

Fix: strip the provider prefix before the `startsWith` check. The full
prefixed ID is preserved in the error message for user clarity.

Co-authored-by: Noetherly <280958447+noetherly@users.noreply.github.com>

src/core/ai/dims.ts

@@ -285,9 +285,10 @@ export function dimsProviderOptions(
       // configured for a smaller width (e.g. 1536) hard-fail at first embed.
       // Azure/OpenAI-compat embeddings are symmetric — inputType ignored.
       // v0.36.0.0 (D13): same range validation as native-openai path.
-      if (modelId.startsWith('text-embedding-3')) {
-        if (isOpenAITextEmbedding3Model(modelId) && !isValidOpenAITextEmbedding3Dim(modelId, dims)) {
-          const max = maxOpenAITextEmbedding3Dim(modelId)!;
+      const bareModelId = modelId.includes('/') ? modelId.split('/').pop()! : modelId;
+      if (bareModelId.startsWith('text-embedding-3')) {
+        if (isOpenAITextEmbedding3Model(bareModelId) && !isValidOpenAITextEmbedding3Dim(bareModelId, dims)) {
+          const max = maxOpenAITextEmbedding3Dim(bareModelId)!;
           throw new AIConfigError(
             `OpenAI model "${modelId}" supports embedding_dimensions in 1..${max}, got ${dims}.`,
             `Set \`embedding_dimensions\` to a value between 1 and ${max} ` +