gemini-omni-flash-preview: previous_interaction_id not supported on Agent Platform route but works on Gemini API route

**Environment:**
- API: REST (curl)
- Model: gemini-omni-flash-preview

**Expected behavior:**
Both routes support `previous_interaction_id` for stateful video editing.

**Actual behavior:**
- generativelanguage.googleapis.com/v1beta/interactions → works
- aiplatform.googleapis.com/v1beta1/projects/{PROJECT}/locations/global/interactions → returns error

**Error response on Agent Platform route:**
{
"error": {
"message": "gemini-omni-flash-preview on this path do not support previous_interaction_id.",
"code": "invalid_request"
}
}

**Reproduction (Agent Platform route - fails):**
curl -sS -X POST \
"https://aiplatform.googleapis.com/v1beta1/projects/{PROJECT}/locations/global/interactions" \
-H "Authorization: Bearer $(gcloud auth print-access-token)" \
-H "Content-Type: application/json" \
-d '{
"model": "gemini-omni-flash-preview",
"previous_interaction_id": "{valid_id_from_previous_interaction}",
"input": "Make the violin invisible.",
"store": true
}'

**Reproduction (Gemini API route - works):**
curl -sS -X POST \
"https://generativelanguage.googleapis.com/v1beta/interactions?key=$API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "gemini-omni-flash-preview",
"previous_interaction_id": "{valid_id}",
"input": "Make the violin invisible."
}'

**Question:**
Is previous_interaction_id intentionally not supported on the Agent Platform
route for this model? If so, please update the documentation to clarify.