Problem

The Xiaomi MiMo API returns errors with the diagnostic in a top-level param field rather than in message:

{"code":"400","message":"Param Incorrect","param":"`text` is not set"}

The error classifier only extracted body.message (Param Incorrect) but NOT body.param (`text` is not set). This caused the multimodal_tool_content_unsupported pattern to never match, resulting in the error being classified as a non-retryable format_error and aborting the session.

Fix

Added extraction of body.param into the error_msg used for pattern matching. Now the `text` is not set pattern correctly triggers the multimodal tool content recovery path (strip images from tool messages and retry).

Before

error_msg = "badrequesterror [http 400] param incorrect"
# Pattern "text is not set" NOT found → classified as format_error → non-retryable → ABORT

After

error_msg = "badrequesterror [http 400] param incorrect `text` is not set"
# Pattern "`text` is not set" FOUND → classified as multimodal_tool_content_unsupported → retryable → strip images + RETRY

Testing

Verified that the pattern matching works with the exact error from the user's session:

error_msg = 'badrequesterror [http 400] param incorrect `text` is not set'
pattern = '`text` is not set'
assert pattern in error_msg  # True

Fixes #27344