Content-free multimodal cache keys¶

build_multimodal_cache_key() derives a stable local cache key from processing metadata without hashing source bytes itself or putting content in the key. Callers provide a previously computed asset SHA-256 digest, media type, provider version, model version, policy version, and any declared preprocessing options.

from openmed.multimodal.cache_key import build_multimodal_cache_key
from openmed.multimodal.digest import digest_asset

asset = digest_asset(b"synthetic image bytes")
key = build_multimodal_cache_key(
    asset_digest=asset,
    media_type="image/png",
    provider_version="doctr-1.0",
    model_version="vision-2.1",
    policy_version="redact-v3",
    preprocessing_options={
        "color_mode": "rgb",
        "resize_mode": "fit",
        "target_width": 512,
        "target_height": 512,
    },
)

The result has the form openmed-multimodal-v1:<sha256>. Mapping order does not affect it. Changing the asset digest, media type, provider version, model version, policy version, or a preprocessing option changes the key.

Preprocessing options¶

Only the following options are accepted:

Option	Allowed values
`channel_mode`	`mono`, `native`, `stereo`
`color_mode`	`grayscale`, `native`, `rgb`, `rgba`
`orientation_mode`	`normalize`, `preserve`
`resize_mode`	`fill`, `fit`, `none`
`clip_duration_seconds`	finite number greater than 0 and at most 86,400
`frame_stride`	integer from 1 through 1,000,000
`render_dpi`	integer from 1 through 9,600
`sample_rate_hz`	integer from 1 through 768,000
`target_height`	integer from 1 through 65,536
`target_width`	integer from 1 through 65,536

Unknown names, arbitrary categorical strings, booleans in numeric fields, nested values, non-finite numbers, and out-of-range numbers fail closed.

Privacy boundary¶

Version fields use a bounded, lowercase version grammar: a single alphanumeric component, a hyphen, an optional v, one to four numeric components, and an optional alpha, beta, rc, or dev suffix (for example, vision-2.1 or policy-3.0-rc1). Generic identifier-shaped strings are not accepted. Paths, URLs, clinical text, credentials, prompts, raw bytes, and free-form option values are rejected without being echoed in errors. The returned key contains only a public schema prefix and a SHA-256 digest.

The helper performs no file access, network access, media hashing, cache storage, eviction, or encryption. Callers remain responsible for computing the asset digest and declaring every preprocessing choice that affects their model.