Module manifest 

Manifest schema, trust model, and fallback chain.

This module implements:

• Manifest — the top-level manifest structure with components and metadata
• ManifestOverlay — a remote overlay that merges onto the baseline
• Trust verification — signature, schema version anti-rollback, expiry
• Three-tier fallback chain — fresh remote → cached remote → bundled baseline

Trust Model

Every remote manifest must pass three trust checks before use:

1. Signature verification — HMAC-SHA256 against a known key
2. Schema version — must be ≥ MIN_SCHEMA_VERSION (anti-rollback)
3. Expiry — if expires_at is set, must not be in the past

Fallback Chain

fresh remote (if trust checks pass)
  ↓ fetch failure
cached remote (if valid cache exists)
  ↓ no cache
bundled baseline (always available, compiled into binary)

Structs

Manifest

The top-level manifest structure.

ManifestComponent

A single component entry within a manifest.

ManifestOverlay

A remote overlay that merges onto a baseline manifest.

ResolvedManifest

Result of manifest fallback resolution.

Enums

ManifestSource

Source of the manifest after fallback resolution.

ManifestTrustError

Errors that can occur during manifest trust verification.

Constants

CURRENT_SCHEMA_VERSION

Current schema version produced/consumed by this binary.

MIN_SCHEMA_VERSION

Minimum supported schema version. Manifests with a lower version are rejected.

Traits

ManifestFetcher

Trait for fetching and caching manifests. Implementations provide the actual remote fetch and cache read/write logic.

Functions

create_signed_manifest

Create a test manifest with a valid signature.

resolve_manifest

Resolve a manifest using the three-tier fallback chain.