Action name mangling

The theoremc::mangle module provides deterministic, injective transformation of canonical action names into Rust identifiers. Each canonical action name (e.g., account.deposit) is mangled into a unique identifier that resolves into the crate::theorem_actions module.

Use mangle_action_name to transform a validated canonical action name:

use theoremc::mangle::mangle_action_name;

let mangled = mangle_action_name("account.deposit");
assert_eq!(mangled.slug(), "account__deposit");
assert_eq!(mangled.hash(), "05158894bfb4");
assert_eq!(mangled.identifier(), "account__deposit__h05158894bfb4");
assert_eq!(
    mangled.path(),
    "crate::theorem_actions::account__deposit__h05158894bfb4",
);

The function assumes its input has already passed canonical action-name validation. It does not re-validate.

The algorithm follows docs/name-mangling-rules.md:

1. Segment escape: replace each _ in a segment with _u. ASCII letters and digits are unchanged.
2. Action slug: split the canonical name on ., escape each segment, and join the escaped segments with __.
3. Hash suffix: compute blake3(canonical_name.as_bytes()) and take the first 12 lowercase hex characters.
4. Mangled identifier: {slug}__h{hash12}.
5. Resolution path: crate::theorem_actions::{identifier}.

The individual building blocks are also public for reuse:

• segment_escape(segment) — escapes underscores in a single segment.
• action_slug(canonical_name) — produces the escaped slug.
• hash12(value) — computes the 12-character blake3 hash prefix.

The escaping rule ensures that different canonical action names always produce different mangled identifiers. For example, a.b_c (slug: a__b_uc) and a_b.c (slug: a_ub__c) produce distinct slugs because _ is escaped to _u while segment boundaries use __.