feat:zk threst model

[Wilfred007]

Summary

Describe the change, the motivation behind it, and any important implementation details.
The threat model covers 16 threat classes (T1–T16), well past the 6-class acceptance bar:

• T1 Trusted-setup/toxic-waste compromise → Z004

• T2 Proof malleability (public-input binding) → Z003

• T3 Nullifier/proof replay → Z001, Z006

• T4/T5 Verifying-key integrity & rotation access control → Z005, Z010

• T6 Under-constrained circuit inputs → Z007

• T1 Trusted-setup/toxic-waste compromise → Z004

• T2 Proof malleability (public-input binding) → Z003

• T3 Nullifier/proof replay → Z001, Z006

• T4/T5 Verifying-key integrity & rotation access control → Z005, Z010

• T6 Under-constrained circuit inputs → Z007

• T7 Curve/field confusion → Z008

• T8/T9 Rollup batch-root validation & Merkle-root spoofing → Z013, Z014

• T10–T13 Insecure randomness, domain-separation, unbounded verify loops, output over-exposure → Z002, Z011, Z009, Z012

• T14–T16 Three gaps the roadmap already flags as detector-exists-but-uncoded (zk_verification_result_ignored, zk_verifier_skippable, zk_missing_constraint) — I proposed stable codes
  Z015–Z017 for these, since the task asked for "existing or newly proposed" mitigations

Each threat has a mainnet-impact assessment and a real-world precedent (Zcash's BCTV14a counterfeiting bug, Trail of Bits' "Frozen Heart" Fiat-Shamir findings, the Nomad Bridge
root-replay incident as a non-ZK analog, and the 0xPARC ZK Bug Tracker). I verified every rule ID, detector function name, and cross-linked file path against the actual source
(finding_codes.rs, rules/*.rs) rather than trusting the docs alone — this caught that the case study's Z002 description ("verification result ignored") is stale drift from the
canonical docs/rules/Z002.md ("insecure randomness"), so I used the canonical definition.

Fixes #

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Maintenance or refactor

Testing

List the commands you ran and the scope of validation.

cargo fmt --all --check
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test -p sanctifier-core --all-features
cargo test -p sanctifier-cli
cd frontend && npm test

Closes #1193
Closes #1194
Closes #1195
Closes #1190

Checklist

• I ran the relevant tests locally, or explained why they were not needed.
• I updated documentation for any user-facing behavior changes.
• I added or updated tests for the change when appropriate.
• I added a changelog or release-notes entry when needed, or confirmed none is required.
• I verified this branch is up to date with main and merge conflicts are resolved.

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