Switch to Hemera

Context

Trident currently uses two hash functions:

• BLAKE3 (external crate) — only for Poseidon2 round constant generation
• Custom Poseidon2 (two implementations) — content addressing, program digests

Hemera (cyber-hemera on crates.io, ~/git/hemera) is the canonical hash primitive of the cyber cyberstate. It is a Poseidon2 sponge over Goldilocks with self-bootstrapped constants derived from the seed "cyber". Output is always 64 bytes (8 Goldilocks elements).

Why

• One hash function for the entire ecosystem, not two custom Poseidon2 impls
• Hemera is battle-tested with pinned test vectors and zero dependencies
• Self-bootstrapped constants (from "cyber" seed) vs BLAKE3-derived constants
• 64-byte output (256-bit collision resistance) vs current 32-byte output
• Tree hashing, XOF, keyed hashing, key derivation — all built in
• Aligns trident with the cyberstate's cryptographic identity

Breaking Change

ContentHash changes from 32 bytes to 64 bytes. All existing hashes (codebase store, lockfiles, program digests) become invalid. This is a clean break — all content must be rehashed.

Inventory: What Changes

Layer 1: Remove BLAKE3 dependency

File	What	Action
Cargo.toml	blake3 = "1"	Remove, add cyber-hemera = "0.2"

Layer 2: Remove custom Poseidon2 implementations

File	LOC	What	Action
src/package/poseidon2.rs	~340	Standalone Goldilocks Poseidon2	Delete entirely
src/field/poseidon2.rs	~295	Generic Poseidon2 over PrimeField	Delete entirely

These are replaced by cyber_hemera::hash() and cyber_hemera::Hasher.

Layer 3: Update ContentHash (32 → 64 bytes)

File	What	Change
src/package/hash/mod.rs	ContentHash([u8; 32])	Change to ContentHash([u8; 64])
src/package/hash/mod.rs:118	hash_file_content()	Replace poseidon2::hash_bytes() with hemera::hash()
src/package/hash/normalize.rs:180,193,204	hash_bytes() calls	Replace with hemera::hash().as_bytes()
src/package/hash/mod.rs	hash_version: 1	Bump to hash_version: 2
src/package/hash/mod.rs	hex display (64 chars)	Update to 128 chars

Layer 4: Update all hash call sites

File	Line	What	Change
src/deploy/mod.rs	87	poseidon2::hash_bytes(tasm)	hemera::hash(tasm)
src/deploy/tests.rs	115	determinism test	Update expected values
src/cli/deploy.rs	150	dry-run hash	hemera::hash()
src/cli/package.rs	92	dry-run hash	hemera::hash()
src/cli/hash.rs	entire	trident hash command	Use hemera, update output format (128 hex chars)
src/package/manifest/resolve.rs	217	source hash	hemera::hash()
src/package/manifest/mod.rs	comment	mentions "BLAKE3"	Fix comment

Layer 5: Update field layer

File	What	Change
src/field/poseidon2.rs	Generic Poseidon2	Delete — hemera is the hash
src/field/mod.rs	pub mod poseidon2	Remove module declaration
src/field/proof.rs	If references poseidon2	Update imports

Layer 6: Update re-exports

File	What	Change
src/lib.rs:30	pub use package::hash	Keep
src/lib.rs:32	pub use package::poseidon2	Remove, add pub use cyber_hemera as hemera
src/package/mod.rs:5	pub mod poseidon2	Remove

Layer 7: Update runtime artifacts

File	What	Change
src/runtime/artifact.rs	source_hash: String	Now 128 hex chars
src/runtime/artifact.rs	per-function hash: String	Now 128 hex chars

Layer 8: Update store (on-disk format)

File	What	Change
src/package/store/mod.rs	Def storage paths	2-char prefix from 128-char hex
src/package/store/mod.rs	Serialization	Update hash field widths
src/package/manifest/lockfile.rs	Lockfile format	128-char hex hashes

Layer 9: Update benchmarks and references

File	What	Change
benches/references/std/crypto/poseidon2.rs	Benchmark reference	Rewrite using hemera
benches/references/std/crypto/merkle.rs	Merkle reference	Use hemera tree hashing
benches/references/std/trinity/inference.rs:365,371	Round constants	Use hemera

Layer 10: Update Trident standard library

File	What	Change
vm/*/hash.tri or equivalent	Hash builtins	Must emit hemera, not old Poseidon2
std/crypto/poseidon2.tri	Stdlib hash	Rename/rewrite as hemera wrapper
Cost tables in src/cost/	Hash cycle costs	Update to hemera's cycle count

Layer 11: Update reference docs

File	What	Change
reference/language.md	Digest type description	Reference hemera
docs/explanation/content-addressing.md	Hash function description	BLAKE3 → hemera
src/README.md	Package description	BLAKE3 → hemera
CLAUDE.md	Key modules section	Update poseidon2 references

Layer 12: Update trisha (companion repo)

What	Change
Cargo.toml	Add cyber-hemera if needed
Any hash verification	Must match hemera output format
Program digest checking	64-byte digests

Execution Order

1. Add hemera dependency, remove blake3 (Cargo.toml)
2. Create src/hemera.rs thin wrapper — re-export cyber_hemera with project-local helpers (content_hash(), program_digest())
3. Update ContentHash — 32 → 64 bytes, bump hash_version
4. Replace all poseidon2::hash_bytes() calls with hemera
5. Delete src/package/poseidon2.rs
6. Delete src/field/poseidon2.rs
7. Update re-exports in lib.rs and package/mod.rs
8. Update CLI (hash command, deploy, package)
9. Update store (on-disk paths, serialization)
10. Update runtime artifacts (ProgramBundle hash fields)
11. Update benchmarks and references
12. Update stdlib and cost tables
13. Update docs (reference, explanation, README)
14. Rebuild trisha and verify compatibility
15. Run full test suite: cargo check, cargo test, trident bench

Verification

After complete switch:

• cargo check — zero warnings
• cargo test — all tests pass (with updated expected values)
• grep -r blake3 src/ — zero hits
• grep -r 'package::poseidon2' src/ — zero hits
• grep -r 'field::poseidon2' src/ — zero hits
• trident hash — outputs 128 hex chars
• trident bench — no regressions
• Content store rehashed under new scheme

Risk

• Trisha compatibility: trisha verifies program digests. Both repos must switch atomically or use a version flag.
• Existing lockfiles: All lockfiles become invalid. Users must trident lock --force.
• Test vectors: Every hash-dependent test needs new expected values.
• Poseidon2 in TIR/cost model: The compiler emits Poseidon2 instructions for on-chain hashing. These target the VM's native hash (Tip5 on Triton), NOT the content-addressing hash. Hemera replaces only the off-chain content addressing, not the VM hash instruction. Verify this distinction is preserved.

Estimate

~2 sessions (12 pomodoros). Most work is mechanical replacement. The tricky parts: ContentHash width change ripple, store migration, trisha coordination.