merge sync into foculus

status: executing. the reconciliation engine and the fork-choice that completes it become one crate.

why

sync's GSet::merge is a pure CRDT union — it keeps both members of a conflict, undefined on collision. foculus's fork-choice is the completion of that merge on conflicts. they are two halves of one reconciliation operation kept in separate repos; sync already does conflict detection (equivocation, chain.rs) while resolution lives nowhere. merging makes the merge function whole and gives one canonical Signal type instead of the drift between sync::Signal, bbg's copy, and foculus's paper spec.

decided with the user: fork-choice is a pluggable strategy, not φ*-always-on. the trusted/single-writer path must never be forced to compile the tri-kernel. and resolution supports both incremental (per-conflict-pair) and batch-at-epoch (per-domain) timing for the foreseeable future — not one or the other.

scope (confirmed: all of sync)

sync self-describes as "device data availability — erasure-coded virtual filesystem" but holds the full VEC substrate: chain (P6), GSet::merge (P1), nmt (P2), das+erasure (P3), vdf, plus vdisk/store/node device-DA and optional iroh transport. moving all of it makes foculus the full node crate = VEC substrate + fork-choice. consistent with "foculus = structural sync with its merge completed."

moves

code (sync → foculus root, keeping crate at root as sync had it, so ../ dep paths stay valid):

• Cargo.toml → foculus/Cargo.toml, rename package + bin cyber-sync → foculus
• Cargo.lock, .gitignore, src/, tests/ → foculus/
• specs/sync.md → foculus/specs/structural-sync.md (the substrate spec, complements protocol.md)
• specs/README.md → dropped (foculus/README.md already indexes specs)
• NOT target/, NOT .git

rewire dependents (crate rename in the same commit — the "eat the cost" the user chose):

• cybergraph/Cargo.toml, cybergraph/cli/Cargo.toml, cyb/core/Cargo.toml: cyber-sync {path=../sync} → foculus {path=../foculus}
• cybergraph/src/lib.rs, cybergraph/src/api.rs, cybergraph/cli/src/main.rs, cyb/core/src/cell.rs: use cyber_sync → use foculus

markdown project references → foculus (8 files, 5 repos): honeycrisp/acpu/README, cybergraph/specs/cli, bbg/specs/cli, soft3/{roadmap/component-boundaries, roadmap/stack-completeness, specs/terms, proposals/cybergraph-sync-tape-architecture}, go-cyber/docs/upgrade-plan. per-file judgment — change crate/path/project refs, not the word "sync" where it means the general concept.

order (build-verify before the irreversible step)

1. move code + rename crate
2. rewire dependents
3. cargo check foculus (no-default-features, skip iroh) then cybergraph — must pass
4. commit the move in foculus + the rewiring in cybergraph/cyb
5. markdown pass
6. only then: rm -rf ~/cyber/sync

known costs, accepted

• sync's git history does not follow into foculus (pragmatic file move, not subtree merge). recoverable from the sync repo until step 6.
• foculus stops being specs-only; it is now a code repo with specs/ alongside src/. the sibling rs/ convention (bbg, nox) is not followed — a faithful move over a restructure. aligning to rs/ later is a separate, optional cleanup.

next after merge (not this pass)

the ForkChoice trait itself — Serialize / MinHash / Focus strategies, both incremental and batch resolution timing. captured in structural-sync.md / protocol.md as the design, scaffolded when the reconciliation entry point is wired to call it.