zit 0.1.0

zit is Fossil's formats and sync protocol reimplemented in Zig from four companion Internet-Drafts (frozen in docs/rfcs/). It is a library first — the delta codec, the artifact formats, the derived repository state, and the HTTP sync protocol as an embeddable API — with a thin CLI over the top. This first tagged release is a working version-control substrate. It is honest about what it does not yet do; the limitations below are deliberate, not bugs.

What's implemented

• Delta codec — the byte-level delta encode/decode of draft-fossil-delta-format-00.
• Artifact formats — the manifest / control-artifact card grammar of draft-fossil-artifact-format-00: every card letter parsed, the §4.4/§4.5 ordering and occurrence rules enforced, and the Z and R checksums modelled. The check-in (manifest), cluster, and tag/control types are interpreted; the collaboration types (wiki, ticket, forum, attachment, technote) are carried opaquely — stored and transported by hash, not read.
• Derived repository state — branch, tag, leaf, and current-trunk views of draft-fossil-repo-state-00, with tag propagation along the check-in DAG.
• HTTP sync — clone, pull, push, and bidirectional sync of draft-fossil-sync-protocol-00, driven by a pure client state machine (bytes in, bytes out) with transport supplied by the caller; plus a serve side that answers the framed protocol.
• CLI — the working-copy and history verbs (init, add, rm, mv, status, stat, diff, extras, clean, addremove, commit, log, open, update, merge, revert, undo, redo, leaves, timeline, branch, tag, amend, info, ls, cat, artifact, annotate, bisect), the sync verbs (serve, clone, pull, push, sync, remote), and store maintenance (pack). open honours --manifest[=r,u,t]; -R reads a repository with no working tree, and -n limits timeline/log to the most recent N as well as previewing the destructive verbs.

No module touches ambient time, randomness, filesystem, or network directly; effects arrive through injected interfaces, so the whole stack replays exactly under seeded deterministic simulation.

What the conformance claim rests on

The drafts are the authority, not Fossil's source: test expectations come from the spec text and its worked examples, and every normative clause a module implements gets a test citing its section. That keeps the claim honest against the spec — but a spec can be misread, so one step checks against the reference implementation.

That step is zig build smoke. It drives the real fossil binary and is the only step that proves conformance against Fossil itself rather than against our own reading of the RFCs. A disagreement there means either zit misread the spec or the spec is wrong — the spec gets an erratum, never the code a workaround.

The exact fossil that smoke passed against matters, so name it:

fossil 2.28 [52445a27f1] (2026-03-11)

What's deliberately deferred, and where it's documented

• diff is working-tree-versus-current-check-in only, and name-status only. It emits A/M/D per path, no textual hunks, and there is no revision-to-revision diff. Documented in zit diff --help.
• The sync server code is a fixed informational placeholder (0000000000000000, sync §9.1) on both client and server. This is not a per-server identity. The per-repository project code, by contrast, is real: derived on init, persisted, emitted by serve, and adopted on clone. Documented at the server_servercode / server_projectcode definitions in src/serve.zig.
• The R and W cards are parsed but not interpreted. The R aggregate content checksum is retained and re-emitted verbatim when present, but is never generated on commit nor verified against content. The W wiki-text card belongs to wiki artifacts, a collaboration type carried opaquely. The opaque-carry boundary is documented in the README Scope section; the card grammar and per-type card masks live in src/artifact.zig.
• Verbs absent versus Fossil: no stash, grep, ui, or settings, and no revision-to-revision diff. The command set is documented in zit help.

Storage

zit pack performs an at-rest re-deltification pass — fossil-style best-of-N delta-base selection plus a monotonic-shrink guard that keeps the smaller of an existing frame and its re-encoding, so repacking a clone of fossil-quality wire deltas is a net win rather than a regression. It is at-rest only: all four RFCs stay conformant and wire interop is preserved, and every repacked frame is hash-verified against the log.

Measured whole-file, index-inclusive, in commit bab9303056:

Repository	Before pack	After pack	Versus fossil
sqlite	207.3 MB (1.40x)	174.4 MB (1.18x)	fossil 147.7 MB
fossil-scm	117.5 MB (1.63x)	108.1 MB (1.50x)	fossil 72.2 MB

Build

Requires Zig 0.16+.

zig build            # build the zit binary into zig-out/bin/
zig build test       # unit tests
zig build smoke      # interop check against a fossil binary on PATH