Review follow-ups on the demand fetch for reads below the horizon:

- A read is refused as below the horizon, and demand-fetched, only when its check-in lies outside the held set K; an unheld payload above C, such as one outside the store cone's paths, keeps its own error and is not fetched. - Annotate no longer refuses without a peer: on a content-horizon store it reports the lines it cannot attribute past C at the horizon, marked BelowHorizon, as a structural store does. AnnotateContext fetches each version as the walk reaches it, so nothing the walk does not read is fetched, up to 200 payloads; past that it returns the partial result. - diffWholeCheckin reports a failed structure classification, and the read paths take the caller's context through to the fetch. - Tests: misclassification above C, annotate over-fetch, the partial result over the limit, and a structural peer withholding the payload. check-in: 52f026832e user: [email protected] tags: feat/demand-fetch-reads, main, trunk

ReadFileContext, ReadFileAtContext, AnnotateContext and DiffContext take RequiredContentOpts and, when a read needs content a horizon store does not hold, fetch exactly the artifacts it names from the peer and read again (draft-fossil-horizon-00 4.4): the payload, and on a structural store first the check-in's manifest, baseline and nodes. The store cone and its horizon do not move; fetched artifacts are held content.

Reads now refuse with content.MissingBelowHorizon, which matches ErrBelowHorizon and names the horizon. Annotate gathers every missing version along its walk into one round and Diff both sides; a read over one round's gimme budget is refused naming DeepenHorizon.

Closes #489 leaf check-in: 8821596379 user: [email protected] tags: feat/demand-fetch-reads, main, trunk

libfossil is a pure-Go implementation of the Fossil SCM, reading and writing the same .fossil SQLite repository format as upstream Fossil.

This is the first public release of code that previously lived in a private repository. The module path is github.com/danmestas/libfossil and the binary is named libfossil to avoid $PATH collisions with upstream fossil.

Included: - Repo lifecycle (create, clone), checkout/checkin, timeline, merge, diff, annotate, shun, tag, branch, bisect, stash, undo/redo - Sync-over-HTTP protocol (client and handler) - Two SQLite drivers: modernc (pure Go, default) and ncruces (wasm-capable) - Observer interfaces (SyncObserver, CheckoutObserver) with an optional OpenTelemetry implementation in observer/otel (separate submodule) - Deterministic simulation testing harness with BUGGIFY fault injection - Kong-based embeddable CLI under cli/ and a standalone binary under cmd/libfossil/ check-in: f5744359d3 user: [email protected] tags: trunk