Timeline

feat(horizon): targeted demand fetch for reads below the horizon check-in: c63cab2f36 user: [email protected] tags: main, trunk

- manifest.Placement computes the horizon's held set at most once per operation, so an annotate walk or a whole-check-in diff no longer rebuilds the check-in graph on every failed read. - AnnotateContext whose peer cannot supply a version returns the partial result, the lines past C marked BelowHorizon, as Annotate does without a peer; only a cancelled context fails it. - AnnotatedLine documents that BelowHorizon lines carry C's identity and that a partial annotate is signalled only by those marks. check-in: 02a2ea3214 user: [email protected] tags: feat/demand-fetch-reads, main, trunk

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

conformance: HZ-4.1-1 scoped to zit and go-libfossil origins check-in: 1455a3803e user: [email protected] tags: main, trunk

perf: carry a cone clone's forwarded delta chains across rounds check-in: b85673a6cb user: [email protected] tags: main, trunk