Proxy time adapter - #904
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A proxy backend names `type Time: Timestamp + Lattice + From<T>`, the time in which the tactic reasons and in which bridges, seeds, matches and emitted records are presented. The tactics convert only frontiers: the join's meet, and the reduce's `upper`, held capabilities, and carried times (back through `T: From<Time>`). `std`'s reflexive `From` makes `Time = T` the unchanged default, which the reference `VecReduceBackend` uses. This separates the timestamp a dataflow advertises from the representation its operators compute with: a backend whose times are dynamically sized can present them to the tactic as a fixed-width, `Copy` value. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MYmDrD6KjihNREYsBvmTpP
A DDIR time is `Product<u64, PointStamp<u64>>`. Its dynamically sized `PointStamp` is what the scope structure needs, but it spills to the heap two scopes deep, and every clone, join and comparison in the proxy tactics walks a vector. An operator knows its scope depth when rendered, and every time it sees has at most that many scope coordinates. `corgi::flat::Flat<K>` holds the epoch and scope coordinates in a `[u64; K]`, padding with zeros where `PointStamp` strips them, so both forms are canonical and their orders agree. It is `Copy`, never allocates, and converts to and from `Time` with `From`, which the proxy tactics use for frontiers. It is never a dataflow's timestamp, so its only path summary is the identity, `()`. `RowTime` reads and writes it directly against a `ColTimes` lane column. The Corgi join and reduce backends take the tactic's time as a parameter, and `Backend::join` and `Backend::reduce` now receive the scope depth, from which Corgi picks `Flat<depth + 1>` up to depth 3, and `Time` itself beyond. Tests check the conversions round-trip and preserve order, join and meet, and that reduce presentation agrees in both representations. Corgi, 1 worker, 5 interleaved runs, medians (master-next -> this): scc 200k edges, 200 x 50 load 713 -> 630 ms churn 4.08 -> 3.47 s count 1M rows, 200 x 500 load 101 -> 95 ms churn 2.28 -> 1.79 s reach 2M edges, 100 x 100 load 805 -> 733 ms churn 484 -> 437 ms kcore 200k edges, 200 x 50 within noise Outputs match; interactive tests pass; AoC 2023 corgi 33/33. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MYmDrD6KjihNREYsBvmTpP
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Support to allow a proxy backend to use a different time type than advertised by the tactic. This is primarily to advertise a dynamic timestamp like
Pointstamp<T>but specialize it to[T; K]behind the scenes.