# artdag-on-sx: Content-addressed dataflow DAG engine

art-dag is rose-ash's media-processing engine: a content-addressed DAG of effects,
executed in three phases — **Analyze → Plan → Execute**. Today it's a separate
Python stack (FastAPI + Celery + JAX + IPFS). Its *engine logic* — dependency
analysis, scheduling, content-addressed memoization, incremental recompute,
composable s-expression effects — is exactly the kind of declarative, substrate-shaped
work SX excels at, and art-dag already speaks s-expressions (its `sexp_effects`).

This subsystem rebuilds the **engine** on SX (not the pixel-pushing): the DAG model,
the three-phase pipeline, and the incremental/memoized executor. Media ops
themselves (JAX kernels, IPFS pins) stay opaque — modelled as abstract node
functions in tests, delegated to injected adapters in production. The win is that
the same SX substrates already serve the phases:

- **Analyze** (deps, reachability, dirtiness) → **Datalog** (recursive reachability —
  the acl/relations shape).
- **Plan** (schedule under constraints) → topological batching now; **miniKanren**
  for constraint-based scheduling later (optional).
- **Execute** (composable effects + content-addressed memo) → SX's own
  `perform`/`cek-resume` + a **persist**-backed content-addressed result cache;
  incremental recompute drops the cost of re-rendering to the dirty subgraph.
- **Optimize** (fuse/dedup effect pipelines) → term rewriting (a later, optional
  consumer of `maude-on-sx`'s engine — see `plans/maude-on-sx.md`).

End-state: a content-addressed dataflow engine in `lib/artdag/` with analyze, plan,
incremental execute, effect-pipeline optimization, and a shared-cache federation
extension — the SX heart of art-dag, with media kernels and storage injected at the
edges.

## Status (rolling)

`bash lib/artdag/conformance.sh` → **158/158** (10 suites: dag, analyze, plan, execute, optimize, fed, cost, serialize, stats, fault)

Base roadmap (Phases 1–6) COMPLETE. Now extending.

## Ground rules

- **Scope:** only `lib/artdag/**` and `plans/artdag-on-sx.md`. Do **not** edit
  `spec/`, `hosts/`, `shared/`, `lib/datalog/**`, `lib/persist/**`, or other
  `lib/<lang>/`. You may **import** the public APIs of `lib/datalog/` (analyze) and
  `lib/persist/` (memo cache / result store).
- **Design lineage, not code reuse.** The existing Python engine lives in the
  repo's top-level `artdag/` (core/ engine, `sexp_effects/`, l1/ tasks). **Read it
  for design lineage** (the 3-phase model, the effect language, content addressing)
  — do **not** import or port its code; this is a fresh SX implementation.
- **Media ops are opaque.** A node's op is an abstract SX function over its inputs
  in tests (e.g. `(fn (a b) …)`); real JAX/IPFS kernels are injected adapters
  behind an interface. The engine is about *scheduling/memo/incremental*, never
  pixels. Determinism: content ids and tests use only the node spec, never a clock.
- **Content addressing is structural.** A node's id is a deterministic digest of
  `(op, sorted input-ids, params)` so identical subgraphs share an id and a cache
  slot — the core property. Use a structural digest helper; if a real SHA-256/CID
  is needed it's an injected host primitive (Blockers if absent), not hand-rolled.
- **Shared-file issues** → "Blockers" with a minimal repro; do not fix here.
- **SX files:** `sx-tree` MCP tools only; `sx_validate` after every edit.
- **Commits:** one feature per commit. Keep Progress log updated and tick boxes.

## Architecture sketch

```
DAG spec (nodes + edges)                 rendered results
        │                                       ▲
        ▼                                       │
lib/artdag/dag.sx                       lib/artdag/execute.sx
  — node = {op, inputs, params}           — effect interp (perform per node)
  — content-id = digest(spec)             — content-addressed memo (persist)
  — topo order, validate                  — incremental: only dirty nodes
        │                                       ▲
        ▼                                       │
lib/artdag/analyze.sx                   lib/artdag/plan.sx
  — Datalog: deps/dependents/reach        — schedule: topo batches, parallelism
  — dirty propagation (dirty closure)     — (miniKanren constraints, later/opt)
        │                                       ▲
        ▼                                       │
lib/artdag/optimize.sx                  lib/artdag/federation.sx
  — fuse adjacent ops, dead-node elim,     — shared cache by content-id (L2-style)
    CSE (free from content-addressing)       result import/export + provenance/trust
```

## Phase 1 — DAG model + content addressing

- [x] `lib/artdag/dag.sx` — node `{:op :inputs :params}`; structural content-id =
  digest of `(op, sorted input-ids, params)`; build/validate a DAG (no dangling
  inputs, no accidental cycles); topological order
- [x] identical-subgraph sharing: two structurally-equal nodes get the same id
- [x] `lib/artdag/tests/dag.sx` — id determinism, subgraph sharing, cycle/dangling
  rejection, topo order
- [x] `lib/artdag/conformance.sh` + scoreboard

## Phase 2 — Analyze (Datalog)

- [x] `lib/artdag/analyze.sx` — project edges to Datalog; `deps-of`, `dependents-of`,
  transitive `reachable` (the recursive-reachability shape)
- [x] **dirty propagation:** given a set of changed nodes, compute the transitive
  set of dependents that must recompute (`dirty-closure`)
- [x] `lib/artdag/tests/analyze.sx` — deep chains, diamonds, dirty closure
  correctness, unaffected nodes stay clean

## Phase 3 — Plan

- [x] `lib/artdag/plan.sx` — schedule into topological **batches** (each batch's
  nodes have all deps satisfied → run in parallel); respect a max-parallelism limit
- [x] plan over the *dirty* subset only (incremental plan)
- [x] `lib/artdag/tests/plan.sx` — batch correctness, parallelism cap, dirty-only plan
- [ ] (optional/later) miniKanren constraint scheduling — flag, don't block on it

## Phase 4 — Execute (incremental + memoized)

- [x] `lib/artdag/execute.sx` — interpret a plan: each node op runs via `perform`
  (mocked op in tests); results keyed by content-id
- [x] **content-addressed memo cache** backed by `lib/persist/`: a node whose
  content-id already has a stored result is skipped (cache hit)
- [x] **incremental execute:** re-running after a leaf change recomputes only the
  dirty closure; everything else is a cache hit
- [x] `lib/artdag/tests/execute.sx` — full run, cache-hit on re-run, incremental
  recompute touches only dirty nodes (assert recompute count)

## Phase 5 — Effect-pipeline optimization

- [x] `lib/artdag/optimize.sx` — rewrite the DAG before execution: dead-node
  elimination (unreachable from outputs), common-subexpression sharing (free from
  content ids), adjacent-op fusion
- [x] optimizations are content-id-preserving where semantically identical; assert
  the optimized DAG produces identical results
- [x] `lib/artdag/tests/optimize.sx` — DCE, CSE dedup, fusion equivalence
- [ ] (optional/later) rule-based optimization via `maude-on-sx`'s rewriting engine —
  flag the integration point, don't block on it

## Phase 6 — Federation (shared content-addressed cache)

- [x] a result computed on one instance is reusable on another by content-id (the
  L2-registry analog): export/import `{content-id → result}` with provenance
- [x] trust gating — accept a remote result only from a trusted peer (mirror the
  fed trust shape; mock the transport in tests)
- [x] revocation/invalidation — drop a remote result if its provenance is withdrawn
- [x] `lib/artdag/tests/fed.sx` — remote cache hit, trust gating, invalidation

## Progress log

- **Ext: public API facade** (`lib/artdag/api.sx`, total 158/158 unchanged).
  Reference index matching the datalog/persist convention: canonical load order +
  the full public surface across all 10 modules + `artdag/version`.

- **Ext: fault-tolerant execution** (fault suite 14/14, total 158/158).
  `lib/artdag/fault.sx`: a node op may fail via `(artdag/fail reason)`; `run-safe`
  confines the failure to that node + its transitive dependents (independent branches
  still compute) and NEVER caches a failed result, so a later run with the fault fixed
  recomputes only the failed closure and cache-hits the good nodes. `failed?`/`fail`
  markers, `failed-nodes`/`failure-count`/`all-ok?`.

- **Ext: execution stats / cache analytics** (stats suite 12/12, total 144/144).
  `lib/artdag/stats.sx` over an exec record: `hit-ratio`, `work-recomputed`/`work-saved`
  (cost-weighted via the cost model), `savings-ratio`, and `exec-summary`. Cold run =
  0 hit ratio / all work ran; warm rerun = ratio 1 / all work saved; incremental = saved
  work counts unchanged nodes, ran work counts the dirty closure.

- **Ext: optimize composition pass** (optimize suite 22/22, total 132/132).
  `artdag/optimize entries outputs fusible?` fuses the entry list then DCEs against
  the output names (sinks survive fusion since they're never absorbed) — fewer nodes,
  identical results. Verified: dead branch dropped + chain fused (4→2), an output that
  is itself "dead" is retained, no-fusible-set still DCEs.

- **Ext: DAG wire serialization** (serialize suite 13/13, total 128/128).
  `lib/artdag/serialize.sx`: `dag->wire` emits a topo-ordered list of
  `(id op inputs params commutative)` records — plain lists with keyword-keyed param
  dicts, which survive `write-to-string`/`read` (string-keyed node dicts do NOT; and
  `()` reads back as nil, so `wire->dag` normalizes empty inputs). `wire->dag`
  reconstructs a runnable dag by content-id (author names dropped); executes
  identically to the original. `wire-verify` recomputes each record's content-id and
  rejects tampered ids or mutated params under a stale id (self-verifying transport).
  `dag->string`/`string->dag` for text transport. Gotcha logged: `sx-parse` primitive
  is unbound in the server env — use `(read (open-input-string s))`.

- **Ext: cost-based scheduling** (cost suite 13/13, total 115/115).
  `lib/artdag/cost.sx`: an injected `cost-fn (op params)` keeps media-op costs opaque
  (`const-cost`, `op-cost table`). `critical-path` = longest weighted path (finish-time
  fold over topo order) = min makespan with unlimited workers. `makespan dag plan
  cost-fn` sums each batch's slowest node — full plan (cap 0) makespan == critical
  path, serial (cap 1) == `total-work`. `speedup` = total-work / makespan. Verified
  weighted paths follow heavy ops and capped makespan never dips below the critical
  path.

- **Phase 6 — Federation (shared content-addressed cache)** (fed suite 15/15, total
  102/102). `lib/artdag/federation.sx`: an instance = `{:cache <persist kv> :prov
  {cid->origin-peer}}`. `fed-export` dumps the whole cache as `{:cid :result :peer}`
  records tagged with the exporter's id; `fed-import` accepts only records from
  trusted peers (trust gating) and records provenance; `fed-pull` imports via an
  injected `fetch-fn(peer-id)` transport (mocked in tests). Because content-ids are
  global, a trusted import makes the importer's run a pure cache hit (recompute 0) —
  the L2-registry analog. `fed-invalidate peer` drops every result provenanced to a
  peer from cache + prov (trust withdrawn → recompute), peer-scoped (other peers'
  results survive) and leaving locally-computed (un-provenanced) results untouched.
  ALL 6 PHASES COMPLETE.

- **Phase 5 — Effect-pipeline optimization** (optimize suite 18/18, total 87/87).
  `lib/artdag/optimize.sx`: `artdag/dce dag outputs` keeps only the outputs plus
  their transitive ancestors (via analyze), preserving surviving content-ids.
  `artdag/cse` == build — structural sharing is inherent to content addressing, so
  identical subexpressions collapse to one node/id and execute once (verified).
  `artdag/fuse entries fusible?` rewrites entries: a maximal 1-to-1 chain of fusible
  unary ops (predecessor used only by its single consumer, both fusible) collapses
  into one `artdag/pipeline` node carrying ordered `{:op :params}` stages, fed by the
  chain head's external input; leaves, fan-out nodes, and non-fusible ops never fuse.
  `artdag/fusing-runner` wraps a base runner to replay pipeline stages — output
  equivalent to the unfused DAG (asserted). Note: CSE auto-dedup means test fixtures
  intended as distinct nodes must use distinct op/params.

- **Phase 4 — Execute (incremental + memoized)** (execute suite 15/15, total 69/69).
  `lib/artdag/execute.sx`: `artdag/execute` folds a plan, computing each node via an
  injected `runner (op params input-results)` (production = `perform` to JAX/IPFS
  adapter; tests = a pure op-table) and memoizing the result in a `lib/persist/` kv
  backend keyed by **content-id**. A node whose content-id is already cached is a hit
  (skipped). The keystone falls out of content addressing: changing a leaf changes the
  ids of its whole dirty closure, so re-running the full plan against a warm cache
  recomputes exactly those nodes and hits the rest — verified by recompute/hit counts
  (5 cold → 0 on rerun → 3 after one leaf change, sibling reused). Cross-DAG sharing
  verified: a different DAG containing a shared subgraph cache-hits it. `run`/`run-dirty`
  helpers; `result-of`/`recompute-count`/`hit-count`/`recomputed` inspection.

- **Phase 3 — Plan** (plan suite 18/18, total 54/54). `lib/artdag/plan.sx`:
  `artdag/plan` schedules a dag into Kahn-wave topological batches — each batch's
  nodes have all in-scope deps satisfied by earlier batches, so they run in parallel.
  A `cap` (>0) splits any wave wider than the cap into consecutive sub-batches;
  `cap<=0` is unlimited. `artdag/plan-dirty` schedules only the dirty closure: deps
  outside the scheduled set (clean cache hits) count as already satisfied, so a
  mid-node change yields just `[[changed]…[downstream]]`. Inspection helpers
  `plan-batches`/`plan-width`/`plan-size`/`plan-flatten`.

- **Phase 2 — Analyze on Datalog** (analyze suite 16/16, total 36/36).
  `lib/artdag/analyze.sx`: `artdag/edge-facts` projects each `(input-id, node-id)`
  pair to an `(edge ...)` fact; `artdag/analyze` builds a `dl-program-data` db with
  recursive `reachable(X,Y) :- edge(X,Y); edge(X,Y),reachable(Y,Z)` (the acl/relations
  reachability shape). Query helpers `deps-of`/`dependents-of` (direct),
  `reachable-from` (transitive downstream), `ancestors-of` (transitive upstream), all
  returning sorted id lists. `dirty-closure` builds a db with `dirty(Y) :- edge(X,Y),
  dirty(X)` seeded by changed-node facts and returns the transitive forward closure —
  keystone test confirms changing a mid node dirties only it + downstream, leaving
  siblings/upstream clean. Content-ids work as opaque Datalog string constants.

- **Phase 1 — DAG model + content addressing** (dag suite 20/20). `lib/artdag/dag.sx`:
  node `{:op :inputs :params :commutative}`; `artdag/content-id` = `"node:"` + a
  deterministic canonical serialization of `(op, inputs, params)` with dict keys
  sorted (param order-insensitive) and commutative ops' inputs sorted (input
  order-insensitive); non-commutative inputs ordered. `artdag/build` takes named
  entries `(name op (input-names) params [commutative?])`, validates (dangling refs,
  cycles via fixpoint topo), resolves input-names→content-ids, dedups identical
  subgraphs to one node + one id (shared across DAGs), returns `{:ok :nodes :names
  :order}`. No host `sort`/`string<?` — hand-rolled `artdag/str<?` over char-codes.
  Gotcha logged: SX `equal?` is representation-sensitive (cons-built vs vector lists
  compare unequal even when identical); `=` is true structural equality — conformance
  harness compares with `=`. `lib/artdag/conformance.sh` + scoreboard.

## Blockers

(none)
