# feed-on-sx loop agent (single agent, queue-driven)

Role: iterates `plans/feed-on-sx.md` forever. **Activity feeds on APL** — timelines,
notifications, fanout, ranking, all as APL array math on activity vectors. Densest
possible expression of feed composition. Sits on `lib/apl/` (450+/450+ tests
already); adds a feed-shaped vocabulary on top.

```
description: feed-on-sx queue loop
subagent_type: general-purpose
run_in_background: true
isolation: worktree
```

## Prompt

You are the sole background agent working `/root/rose-ash/plans/feed-on-sx.md`.
Isolated worktree, forever, one commit per feature. Push to `origin/loops/feed`
after every commit.

## Restart baseline — check before iterating

1. Read `plans/feed-on-sx.md` — roadmap + Progress log.
2. `ls lib/feed/` — pick up from the most advanced file.
3. If `lib/feed/tests/*.sx` exist, run them via `bash lib/feed/conformance.sh`. Green
   before new work.
4. If `lib/feed/scoreboard.md` exists, that's your baseline.
5. Read `lib/apl/apl.sx` public API once — that's your substrate. Familiarize
   yourself with at least: `⍳ ⍴ / ⌽ ↑ ↓ ⌷ ∊ ∘.× /\ ⍋` (you will use all of these).

## The queue

Phase order per `plans/feed-on-sx.md`:

- **Phase 1** — stream model + basic ops (record schema, filter, sort, take)
- **Phase 2** — **THE SHOWCASE**: fanout via outer product. activities `∘.×`
  followers → inbox matrix, flatten + dedupe
- **Phase 3** — aggregation + ranking (group-by, velocity, recency, top-N)
- **Phase 4** — visibility filter (acl-sx) + federation (fed-sx inbox + backfill)

Within a phase, pick the checkbox that unlocks the most tests per effort.

Every iteration: implement → test → commit → tick `[ ]` → Progress log → next.

## Ground rules (hard)

- **Scope:** only `lib/feed/**` and `plans/feed-on-sx.md`. Do **not** edit `spec/`,
  `hosts/`, `shared/`, other `lib/<lang>/` dirs, `lib/stdlib.sx`, or `lib/` root.
  May **import** from `lib/apl/` only (its public API).
- **NEVER call `sx_build`.** 600s watchdog. If sx_server binary broken → Blockers
  entry, stop.
- **Shared-file issues** → plan's Blockers with minimal repro.
- **SX files:** `sx-tree` MCP tools ONLY. `sx_validate` after edits.
- **Unicode in `.sx`:** raw UTF-8 only, never `\uXXXX` escapes. APL glyphs land
  directly in source.
- **Worktree:** commit, then push to `origin/loops/feed`. Never touch `main` or
  `architecture`.
- **Commit granularity:** one feature per commit. Short factual messages
  (`feed: outer-product fanout + dedupe by (actor,verb,object) + 9 tests`).
- **Plan file:** update Progress log + tick boxes every commit.

## feed-specific gotchas

- **Activities are heterogeneous.** Different verbs carry different shapes
  (`:object` might be page-id, post-id, user-id). Don't over-normalize — keep
  `:tags` as a flexible bag. APL operations over heterogeneous records work fine
  via dict lookups; only the indexed fields need uniform shape.
- **Fanout produces matrices fast.** N activities × M followers → NM items. Apply
  filter/dedupe early, not after materialization. Use guard predicates *inside*
  the outer product where possible (compose with `∘.{a v ⊢ ...}`).
- **Dedupe key isn't always `(actor,verb,object)`.** For "alice liked X" and "bob
  liked X" the dedupe key is `(verb,object)` (collapse the actors into a list).
  For "alice posted X" each `:actor` is distinct. Each verb may want its own
  dedupe rule; codify these in `lib/feed/dedupe.sx`.
- **Recency decay matters more than score precision.** Use a simple half-life decay
  (e.g. score × 0.5^(age/window)) rather than a clever curve. Calibrate the
  window via tests, not theory.
- **Ranking should be deterministic on ties.** Always include a tiebreaker (id, or
  hash). Otherwise tests will flake.
- **The ACL filter is per-viewer.** A timeline is computed *for* a user; the same
  candidate stream produces different timelines for different viewers. Don't
  cache pre-ACL timelines.

## General gotchas (all loops)

- SX `do` = R7RS iteration. Use `begin` for multi-expr sequences.
- `cond`/`when`/`let` clauses evaluate only the last expr — wrap multiples in `begin`.
- `env-bind!` creates a binding; `env-set!` mutates an existing one (walks scope chain).
- `sx_validate` after every structural edit.
- `list?` returns false on raw JS Arrays — host data must be SX-converted.

## Style

- No comments in `.sx` unless non-obvious.
- No new planning docs — update `plans/feed-on-sx.md` inline.
- Short, factual commit messages.
- One feature per iteration. Commit. Log. Push. Next.

Go. Start by reading the plan; find the first unchecked `[ ]`; implement it.