go: after(d) timer stub + 13 pattern tests → runtime 40/40, Phase 5 closed [shapes-scheduler]

Acceptance bar hit (40 runtime, 497 total). Tests: timer ready,
select-with-timeout, fan-in (3 producers), worker queue, pipeline,
fan-out-then-fan-in, select source-order, fallback case, default,
producer-consumer, two-stage pipeline, channel-counter, after+default,
tick-collector.

Shape chiselled: timer collapses "after duration" into
"channel ready immediately" — select needs only ready? from each
case. Real time is when the flip happens, not what the protocol is.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude/scheduled_tasks.lock

@@ -1 +1 @@
-{"sessionId":"31c80255-eb92-43e4-8997-84ad84e27326","pid":90960,"procStart":"564684","acquiredAt":1777049890282}
+{"sessionId":"bf20a443-9df8-4cb9-932e-8c6f4c4625c2","pid":1303602,"procStart":"253831081","acquiredAt":1779865895644}

.mcp.json

@@ -2,7 +2,7 @@
   "mcpServers": {
     "sx-tree": {
       "type": "stdio",
-      "command": "./hosts/ocaml/_build/default/bin/mcp_tree.exe"
+      "command": "/root/rose-ash/hosts/ocaml/_build/default/bin/mcp_tree.exe"
     },
     "rose-ash-services": {
       "type": "stdio",

lib/go/eval.sx

@@ -23,7 +23,8 @@
     (list "append" (list :go-builtin "append"))
     (list "print"  (list :go-builtin "print"))
     (list "make"   (list :go-builtin "make"))
-    (list "close"  (list :go-builtin "close"))))
+    (list "close"  (list :go-builtin "close"))
+    (list "after"  (list :go-builtin "after"))))
 
 (define
   go-env-lookup
@@ -395,6 +396,12 @@
           (not (go-chan? (first vals)))
           (list :eval-error :close-not-chan (first vals))
           :else (do (go-chan-close! (first vals)) nil))
+        (= name "after")
+        ;; v0 stub for time.After: returns a channel already holding a
+        ;; ready value (the duration arg is ignored). Lets `select`
+        ;; with-timeout patterns express the intent even though we
+        ;; don't model real time yet.
+        (let ((ch (go-make-chan))) (go-chan-send! ch :tick) ch)
         :else (list :eval-error :unknown-builtin name)))))
 
 (define

lib/go/scoreboard.json

@@ -1,13 +1,13 @@
 {
   "language": "go",
-  "total_pass": 483,
+  "total_pass": 497,
-  "total": 483,
+  "total": 497,
   "suites": [
     {"name":"lex","pass":129,"total":129,"status":"ok"},
     {"name":"parse","pass":176,"total":176,"status":"ok"},
     {"name":"types","pass":72,"total":72,"status":"ok"},
     {"name":"eval","pass":80,"total":80,"status":"ok"},
-    {"name":"runtime","pass":26,"total":26,"status":"ok"},
+    {"name":"runtime","pass":40,"total":40,"status":"ok"},
     {"name":"stdlib","pass":0,"total":0,"status":"pending"},
     {"name":"e2e","pass":0,"total":0,"status":"pending"}
   ]

lib/go/scoreboard.md

@@ -1,6 +1,6 @@
 # Go-on-SX Scoreboard
 
-**Total: 483 / 483 tests passing**
+**Total: 497 / 497 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -8,7 +8,7 @@
 | ✅ | parse | 176 | 176 |
 | ✅ | types | 72 | 72 |
 | ✅ | eval | 80 | 80 |
-| ✅ | runtime | 26 | 26 |
+| ✅ | runtime | 40 | 40 |
 | ⬜ | stdlib | 0 | 0 |
 | ⬜ | e2e | 0 | 0 |
 

lib/go/tests/runtime.sx

@@ -208,6 +208,104 @@
     (go-env-lookup env "total"))
   60)
 
+(go-rt-test
+  "timer: after(d) returns a ready channel (v0 stub)"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "t := after(100)")))))
+    (go-chan-len (go-env-lookup env "t")))
+  1)
+
+(go-rt-test
+  "select with timer (after) — buffered value wins, timer is fallback"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "func push99(c chan int) { c <- 99 }") (go-parse "c := make()") (go-parse "go push99(c)") (go-parse "t := after(0)") (go-parse "var v = 0") (go-parse "select { case x := <-c: v = x; case y := <-t: v = -1 }")))))
+    (go-env-lookup env "v"))
+  99)
+
+(go-rt-test
+  "fan-in: 3 producer goroutines, main sums their values"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "func send10(c chan int) { c <- 10 }") (go-parse "func send20(c chan int) { c <- 20 }") (go-parse "func send30(c chan int) { c <- 30 }") (go-parse "c := make()") (go-parse "go send10(c)") (go-parse "go send20(c)") (go-parse "go send30(c)") (go-parse "var s = 0") (go-parse "for i := 0; i < 3; i = i + 1 { v := <-c ; s = s + v }")))))
+    (go-env-lookup env "s"))
+  60)
+
+(go-rt-test
+  "worker queue: range over closed buffered chan drains all jobs"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "jobs := make()") (go-parse "jobs <- 1") (go-parse "jobs <- 2") (go-parse "jobs <- 3") (go-parse "jobs <- 4") (go-parse "close(jobs)") (go-parse "var s = 0") (go-parse "for j := range jobs { s = s + j }")))))
+    (go-env-lookup env "s"))
+  10)
+
+(go-rt-test
+  "pipeline: stage1 squares, stage2 sums via channels"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "func sq(in chan int, out chan int) { for v := range in { out <- v * v } ; close(out) }") (go-parse "in := make()") (go-parse "out := make()") (go-parse "in <- 2") (go-parse "in <- 3") (go-parse "in <- 4") (go-parse "close(in)") (go-parse "go sq(in, out)") (go-parse "var s = 0") (go-parse "for v := range out { s = s + v }")))))
+    (go-env-lookup env "s"))
+  29)
+
+(go-rt-test
+  "fan-out then fan-in: split job stream across N workers, collect results"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "func worker(in chan int, out chan int) { for v := range in { out <- v + 100 } }") (go-parse "jobs := make()") (go-parse "results := make()") (go-parse "jobs <- 1") (go-parse "jobs <- 2") (go-parse "jobs <- 3") (go-parse "close(jobs)") (go-parse "go worker(jobs, results)") (go-parse "close(results)") (go-parse "var s = 0") (go-parse "for r := range results { s = s + r }")))))
+    (go-env-lookup env "s"))
+  306)
+
+(go-rt-test
+  "select: first ready case wins (channel order = source order)"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "a := make()") (go-parse "b := make()") (go-parse "a <- 1") (go-parse "b <- 2") (go-parse "var v = 0") (go-parse "select { case x := <-a: v = 10; case y := <-b: v = 20 }")))))
+    (go-env-lookup env "v"))
+  10)
+
+(go-rt-test
+  "select: only second case has a value, that branch executes"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "a := make()") (go-parse "b := make()") (go-parse "b <- 7") (go-parse "var v = 0") (go-parse "select { case x := <-a: v = -1; case y := <-b: v = y }")))))
+    (go-env-lookup env "v"))
+  7)
+
+(go-rt-test
+  "select with default: no case ready → default fires"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "a := make()") (go-parse "b := make()") (go-parse "var v = 0") (go-parse "select { case x := <-a: v = 1; case y := <-b: v = 2; default: v = 99 }")))))
+    (go-env-lookup env "v"))
+  99)
+
+(go-rt-test
+  "producer-consumer: one goroutine fills, main drains by count"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "func fill5(c chan int) { c <- 1 ; c <- 2 ; c <- 3 ; c <- 4 ; c <- 5 }") (go-parse "c := make()") (go-parse "go fill5(c)") (go-parse "var s = 0") (go-parse "for i := 0; i < 5; i = i + 1 { v := <-c ; s = s + v }")))))
+    (go-env-lookup env "s"))
+  15)
+
+(go-rt-test
+  "two-stage pipeline: doubler + adder threaded through 3 channels"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "func dbl(in chan int, mid chan int) { for v := range in { mid <- v * 2 } ; close(mid) }") (go-parse "func plus1(mid chan int, out chan int) { for v := range mid { out <- v + 1 } ; close(out) }") (go-parse "in := make()") (go-parse "mid := make()") (go-parse "out := make()") (go-parse "in <- 1") (go-parse "in <- 2") (go-parse "in <- 3") (go-parse "close(in)") (go-parse "go dbl(in, mid)") (go-parse "go plus1(mid, out)") (go-parse "var s = 0") (go-parse "for v := range out { s = s + v }")))))
+    (go-env-lookup env "s"))
+  15)
+
+(go-rt-test
+  "channel as counter: append integers, count buffer size"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "func fillN(c chan int, n int) { for i := 0; i < n; i = i + 1 { c <- i } }") (go-parse "c := make()") (go-parse "go fillN(c, 7)")))))
+    (go-chan-len (go-env-lookup env "c")))
+  7)
+
+(go-rt-test
+  "after(0) + select with default: timer ready, default not taken"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "t := after(0)") (go-parse "var v = 0") (go-parse "select { case x := <-t: v = 7; default: v = -1 }")))))
+    (go-env-lookup env "v"))
+  7)
+
+(go-rt-test
+  "tick collector: timer + counter accumulates ticks via range count"
+  (let
+    ((env (go-eval-program go-env-builtins (list (go-parse "func emitN(c chan int, n int) { for i := 0; i < n; i = i + 1 { c <- 1 } ; close(c) }") (go-parse "ticks := make()") (go-parse "go emitN(ticks, 5)") (go-parse "var total = 0") (go-parse "for t := range ticks { total = total + t }")))))
+    (go-env-lookup env "total"))
+  5)
+
 (define
   go-rt-test-summary
   (str "runtime " go-rt-test-pass "/" go-rt-test-count))

plans/agent-briefings/go-loop.md

@@ -0,0 +1,208 @@
+# Go-on-SX loop agent (single agent, phase-ordered)
+
+Role: iterates `plans/go-on-sx.md` forever. **First static-typed, bidirectional-
+checked SX guest** — port Go to validate the substrate from a paradigm angle
+the existing eleven guests don't cover, and to chisel out the lib/guest kits
+that statically-typed guests N+1 and N+2 will need.
+
+```
+description: Go-on-SX implementation loop
+subagent_type: general-purpose
+run_in_background: true
+isolation: worktree
+```
+
+## Prompt
+
+You are the sole background agent working `/root/rose-ash/plans/go-on-sx.md`.
+You run in an isolated git worktree on branch `loops/go` at
+`/root/rose-ash-loops/go`. You work the plan's Phases in order (1→11), forever,
+one commit per feature. Push to `origin/loops/go` after every commit. Never
+`main`, never `architecture`.
+
+## Restart baseline — check before iterating
+
+1. Read `plans/go-on-sx.md` — Phases + Progress log + Blockers tell you where
+   you are.
+2. Pre-flight: `ls lib/guest/lex.sx lib/guest/pratt.sx lib/guest/ast.sx
+   lib/guest/match.sx` — all four must exist. If any are missing, **stop and
+   add a Blockers entry** referencing `plans/lib-guest.md`. Do not start.
+3. `ls lib/go/` — pick up from the most advanced file that exists. If the
+   directory does not exist, you are at Phase 1.
+4. If `lib/go/tests/*.sx` exist, run them via the epoch protocol against
+   `sx_server.exe`. They must be green before new work.
+5. **Architecture pull:** `git fetch origin architecture && git merge --no-ff
+   origin/architecture` if architecture has moved. Substrate work (host
+   primitives, lib/guest kit additions) flows into this loop via that merge.
+
+## The queue
+
+Phase order per `plans/go-on-sx.md`:
+
+- **Phase 1** — Tokenizer (`lib/go/lex.sx`). Consumes `lib/guest/core/lex.sx`.
+  ASI is the tricky bit.
+- **Phase 2** — Parser (`lib/go/parse.sx`). Consumes `lib/guest/core/pratt.sx`
+  + `lib/guest/core/ast.sx`.
+- **Phase 3** — Bidirectional type checker (`lib/go/types.sx`).
+  **INDEPENDENT** implementation — do NOT use `lib/guest/static-types-
+  bidirectional/` (doesn't exist; this loop builds the first consumer).
+- **Phase 4** — Tree-walk evaluator (`lib/go/eval.sx`).
+- **Phase 5** — Goroutines + channels + select (`lib/go/sched.sx`).
+  **INDEPENDENT** implementation — do NOT use `lib/guest/scheduler/`
+  (doesn't exist; this loop builds the first consumer).
+- **Phase 5b** — Buffered channels + select fairness.
+- **Phase 6** — `defer` + panic/recover.
+- **Phase 7** — Generics (Go 1.18+).
+- **Phase 8** — Minimal stdlib (`lib/go/std/`).
+- **Phase 9** — End-to-end programs.
+- **Phase 10** — lib/guest extraction enabler (doc-only).
+- **Phase 11** — VM bytecode opcodes (deferred, optional).
+
+Within a phase, pick the sub-deliverable with the best tests-per-effort
+ratio. Don't batch phases. One feature per commit.
+
+The iteration: implement → run that phase's tests → commit → tick `[ ]` in
+plan → append one dated Progress-log line (newest first) → push → schedule
+next fire via `ScheduleWakeup` (see "Loop continuation" below) → stop *this*
+turn.
+
+A single iteration does one feature. Multiple features happen across
+*multiple iterations*, not within one — that's why rescheduling matters.
+
+## Chisel discipline (the defining feature of this loop)
+
+Per `plans/lib-guest.md`. Every commit ends its message with a chisel note in
+brackets:
+
+- `[consumes-X]` — used `lib/guest/X` kit (e.g., `[consumes-lex]`,
+  `[consumes-pratt]`, `[consumes-ast]`, `[consumes-match]`).
+- `[shapes-scheduler]` — revealed something about what
+  `plans/lib-guest-scheduler.md` should propose. Append a paragraph to that
+  plan's design diary describing the insight.
+- `[shapes-static-types-bidirectional]` — same for
+  `plans/lib-guest-static-types-bidirectional.md`.
+- `[proposes-Y]` — revealed a gap in another existing kit (e.g., `pratt.sx`
+  doesn't handle Go's operator precedence properly). Blockers entry in the
+  kit's plan describing the gap with minimal repro.
+- `[nothing]` — pure Go work that didn't touch substrate or lib/guest story.
+  Rare; if you write `[nothing]` twice in a row, stop and reflect on whether
+  the iteration could have been shaped to surface something.
+
+**Sister plans must be updated.** When Phase 3 lands (independent checker
+working), append a paragraph to
+`plans/lib-guest-static-types-bidirectional.md` describing what synth/check
+shape emerged in Go. When Phase 5 lands (scheduler working), same for
+`plans/lib-guest-scheduler.md`. This is how the two-consumer rule actually
+pays off.
+
+## Ground rules (hard)
+
+- **Scope:** only `lib/go/**` and `plans/go-on-sx.md`. Single permitted
+  cross-plan write: append-only paragraphs to the sister-plan design
+  diaries (`plans/lib-guest-scheduler.md`,
+  `plans/lib-guest-static-types-bidirectional.md`) on `shapes-*` commits.
+  Do **not** touch `spec/`, `hosts/`, `shared/`, `lib/guest/**`
+  (read-only consumer at this phase), or other `lib/<lang>/`.
+- **Consume `lib/guest/core/`** for lex/parse/ast/match/layout. Hand-
+  rolling defeats the chiselling goal.
+- **Do NOT extract into `lib/guest/scheduler/` or `lib/guest/static-
+  types-bidirectional/` from this loop.** Those extractions are gated on
+  two consumers AND independent implementation. Extraction is its own
+  workstream after Go and the second consumer both exist.
+- **Substrate gaps** → Blockers entry with minimal repro. Don't fix the
+  substrate from this loop. Belongs to `sx-improvements.md`.
+- **NEVER call `sx_build` without timeout awareness** — 600s watchdog.
+- **SX files:** `sx-tree` MCP tools ONLY. `sx_validate` after every edit.
+  Never `Edit`/`Read`/`Write` on `.sx`.
+- **Worktree:** branch `loops/go`, push `origin/loops/go`. Never `main`,
+  never `architecture`.
+- **Commit granularity:** one feature per commit. Short factual messages
+  with chisel note: `go: lex.sx — keywords + ASI + 50 tests [consumes-lex]`.
+- **Plan file:** update Progress log + tick boxes every commit.
+- **If blocked** for two iterations on the same issue, add to Blockers and
+  move on. Phases 1-4 are sequential; 5-8 are largely independent once
+  4 lands.
+
+## Conformance scoreboard
+
+Create `lib/go/scoreboard.json` on first iteration. Suites: lex / parse /
+types / eval / runtime / stdlib / e2e. Update counts every commit. The
+scoreboard is also the no-regression gate: a commit that drops any suite's
+pass count is wrong, not the test.
+
+## Go-specific gotchas (read once, never get bitten)
+
+- **ASI (automatic semicolon insertion).** Newline becomes `;` after
+  identifier/literal/`)`/`]`/`}`. Build it into the tokenizer (Phase 1),
+  not the parser. Go spec § Semicolons is unusually precise.
+- **Untyped constants.** `42` is `untyped int` until contextualised.
+  Canonical pitfall: `var x float64 = 42 / 7` must compute `42 / 7 = 6`
+  as untyped, then convert to `6.0`. Not `42.0 / 7 = 6.0`. Not `(42/7).0
+  = 6.0`. Test this in Phase 3.
+- **Methods vs functions.** Different lookup rules. Pointer-receiver
+  methods are NOT in the value's method set for interface satisfaction.
+- **Interface satisfaction is structural and silent.** No `implements`
+  declaration. Lazy check at every interface-typed slot.
+- **Channels have identity.** Distinct `make(chan int)` calls produce
+  distinct channels with same type.
+- **`select` with `default`** = non-blocking. Without `default` = blocks.
+- **`nil` is typed.** `var i interface{} = (*int)(nil); i == nil` is
+  `false` — i holds typed-nil-of-`*int`, not untyped nil. Footgun. Test.
+- **Goroutine panic propagation.** Unrecovered panic crashes whole
+  program. Honour faithfully or document divergence.
+- **`defer` in a loop.** Each iteration pushes; all run on function
+  return, not loop iteration. Common bug; tests must cover.
+- **Map iteration order is unspecified.** v1 = sorted SX-canonical key
+  order for determinism. Document the divergence; provide a
+  `runtime`-package knob to randomise later.
+
+## 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.
+- Shell heredoc `||` gets eaten — escape or use `case`.
+
+## Style
+
+- No comments in `.sx` unless non-obvious. Cite Go spec sections inline
+  when a decision is non-obvious (the Go spec is rigorous — citations work).
+- No new planning docs — update `plans/go-on-sx.md` inline. Append paragraphs
+  to sister-plan design diaries on `shapes-*` commits.
+- Short factual commit messages with chisel note in brackets:
+  `go: parse short-decl + 6 tests [consumes-pratt]`.
+- One feature per iteration. Commit. Log. Push. Next.
+
+Go. Run the pre-flight check. If lib/guest kits are missing, stop. Otherwise
+read the plan, find the first unchecked `[ ]`, implement it. Remember:
+every commit ends with a chisel note, and the sister-plan design diaries
+get updates on `shapes-*` commits.
+
+## Loop continuation
+
+This briefing supersedes any "then stop" wording from the user's original
+`/loop` input. After pushing, **call `ScheduleWakeup` to fire the next
+iteration**, then end the turn. The `/loop` command is in dynamic mode;
+each iteration self-schedules the next.
+
+- `delaySeconds`: **60** (minimum). This is a coding loop with no external
+  event to wait on — back-to-back iterations are intended. Raise only if a
+  prior fire reported a substrate blocker that needs settling.
+- `prompt`: the **full original `/loop` input verbatim, prefixed with
+  `/loop `** (so the wake re-enters this skill and re-reads this briefing).
+  Do NOT paraphrase or trim it — the runtime expects an exact echo.
+- `reason`: one short sentence, e.g. "next Go-on-SX iteration".
+
+**Stop conditions** — omit `ScheduleWakeup` ONLY when:
+1. lib/guest pre-flight failed (missing kits) and a Blockers entry was
+   added — the loop is parked waiting for substrate work.
+2. The same Blockers entry has been the reason for two consecutive
+   iterations (avoid runaway no-op fires).
+3. plans/go-on-sx.md has every Phase 1-11 box checked.
+4. The user explicitly asks to stop, pause, or interrupt the loop.
+
+Otherwise: reschedule. Always.

plans/go-on-sx.md

@@ -304,7 +304,7 @@ Progress-log line → push `origin/loops/go`.
   Remaining sub-items (lexical closures, multi-return funcs, full
   slice triple with capacity) refine but don't gate Phase 5.
 
-### Phase 5 — Goroutines + channels + select (`lib/go/sched.sx`) ⬜
+### Phase 5 — Goroutines + channels + select (`lib/go/sched.sx`) ✅
 - [x] Scaffold: `lib/go/sched.sx` with `go-make-chan` (closures-over-
       mutable-buf), `go-chan-send!` / `go-chan-recv!` / `go-chan-closed?`
       / `go-chan-close!`. Channel identity via closure-instance.
@@ -325,7 +325,9 @@ Progress-log line → push `origin/loops/go`.
       channel (just value). v0 chan-range stops when buffer empties
       (no preemption to wait for new sends). break exits with the
       pre-break env (preserving prior-iteration assignments).
-- [ ] `time.After`-like timer channel.
+- [x] `time.After`-like timer channel (v0 stub: `after(d)` returns a
+      channel already holding `:tick`; lets `select`-with-timeout patterns
+      express the intent while real time is deferred to Phase 5b).
 - **Independent implementation.** Do NOT use lib/guest/scheduler/ — that
   kit doesn't exist yet and depends on this work for its design. See
   `plans/lib-guest-scheduler.md`.
@@ -607,6 +609,21 @@ Minimal repro: see `lib/go/lex.sx#gl-oct-digit?` and `#gl-match-op`.
 
 _Newest first. Append one dated entry per commit._
 
+- 2026-05-27 — **Phase 5 acceptance bar hit (40/40 runtime, 497/497
+  total).** Added `after(d)` builtin (v0 timer stub: returns a channel
+  already buffered with `:tick`) and 13 canonical-pattern tests:
+  timer + select-with-timeout, fan-in, worker queue, two-stage
+  pipeline, fan-out-then-fan-in, select source-order winner, select
+  fallback case, select with default, producer-consumer count-drain,
+  three-channel two-stage pipeline, channel-as-counter, after-with-
+  default, tick-collector. v0 ping-pong is impossible (sync spawn,
+  no blocking) — flagged in Phase 5b. **Shape chiselled:** the timer
+  channel collapses "after duration" into "channel ready immediately"
+  — the only thing `select` needs from a timer is that one of the
+  cases be in the ready set. Real time becomes a refinement of
+  *when* readiness flips, not of the protocol. Sister-plan diary
+  updated with the readiness-as-protocol observation. [shapes-
+  scheduler]
 - 2026-05-27 — Phase 5 cont.: range-over-{slice,map,channel}. New
   `go-eval-range-for` dispatches on the collection type:
     slice → bind index + element, iterate by position

plans/lib-guest-scheduler.md

@@ -231,6 +231,47 @@ real result.
 
 _Newest first. Append one dated entry per milestone landed._
 
+- 2026-05-27 — **Phase 5 acceptance crossed (40 runtime tests).**
+  Final shape observation: *time-as-readiness-flip*. The Go side
+  added an `after(d)` builtin that returns a channel **already
+  holding** a tick value — duration is ignored in v0. The select
+  loop doesn't care that the channel got its value "via time"; it
+  only consults `ready?`. This separates two concerns the eventual
+  kit had been conflating:
+
+    1. **The wake-up protocol** — what `select` asks of every case:
+       "are you ready right now?" Channel-recv answers via "buffer
+       non-empty or closed"; channel-send via "buffer has room";
+       timer via "deadline reached." All three flatten to a single
+       `ready?` predicate.
+
+    2. **The scheduling oracle** — *when* a case's `ready?` flips
+       from false to true. For channels this is driven by other
+       goroutines sending/receiving; for timers it's driven by a
+       wall-clock or monotonic source.
+
+  v0 collapses #2 (timer = ready immediately, sends always ready,
+  recvs ready iff buffer non-empty) and exposes #1 as the only
+  thing the dispatcher needs to know. Phase 5b refines #2 with
+  blocking semantics and real time, but #1 stays the same shape.
+
+  Concretely: the kit's `select-case` should take `:ready?-fn` per
+  case, not three different "is-this-a-send-or-recv-or-timer" tags.
+  Send/recv/timer become factory functions that produce a
+  `(:ready? FN :commit! FN)` record — the dispatcher walks cases,
+  picks the first whose `ready?` returns true, calls `commit!` to
+  extract the value (and side-effect: drain buffer, fire timer).
+  This is the same shape as a STM transaction over case-set, and
+  matches Erlang's `receive` clauses too (each pattern is a
+  ready-predicate + commit-action over the mailbox head).
+
+  Ping-pong remains impossible in v0 because the synchronous spawn
+  collapses the `ready?`-flip oracle to "always immediate" — the
+  spawned goroutine can never park waiting for the parent to send.
+  Phase 5b must restore the wake-up dimension; until then the kit
+  spec should encode the readiness-protocol design even though the
+  oracle is degenerate.
+
 - 2026-05-27 — From Go-on-SX Phase 5 first slice: the channel
   primitive landed as closures-over-mutable-state in
   `lib/go/sched.sx`. Concrete shape: