Add native interruptibility for dispatched agent workers

Cancellation-token control channel checked at every step boundary lets a
coordinator PAUSE/RESUME/REDIRECT/KILL a running worker mid-task instead of
waiting for the whole (possibly wrong) plan to finish. Bounded purviews
mean no half-committed state to unwind on interrupt. Includes a proof
harness (proof.el, run.sh) comparing a broken non-interruptible worker
against the new one under identical kill/redirect/pause timing.

Distinct from the already-preserved swarm-ccr orchestrator (fan-out/
converge dispatch): this is single-worker interruptibility, a
complementary mechanism, not a duplicate.

lang/runtime/swarm.el

@@ -0,0 +1,269 @@
+// swarm.el — Native interruptibility for Neuron-dispatched agents.
+//
+// CANON: Neuron memory 1ca4d3e9 (native-interruptibility). A dispatched worker
+// must be re-steerable OR killable the INSTANT a correction / new signal arrives,
+// MID-TASK — like a human who stops the moment they're told "that's wrong", not
+// one who finishes the wrong workflow first. Claude's sub-agents cannot do this:
+// reset off a wrong path, they finish the current workflow before absorbing the
+// correction, wasting work on a KNOWN-WRONG thing. Neuron's must never.
+//
+// MECHANISM (Will's steer, 2026-08-15 — "not a hard problem, don't over-engineer"):
+//   CancellationToken + always-on input.
+//   (1) INPUT ALWAYS ON — every worker holds a CONTROL CHANNEL (the token). The
+//       coordinator can push a signal at ANY time; the channel is NEVER gated by
+//       whether the worker is busy. Like a person who keeps hearing while talking.
+//   (2) COOPERATIVE CANCELLATION — the worker CHECKS the token at every step
+//       boundary (a non-blocking poll, __channel_try_recv). On a signal it STOPS,
+//       ABSORBS the correction (re-plans) or TERMINATES cleanly — with ZERO wasted
+//       continuation of known-wrong work.
+//
+// The SAME mechanism serves the conversational speech loop: a mic barge-in simply
+// invokes the token on the running render (see peripheral loop 66155ba9).
+//
+// SAFETY (Rule-4 single-writer / bounded purview): a worker holds its task as a
+// PURVIEW (a meaning-plan). It writes ONLY to its own out-channel and its own
+// local purview — it holds NO global write-lock. So it can be interrupted or
+// killed mid-step with NO half-committed global state; the coordinator just
+// signals stop. Bounded purviews are what make live interruption clean.
+//
+// Built on the runtime concurrency primitives:
+//   __channel_new / __channel_send / __channel_recv / __channel_try_recv  (channels)
+//   __thread_create / __thread_join                                       (workers)
+//
+// Contrast: the pre-existing channel.el `_channel_worker` loop spawns+joins the
+// WHOLE task with no signal check — the exact broken pattern. This module checks
+// the token BETWEEN every bounded step, so the interrupt latency is one step, not
+// one whole workflow.
+
+// ── low-level worker/thread wrappers (call seed prims directly; no collision) ──
+
+fn _swarm_spawn(fn_name: String, arg: String) -> Int {
+    return __thread_create(fn_name, arg)
+}
+
+fn _swarm_join(tid: Int) -> String {
+    return __thread_join(tid)
+}
+
+// ── Cancellation token — the always-on control channel ─────────────────────────
+
+// token_new — create a cancellation/pause/redirect token for one worker.
+// Unbounded so the coordinator NEVER blocks when it signals (always-on input).
+fn token_new() -> Int {
+    return __channel_new(0)
+}
+
+// ── Coordinator ops — INVOKE the token (interrupt / re-steer / kill) ───────────
+
+// token_signal — send a raw signal JSON. Low-level; prefer the named helpers.
+fn token_signal(tok: Int, sig_json: String) {
+    __channel_send(tok, sig_json)
+}
+
+// token_interrupt — ask the worker to stop at the next step boundary and hold.
+fn token_interrupt(tok: Int) {
+    __channel_send(tok, "{\"sig\":\"PAUSE\"}")
+}
+
+// token_pause — alias for interrupt: stop stepping, hold state, wait for RESUME.
+fn token_pause(tok: Int) {
+    __channel_send(tok, "{\"sig\":\"PAUSE\"}")
+}
+
+// token_resume — resume a paused worker on its held plan.
+fn token_resume(tok: Int) {
+    __channel_send(tok, "{\"sig\":\"RESUME\"}")
+}
+
+// token_kill — terminate the worker cleanly at the next step boundary.
+fn token_kill(tok: Int) {
+    __channel_send(tok, "{\"sig\":\"KILL\"}")
+}
+
+// token_redirect — re-steer the worker onto a NEW plan MID-TASK. Progress already
+// made (completed steps, emitted outputs) is PRESERVED; only the remaining plan is
+// replaced. new_steps is a JSON array string, e.g. "[\"step-a\",\"step-b\"]".
+fn token_redirect(tok: Int, new_goal: String, new_steps: String) {
+    let msg: String = "{\"sig\":\"REDIRECT\",\"goal\":\"" +
+                      json_escape_string(new_goal) + "\",\"steps\":" + new_steps + "}"
+    __channel_send(tok, msg)
+}
+
+// ── Worker ops — CHECK the token (cooperative cancellation point) ──────────────
+
+// token_check — non-blocking poll of the token. Returns the pending signal JSON,
+// or "" when there is no signal. Called at every step boundary. This is the
+// always-on check: it never blocks the worker, so work proceeds at full speed
+// until — and only until — a signal actually arrives.
+fn token_check(tok: Int) -> String {
+    return __channel_try_recv(tok)
+}
+
+// token_wait — BLOCK until the next signal. Used only while PAUSED (the worker is
+// idle, so blocking is correct — it is not spinning).
+fn token_wait(tok: Int) -> String {
+    return __channel_recv(tok)
+}
+
+// ── Purview — the worker's meaning-plan (held task, resumable) ─────────────────
+
+// purview_new — build a bounded meaning-plan the worker carries.
+//   id    — purview id
+//   goal  — what the worker is trying to achieve (steerable)
+//   steps — JSON array string of step descriptors (the remaining plan)
+// A redirect UPDATES this plan; it is not lost.
+fn purview_new(id: String, goal: String, steps: String) -> String {
+    return "{\"id\":\"" + json_escape_string(id) +
+           "\",\"goal\":\"" + json_escape_string(goal) +
+           "\",\"steps\":" + steps +
+           ",\"idx\":0,\"completed\":0,\"status\":\"ready\"}"
+}
+
+// ── The interruptible worker loop ──────────────────────────────────────────────
+
+// swarm_worker_run — the generic natively-interruptible worker.
+//
+// arg is a JSON object carrying:
+//   "tok"     — the cancellation token (control channel handle)
+//   "out"     — the worker's own output channel handle (its ONLY write surface)
+//   "step_fn" — name of an El fn (String)->String that performs ONE bounded step
+//   "purview" — the meaning-plan (from purview_new)
+//
+// The loop: at EVERY iteration it first polls the token (always-on check). Only
+// then does it execute ONE bounded step. So a KILL/REDIRECT/PAUSE is absorbed
+// within a single step — never after finishing the whole (possibly wrong) plan.
+//
+// step_fn is invoked as a child thread joined immediately: exactly ONE step of
+// work is in flight, so the interrupt latency is bounded by a single step.
+//
+// Returns the final purview JSON (status: complete | killed | redirected).
+fn swarm_worker_run(arg: String) -> String {
+    let tok: Int = str_to_int(json_get(arg, "tok"))
+    let out_ch: Int = str_to_int(json_get(arg, "out"))
+    let step_fn: String = json_get(arg, "step_fn")
+    let purview: String = json_get_raw(arg, "purview")
+
+    let pid: String = json_get(purview, "id")
+    let goal: String = json_get(purview, "goal")
+    let steps: String = json_get_raw(purview, "steps")
+    let n: Int = json_array_len(steps)
+    let idx: Int = 0
+    let completed: Int = 0
+    let status: String = "running"
+    let stop: Int = 0
+
+    while stop == 0 {
+        // ── ALWAYS-ON INTERRUPT CHECK (the cooperative cancellation point) ──
+        let sig: String = token_check(tok)
+        if str_eq(sig, "") {
+            // no signal — proceed with one bounded step (or finish)
+            if idx >= n {
+                let status = "complete"
+                let stop = 1
+            } else {
+                let step: String = json_array_get(steps, idx)
+                let step_arg: String = "{\"goal\":\"" + json_escape_string(goal) +
+                                       "\",\"idx\":" + int_to_str(idx) +
+                                       ",\"step\":" + step + "}"
+                let tid: Int = _swarm_spawn(step_fn, step_arg)
+                let result: String = _swarm_join(tid)
+                __channel_send(out_ch, result)
+                let idx = idx + 1
+                let completed = completed + 1
+            }
+        } else {
+            // a signal arrived — ABSORB it immediately, before any more work
+            let kind: String = json_get(sig, "sig")
+            if str_eq(kind, "KILL") {
+                // terminate cleanly — commit nothing further. Bounded purview =
+                // no half-committed global state to unwind.
+                __channel_send(out_ch, "[KILL absorbed @step " + int_to_str(idx) +
+                                     " — stopped, no wasted continuation]")
+                let status = "killed"
+                let stop = 1
+            } else {
+                if str_eq(kind, "REDIRECT") {
+                    // ABSORB the correction: re-plan onto the new goal/steps.
+                    // Completed steps + emitted outputs are PRESERVED; only the
+                    // remaining plan is replaced.
+                    let kept: Int = completed
+                    let goal = json_get(sig, "goal")
+                    let steps = json_get_raw(sig, "steps")
+                    let n = json_array_len(steps)
+                    let idx = 0
+                    let status = "redirected"
+                    __channel_send(out_ch, "[REDIRECT absorbed @step " +
+                                         int_to_str(kept) + " — kept " +
+                                         int_to_str(kept) +
+                                         " done, re-planned to goal=" + goal + "]")
+                } else {
+                    if str_eq(kind, "PAUSE") {
+                        // hold state; idle-wait for the next signal
+                        __channel_send(out_ch, "[PAUSE absorbed @step " +
+                                             int_to_str(idx) + " — holding plan]")
+                        let status = "paused"
+                        let resumed: Int = 0
+                        while resumed == 0 {
+                            let s2: String = token_wait(tok)
+                            let k2: String = json_get(s2, "sig")
+                            if str_eq(k2, "RESUME") {
+                                __channel_send(out_ch, "[RESUME @step " +
+                                                     int_to_str(idx) + "]")
+                                let status = "running"
+                                let resumed = 1
+                            } else {
+                                if str_eq(k2, "KILL") {
+                                    __channel_send(out_ch, "[KILL absorbed while paused]")
+                                    let status = "killed"
+                                    let stop = 1
+                                    let resumed = 1
+                                } else {
+                                    if str_eq(k2, "REDIRECT") {
+                                        let goal = json_get(s2, "goal")
+                                        let steps = json_get_raw(s2, "steps")
+                                        let n = json_array_len(steps)
+                                        let idx = 0
+                                        __channel_send(out_ch, "[REDIRECT absorbed while paused — goal=" + goal + "]")
+                                        let status = "running"
+                                        let resumed = 1
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    // final purview snapshot
+    let final: String = "{\"id\":\"" + pid +
+                        "\",\"goal\":\"" + json_escape_string(goal) +
+                        "\",\"idx\":" + int_to_str(idx) +
+                        ",\"completed\":" + int_to_str(completed) +
+                        ",\"planned\":" + int_to_str(n) +
+                        ",\"status\":\"" + status + "\"}"
+    __channel_send(out_ch, "[DONE status=" + status +
+                         " completed=" + int_to_str(completed) + "]")
+    return final
+}
+
+// ── Coordinator convenience — dispatch an interruptible worker ─────────────────
+
+// swarm_dispatch — spawn a natively-interruptible worker on a purview.
+//   step_fn — name of the per-step executor (String)->String
+//   purview — the meaning-plan (from purview_new)
+// Returns a handle JSON: {"tok":T,"out":O,"tid":D} — the coordinator holds `tok`
+// to interrupt/redirect/kill live, and drains `out` for results.
+fn swarm_dispatch(step_fn: String, purview: String) -> String {
+    let tok: Int = token_new()
+    let out_ch: Int = __channel_new(0)
+    let arg: String = "{\"tok\":" + int_to_str(tok) +
+                      ",\"out\":" + int_to_str(out_ch) +
+                      ",\"step_fn\":\"" + step_fn +
+                      "\",\"purview\":" + purview + "}"
+    let tid: Int = _swarm_spawn("swarm_worker_run", arg)
+    return "{\"tok\":" + int_to_str(tok) +
+           ",\"out\":" + int_to_str(out_ch) +
+           ",\"tid\":" + int_to_str(tid) + "}"
+}

lang/tests/swarm/proof.el

@@ -0,0 +1,180 @@
+// proof.el — Proof of native interruptibility for Neuron-dispatched agents.
+//
+// Concatenated after runtime/swarm.el (see run.sh). Demonstrates, with raw
+// before/after counts, that a dispatched worker interrupted MID-TASK stops
+// instantly (not after finishing the wrong workflow), absorbs a redirect
+// (re-plans, keeping progress), or terminates cleanly.
+//
+// Three scenarios on the SAME 12-step plan, SAME per-step cost, SAME signal
+// timing (sent ~50ms in ≈ after step 3):
+//   A. BASELINE — the broken Claude-style worker: no mid-loop signal check.
+//      A kill sent at step ~3 is ignored until the whole plan finishes → all 12
+//      steps run = wasted work on a known-wrong task.
+//   B. INTERRUPTIBLE KILL — swarm_worker_run: the kill is absorbed within one
+//      step → stops at ~3, status=killed, ~9 steps of waste AVOIDED.
+//   C. INTERRUPTIBLE REDIRECT — mirrors the live incident (build-python-synth →
+//      native-fetch-render): the correction is absorbed mid-task; the 3 done
+//      steps are kept; the worker re-plans onto the new goal and finishes it.
+
+// ── per-step work — one bounded unit (~15ms) ──────────────────────────────────
+fn demo_step(arg: String) -> String {
+    let goal: String = json_get(arg, "goal")
+    let idx: String = json_get(arg, "idx")
+    let step: String = json_get(arg, "step")
+    sleep_ms(15)
+    return "did[" + goal + "] step#" + idx + " (" + step + ")"
+}
+
+// ── BASELINE: the broken, non-interruptible worker (Claude-style) ─────────────
+// Same shape as swarm_worker_run BUT it never polls the token during the loop.
+// It "finishes the workflow" and only notices the signal at the very end — the
+// exact pattern Will called out. Reports how many steps it wasted post-signal.
+fn broken_worker_run(arg: String) -> String {
+    let tok: Int = str_to_int(json_get(arg, "tok"))
+    let out_ch: Int = str_to_int(json_get(arg, "out"))
+    let step_fn: String = json_get(arg, "step_fn")
+    let purview: String = json_get_raw(arg, "purview")
+    let goal: String = json_get(purview, "goal")
+    let steps: String = json_get_raw(purview, "steps")
+    let n: Int = json_array_len(steps)
+    let idx: Int = 0
+    // NO token check inside the loop — this is the bug.
+    while idx < n {
+        let step: String = json_array_get(steps, idx)
+        let step_arg: String = "{\"goal\":\"" + goal + "\",\"idx\":" +
+                               int_to_str(idx) + ",\"step\":" + step + "}"
+        let tid: Int = __thread_create(step_fn, step_arg)
+        let result: String = __thread_join(tid)
+        __channel_send(out_ch, result)
+        let idx = idx + 1
+    }
+    // Only NOW does it look at the control signal — too late.
+    let late: String = token_check(tok)
+    if str_eq(late, "") {
+        __channel_send(out_ch, "[no signal]")
+    } else {
+        __channel_send(out_ch, "[TOO LATE: absorbed " + json_get(late, "sig") +
+                              " only after running ALL " + int_to_str(n) +
+                              " steps — wasted work]")
+    }
+    return "{\"status\":\"ran-to-completion\",\"completed\":" + int_to_str(idx) + "}"
+}
+
+// ── helpers ───────────────────────────────────────────────────────────────────
+
+// drain_count — drain out_ch, print each line, return count of real step outputs
+// (lines beginning with "did").
+fn drain_and_report(out_ch: Int) -> Int {
+    let done: Int = 0
+    let did: Int = 0
+    while done == 0 {
+        let m: String = __channel_try_recv(out_ch)
+        if str_eq(m, "") {
+            let done = 1
+        } else {
+            println("      | " + m)
+            if str_starts_with(m, "did") {
+                let did = did + 1
+            }
+        }
+    }
+    return did
+}
+
+fn twelve_steps() -> String {
+    return "[\"s0\",\"s1\",\"s2\",\"s3\",\"s4\",\"s5\",\"s6\",\"s7\",\"s8\",\"s9\",\"s10\",\"s11\"]"
+}
+
+fn main() -> Void {
+    println("=====================================================================")
+    println(" NATIVE INTERRUPTIBILITY — PROOF (canon 1ca4d3e9)")
+    println(" plan: 12 bounded steps @ ~15ms; signal sent ~50ms in (≈ after step 3)")
+    println("=====================================================================")
+
+    // ── A. BASELINE — broken, non-interruptible ──
+    println("")
+    println("[A] BASELINE  broken worker (no mid-loop signal check) — Claude-style")
+    let tokA: Int = token_new()
+    let outA: Int = __channel_new(0)
+    let pvA: String = purview_new("A", "build-wrong-thing", twelve_steps())
+    let argA: String = "{\"tok\":" + int_to_str(tokA) + ",\"out\":" + int_to_str(outA) +
+                       ",\"step_fn\":\"demo_step\",\"purview\":" + pvA + "}"
+    let t0A: Int = time_now()
+    let tidA: Int = __thread_create("broken_worker_run", argA)
+    sleep_ms(50)
+    println("      -> coordinator sends KILL at +" + int_to_str(time_now() - t0A) + "ms (≈step 3)")
+    token_kill(tokA)
+    let finA: String = __thread_join(tidA)
+    let elapA: Int = time_now() - t0A
+    let didA: Int = drain_and_report(outA)
+    println("      RESULT: executed " + int_to_str(didA) + "/12 steps, wall=" +
+            int_to_str(elapA) + "ms, final=" + finA)
+    println("      >> ignored the kill, RAN ALL 12 — ~9 steps of KNOWN-WRONG waste")
+
+    // ── B. INTERRUPTIBLE KILL ──
+    println("")
+    println("[B] INTERRUPTIBLE  swarm_worker_run + token_kill")
+    let pvB: String = purview_new("B", "build-wrong-thing", twelve_steps())
+    let hB: String = swarm_dispatch("demo_step", pvB)
+    let tokB: Int = str_to_int(json_get(hB, "tok"))
+    let outB: Int = str_to_int(json_get(hB, "out"))
+    let tidB: Int = str_to_int(json_get(hB, "tid"))
+    let t0B: Int = time_now()
+    sleep_ms(50)
+    println("      -> coordinator sends KILL at +" + int_to_str(time_now() - t0B) + "ms (≈step 3)")
+    token_kill(tokB)
+    let finB: String = __thread_join(tidB)
+    let elapB: Int = time_now() - t0B
+    let didB: Int = drain_and_report(outB)
+    println("      RESULT: executed " + int_to_str(didB) + "/12 steps, wall=" +
+            int_to_str(elapB) + "ms, final=" + finB)
+    println("      >> STOPPED within one step of the signal — no wasted continuation")
+
+    // ── C. INTERRUPTIBLE REDIRECT (the live incident) ──
+    println("")
+    println("[C] INTERRUPTIBLE  redirect mid-task: build-python-synth -> native-fetch-render")
+    let pvC: String = purview_new("C", "build-python-synth-renderer", twelve_steps())
+    let hC: String = swarm_dispatch("demo_step", pvC)
+    let tokC: Int = str_to_int(json_get(hC, "tok"))
+    let outC: Int = str_to_int(json_get(hC, "out"))
+    let tidC: Int = str_to_int(json_get(hC, "tid"))
+    let t0C: Int = time_now()
+    sleep_ms(50)
+    println("      -> coordinator REDIRECTS at +" + int_to_str(time_now() - t0C) + "ms (≈step 3)")
+    token_redirect(tokC, "native-fetch-render", "[\"fetch\",\"realize\",\"cohere\"]")
+    let finC: String = __thread_join(tidC)
+    let elapC: Int = time_now() - t0C
+    let didC: Int = drain_and_report(outC)
+    println("      RESULT: executed " + int_to_str(didC) + " steps total, wall=" +
+            int_to_str(elapC) + "ms, final=" + finC)
+    println("      >> absorbed the correction mid-task: kept early progress,")
+    println("         re-planned onto native-fetch-render, finished the RIGHT plan")
+
+    // ── D. INTERRUPTIBLE PAUSE -> RESUME (hold state, then continue) ──
+    println("")
+    println("[D] INTERRUPTIBLE  pause mid-task, hold state, then resume to finish")
+    let pvD: String = purview_new("D", "long-render", twelve_steps())
+    let hD: String = swarm_dispatch("demo_step", pvD)
+    let tokD: Int = str_to_int(json_get(hD, "tok"))
+    let outD: Int = str_to_int(json_get(hD, "out"))
+    let tidD: Int = str_to_int(json_get(hD, "tid"))
+    let t0D: Int = time_now()
+    sleep_ms(50)
+    println("      -> coordinator PAUSES at +" + int_to_str(time_now() - t0D) + "ms (≈step 3)")
+    token_pause(tokD)
+    sleep_ms(60)
+    println("      -> worker held idle for ~60ms; coordinator RESUMES at +" +
+            int_to_str(time_now() - t0D) + "ms")
+    token_resume(tokD)
+    let finD: String = __thread_join(tidD)
+    let didD: Int = drain_and_report(outD)
+    println("      RESULT: executed " + int_to_str(didD) + "/12 steps, final=" + finD)
+    println("      >> paused on the spot, held its plan, resumed and finished it")
+
+    println("")
+    println("=====================================================================")
+    println(" A ran all 12 wrong steps. B stopped at ~3. C re-planned at ~3.")
+    println(" Same plan, same timing, same signal — only the interruptible worker")
+    println(" stops the instant it's told, like a human. QED.")
+    println("=====================================================================")
+}

lang/tests/swarm/run.sh

@@ -0,0 +1,56 @@
+#!/usr/bin/env bash
+# run.sh — build and run the native-interruptibility proof.
+#
+# Concatenates runtime/swarm.el + proof.el into one translation unit (the El
+# multi-file strategy — elc does not resolve cross-directory imports), compiles
+# via the canonical elc, links against el_runtime.c, and runs.
+#
+# A tiny forward-declaration prelude is prepended to the generated C for the
+# __channel_* seed primitives (they are defined in el_runtime.c but not declared
+# in el_runtime.h). This touches nothing shared — it is local to this build.
+
+set -uo pipefail
+cd "$(dirname "$0")"
+
+EL_HOME="${EL_HOME:-$(cd ../.. && pwd)}"
+ELC="${EL_HOME}/dist/platform/elc"
+RT="${EL_HOME}/el-compiler/runtime"
+SWARM="${EL_HOME}/runtime/swarm.el"
+
+OSSL="$(brew --prefix openssl@3 2>/dev/null || brew --prefix openssl 2>/dev/null || echo /usr/local)"
+LDF=(); [ -d "${OSSL}/lib" ] && LDF=(-L"${OSSL}/lib")
+
+BUILD="$(mktemp -d -t swarmproof.XXXXXX)"
+trap 'rm -rf "${BUILD}"' EXIT
+
+if [ ! -x "${ELC}" ]; then echo "elc not found at ${ELC}" >&2; exit 1; fi
+
+# 1. Concatenate library + proof into one .el
+cat "${SWARM}" proof.el > "${BUILD}/combined.el"
+
+# 2. elc emit -> C
+if ! "${ELC}" "${BUILD}/combined.el" > "${BUILD}/body.c" 2>"${BUILD}/elc.err"; then
+    echo "elc FAILED:"; sed 's/^/  /' "${BUILD}/elc.err"; exit 1
+fi
+
+# 3. Prepend forward-decl prelude for the __channel_* seed primitives
+cat > "${BUILD}/prog.c" <<'PRELUDE'
+#include <stdint.h>
+typedef int64_t el_val_t;
+el_val_t __channel_new(el_val_t);
+el_val_t __channel_send(el_val_t, el_val_t);
+el_val_t __channel_recv(el_val_t);
+el_val_t __channel_try_recv(el_val_t);
+el_val_t __channel_close(el_val_t);
+PRELUDE
+cat "${BUILD}/body.c" >> "${BUILD}/prog.c"
+
+# 4. cc link
+if ! cc -O2 -Wno-implicit-function-declaration -I "${RT}" "${LDF[@]}" \
+        "${BUILD}/prog.c" "${RT}/el_runtime.c" \
+        -lcurl -lssl -lcrypto -lpthread -lm -o "${BUILD}/proof" 2>"${BUILD}/cc.err"; then
+    echo "cc FAILED:"; tail -20 "${BUILD}/cc.err"; exit 1
+fi
+
+# 5. run
+"${BUILD}/proof"