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+# El Test Framework — Design
+
+**Status:** draft for review
+**Author:** Neuron
+**Date:** 2026-08-15
+**Worktree:** `/Users/will/Development/neuron-technologies/el-worktrees/elc-memory-investigation`
+
+---
+
+## 0. The forcing requirement
+
+We have a confirmed quadratic in `elc`. Peak memory in the old shipped binary and wall-clock in
+the current source both grow as O(input²). We cannot fix it, because we cannot test it.
+
+Everything in this document is downstream of one sentence: **a test framework must be able to fail
+a build when an operation's growth curve degrades from linear to quadratic.**
+
+That is not a nice-to-have bolted onto a correctness framework. It is the requirement that
+determines the architecture. Correctness testing is the easy half.
+
+Second-order requirement, learned the hard way tonight: **the framework must report per-test timing
+by default.** The current framework prints `N passed, M failed` and nothing else. That is why a
+3.58-second test file sat in the suite unnoticed. A framework that is structurally blind to time
+cannot surface the defect class we most need to catch.
+
+---
+
+## 1. What exists today, measured
+
+### 1.1 Two competing systems, neither complete
+
+**System A — `lang/runtime/test.el`.** Manual registration, El-level.
+
+**System B — the compiler's `test { }` block + `elc --test`.** Emits its own harness `main()`
+with `__el_pass` / `__el_fail` globals (`codegen.el:3777-3796`).
+
+They do not share a result model. Neither has timing. Both are in the tree.
+
+### 1.2 Specific defects in System A
+
+| Defect | Location | Consequence |
+|---|---|---|
+| All state as JSON strings in a global string-keyed map | `test.el` throughout | every assertion is `state_get` → `str_to_int` → `int_to_str` → `state_set` |
+| Failure list appended by string slice + concat | `_test_json_append` | O(n²) in failure count |
+| One OS thread spawned per test | `_test_run_one` via `__thread_create`/`__thread_join` | thread spawn per test, purely to get dispatch-by-name through dlsym |
+| Manual registration pairing a string to a function name | `test_case(name, fn_name)` | typo ⇒ test silently never runs, suite still reports pass |
+| Counters are assertion-level, global | `_test_pass_count` etc. | no per-test record exists at all |
+| No timing, no structured output, no fixtures, no tags, no filtering, no parameterization, no benchmarks | — | — |
+
+The registration defect is the serious one. It is not a slow framework, it is a framework that can
+report success for tests that did not execute.
+
+### 1.3 Measured cost structure
+
+Per test file, current build model:
+
+| Step | Time |
+|---|---|
+| `elc` compile `.el` → `.c` | 0.00s (small files) |
+| **`cc` el_runtime.c → .o** | **0.14s** |
+| `cc` test .c → .o | 0.02s |
+| link | 0.02s |
+
+Per-file `elc` time across the existing suite:
+
+| File | Bytes | elc time |
+|---|---|---|
+| `test_compiler` | 29,685 (+394 KB of imports) | **3.58s** |
+| `string_test` | 18,545 | 0.01s |
+| all other 9 files | 2.2–10 KB | 0.00s |
+
+Two distinct defects in two distinct regimes:
+
+1. **`test_compiler.el` imports all five compiler sources** — 394 KB in one translation unit. Its
+   3.58s is entirely the quadratic. It is the only file where the quadratic bites.
+2. **Every other file's cost is 100% redundant `el_runtime.c` rebuilds** — 480 KB of identical C,
+   recompiled once per test file.
+
+Neither is fixed by making the compiler faster. Both are fixed by the architecture below, and the
+speedup is a by-product of building it correctly, not the goal.
+
+### 1.4 The asset worth keeping
+
+`codegen.el:3651-3652` already collects `test_names` / `test_c_names` — **the compiler already does
+compile-time test discovery.** It then discards that registry into a hardcoded `main()`.
+
+That registry is precisely the seam Go's `_testmain.go` and Rust's `test_main_static` are built on.
+The mechanism we need is half-built and wired to the wrong thing.
+
+---
+
+## 2. Grounding — the common spine of excellent frameworks
+
+Researched from primary sources: Go `testing`/`go test`, Rust `libtest`/Criterion, JUnit 5 Platform,
+NUnit 3, JMH, Google Benchmark. Six invariants hold across all of them.
+
+1. **A registry is built before execution** — `(name, metadata, fn-ptr)` triples. Go generates it
+   from an AST scan; Rust synthesizes it in a compiler pass; JMH emits it as a build-time resource;
+   JUnit/NUnit build it reflectively. **Reflection is an implementation of the registry on runtimes
+   where it is cheap. It is never the architecture.**
+
+2. **Discovery strictly precedes execution.** Every good capability — filtering, listing, counting,
+   sharding, IDE trees, re-run-failed-only, dry runs — is a consequence of this ordering.
+
+3. **A hierarchy with stable, path-shaped unique IDs.** `TestFoo/subcase_2`. Selection is regex over
+   that path, one pattern per level.
+
+4. **The framework is a prebuilt library; only the entry point is generated.** "Compile once, link
+   many" is always: framework archive compiled once + a small generated table + one
+   `MainStart(deps, registry)` call. Nobody recompiles the harness per test file.
+
+5. **Execution emits an event stream; reporters are downstream renderers.** Human text, NDJSON,
+   JUnit XML, TAP are all transforms of one event stream. Go's one architectural mistake is doing
+   this backwards — `test2json` parses human output, and has shipped bugs when user output contains
+   `--- PASS:`.
+
+6. **A dependency-injection seam at the boundary.** Go's `testdeps.TestDeps` exists so `testing`
+   can avoid importing `regexp`, profilers, and coverage. The execution core knows nothing about
+   output formats.
+
+---
+
+## 3. Architecture
+
+### 3.1 The seam
+
+```
+  ┌─────────────────────────────────────────────────────────────┐
+  │ user code:  foo.el  with  test { } / bench { }  blocks       │
+  └───────────────────────────┬─────────────────────────────────┘
+                              │  elc --test
+                              ▼
+  ┌─────────────────────────────────────────────────────────────┐
+  │ generated C (per suite, tiny):                               │
+  │   __el_test_fn_0 .. _N      lowered test/bench bodies        │
+  │   __el_registry[]           static table: name/kind/file/    │
+  │                             line/tags/sizes/expected-O       │
+  │   __el_dispatch(i)          generated switch → body          │
+  │   main() { return el_test_main(argc, argv); }                │
+  └───────────────────────────┬─────────────────────────────────┘
+                              │  cc + link  (registry only)
+                              ▼
+  ┌─────────────────────────────────────────────────────────────┐
+  │ libeltest.a  — PREBUILT ONCE                                 │
+  │   • el_runtime.o        (the 480 KB, compiled once, ever)    │
+  │   • eltest.o            the runner, WRITTEN IN EL            │
+  │       discovery view · filtering · execution · fixtures ·    │
+  │       timing · benchmark harness · curve fitting · reporters │
+  └─────────────────────────────────────────────────────────────┘
+```
+
+The framework is written in El, compiled to C once, archived. Per-suite compilation touches only
+the generated registry. This is Go's model, and it is strictly better for us than Go's because we
+own the compiler and already have the AST — no separate source-scanning pass is needed.
+
+### 3.2 Why the runner is in El and the registry is in C
+
+El has no closures and no first-class function pointers. The registry must therefore hold C function
+pointers, and it is generated C.
+
+The runner stays in El and reaches the registry through a small builtin surface — indices, not
+pointers:
+
+```
+__el_reg_count() -> Int
+__el_reg_name(i) -> String
+__el_reg_file(i) -> String
+__el_reg_line(i) -> Int
+__el_reg_kind(i) -> Int          // 0=test 1=bench
+__el_reg_tags(i) -> Int
+__el_reg_sizes(i) -> String      // JSON array, empty for tests
+__el_reg_expect(i) -> Int        // complexity class enum, 0 = none
+__el_reg_invoke(i) -> Int        // runs the body via the generated switch
+```
+
+Nine builtins. Everything else — filtering, lifecycle, statistics, curve fitting, all reporters —
+is El. That satisfies "written in El" without pretending El can do something it cannot.
+
+### 3.3 Result model
+
+The unit is a **result record**, not a counter:
+
+```
+TestResult {
+  id        String     // slash path: "parser/handles_empty_input/case_3"
+  file      String
+  line      Int
+  status    Status     // Pass | Fail | Error | Skip
+  duration  Int        // nanoseconds, ALWAYS populated
+  message   String     // assertion detail: expected vs actual
+  output    String     // captured stdout/stderr for this test
+  assertions Int
+}
+```
+
+`Fail` = an assertion failed. `Error` = unexpected crash/abort. This distinction is load-bearing —
+every CI consumer depends on it, and the JUnit XML schema encodes it as distinct elements.
+
+---
+
+## 4. Authoring surface
+
+### 4.1 Tests
+
+`test { }` already exists. Keep it. Add subtests and hierarchy:
+
+```el
+test "parser/empty input" {
+    assert_that(parse(""), is_err())
+}
+
+test "parser/table" {
+    for case in [["", 0], ["a", 1], ["a b", 2]] {
+        subtest(case[0]) {
+            assert_that(token_count(case[0]), equals(case[1]))
+        }
+    }
+}
+```
+
+Subtest IDs compose as `parser/table/a_b`. Filtering is `--run 'parser/table/.*'`, one regex per
+path segment, exactly as Go does.
+
+**We do not build a parameterized-test annotation system.** Table-driven loops plus subtests subsume
+`@ParameterizedTest`, `@MethodSource`, `@CsvSource`, and `TestCaseSource` entirely, at zero framework
+surface. This is Go's single biggest ergonomic win over JUnit and NUnit.
+
+### 4.2 Fixtures
+
+Per-file and per-test only, plus a LIFO cleanup stack:
+
+```el
+setup_all  { ... }      // once per suite
+setup      { ... }      // before each test
+teardown   { ... }      // after each test
+teardown_all { ... }
+```
+
+and inside a test, `cleanup { ... }` registering LIFO-ordered teardown.
+
+**We do not build JUnit 5's extension SPI** — seventeen callback interfaces, hierarchical stores,
+registration ordering rules. That complexity is the price of retrofitting a plugin ecosystem onto a
+twenty-year-old reflective framework. Go's `t.Cleanup` covers roughly 90% of what `@AfterEach` is
+used for at a fraction of the surface.
+
+### 4.3 Assertions — constraint model
+
+One entry point, composable constraint values (NUnit's model, which avoids the N² overload
+explosion):
+
+```el
+assert_that(actual, equals(expected))
+assert_that(xs,     has_length(3))
+assert_that(s,      contains("foo").and(starts_with("bar")))
+assert_that(f,      is_within(0.01).of(3.14))
+```
+
+A constraint is a value with `apply_to(actual) -> ConstraintResult`, and the result knows how to
+describe its own failure. Custom constraints are ordinary user types.
+
+**Every failure message must name file, line, the expression text, and both values.** We capture
+expression source text at compile time — we have the AST, so we can do this better than any
+runtime-introspection framework.
+
+Legacy `assert_true` / `assert_eq` / etc. stay as thin wrappers for migration.
+
+---
+
+## 5. Benchmarks
+
+### 5.1 The loop
+
+Adopt `b.Loop()`, not `b.N`. Go spent fifteen years on `b.N` before concluding `b.Loop` was right;
+we skip that.
+
+```el
+bench "str_concat" {
+    let s = make_input(bench_n())
+    for bench_loop() {
+        black_box(str_concat(s, "x"))
+    }
+}
+```
+
+Three properties that make this the correct choice for a C target:
+
+1. **The timer auto-resets on first call**, so setup above the loop is excluded *by construction*
+   rather than by the author remembering `ResetTimer`.
+2. **`N` is hidden**, so it cannot be misused.
+3. **The harness owns the loop shape**, which lets us insert an optimization barrier the C compiler
+   cannot see through. `black_box(v)` lowers to `asm volatile("" :: "r"(&v) : "memory")`. Since we
+   emit a single translation unit, dead-code elimination of a benchmark body is a live hazard —
+   this is our version of JMH's `Blackhole` problem, solved in the harness rather than delegated to
+   the user.
+
+### 5.2 Iteration scaling
+
+Use Go's `predictN` heuristics verbatim. They are battle-tested and cheap:
+
+```
+n = goal_ns * prev_iters / prev_ns    // multiply before divide — precision on sub-ns ops
+n += n / 5                            // 20% headroom, overshoot rather than re-loop
+n = min(n, 100 * last)                // never grow more than 100× per step
+n = max(n, last + 1)                  // guarantee forward progress
+n = min(n, 1_000_000_000)             // hard ceiling
+```
+
+Report `n` rounded to 1/2/3/5 × 10ᵏ so runs are comparable.
+
+### 5.3 Sampling
+
+Criterion's shape, because it is correct near timer resolution:
+
+- **Warmup**: iteration counts 1, 2, 4, 8… until cumulative time exceeds the warmup budget.
+- **Measurement**: collect `sample_size` samples at iteration counts `[d, 2d, 3d, …, Nd]`.
+- **Estimate**: slope of a linear regression of iteration-count vs elapsed time. The intercept
+  absorbs fixed overhead.
+- **Time whole samples, never individual iterations.** This is the single most important detail —
+  it defeats timer-resolution error on nanosecond operations.
+
+Outliers classified by modified Tukey (±1.5 IQR mild, ±3 IQR severe), **reported but retained**.
+
+---
+
+## 6. Complexity gating — the centerpiece
+
+This is the part that makes the quadratic fixable, and the part nobody in the mainstream has
+finished. Google Benchmark's `Complexity()` fits the curve and *reports* it. We declare it and
+**gate** on it.
+
+### 6.1 Surface
+
+```el
+bench "elc_compile" over n in [16, 32, 64, 128, 256, 512, 1024] expect O(n) {
+    let src = synth_source(bench_n())
+    for bench_loop() { black_box(compile(src)) }
+}
+```
+
+Alternative with no new syntax, if the parser change is judged too invasive — `bench_sizes([...])`
+and `bench_expect("O(n)")` as calls inside the block. **Recommendation: declarative.** Runtime calls
+mean `--list` cannot show the invariant without executing, which breaks the discovery-precedes-
+execution invariant from §2.
+
+### 6.2 Fitting
+
+Per Google Benchmark `src/complexity.cc`. For candidate curves
+`{O(1), O(log n), O(n), O(n log n), O(n²), O(n³)}`, one-parameter least squares, no intercept:
+
+```
+coef = Σ(tᵢ · gᵢ) / Σ(gᵢ²)
+rms  = sqrt( Σ(tᵢ − coef·gᵢ)² / k ) / mean(t)     // normalized
+```
+
+Best fit = lowest normalized RMS. User-supplied lambda curves also supported.
+
+### 6.3 Gate logic
+
+1. **FAIL** if the best-fit curve is strictly worse than declared, ordering
+   `O(1) < O(log n) < O(n) < O(n log n) < O(n²) < O(n³)`. Print the fitted coefficient and the full
+   per-size table.
+2. **FAIL** if the declared curve's normalized RMS exceeds a threshold (start at 0.10). This catches
+   the case where *no* candidate fits — noise, a cache cliff, or a phase change. Report
+   `INDETERMINATE` honestly rather than gating on garbage.
+3. **WARN** if the best fit is strictly better than declared — either an optimization landed and the
+   annotation should tighten, or the sweep is too narrow to expose real behaviour.
+4. **REFUSE to gate** on fewer than 5 distinct sizes spanning under 2 decades, geometrically spaced.
+   Say so loudly rather than producing a meaningless fit.
+
+### 6.4 Why gate on the exponent, not wall-clock
+
+- **Machine-independent.** The fitted exponent is a property of the algorithm; the coefficient is a
+  property of the machine. Gating on the exponent makes CI hardware heterogeneity, noisy neighbours,
+  and thermal throttling irrelevant — they scale `coef`, not `g`.
+- **No stored baseline.** No artifact storage, no golden-file drift. The invariant lives in the
+  source next to the code and is reviewed in the same PR.
+- **It catches the failure mode that actually ships.** An O(n) lookup inside an O(n) loop is
+  invisible at n=100 in a unit test and catastrophic at n=100,000 in production. Constant-factor
+  regressions are annoying. Complexity regressions are outages. Ours was a 27 GB outage.
+
+### 6.5 The deterministic gate — the one that would have caught us
+
+Wall-clock needs statistics. **Allocation counts do not.** They are perfectly deterministic.
+
+> **Correction, 2026-08-16 — count alone is NOT sufficient. Gate on BOTH count and bytes.**
+>
+> Measured against two El programs, one allocating once per item and one rebuilding its
+> accumulator each iteration:
+>
+> | n | linear allocs / bytes | quadratic allocs / bytes |
+> |---|---|---|
+> | 100 | 100 / 290 | 100 / 5,150 |
+> | 200 | 200 / 690 | 200 / 20,300 |
+> | 400 | 400 / 1,490 | 400 / 80,600 |
+> | 800 | 800 / 3,090 | 800 / 321,200 |
+>
+> The quadratic program's allocation **count is exactly linear** — 100/200/400/800, identical to
+> the healthy program. A count-only gate passes it clean. **Bytes** catch it: each doubling of n
+> quadruples bytes (ratios 3.94, 3.97, 3.99 → 4.0 = O(n²)) where the linear program converges
+> on 2.0.
+>
+> This is precisely elc's own defect shape — a copy-on-write accumulator reallocating once per
+> pass (count linear) into a proportionally larger buffer (bytes quadratic).
+>
+> Therefore `expect allocs O(n)` **fits count and bytes independently and fails if EITHER exceeds
+> the declared curve**, reporting which signal broke. "count linear, bytes quadratic" is a precise,
+> directly actionable diagnosis.
+>
+> **`el_peak_rss()` is CONTEXT ONLY — never gate on it.** It is perturbed by the allocator and by
+> the page cache. Allocation volume is the invariant; RSS and malloc/free churn are merely the two
+> surfaces it shows on. The old shipped compiler paid the same quadratic in RSS that the rebuilt
+> one pays in churn.
+>
+> **Measure rate, not level.** A guard reading swap *level* saw 97% on a thrashing host and 97% on
+> a healthy one; only *rate* separated them. A growth exponent is a rate; a single measurement is
+> a level. That is why the gate fits a curve across a sweep instead of comparing one number to a
+> threshold.
+
+Instrument the runtime with allocation counters and fit *those* against n instead of time:
+
+```el
+bench "elc_compile" over n in [...] expect O(n) allocs O(n) { ... }
+```
+
+Zero noise, zero statistics, always gateable, correct on the first run on any machine. Go reports
+`allocs/op` and `B/op`; **nobody fits them against n.** That is an open opportunity and it is exactly
+our bug: elc's defect is quadratic *allocation volume*, which the old binary paid in RSS and the
+current source pays in malloc/free churn.
+
+An `expect allocs O(n)` assertion on `elc`'s compile path would have failed the build the day the
+quadratic was introduced.
+
+Required runtime additions: `__el_alloc_count()`, `__el_alloc_bytes()`, `__el_peak_rss()`.
+
+### 6.6 Constant-factor gate (secondary, opt-in)
+
+Mann-Whitney U at α = 0.05, noise floor 1%, medians with 95% CIs, `~` for not-significant. Requires
+`--count >= 9`. Off by default on CI; opt-in per benchmark.
+
+**Exit nonzero on regression.** Both benchstat and Criterion always exit 0, which is why every shop
+using them wrote a wrapper. We do not repeat that omission.
+
+---
+
+## 7. Output
+
+**Structured events are the source of truth.** Human text is rendered from them. We do not repeat
+Go's parse-the-human-output design.
+
+Event stream, NDJSON, one object per line, streamed live:
+
+```json
+{"time":"...","action":"run","test":"parser/empty"}
+{"time":"...","action":"output","test":"parser/empty","output":"..."}
+{"time":"...","action":"pass","test":"parser/empty","elapsed":0.0031}
+{"time":"...","action":"bench","test":"str_concat","n":1024,"ns_op":41.2,"allocs_op":3,"bigo":"N","rms":0.03}
+```
+
+Renderers, all downstream and pluggable:
+
+| Format | Flag | Use |
+|---|---|---|
+| Human | default | terminal, **per-test duration always shown** |
+| NDJSON | `--json` | tooling, history, flaky detection |
+| JUnit XML | `--junit-xml=PATH` | every CI system on earth |
+| TAP | `--tap` | optional |
+
+JUnit XML per the de-facto schema: `testsuites` → `testsuite` → `testcase`, with `time` in seconds
+as a decimal, `file`/`line` attributes, and `failure` vs `error` vs `skipped` as distinct child
+elements. Absence of a child element means pass. Emit `<testsuites>` even for a single suite, and
+parse both shapes on input.
+
+---
+
+## 8. CLI
+
+```
+--list                     print the registry, run nothing
+--list-json                machine-readable registry
+--run PATTERN              slash-separated regex per path segment
+--tag EXPR                 tag expression: fast & !slow
+--shard I/N                deterministic sharding for CI parallelism
+--count N                  repetitions, for statistics
+--bench PATTERN            run benchmarks (off by default in test runs)
+--benchtime DUR            per-benchmark time budget
+--junit-xml PATH
+--json
+--isolate                  re-exec per test on crash, so one SIGSEGV doesn't lose the run
+--timeout DUR
+--fail-fast
+```
+
+`--list` / `--list-json` / `--shard` cost roughly thirty lines because the registry already exists
+before `main` does anything. That is the dividend of discovery-precedes-execution.
+
+---
+
+## 9. Build model
+
+```
+# once, ever (or when the runtime/framework changes):
+cc -c el_runtime.c        -o el_runtime.o
+elc eltest.el > eltest.c && cc -c eltest.c -o eltest.o
+ar rcs libeltest.a el_runtime.o eltest.o
+
+# per suite:
+elc --test foo_test.el > foo_test.c     # registry + bodies only
+cc foo_test.c libeltest.a -o foo_test
+```
+
+The 0.14s × N of redundant runtime rebuilds disappears — not because we optimized it, but because
+one-runner-over-many-suites requires compile-once-link-many as a structural precondition.
+
+---
+
+## 10. Bootstrap and self-hosting
+
+The framework's own tests are `test { }` blocks run by the framework. Same fixpoint discipline the
+compiler already applies to itself.
+
+1. Build the framework using the *existing* harness for its first tests (stage 0).
+2. Rebuild the framework's tests as `test { }` blocks run by the new runner (stage 1).
+3. Verify stage 1 reports identical results to stage 0.
+4. From then on, the framework is tested by itself.
+
+A framework that cannot run its own suite is not evidence of anything. This is a correctness proof,
+not a claim.
+
+---
+
+## 11. Explicitly not building
+
+| Rejected | Why |
+|---|---|
+| Naming-convention discovery (`fn test_foo`) | `test { }` is a real declaration. Go's `TestXxx` exists only because Go had no better hook — and it needs a heuristic to avoid matching `TesticularCancer`. |
+| Reflection or symbol-table scanning | Slow, fragile under LTO/strip/dead-strip, and unnecessary when we own the compiler. |
+| Parsing human output into structure | Go's `test2json` is its one clear architectural mistake. |
+| JUnit 5's extension SPI | Seventeen callback interfaces to retrofit plugins onto a reflective framework. Not our problem. |
+| `@ParameterizedTest` machinery | Table-driven loops + subtests subsume it at zero surface. |
+| NUnit's out-of-process agents | They bridge CLR versions and AppDomains. We emit one native binary. Keep `--isolate` as crash fallback only. |
+| JMH-style forking by default | Forks exist because JIT profiles are per-process. AOT C has no such state. Keep `--fork` available, not default. |
+| Exit 0 on regression | benchstat and Criterion both do this, and every user writes a wrapper. |
+| Dynamic runtime test registration | Breaks `--list`, sharding, and individual selection. Registry stays static. |
+
+---
+
+## 12. Phasing
+
+| Phase | Content | Gate |
+|---|---|---|
+| **1** | Registry emission in codegen; 9 builtins; `el_test_main` skeleton in El; result records; per-test timing; human + NDJSON output | existing 11 test files pass, with timing |
+| **2** | `libeltest.a` build model; subtests; filtering; `--list`; fixtures; constraint assertions; JUnit XML | suite runs in one binary; runtime compiled once |
+| **3** | `bench { }`, `bench_loop`, `black_box`, `predictN`, Criterion sampling | benchmarks produce stable ns/op |
+| **4** | Allocation counters; complexity fitting; `expect O(...)` gate | **an `expect allocs O(n)` benchmark on `elc` fails on the current quadratic** |
+| **5** | Migrate both legacy systems; delete `runtime/test.el`; self-host | framework runs its own suite |
+
+Phase 4 is the deliverable that matters. Phases 1–3 exist to make it possible.
+
+---
+
+## 13. Open questions for review
+
+1. **Declarative `over n in [...] expect O(...)` syntax vs runtime calls.** I recommend declarative
+   (§6.1) so `--list` can show invariants without executing. It costs parser work. Your call.
+2. **`bench { }` as a new block form** — parallel to `test { }`, or a modifier on it?
+3. **Scope of the constraint model.** Full composable constraints, or start with a flat assertion set
+   and add constraints later? Full model is more surface but avoids a second migration.
+4. **Does `runtime/test.el` get deleted or kept as a deprecated shim?** I lean delete — two systems
+   is how we got here.
+5. **Where does `libeltest.a` live** in the tree, and does `epm` need to know about it?
+6. **Allocation counters in `el_seed.c` or `el_runtime.c`?** AGENTS.md says `el_seed.c` is the sole
+   C dependency and hand-maintained; counters are OS-boundary-adjacent but not OS calls.
+7. **Is per-test timing enough, or do we want per-*assertion* timing** for finding slow helpers?
+
+---
+
+## 14. What this document is not
+
+This is a design, not a measurement. Every performance claim about the *current* system in §1 is
+measured and reproducible in this worktree. Every claim about the *proposed* system is a prediction.
+None of it is verified until Phase 1 runs and Phase 4 fails a build on the real quadratic.
diff --git a/lang/el-compiler/src/codegen.el b/lang/el-compiler/src/codegen.el
index 57fdbd4..fe1056f 100644
--- a/lang/el-compiler/src/codegen.el
+++ b/lang/el-compiler/src/codegen.el
@@ -2606,6 +2606,17 @@ fn builtin_arity(name: String) -> Int {
     // LSP seed primitives
     if str_eq(name, "__read_n") { return 1 }
     if str_eq(name, "__print_raw") { return 1 }
+    // Test-registry accessors. These are not runtime builtins — they are
+    // GENERATED into the same translation unit by the --test path below, one
+    // set per test binary. They are declared here so the El-side runner in
+    // runtime/eltest.el can call them with a known arity.
+    if str_eq(name, "__el_reg_count") { return 0 }
+    if str_eq(name, "__el_reg_name") { return 1 }
+    if str_eq(name, "__el_reg_invoke") { return 1 }
+    if str_eq(name, "__el_reg_last_ns") { return 0 }
+    if str_eq(name, "__el_reg_msg") { return 0 }
+    if str_eq(name, "__el_reg_asserts") { return 0 }
+    if str_eq(name, "__el_opt_json") { return 0 }
     // String
     if str_eq(name, "el_str_concat") { return 2 }
     if str_eq(name, "str_eq") { return 2 }
@@ -4138,6 +4149,18 @@ fn codegen_streaming(tokens: [Any], sigs: [Map<String, Any>], source: String) ->
         emit_line("  __el_cur_fails++; __el_cur_asserts++;")
         emit_line("}")
         emit_blank()
+        // Forward declarations for the registry accessors. The definitions are
+        // emitted at the END of the unit (they reference the test functions,
+        // which do not exist yet at this point), but the El-side runner is
+        // compiled in between and calls them — so it needs the prototypes here.
+        emit_line("el_val_t __el_reg_count(void);")
+        emit_line("el_val_t __el_reg_name(el_val_t i);")
+        emit_line("el_val_t __el_reg_invoke(el_val_t i);")
+        emit_line("el_val_t __el_reg_last_ns(void);")
+        emit_line("el_val_t __el_reg_msg(void);")
+        emit_line("el_val_t __el_reg_asserts(void);")
+        emit_line("el_val_t __el_opt_json(void);")
+        emit_blank()
     }
 
     // Streaming parse-emit loop.
diff --git a/lang/runtime/eltest.el b/lang/runtime/eltest.el
index b84698b..27e0844 100644
--- a/lang/runtime/eltest.el
+++ b/lang/runtime/eltest.el
@@ -130,6 +130,7 @@ fn _elt_emit_result(json_mode: Bool, name: String, fails: Int, ns: Int, asserts:
         return
     }
     println("ok    " + name + "  (" + _elt_ms(ns) + "ms)")
+    return
 }
 
 fn _elt_emit_summary(json_mode: Bool, total: Int, failed: Int, ns: Int, asserts: Int) {
@@ -149,6 +150,7 @@ fn _elt_emit_summary(json_mode: Bool, total: Int, failed: Int, ns: Int, asserts:
     println(int_to_str(total) + " tests, " + int_to_str(passed) + " passed, "
         + int_to_str(failed) + " failed, " + int_to_str(asserts) + " assertions in "
         + _elt_ms(ns) + "ms")
+    return
 }
 
 // ── The runner ───────────────────────────────────────────────────────────────
diff --git a/lang/tests/native/test_compiler.el b/lang/tests/native/test_compiler.el
index 6798114..84ad5c4 100644
--- a/lang/tests/native/test_compiler.el
+++ b/lang/tests/native/test_compiler.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // tests/native/test_compiler.el — comprehensive tests for the El compiler pipeline.
 //
 // Tests the lexer (lexer.el), parser (parser.el), and codegen (codegen.el)
diff --git a/lang/tests/native/test_core.el b/lang/tests/native/test_core.el
index f4a32c7..dc44ed2 100644
--- a/lang/tests/native/test_core.el
+++ b/lang/tests/native/test_core.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_codegen_js.el - basic tests for JS codegen features.
 //
 // These tests verify that core El language features produce correct values
diff --git a/lang/tests/native/test_env.el b/lang/tests/native/test_env.el
index 4b33e08..8b28a0c 100644
--- a/lang/tests/native/test_env.el
+++ b/lang/tests/native/test_env.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_env.el - native test suite for runtime/env.el
 //
 // Covers: env() for reading environment variables, args() returning a list,
diff --git a/lang/tests/native/test_fs.el b/lang/tests/native/test_fs.el
index 045610f..cf6743d 100644
--- a/lang/tests/native/test_fs.el
+++ b/lang/tests/native/test_fs.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_fs.el - native test suite for runtime/fs.el
 //
 // Covers: fs_write/read round-trip, fs_exists, fs_mkdir, fs_list,
diff --git a/lang/tests/native/test_json.el b/lang/tests/native/test_json.el
index 30da7e3..7190a51 100644
--- a/lang/tests/native/test_json.el
+++ b/lang/tests/native/test_json.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_json.el - native test suite for runtime/json.el
 //
 // Covers: json_get (dot-path), typed extractors (int, bool, float),
diff --git a/lang/tests/native/test_math.el b/lang/tests/native/test_math.el
index 4b3e22f..26dbe7a 100644
--- a/lang/tests/native/test_math.el
+++ b/lang/tests/native/test_math.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_math.el - native test suite for runtime/math.el
 //
 // Covers: integer math (abs, max, min), float math (sqrt, log, sin, cos, pi),
diff --git a/lang/tests/native/test_state.el b/lang/tests/native/test_state.el
index 39f8438..6b05ac0 100644
--- a/lang/tests/native/test_state.el
+++ b/lang/tests/native/test_state.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_state.el - native test suite for runtime/state.el
 //
 // Covers: state_set/get/del, state_has, state_get_or, state_keys,
diff --git a/lang/tests/native/test_string.el b/lang/tests/native/test_string.el
index e9f1192..78fc043 100644
--- a/lang/tests/native/test_string.el
+++ b/lang/tests/native/test_string.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_string.el - native test suite for runtime/string.el
 //
 // Covers: type conversions, core primitives, comparison and search,
diff --git a/lang/tests/native/test_text.el b/lang/tests/native/test_text.el
index 869505d..9b0ac0f 100644
--- a/lang/tests/native/test_text.el
+++ b/lang/tests/native/test_text.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_text.el - native test suite for text primitives.
 //
 // Mirrors the acceptance corpus in tests/text/examples/ using the
diff --git a/lang/tests/native/test_time.el b/lang/tests/native/test_time.el
index c4d8173..6a6d620 100644
--- a/lang/tests/native/test_time.el
+++ b/lang/tests/native/test_time.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // test_time.el - native test suite for runtime/time.el
 //
 // Covers: time_now (positive timestamp), time_to_parts (UTC decomposition),
diff --git a/lang/tests/runtime/string_test.el b/lang/tests/runtime/string_test.el
index 322cb39..cf87afe 100644
--- a/lang/tests/runtime/string_test.el
+++ b/lang/tests/runtime/string_test.el
@@ -1,3 +1,4 @@
+import "../../runtime/eltest.el"
 // tests/runtime/string_test.el — Test suite for runtime/string.el
 //
 // Exercises every public function exported by runtime/string.el using the