el/docs/v1/experiments/cycles/06-the-crossing-resolves-at-emission.md

# the crossing resolves at emission

One `Ishikawa → scientific method → Six Sigma` loop. The record below is the
commit message as written at the time, before the outcome was known to anyone
reading this file.

## Record — `35b07ba`

```
EXPERIMENT: resolve the crossing at execution, not at emission

HYPOTHESIS (Will's): a compiler whose one compiled mechanism is extending the
LANGUAGE — not the compiler — can compose without recompilation.

ISHIKAWA — why does a construct require a recompile today?
  method       codegen inlines the target call into the body
  machine      the binary has no table to consult
  material     the declaration lives in source, read at compile time
  measurement  nothing observes what applied at runtime
  root cause   the crossing is resolved at EMISSION, not at EXECUTION

CHANGE: codegen emits one unconditional indirection per fn. Which constructs
apply is read from a table that can be written AFTER the binary exists;
targets resolve through dlsym against the running image.

PREDICTIONS AND RESULTS
  P1 a construct declared after the build applies       TRUE
  P2 an unlinked target is skipped, not fatal           TRUE
  P3 emitting on every fn is measurably slower          FALSE — 0.37s -> 0.36s
                                                        with 267 indirections and
                                                        no bindings. Free unused.
  P4 the compiler still self-hosts                      TRUE (see note)

DEMONSTRATED: an El program with NO decorator in its source, already compiled
and linked, picked up a construct declared afterwards:

    $ /tmp/seamrun                       -> 7
    $ echo 'work audited entry audit_entry' > constructs.txt
    $ EL_CONSTRUCTS=constructs.txt /tmp/seamrun
      AUDIT: work applied by audited
      7

P4 note: my first fixpoint test was wrong, not the code. I compared gen1 to
gen2, which must differ whenever codegen's output changes. gen2 == gen3, 267
seam sites, stable.

MEASURED COST, and the root cause was not where I looked
  0 bindings                    0.36s vs 0.37s baseline   free
  2 bindings, dlsym per call    2.45s                     6.6x
  2 bindings, resolved once     0.69s                     3.5x recovered
The table scan was never the cost. dlsym walks the dynamic symbol table on
every call. Resolve once and cache — which is the smallest form of what
salience does for memory: what is hot stays resolved. The 0.69s residual is
audit_entry's own printf on two of the compiler's hottest functions, not seam
overhead.

CONSEQUENCE: the five compile-time declaration kinds on iteration-1 are a
compile-time specialisation of something that resolves at runtime. They are not
wrong, but they are not the mechanism — the mechanism is one indirection, and a
kind is data.
```

## Record — `886626a`

```
seam refusal + control tests: a runtime binding can short-circuit

Prediction 3 was FALSE. I expected refusal to be impossible through the seam
because the entry indirection discarded its return. One line:

    { el_val_t __s = el_seam_run(EL_STR(f), 0, 0); if (__s) return __s; }

work() returns 7; bound to a refusing construct AFTER the build it returns 42.
So three of the five compile-time kinds are runtime-bindable: entry injection,
exit injection, and refusal. wraps_body needs invocation control and
prohibits_outside is compile-time by nature.

104/104 native compiler tests pass.
```

## Record — `28d19da`

```
strip the compile-time machinery the seam replaces

PREDICTION: codegen.el drops below 4661, its size before any of these passes.
RESULT: FALSE. 5157 -> 5096. Still +435 over baseline.

  injects_at_entry   collapsed into the seam            removed
  guards_at_entry    collapsed into the seam            removed
  injects_at_exit    needs the body-helper wrapper      STRUCTURAL
  wraps_body         needs the closure + wrapper        structural
  prohibits_outside  a #error cannot be emitted at runtime

The wrapper is not a consequence of compile-time resolution. Early returns must
be routed through something no matter when the target is resolved, so exit
injection was never going to collapse. I predicted it would because I had
conflated "resolved late" with "emitted less".

What did collapse is entry injection and refusal -- 61 lines of compiler
replaced by one refusable indirection, with the capability now bindable after
the binary exists.

8 tests fail, and they are exactly the 8 controls for compile-time entry
injection and guards. No unrelated breakage: the controls reported precisely
what moved. They assert emission of something that now happens at runtime, so
they need rewriting as integration tests -- which the framework does not
currently support, because runtime binding needs a built binary and an
environment, not compile_capture.

Verified after the strip: fixpoint gen2==gen3, observation and refusal both
work through the seam with the compiler knowing nothing about either.
```

## Record — `8bbb750`

```
control the claim that cannot be unit tested

The seam's whole claim is that a construct declared AFTER a binary exists
applies to that already-built program. compile_capture only sees emitted text,
so it structurally cannot check this: it needs a built binary, a linked target,
and an environment. Verified by hand until now, which is the standing problem
this session has been about.

tests/integration/seam_binding.sh builds a probe from El source containing no
construct at all, links a target that El never references, and asserts:

  ok  unbound program is unaffected
  ok  a construct declared AFTER the build applies
  ok  a construct declared after the build can REFUSE
  ok  an unlinked target is skipped, not fatal
  ok  a binding for a different fn does not fire
  ok  two constructs compose on one crossing

  6 assertions, 6 passed, 0 failed

The eight controls that failed after the strip were replaced, not repaired.
They asserted compile-time emission of capability that moved to runtime;
contorting them would have kept an assertion whose subject no longer exists.
Three took their place, asserting the emitted shape, and the behaviour they
used to cover is now the integration harness's job -- which is the honest
division, since the shape and the behaviour are no longer the same fact.

99/99 native compiler tests pass. Fixpoint holds.
```

## Record — `24f7fb5`

```
land the runtime seam: resolve the crossing at execution

Five compile-time passes added 491 lines to the thing that was supposed to stop
growing. The seam is ~55 lines of C and one line of emission, and it does at
runtime what three of those five kinds did at compile time -- for programs that
are already built.

  a construct declared AFTER the binary exists applies to it
  free when unused: 0.36s vs 0.37s baseline across 267 indirections
  dlsym was the cost, not the table scan; resolve-once recovered 3.5x
  refusal works, composition works, unlinked targets are skipped not fatal

injects_at_exit and wraps_body do NOT collapse: early returns must route
through the body-helper wrapper regardless of when the target is resolved. The
wrapper is structural, which I had wrong. prohibits_outside cannot move at all
-- a #error has no runtime.

Controls: 99/99 native compiler tests, plus tests/integration/seam_binding.sh
(6/6) for the claim compile_capture structurally cannot see.
```