iter embedding-abi-m1.1 (PARTIAL 3/7): schema + surface + baseline prerequisites; plan Repair

Tasks 1-3 of docs/plans/embedding-abi-m1.1.md, a verified known-good
subset (cargo build --workspace exit 0; full workspace green; the
roundtrip_cli all-examples gate green):

- Task 1: CLI build-path MissingEntryMain baseline pin
  (examples/embed_noentry_baseline.ail + embed_missing_main_baseline.rs;
  triple-assertion, layered on the green codegen-unit pin lib.rs:3314).
- Task 2: additive FnDef.export: Option<String> (serde default +
  skip_serializing_if, modelled on FnDef.doc); compile-driven thread
  of export: None across ~85 FnDef/AstFnDef literals / 18 files incl.
  all in-source #[cfg(test)] mod tests + drift/hash/spec-drift
  literals + the codegen lib.rs:3320 in-source pin; hash-stability
  golden pin; DESIGN.md fn-JSON "export" line. DONE_WITH_CONCERNS
  (plan symbol content_hash_fn -> def_hash per hash_pin.rs, plan-
  pseudo-vs-reality class, plan corrected).
- Task 3: Form-A (export "<sym>") modifier — parse_export +
  parse_fn thread + write_fn_def emission + form_a.md grammar;
  byte-identical round-trip.

Task 4 BLOCKED (Boss plan-defect: fixtures declared module != file
stem; AILang's loader hard-enforces module==stem at workspace.rs:438,
so ail check panicked on load before the gate). Boss resolution
(Option 2, overriding the orchestrator's Option 1, rationale in the
journal + plan Design-decision 6): keep descriptive embed_* filenames,
rename fixture MODULES to their stems — the C symbol backtest_step
stays via (export ...), demonstrating spec Decision 2's mangling-
decoupling rather than violating it; archive becomes
libembed_backtest_step.a, internal symbol @ail_embed_backtest_step_step,
host.c unchanged. Plan fixed (Design-decision 6 + Task-4 module==stem
+ Task-5/6/7 dependent strings + the no-*. Float-head + content_hash_fn
concerns folded). Headline fixture corrected; blocked-Task-4 WIP
discarded (recreated by the [4,7] re-dispatch from the fixed plan).

PARTIAL commit (not the iter's final commit): the implement Repair
path mandates committing the known-good subset so the [4,7]
re-dispatch starts from a clean tree that includes Tasks 1-3 (Tasks
4-7 structurally depend on the schema field + surface). INDEX line
added when the full iter lands post-re-dispatch.

crates/ailang-surface/src/print.rs

@@ -156,6 +156,13 @@ fn write_fn_def(out: &mut String, fd: &FnDef, level: usize) {
         write_string_lit(out, doc);
         out.push(')');
     }
+    if let Some(export) = &fd.export {
+        out.push('\n');
+        indent(out, level + 1);
+        out.push_str("(export ");
+        write_string_lit(out, export);
+        out.push(')');
+    }
     // Iter 19b: emit one `(suppress ...)` clause per entry, after the
     // doc string and before the type. Round-trip stable: parser
     // re-reads each clause back into [`FnDef::suppress`].
@@ -779,6 +786,7 @@ mod tests {
                 params: vec!["x".into()],
                 body: Term::Var { name: "x".into() },
                 doc: None,
+                export: None,
                 suppress: vec![],
             })],
         };