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-core/tests/design_schema_drift.rs

@@ -282,6 +282,7 @@ fn design_md_anchors_every_def_kind() {
         ty: Type::fn_implicit(vec![], Type::int(), vec![]),
         params: vec![],
         body: Term::Lit { lit: Literal::Int { value: 0 } },
+    export: None,
     };
     let const_def = ConstDef {
         name: "k".into(),

crates/ailang-core/tests/embed_export_hash_stable.rs

@@ -0,0 +1,35 @@
+//! Additive-field hash stability (Embedding-ABI M1): adding
+//! `FnDef.export: Option<String>` with
+//! `#[serde(default, skip_serializing_if = "Option::is_none")]`
+//! must leave every pre-M1 canonical-JSON hash bit-identical when
+//! `export` is `None`. A round-trip-able fixture WITHOUT `export`
+//! hashes identically to a hand-frozen pre-M1 golden.
+//!
+//! The hashing entry point is `ailang_core::hash::def_hash(&Def)` —
+//! the exact one `crates/ailang-core/tests/hash_pin.rs` uses (the
+//! plan's `content_hash_fn(&FnDef)` symbol does not exist; the plan
+//! NOTE authorises mirroring `hash_pin.rs`'s entry point when the
+//! name differs). The golden below was captured pre-field via
+//! `def_hash` on the same `f : (Int)->Int / body=x` shape.
+
+use ailang_core::ast::*;
+use ailang_core::hash::def_hash;
+
+#[test]
+fn fn_without_export_hash_is_unchanged() {
+    // A minimal pre-M1-shaped fn (no export). Its content hash must
+    // equal the value captured before the field existed.
+    let def = Def::Fn(FnDef {
+        name: "f".into(),
+        ty: Type::fn_implicit(vec![Type::int()], Type::int(), vec![]),
+        params: vec!["x".into()],
+        body: Term::Var { name: "x".into() },
+        doc: None,
+        suppress: vec![],
+        export: None,
+    });
+    // GOLDEN: captured pre-field (Step 2) from `def_hash` on this shape.
+    let golden = "b4662aa70839f60b";
+    assert_eq!(def_hash(&def), golden,
+        "pre-M1 fn hash drifted — additive-field invariant violated");
+}

crates/ailang-core/tests/hash_pin.rs

@@ -45,6 +45,7 @@ fn sample_fn() -> Def {
         },
         suppress: vec![],
         doc: None,
+    export: None,
     })
 }
 

crates/ailang-core/tests/spec_drift.rs

@@ -260,6 +260,7 @@ fn spec_mentions_every_def_kind() {
         ty: Type::fn_implicit(vec![], Type::int(), vec![]),
         params: vec![],
         body: Term::Lit { lit: Literal::Int { value: 0 } },
+    export: None,
     };
     let const_def = ConstDef {
         name: "k".into(),