iter raw-buf.6 kernel-stub-retirement (DONE 5/5): retire the stub, raw_buf is the sole base extension (refs #7)

Closes the raw-buf milestone. raw_buf (shipped raw-buf.1-.5; the
owned-drop resolution landed under bug #42/#43) has subsumed every
ratification role kernel_stub held -- Term::New end-to-end, the
param-in reject, kernel-tier auto-import, the monomorphic intrinsic
path, and the type-scoped polymorphic intrinsic mechanism (RawBuf's
four ops). The stub is now redundant; this iteration removes it.

Pure removal (-636/+49 across 22 files, 7 deleted):
- Rust surface: drop `mod kernel_stub` + `STUB_AIL` re-export
  (ailang-kernel), `parse_kernel_stub` + its workspace injection
  (ailang-surface), the `answer` + two `StubT_peek__{Int,Float}`
  INTERCEPTS entries + their three emit fns (ailang-codegen). The
  (intrinsic) markers leave with the deleted source, so the
  marker<->entry bijection holds in lockstep.
- Source + tests: delete crates/ailang-kernel/src/kernel_stub/,
  kernel_stub_module_round_trips, the two stub-consumer e2e tests,
  and mono_scoped_symbol.rs (its scope-qualified-mono mechanism is
  now pinned by RawBuf's ops + the intercepts bijection).
- Fixtures: delete kernel_answer.ail, new_stubt_smoke.ail,
  peek_mono_pin_smoke.ail, and fieldtest kem_3_stub_consumer.ail
  (referenced the deleted StubT; documented a since-fixed bug).
- Pins: re-baseline both workspace-count content-pins 5 -> 4
  (workspace_pin.rs + the e2e.rs twin) and regenerate all five IR
  snapshots (400 stub-IR lines removed; no user IR changed -- the
  stub auto-injected into every build).
- Ledger: design/INDEX.md + design/models/0007 to present-state
  (raw_buf is the live ratifier; raw-buf milestone shipped, series
  pending), plus architecture-comment sweep across workspace.rs,
  mono.rs, check/codegen lib.rs, workspace_kernel.rs.

Scope decisions (orchestrator, pre-plan): the self-contained inline
serde_json check-layer fixtures in ailang-check/src/lib.rs keep their
incidental StubT/kernel_stub sample names (they construct what they
reference; not stub-ratification) -- the one permitted residual.
kem_4 fieldtest kept (uses a user NumBox ADT, comment-only edit).
hash.rs `name: "answer"` left (generic serde doc example).

Plan-gap caught at implement: the planner's verbatim edit list
under-enumerated four honesty sites; one (mono.rs:562) carried a
literal `StubT_peek__Int` -- a hard-gate symbol the verbatim list
missed, which would have failed Task 4's removal gate. Filled
(comment-only, no behaviour). Confirms the planner self-review
filter-completeness risk; the implement gate caught it.

Verification: full workspace suite green (0 failed); hard symbol gate
(STUB_AIL|parse_kernel_stub|emit_answer|emit_stubt_peek|StubT_peek__)
zero matches across crates/ examples/ design/; soft gate residual only
the kept inline fixtures; kernel crate is lib.rs + raw_buf/ only.
Regression: compile_check 24/24 stable (exit 0; uniform downward
check_ms within tol -- stub no longer parsed per compile), cross_lang
25/25, check 34/34 stable (exit 0; an earlier exit-1 on
rc_over_bump was machine-load ratio noise -- denominator bump_s got
faster, rc_s also improved -- confirmed green on re-run, not
baselined).

crates/ailang-kernel/src/kernel_stub/mod.rs

@@ -1,16 +0,0 @@
-//! Kernel-stub submodule — minimal ratifying fixture for the
-//! kernel-extension-mechanics milestone (prep.3). The Form-A text
-//! lives in the sibling `source.ail`.
-//!
-//! No domain content. Retired when the `raw-buf` milestone lands
-//! its real kernel-tier consumer (raw-buf.4); until then it stays
-//! as the ratifying-fixture anchor.
-
-/// Source-of-truth Form-A text for the stub kernel module. Parsed
-/// by `ailang_surface::parse_kernel_stub` (and round-trip-pinned by
-/// `kernel_stub_module_round_trips` in `design_schema_drift.rs`).
-///
-/// Ships a `(fn new ...)` def so consumers can spell `(new StubT 42)`
-/// (Term::New end-to-end, per prep.3 fieldtest F4) and an `answer`
-/// `(intrinsic)` fn whose `INTERCEPTS` entry the bijection test pins.
-pub const SOURCE: &str = include_str!("source.ail");

crates/ailang-kernel/src/kernel_stub/source.ail

@@ -1,20 +0,0 @@
-(module kernel_stub
-  (kernel)
-  (data StubT (vars a)
-    (ctor Stub a)
-    (param-in (a Int Float)))
-  (fn new
-    (doc "Construct StubT<Int> from an Int. Exercises Term::New end-to-end.")
-    (type (fn-type (params (con Int)) (ret (con StubT (con Int)))))
-    (params x)
-    (body (term-ctor StubT Stub x)))
-  (fn answer
-    (doc "Ratifies the intrinsic mechanism end-to-end: codegen intercept answer emits ret i64 42.")
-    (type (fn-type (params) (ret (con Int))))
-    (params)
-    (intrinsic))
-  (fn peek
-    (doc "Ratifies the type-scoped polymorphic intrinsic mechanism: StubT.peek is polymorphic over a (param-in {Int,Float}) and type-scoped to StubT. Codegen intercepts StubT_peek__Int / StubT_peek__Float emit a load of the Stub payload. Retires with the stub in raw-buf.5.")
-    (type (forall (vars a) (fn-type (params (borrow (con StubT a))) (ret a))))
-    (params s)
-    (intrinsic)))

crates/ailang-kernel/src/lib.rs

@@ -5,11 +5,9 @@
 //!
 //! The acyclic dependency chain is preserved:
 //! `ailang-surface → ailang-kernel → ailang-core`. Per-module parse
-//! hops live in `ailang-surface` (`parse_kernel_stub`, …) so this
+//! hops live in `ailang-surface` (`parse_raw_buf`, …) so this
 //! crate carries zero parser code.
 
-mod kernel_stub;
 mod raw_buf;
 
-pub use kernel_stub::SOURCE as STUB_AIL;
 pub use raw_buf::SOURCE as RAW_BUF_AIL;