plan/checkpoint: #compiler/compiler_call is DELETED not bridged — BuildOptions → abi(.zig) extern compiler

Direction correction (user): the VM does NOT get a transitional compiler_call →
hook-registry shim. BuildOptions is re-expressed as abi(.zig) extern compiler
functions (the compiler-API the VM already dispatches via callCompilerFn), and the
#compiler attribute + compiler_call op + Value-based hook Registry are deleted.

Also record that 4D (host FFI) is DONE via the arena/absolute-pointer allocator
(the earlier pin/tag hazard is moot — the arena never moves an allocation), and
that 0602/0603 stay on legacy fallback until the BuildOptions migration lands.
No code change (reverted the speculative compiler_call bridge).

current/PLAN-COMPILER-VM.md

@@ -408,34 +408,43 @@ are legitimate negative-test bails that BECOME VM diagnostics, 1145 is a scan ar
 - **4C — `#insert` on the VM (role B).** Re-wire `evalComptimeString` through `tryEval`;
   the lowering-time-IR hardening that forced the 0737 revert is already in place. Verify
   the `#insert` corpus parity.
-- **4D — host FFI + `#compiler` hooks on the VM (role D + substrate). The big one.**
-  - **4D.1** Host-FFI escape in `Vm.invoke`: for an extern/bodyless callee not modeled by
-    `callMemBuiltin`, route to `host_ffi` trampolines — marshal each arg (scalar word, or
-    flat `Addr` → real host pointer `machine.mem.items.ptr + addr`), call, map the return.
-    **Central hazard:** flat-memory buffer realloc-on-growth invalidates a live host
-    pointer — PIN the buffer (or copy) while a host pointer is outstanding. (Note: `#run`
-    already calls host extern via the interp today, so host effects at comptime are not a
-    new policy.)
-  - **4D.2** `compiler_call`: route to the hook registry. Transitional shim first — convert
-    flat↔`Value` at the boundary (`regToValue`/`valueToReg`) so hooks work unchanged; then
-    (in 4F) rewrite `HookFn` to a flat-memory ABI to drop `Value`.
-- **4E — post-link bundler on the VM (role C).** Depends on 4D. Route
-  `core.invokeByFuncId` / `main.zig`'s post-link call through the VM. **No corpus
-  coverage** (only runs on `sx build --bundle/--apk`) — add dedicated bundle smoke tests
-  (min `.app` + `.apk`); gate on real bundle builds, not just `zig build test`. Riskiest
-  phase.
+- **4D — host FFI on the VM (role D substrate). DONE.** Solved by a better allocator, not a
+  pin/tag scheme: the comptime memory is now an **arena** of stable host allocations and `Addr`
+  IS a real host pointer (`4D.0`, `625ba0f`), so a flat-memory pointer and an FFI-returned host
+  pointer are the same value — no translation, no realloc hazard. `Vm.callHostExtern`
+  (`4D.1`, `e7a8708`) dispatches ANY extern via `host_ffi` dlsym + trampolines (args/returns pass
+  untouched); `4D.2` (`6a7f690`) adds slice/string args (→ NUL-term `char*`) + float guards.
+  Examples 0636/0637. **(Superseded sub-note:** the earlier "pin the buffer / flat↔host translate"
+  hazard is moot — the arena never moves an allocation.)
+- **`#compiler` / `compiler_call` — NOT bridged on the VM. DELETED, not ported (decision
+  2026-06-18).** `BuildOptions` is RE-EXPRESSED as **`abi(.zig) extern compiler`** functions (the
+  compiler-API surface the VM already dispatches via `callCompilerFn`), and the `#compiler` struct
+  attribute + the `compiler_call` IR op + the `Value`-based hook `Registry` (`compiler_hooks.zig`)
+  all **go away**. So there is NO transitional `compiler_call`→hooks shim on the VM — `0602`/`0603`
+  stay on legacy fallback until this migration lands. Migration shape (part of the end state, with
+  the bundler): (1) each `BuildOptions` setter/getter becomes a `compiler` function in
+  `compiler_lib.bound_fns` + `Vm.callCompilerFn`, reading flat-memory args + a **`BuildConfig`
+  threaded into the VM** (the same `BuildConfig` `main.zig` forwards); (2) `library/modules/build.sx`
+  declares them `abi(.zig) extern compiler` instead of `struct #compiler`; (3) delete the
+  `compiler_call` op, `compiler_hooks.zig`'s `HookFn`/`Registry`, and the `#compiler` parse/lower
+  path. The `BuildConfig` threading is the shared prerequisite with the bundler (4E).
+- **4E — post-link bundler on the VM (role C).** Depends on the FFI escape (done) + the
+  `BuildConfig`-on-the-VM threading above. Route `core.invokeByFuncId` / `main.zig`'s post-link
+  call through the VM. **No corpus coverage** (only runs on `sx build --bundle/--apk`) — add
+  dedicated bundle smoke tests (min `.app` + `.apk`); gate on real bundle builds, not just
+  `zig build test`. Riskiest phase.
 - **4F — flip + delete (the end state).** Flip the VM to default (retire `-Dcomptime-flat`);
-  delete `interp.zig` (`Interpreter`/`Value`/`defineEnum`…/`reflectTypeInfo`/`callExtern`);
-  drop the `regToValue`/`valueToReg` bridge; rewrite `HookFn` to the flat-memory ABI
-  (drops `Value`); simplify `core.zig` (`invokeByFuncId` → VM) + `main.zig` (`last_bail_*`
-  → VM diagnostics); remove the dual-path `compiler_lib` handlers (keep only VM-native
-  `callCompilerFn`); re-express `define`/`make_enum` as sx over the compiler-API (allocation
-  works on the sole evaluator) and land the original 0141 repro as a corpus test.
+  delete `interp.zig` (`Interpreter`/`Value`/`defineEnum`…/`reflectTypeInfo`/`callExtern`); drop
+  the `regToValue`/`valueToReg` bridge; simplify `core.zig` (`invokeByFuncId` → VM) + `main.zig`
+  (`last_bail_*` → VM diagnostics); remove the dual-path `compiler_lib` handlers (keep only
+  VM-native `callCompilerFn`); re-express `define`/`make_enum` as sx over the compiler-API
+  (allocation works on the sole evaluator) and land the original 0141 repro as a corpus test.
 
-**Dependencies:** 4A → (4B, 4C independent) ; 4D → 4E ; all → 4F.
-**Top risks:** (1) flat-pointer escape to host FFI on buffer realloc (4D.1); (2) the bundler
-has no corpus guard (4E needs dedicated tests); (3) `Value` deletion is gated on the
-flat-memory `HookFn` rewrite (4D.2→4F).
+**Dependencies:** 4A → (4B, 4C independent) ; FFI(done)+`BuildConfig`-on-VM → (BuildOptions
+migration, 4E) → 4F.
+**Top risks:** (1) the bundler has no corpus guard (4E needs dedicated tests); (2) deleting
+`#compiler`/`compiler_call` + re-expressing `BuildOptions` over the compiler-API touches the whole
+build/bundle path — stage it behind real bundle builds.
 
 ## Open questions (resolve as reached, record decisions here)