P5.2 metadata queries: c_object_paths / link_libraries on the VM

Two abi(.compiler) build-pipeline primitives the sx driver will pass to link:
- c_object_paths() -> List(string)  (#import c companion objects)
- link_libraries() -> List(string)  (#library names)

They live in a new stdlib home library/modules/std/build.sx and are serviced
by comptime_vm.callCompilerFn reading two new BuildConfig fields that main.zig
forwards before the post-link callback. New reusable VM helper makeStringList
builds a List(string) in flat memory from the call's result type offsets
(target-aware); invoke/callCompilerFn now thread ins.ty for that. Legacy
handlers bail loudly (VM-only by nature — post-link; List(string) isn't
faithfully buildable in the legacy Value model, 0141).

Smoke test examples/1662-platform-build-pipeline-queries (AOT + a 1-line C
#source → one object): a post-link callback verifies the VM-built list is
well-formed; build exit 0 only if so (negative-probe confirmed a real guard).

emit_object + link (the actions) deferred to P5.2b — they replace the Zig
driver's auto-emit/auto-link and need a host-installed callback vtable.

703/0 both gates.

current/CHECKPOINT-COMPILER-API.md

@@ -86,10 +86,20 @@ with ONE welded mechanism. Branch: `reify` (off `master`). Update after every st
 > in; VM bail → hard build error (`comptime_vm.last_bail_reason` surfaced by `main.printInterpBailDiag`). Smoke
 > test `1661-platform-post-link-vm-list` (AOT) — a post-link callback that GROWS a `List` (0141: works on VM,
 > bails on legacy with `struct_get`); build succeeds (exit 0) only via the VM. `flushInterpOutput` deleted (VM
-> writes `out` direct via host-FFI). **702/0 both gates.** **NEXT — P5.2:** expose `emit_object` + `link`
-> (reuse `target.zig`) + metadata queries (`c_object_paths`/`link_libraries`/host-triple) as `abi(.compiler)`
-> primitives taking EXPLICIT args. Then P5.3 (`on_build` slot — invoke WITH the `BuildConfig` arg; needs a VM
-> entry that marshals args, the gap `invokeByFuncId` rejects today) · P5.4 (sx `default_build` + delete
+> writes `out` direct via host-FFI). **702/0 both gates.** **P5.2 metadata queries DONE (2026-06-19, newest Log
+> entry):** `c_object_paths() -> List(string)` + `link_libraries() -> List(string)` are `abi(.compiler)` primitives
+> (new stdlib home `library/modules/std/build.sx`), serviced by `comptime_vm.callCompilerFn` reading `BuildConfig`
+> fields `main.zig` forwards (`c_object_paths`/`link_libraries`). New reusable VM helper `makeStringList` builds a
+> `List(string)` in flat memory (target-aware via the result type's offsets); `invoke`/`callCompilerFn` now thread
+> the call's result type (`ins.ty`). Legacy handlers bail loudly (VM-only by nature — post-link). Smoke test
+> `1662-platform-build-pipeline-queries` (AOT, C companion → 1 object): a post-link callback checks the VM-built
+> list is well-formed; build exit 0 ONLY if so (negative-probe verified: wrong count → "post-link callback
+> returned false", exit 1). **703/0 both gates.** **NEXT — P5.2b: `emit_object` + `link` (the ACTIONS).** These
+> are NOT data reads — in the end state the Zig driver stops auto-emitting/auto-linking and the sx driver calls
+> them, so they need the driver-restructuring (a callback vtable the host installs into the VM, since
+> `comptime_vm.zig` can't depend on `core`/`main`/`target`). `link` is fallible (`-> !`) — its failable return
+> shape is the new VM piece. Then P5.3 (`on_build` slot — invoke WITH the `BuildConfig` arg; needs a VM entry
+> that marshals args, the gap `invokeByFuncId` rejects today) · P5.4 (sx `default_build` + delete
 > `#compiler`/`compiler_call`/`compiler_hooks` + the S5a `build_options`/`set_post_link_callback`) — P5.4 kills
 > the 4 strict `compiler_call` bails (1609/1614/1615/1616).
 > **FINAL atomic step (4F):** (`out` already done — VM-native via libc `write`) handle `interp_print_frames` +
@@ -403,6 +413,28 @@ when reached (sentinels or accessor fns; see the design doc Risks).
   `List` growth; orthogonal, see `current/CHECKPOINT-METATYPE.md`.)
 
 ## Log
+- **P5.2 (metadata queries) — `c_object_paths` / `link_libraries` compiler primitives + the VM `List(string)` builder (2026-06-19).**
+  Phase 5 step 2 (the read-only slice): two `abi(.compiler)` primitives that the sx build driver will pass to
+  `link` — `c_object_paths() -> List(string)` (the `#import c` companion `.o`s) and `link_libraries() -> List(string)`
+  (the `#library` names). They live in a NEW stdlib file `library/modules/std/build.sx` (the Phase 5 home the sx
+  `default_build` grows into) and are serviced by `comptime_vm.callCompilerFn` reading two new `BuildConfig`
+  fields (`c_object_paths`/`link_libraries`) that `main.zig` forwards before the post-link callback (alongside
+  `binary_path`/`target_triple`/…). **Reusable new piece:** `Vm.makeStringList(table, list_ty, items)` builds a
+  `List(string)` in flat memory — backing array of `string` fat pointers + the `{items,len,cap}` struct, all laid
+  out from the RESULT type's field offsets/types (target-aware, no hardcoded layout). To get the result type,
+  `invoke`/`callCompilerFn` now thread the call instruction's `ins.ty` (the only call-result-type need so far).
+  Legacy (`compiler_lib`) handlers for these bail loudly (`handleBuildPipelineQuery`) — they're VM-only by nature
+  (the post-link callback always runs on the VM since P5.1), and a `List(string)` isn't faithfully buildable in
+  the legacy `Value` model (0141). Registered on `bound_fns` so `weldedCompilerFn` recognizes them. **Smoke test**
+  `examples/1662-platform-build-pipeline-queries` (AOT + a 1-line C `#source` → exactly one C object): a post-link
+  callback asserts `c_object_paths().len == 1`, `items[0].len > 0`, and iterates `link_libraries()` (liveness
+  touch) — build exit 0 only if the VM-built list is well-formed. **Negative-probe verified** a real guard (forcing
+  `len != 2` → "post-link callback returned false", build exit 1). **No unit test for `makeStringList`** —
+  constructing a `List(string)` `TypeId` in the test harness needs generic instantiation; the corpus test
+  exercises the real stdlib type end-to-end with a non-empty list + a negative guard instead. **`emit_object` +
+  `link` (the ACTIONS) deferred to P5.2b** — they must replace the Zig driver's auto-emit/auto-link (not duplicate
+  it), so they need the driver-restructuring + a host-installed callback vtable (the VM can't depend on
+  `core`/`main`/`target`). **703/0 both gates** + strict JIT run clean (no `compiler_call` bail).
 - **P5.1 (= 4E) — the post-link build driver runs on the VM (NO fallback); smoke test 1661 (2026-06-19).**
   Phase 5 step 1: `core.invokeByFuncId` — the post-codegen / post-link callback invocation `main.zig` fires after
   `target.link` — now routes the callback through the **comptime VM** (`comptime_vm.tryEval`) instead of the

current/PLAN-COMPILER-VM.md

@@ -504,8 +504,15 @@ The compiler's whole post-IR role: codegen → build the CLI-derived `BuildConfi
   `examples/1661-platform-post-link-vm-list` (AOT): a post-link callback GROWS a `List` (0141 — works on the VM,
   bails on legacy with `struct_get`), so the build succeeds (exit 0) only via the VM. Non-empty callback `args`
   rejected loudly (the `on_build(config)` arg-marshaling entry is P5.3). **702/0 both gates.**
-- **P5.2 — primitives:** expose `emit_object` + `link` (reuse `target.zig` linker) + metadata queries
-  (`c_object_paths`/`link_libraries`/host-triple) as `abi(.compiler)` fns taking explicit args.
+- **P5.2 — primitives.** Split: the read-only **metadata queries are DONE (2026-06-19)** — `c_object_paths() ->
+  List(string)` + `link_libraries() -> List(string)` as `abi(.compiler)` fns (stdlib `library/modules/std/build.sx`),
+  serviced by `comptime_vm.callCompilerFn` over `BuildConfig` fields `main.zig` forwards; new VM `makeStringList`
+  builds the `List(string)` in flat memory from the call's result type (`ins.ty` now threaded through
+  `invoke`/`callCompilerFn`). Smoke test `1662-platform-build-pipeline-queries` (AOT + C companion). 703/0 both
+  gates. **P5.2b — the ACTIONS (`emit_object -> !string`, `link(...) -> !`, reuse `target.zig`):** still TODO —
+  they replace the Zig driver's auto-emit/auto-link, so they need the driver restructuring + a host-installed
+  callback vtable (`comptime_vm.zig` can't depend on `core`/`main`/`target`); `link`'s fallible `-> !` return is
+  the new VM shape.
 - **P5.3 — `on_build` slot:** a comptime-assignable compiler slot (GENERALIZES today's `post_link_callback_fn`:
   an assignable typed global with a stdlib default, vs a setter). `#run on_build = build;` captures the
   `FuncId`; the compiler invokes it post-codegen with the CLI-derived `BuildConfig`.