fix(lower): #insert-expansion visibility exemption + close 0106 [stdlib B attempt-2]

Folds the coupled 0106 fix into Phase B. attempt-1 tightened the bare-name
visibility adapters (isNameVisible/isCImportVisible) to the flat_import_graph
edge set via the unified isVisible(.user_bare_flat/.c_import_bare) predicate;
that surfaced issue 0106 — std.print / log.* expand `#insert build_format(fmt)`
(comptime call) and `#insert "out(result);"` (inserted stmt) in the CONSUMER's
current_source_file, so their library-internal bare names were policed against
the consumer's imports and errored (run_examples 471 -> 467).

Fix: a precise, named exemption. Lowering.in_insert_expansion is set across
lowerInsertExprValue (the comptime eval + the parsed-back statements); the two
visibility adapters fall open while it is set — mirroring the existing
UFCS-alias / mangled-local "compiler indirection" exemptions. NOT a blanket
skip: scoped to #insert-expanded code, ordinary bare references stay policed.
Library-internal call bodies (build_format's concat/substr) already resolve in
the defining module — lowerFunctionBodyInto pins their current_source_file.

The flat tightening stays: a bare reference to a namespaced-only import's
internal name now correctly errors ('<name>' is not visible). This is the
Agra-ratified user-visible semantics change.

- face #1 pinned: examples/0736-modules-namespaced-only-bare-not-visible.sx
  (+ a.sx) — exit 1 + stderr; fail-before (import_graph compiled it, exit 0) /
  pass-after (flat set errors, exit 1).
- face #2 restored: examples 0015 / 0700 / 0718 / 1030 pass again.
- run_examples 471 -> 472 (the new regression).
- issues/0106 marked RESOLVED; readme.md documents namespaced-only visibility.

Collectors + unified predicate from attempt-1 (resolver.zig) unchanged; nothing
routes resolution AUTHOR-SELECTION through them yet (that is Phase C).

issues/0106-namespaced-import-bare-visibility-over-permissive.md

@@ -1,5 +1,36 @@
 # 0106 — namespaced-import internal names are silently bare-visible (over-permissive `isNameVisible`)
 
+> **RESOLVED** (flow stdlib/B attempt-2). Two coupled changes:
+>
+> 1. **Tightened bare visibility to the flat edge set.** `isNameVisible` /
+>    `isCImportVisible` now route through the unified `isVisible` predicate over
+>    `user_bare_flat` / `c_import_bare` (both join over `flat_import_graph`, not
+>    `import_graph`). A namespaced-only import's internal name is no longer
+>    bare-visible — face #1 now errors `'<name>' is not visible; #import the
+>    module that declares it`.
+> 2. **`#insert`-expansion visibility exemption.** The flat tightening alone broke
+>    `std.print` / `log.*`: a library metaprogram's `#insert build_format(fmt)`
+>    (comptime call) and `#insert "out(result);"` (inserted statement) expand in
+>    the CALL SITE's `current_source_file`, so their bare names (`build_format`,
+>    `out`, `emit`) were policed against the consumer's imports. Fix: a precise,
+>    named exemption — `Lowering.in_insert_expansion` is set across
+>    `lowerInsertExprValue` (the comptime eval + the parsed-back statements), and
+>    `isNameVisible` / `isCImportVisible` fall open while it is set. This mirrors
+>    the existing UFCS-alias / mangled-local "compiler indirection" exemptions; it
+>    is NOT a blanket skip (it scopes to `#insert`-expanded code; ordinary bare
+>    references are still policed). Library-internal call bodies (e.g.
+>    `build_format`'s `concat` / `substr`) already resolve correctly — they lower
+>    via `lowerFunctionBodyInto`, which pins `current_source_file` to the defining
+>    module.
+>
+> Root cause: `isNameVisible` walked `import_graph` (flat AND namespaced edges)
+> where a bare name should join only over `flat_import_graph`.
+> Regression: `examples/0736-modules-namespaced-only-bare-not-visible.sx` (+
+> `0736-…/a.sx`) — face #1 pinned (exit 1 + the stderr). Face #2 restored:
+> `examples/0015 / 0700 / 0718 / 1030` pass again (`run_examples` 471 → 472).
+> Fix in `src/ir/lower.zig` (`in_insert_expansion` + the two adapters) +
+> `src/ir/resolver.zig` (`VisibilityMode` modes, landed in attempt-1).
+
 **Symptom.** A bare reference to a top-level name authored in a module that the
 consumer imports **only namespaced** (`ns :: #import "m.sx"`) is silently
 visible from the consumer. Observed: it compiles + runs. Expected: an error —