ir: whole-program passes pin the source context per decl (fix 0122)

convergeClosureShapeSets, checkErrorFlow, and the unknown-type loop ran
under whatever current_source_file the previous phase left behind —
closure-literal annotations resolved (and reject/unknown-type
diagnostics rendered) against an arbitrary module. Latent while std.sx
was a single file (the ambient happened to be the main file); the
re-export facade restructure exposed it. Each walk now pins
setCurrentSourceFile per decl / per fn (body.source_file is already
stamped by resolveImports). Coverage: examples 0129/1047/1049/1052/
1053/1056 against the facade std.sx. Gates: zbt 426/426, suite 588/588.

issues/0122-whole-program-passes-ambient-source-context.md

@@ -0,0 +1,64 @@
+# 0122 — whole-program passes resolve/diagnose under a stale ambient source
+
+> **RESOLVED** (2026-06-11, same session — found and fixed during the
+> std.sx-as-pure-re-exports restructure, Agra-directed). Three
+> whole-program passes ran under whatever `current_source_file` the
+> previous pipeline phase happened to leave behind, instead of pinning
+> the context per declaration:
+>
+> 1. `ErrorAnalysis.convergeClosureShapeSets` (error_analysis.zig) —
+>    resolves closure-literal param/return annotations; a stale context
+>    made example-declared nominal types (`Point`, `Color`) fail the E4
+>    visibility gate with `type 'X' is not visible` attributed to
+>    nonsense std.sx spans. Fixed: pin `setCurrentSourceFile` per
+>    `fn_ast_map` entry from `body.source_file` (already stamped by
+>    resolveImports).
+> 2. `ErrorFlow.checkErrorFlow` (error_flow.zig) — the flow walk
+>    resolves types via `inferExprType` AND emits its reject
+>    diagnostics; both used the ambient file. Fixed: pin per decl.
+> 3. The `UnknownTypeChecker` unknown-type loop
+>    (semantic_diagnostics.zig) — emitted with the ambient file
+>    (`checkBindingNames` beside it already saved/restored per node).
+>    Fixed: pin `diagnostics.current_source_file` per decl.
+>
+> Latent on master for all three — the ambient just happened to be the
+> main file with the old single-file std.sx; the restructured std.sx
+> (namespace part-file imports) reordered the pipeline's last-touched
+> module and exposed them. Pinned coverage: examples 0129 / 1047 /
+> 1049 / 1052 / 1053 / 1056 (closure shapes with nominal types,
+> error-flow reject attribution) fail without the fixes once std.sx is
+> the re-export facade. Gates: zig build test 426/426, suite 588/588.
+
+## Symptom
+
+With a std.sx whose first declarations are namespace imports, programs
+using closures with user-struct parameter types failed
+`type 'Point' is not visible; #import the module that declares it`
+attributed to meaningless std.sx spans, and error-flow / unknown-type
+diagnostics for main-file code rendered against std.sx's line table
+(e.g. expected `examples/foo.sx:22:21`, got `std.sx:16:25`).
+
+## Reproduction
+
+Against the pre-fix compiler with the re-export std.sx:
+
+```sx
+#import "modules/std.sx";
+Point :: struct { x, y: s32; }
+main :: () {
+    f := closure((p: Point) -> Point => Point.{ x = p.x + 1, y = p.y });
+    r := f(Point.{ x = 1, y = 2 });
+    out("done\n");
+}
+```
+
+## Investigation prompt
+
+(Resolved — kept for the record.) The root pattern: any pass that runs
+after module scanning and either resolves source-gated names or emits
+diagnostics MUST pin the visibility/rendering context per declaration
+(`setCurrentSourceFile(decl.source_file)` — syncs the lowering context
+and the diagnostics renderer), never inherit the ambient. Fn bodies
+carry `body.source_file` (stamped by resolveImports) for fn-keyed
+walks. When auditing for siblings, check every `lowerRoot` phase that
+walks `fn_ast_map` or the program decl list.