docs(ffi-linkage): note -Dupdate-goldens churn resolved (1-byte conform)

current/CHECKPOINT-EXTERN-EXPORT.md

@@ -202,10 +202,14 @@ Part A ratified (bare / postfix / `⇒ callconv(.c)` / lib-separate). Part B:
 - (4.diag2) Added `examples/1175-diagnostics-extern-export-conflict.sx` — `extern export` on
   one fn decl previously gave bare "expected ';'". `xfail` (golden = clean message) → `green`:
   `parseFnDecl` rejects a second linkage keyword after `parseOptionalExternExport`. Suite
-  green (643/444). **PHASE 4 COMPLETE → PART A DONE.** (Workflow note: `-Dupdate-goldens`
-  keeps newline-normalizing the 5 empty-stderr files [1226/1227/1348/1349/1426] — revert
-  that churn after each regen; a flaky `0712-sha256-streaming` timeout appears only under
-  concurrent `zig build` load, not a real failure.)
+  green (643/444). **PHASE 4 COMPLETE → PART A DONE.**
+- (golden-fix) **`-Dupdate-goldens` churn RESOLVED.** Root cause was NOT a code bug:
+  `writeGolden` always writes `content + "\n"` (empty → canonical 1-byte `\n`, used by 484
+  of 489 empty goldens). The 5 churning stderr files [1226/1227/1348/1349/1426] were 0-byte
+  *outliers* (verify trims trailing `\n` so both forms passed, but regen always rewrote them
+  to 1-byte). Conformed all 5 to the 1-byte form → `-Dupdate-goldens` is now idempotent, no
+  more churn. (Separately: a flaky `0712-sha256-streaming` >10s timeout appears only under
+  concurrent `zig build` load — not a real failure; re-run serially.)
 
 ## Known issues
 - **Workflow hazard (1.2):** an editor format-on-save (or `zig fmt`) clobbered the