build: REDBEAR_SKIP_ABI_STALENESS for fast single-recipe iteration

Iterating on one recipe (e.g. redbear-iwlwifi) forced a ~30-min re-churn every
rerun: the relibc-consumer invalidation (build/sysroot wipe + pkgar/target
deletion) re-cooked dozens of cached packages before reaching the edited one,
even when relibc was unchanged. Add REDBEAR_SKIP_ABI_STALENESS=1 to skip both
the layer-B build/sysroot clean and the layer-C invalidation loops. The
cookbook BLAKE3 dep-hash cache still re-cooks recipes whose sources changed, so
the edited package rebuilds while everything else stays cached — the rerun goes
straight to it. Safe only when relibc ABI is unchanged (documented + escape is
opt-in); unset to restore the stale-binary safety net when bumping relibc/base.
Documented in --help alongside REDBEAR_FORCE_TOOLCHAIN_RECOOK.

local/scripts/build-redbear.sh

@@ -284,6 +284,15 @@ Configs:
 Environment:
   REDBEAR_RELEASE     If set, builds from immutable release archives.
                       Override to empty for development builds.
+  REDBEAR_SKIP_ABI_STALENESS=1
+                      Fast iteration: skip the relibc-consumer invalidation
+                      churn so a rerun goes straight to the recipe you changed
+                      (the cookbook cache still re-cooks changed sources). Safe
+                      ONLY when relibc's ABI is unchanged. Unset it whenever you
+                      bump relibc/base, or stale binaries may ship.
+  REDBEAR_FORCE_TOOLCHAIN_RECOOK=1
+                      Force a full re-cook of preserved toolchain packages
+                      (llvm21/clang21/lld21/rust) on a relibc change.
 EOF
 }
 
@@ -652,7 +661,7 @@ if [ "$NO_CACHE" != "1" ]; then
     done
 
 
-    if [ "$USERSPACE_RUNTIME_STALE" = "1" ]; then
+    if [ "$USERSPACE_RUNTIME_STALE" = "1" ] && [ "${REDBEAR_SKIP_ABI_STALENESS:-0}" != "1" ]; then
         echo ">>> Cleaning stale build/sysroot dirs (userspace-linked runtime changed)..."
         find "$PROJECT_ROOT/recipes" "$PROJECT_ROOT/local/recipes" \
             \( -path "*/target/x86_64-unknown-redox/build" \
@@ -736,7 +745,17 @@ if [ "$NO_CACHE" != "1" ]; then
         find "$PROJECT_ROOT/recipes" "$PROJECT_ROOT/local/recipes" \
             -path "*/$pkg/target" -type d -exec rm -rf {} + 2>/dev/null || true
     }
-    if [ "$relibc_rebuilding" = "1" ]; then
+    if [ "${REDBEAR_SKIP_ABI_STALENESS:-0}" = "1" ]; then
+        # Fast-iteration escape hatch: skip the entire relibc-consumer
+        # invalidation. Safe ONLY when relibc's ABI is unchanged (e.g. iterating
+        # on a single driver/app recipe). The cookbook's own BLAKE3 dep-hash
+        # cache still rebuilds recipes whose sources changed, so your edited
+        # package re-cooks while everything else stays cached — no 30-min churn
+        # to re-reach it. Unset to restore the stale-binary safety net (which is
+        # required whenever relibc/base actually changed).
+        echo ">>> REDBEAR_SKIP_ABI_STALENESS=1 — skipping relibc-consumer invalidation"
+        echo ">>> (fast iteration; assumes relibc ABI unchanged). Unset to restore it."
+    elif [ "$relibc_rebuilding" = "1" ]; then
         echo ">>> relibc is rebuilding — it is statically linked into every"
         echo ">>> userspace binary, so ALL packages are invalidated to force a"
         echo ">>> clean relink (correctness over speed; prevents stale-binary skew)."