feat: build system transition to release fork + archive hardening

Release fork infrastructure:
- REDBEAR_RELEASE=0.1.1 with offline enforcement (fetch/distclean/unfetch blocked)
- 195 BLAKE3-verified source archives in standard format
- Atomic provisioning via provision-release.sh (staging + .complete sentry)
- 5-phase improvement plan: restore format auto-detection, source tree
  validation (validate-source-trees.py), archive-map.json, REPO_BINARY fallback

Archive normalization:
- Removed 87 duplicate/unversioned archives from shared pool
- Regenerated all archives in consistent format with source/ + recipe.toml
- BLAKE3SUMS and manifest.json generated from stable tarball set

Patch management:
- verify-patches.sh: pre-sync dry-run report (OK/REVERSED/CONFLICT)
- 121 upstream-absorbed patches moved to absorbed/ directories
- 43 active patches verified clean against rebased sources
- Stress test: base updated to upstream HEAD, relibc reset and patched

Compilation fixes:
- relibc: Vec imports in redox-rt (proc.rs, lib.rs, sys.rs)
- relibc: unsafe from_raw_parts in mod.rs (2024 edition)
- fetch.rs: rev comparison handles short/full hash prefixes
- kibi recipe: corrected rev mismatch

New scripts: restore-sources.sh, provision-release.sh, verify-sources-archived.sh,
check-upstream-releases.sh, validate-source-trees.py, verify-patches.sh,
repair-archive-format.sh, generate-manifest.py

Documentation: AGENTS.md, README.md, local/AGENTS.md updated for release fork model

src/bin/repo.rs

@@ -715,6 +715,20 @@ fn handle_fetch(
     allow_offline: bool,
     logger: &PtyOut,
 ) -> anyhow::Result<FetchResult> {
+    // In release mode, explicit fetch is forbidden. Cook's internal fetch
+    // (allow_offline=true) is still allowed since it respects COOKBOOK_OFFLINE.
+    if !allow_offline {
+        if let Ok(release) = env::var("REDBEAR_RELEASE") {
+            if !release.is_empty() {
+                bail!("{}", Error::Other(format!(
+                    "Fetch is disabled in release mode (REDBEAR_RELEASE={}). \
+                     Sources are immutable. To refresh, run: provision-release.sh",
+                    release
+                )));
+            }
+        }
+    }
+
     let source_dir = match config.cook.offline && allow_offline {
         true => fetch_offline(&recipe, logger),
         false => fetch(&recipe, !recipe.is_deps, logger),
@@ -789,6 +803,17 @@ fn handle_clean(
         cached = false;
     }
     let dir = recipe.dir.join("source");
+    if matches!(*command, CliCommand::Unfetch) {
+        // In release mode, unfetch is forbidden — sources are immutable
+        if let Ok(release) = std::env::var("REDBEAR_RELEASE") {
+            if !release.is_empty() {
+                anyhow::bail!(
+                    "Unfetch is disabled in release mode (REDBEAR_RELEASE={}). Sources are immutable.",
+                    release
+                );
+            }
+        }
+    }
     if dir.exists() && matches!(*command, CliCommand::Unfetch) {
         if is_local_overlay(&recipe.dir) && !redbear_allow_local_unfetch() {
             eprintln!(