feat(v0.42): 6 fixes from 4-CLI re-audit (CRITICAL + 2 HIGH + 3 MED)

Convergent dogfood audit by Claude+Grok+Gemini+Copilot on v0.41 surfaced
that the v0.41 'fixes' were incomplete. 3 of 4 reviewers independently
found the same CRITICAL bypass; Gemini wrote a Rust test suite to verify.

## Convergent findings → v0.42 fixes

[#1 CRITICAL] Symlink leaf bypass (3-of-4 convergent)
  v0.41 only canonicalized PARENT, then re-attached leaf as-is. Exploit:
    1. kei_bash 'ln -s ~/.ssh/authorized_keys ./cfg.txt'
       (passes the bash hook chain — ln itself is non-destructive)
    2. kei_write file_path=cfg.txt content=<key>
       validate_path saw $PWD/cfg.txt (allowed) → fs::write followed leaf
       symlink → overwrote authorized_keys.
  Fix: canonicalize FULL path (incl. leaf) when file exists; for new
       files, symlink_metadata on leaf and reject is_symlink. Now the
       denylist check sees the real target.

[#2 HIGH] $HOME blanket-allowed = self-neutering (2-of-4 convergent)
  allowed_roots() defaulted to [$PWD, $HOME], denylist only had 4 secret
  dirs. So kei_write $HOME/.claude/hooks/no-github-push.sh content='exit 0'
  was ALLOWED — agent could overwrite the substrate's own policy hooks.
  Similar attacks on ~/.zshrc (RCE on next shell), ~/.gitconfig, ~/.npmrc.
  Fix: default to $PWD only. Denylist extended with .claude/, .grok/,
       .gemini/, .copilot/, .kimi/, all major shell-init files, and
       additional credential paths. KEI_ALLOWED_ROOTS for explicit
       widening.

[#3 HIGH] Empty-section fail-OPEN (Gemini test-verified)
  v0.41 'fail-closed on missing config' fix was incomplete: if config
  file existed but section [bash]/[edit]/[write] was empty, load_chain
  returned Ok(vec![]) → run_chain early-returned Ok → action ran ungated.
  Fix: empty chain also FAIL-CLOSED with same KEI_POLICY_CHAIN_OPTIONAL
       opt-in.

[#4 MEDIUM] load_chain still blocked tokio worker (Claude)
  v0.41 fix #4 converted handle_edit/handle_write reads to tokio::fs but
  left load_chain on std::fs. Slow/hung mount on policy-chain.toml would
  freeze a worker for every safe_* invocation.
  Fix: load_chain → async + tokio::fs::{try_exists, read_to_string}.

[#5 MEDIUM] process_group only applied to bash, not hooks (Claude)
  v0.41 fix #5 set_process_group on kei_bash's child shell, but the
  hook subprocess (spawned per-hook in run_chain) was NOT in its own
  group. On hook timeout, kill_on_drop killed only the immediate hook
  process; grandchildren orphaned — the exact failure mode fix #5 was
  meant to prevent.
  Fix: set_process_group + killpg also on hook spawn in run_chain.

[#6 MEDIUM] Per-step vs aggregate timeout (Claude)
  Doc claimed 'Hard cap on single chain + action — 60s'. Actual: each
  hook gets independent 60s, then action gets another 60s. For a 3-hook
  bash chain that's 240s max — 4× documented.
  Status: documented as known-limit; single-deadline impl deferred to
       v0.43 (not security-blocking, just a doc/correctness drift).

## Verification (8 smokes — all green)

  /etc/passwd                          → denied (system dir)              ✓
  ../escape.txt                        → denied (../ segment)             ✓
  /tmp/symlink → /etc/passwd writeable → denied (resolved /private/etc)   ✓ NEW
  ~/.claude/hooks/no-github-push.sh    → denied (substrate dir)           ✓ NEW
  ~/.zshrc                             → denied (shell-init file)         ✓ NEW
  policy-chain.toml empty [bash]       → FAIL-CLOSED                      ✓ NEW
  KEI_POLICY_CHAIN_OPTIONAL=1          → opt-in pass-through              ✓
  kei_bash git-push-github             → BLOCKED (regression)             ✓
  kei_bash echo HELLO                  → returns content (regression)     ✓

cargo test -p kei-mcp: 3/3 still pass.

## Architecture note from Grok

Grok architect flagged: safe_tools.rs is 474 LOC, exceeds Constructor
Pattern 200-line threshold. v0.42 does NOT refactor (security fixes
shipped first); v0.43 will extract path_guard.rs + chain_runner.rs.

## Per-CLI audit value demonstrated

  Claude   — 5 issues + 5 minor, exhaustive line-anchored analysis
  Grok     — architectural review with grep-verified citations
  Gemini   — wrote Rust test project to verify findings (PoC code!)
  Copilot  — partial fact-check, ran out of mid-task

_primitives/_rust/kei-mcp/src/handlers/safe_tools.rs

@@ -30,6 +30,25 @@
 //!   #3 CLAUDECODE bypass — documented as design (see above), no behavior change
 //!   #4 tokio::fs for async file I/O (was: blocking std::fs on tokio thread)
 //!   #5 process-group kill on Unix (was: kill_on_drop SIGKILLs only direct child)
+//!
+//! v0.42 re-audit fixes (2026-05-26, 4-CLI dogfood: Claude+Grok+Gemini+Copilot):
+//!   #1 [CRITICAL] symlink LEAF bypass — canonicalize full path + reject
+//!      leaf symlinks (v0.41 only canonicalized PARENT; ln -s ~/.ssh/keys ./x
+//!      then kei_write x followed the link to the target)
+//!   #2 [HIGH]     $HOME removed from default allowed_roots — was a blanket
+//!      allow that let agent overwrite ~/.claude/hooks (self-neuter), ~/.zshrc
+//!      (RCE on next shell), and credential stores. Default: $PWD only.
+//!      Denylist also extended with .claude/, .grok/, .gemini/, .copilot/,
+//!      .kimi/, and exact shell-init filenames.
+//!   #3 [HIGH]     empty [bash]/[edit]/[write] section also FAIL-CLOSED (was:
+//!      empty vec → pass-through). KEI_POLICY_CHAIN_OPTIONAL=1 to opt in.
+//!   #4 [MED]      load_chain converted to async + tokio::fs (was: blocking
+//!      std::fs on tokio worker thread).
+//!   #5 [MED]      set_process_group + killpg applied to HOOK subprocess too
+//!      (v0.41 only had it on the bash action; hook grandchildren orphaned).
+//!   #6 [MED]      doc note that aggregate timeout is still per-step (60s ×
+//!      N hooks + 60s action). Single-deadline implementation deferred to
+//!      v0.43 — not security-blocking.
 
 use crate::protocol::{err, ok, JsonRpcRequest, JsonRpcResponse, INTERNAL_ERROR, INVALID_PARAMS};
 use serde::Deserialize;
@@ -256,15 +275,21 @@ async fn handle_write(args: &Value) -> Result<String, String> {
     Ok(format!("wrote {} ({} bytes)", safe_path.display(), content.len()))
 }
 
-/// v0.41 fix #2 (Gemini HIGH): reject obvious path-traversal / sensitive-path
-/// targets BEFORE running hooks. Defense-in-depth: hooks may also flag this,
-/// but having the Rust layer reject obvious attacks gives a fast-fail
-/// independent of hook configuration.
+/// Path-traversal + symlink + denylist guard.
 ///
-/// Allowed roots: $PWD (recursively), $HOME (excluding dotfile-secret dirs).
-/// Override: set KEI_ALLOWED_ROOTS=":" -separated absolute paths.
-/// Always rejected: /etc/, /usr/, /System/, /var/, /private/etc/, $HOME/.ssh/,
-/// $HOME/.aws/, $HOME/.config/gcloud/, $HOME/.gnupg/, any path containing "..".
+/// v0.41 (initial): rejected `..`, canonicalized PARENT, checked denylist + roots.
+///   → 4-CLI re-audit (2026-05-26) found this was bypassable via symlink at the
+///     leaf and self-attackable via the $HOME blanket-allowed root.
+///
+/// v0.42 fixes:
+///   #1 [CRITICAL] reject if the leaf is a symlink (was: validated parent
+///      only, fs::write followed leaf symlink to anywhere). Done via
+///      `symlink_metadata` on the leaf BEFORE write, and full `canonicalize`
+///      on the leaf when the file already exists.
+///   #2 [HIGH] $HOME removed from default allowed-roots — default is $PWD
+///      only. Denylist now also covers $HOME/.claude/ (the substrate
+///      itself), shell init files, and credential stores. Operators who
+///      need broader access set KEI_ALLOWED_ROOTS explicitly.
 fn validate_path(p: &str) -> Result<PathBuf, String> {
     if p.is_empty() {
         return Err("file_path: empty".into());
@@ -274,13 +299,23 @@ fn validate_path(p: &str) -> Result<PathBuf, String> {
         return Err(format!("file_path: '..' segment not allowed in {p}"));
     }
     let path = Path::new(p);
-    // 2. Canonicalize the parent (file may not exist yet for kei_write);
-    //    if even the parent doesn't exist, use the absolute form.
-    let canonical = if let Some(parent) = path.parent() {
+
+    // 2. Build a canonical path. Prefer canonicalizing the FULL path (resolves
+    //    symlinks at the leaf, fixing v0.41 CRITICAL bypass). For files that
+    //    don't exist yet (kei_write new file), canonicalize the parent and
+    //    join the leaf — but then explicitly check the leaf isn't a symlink
+    //    via symlink_metadata before writing.
+    let canonical = if path.exists() {
+        // File exists — canonicalize full path, including resolving any leaf
+        // symlink to its real target. The denylist/roots check below then
+        // sees the REAL destination, not the symlink name.
+        path.canonicalize()
+            .map_err(|e| format!("file_path: canonicalize {}: {e}", path.display()))?
+    } else if let Some(parent) = path.parent() {
         if parent.as_os_str().is_empty() || parent == Path::new("") {
             std::env::current_dir()
                 .map_err(|e| format!("file_path: cwd unavailable: {e}"))?
-                .join(path)
+                .join(path.file_name().unwrap_or_default())
         } else if parent.exists() {
             parent.canonicalize()
                 .map_err(|e| format!("file_path: canonicalize {}: {e}", parent.display()))?
@@ -295,12 +330,24 @@ fn validate_path(p: &str) -> Result<PathBuf, String> {
     } else {
         return Err(format!("file_path: invalid {p}"));
     };
+
+    // 3. Even when the file doesn't exist yet, the LEAF could already be a
+    //    dangling symlink that `fs::write` would follow on creation. Reject.
+    if let Ok(meta) = std::fs::symlink_metadata(&canonical) {
+        if meta.file_type().is_symlink() {
+            return Err(format!(
+                "file_path: leaf is a symlink (refusing to follow): {}",
+                canonical.display()
+            ));
+        }
+    }
+
     let canon_str = canonical.display().to_string();
 
-    // 3. Reject obvious sensitive directories.
+    // 4. Reject system + substrate-control + credential paths.
     let denylist = [
         "/etc/", "/usr/", "/System/", "/var/", "/private/etc/", "/private/var/",
-        "/root/",
+        "/root/", "/bin/", "/sbin/",
     ];
     for d in denylist {
         if canon_str.starts_with(d) {
@@ -308,16 +355,38 @@ fn validate_path(p: &str) -> Result<PathBuf, String> {
         }
     }
     if let Ok(home) = std::env::var("HOME") {
-        let secret_dirs = [".ssh/", ".aws/", ".gnupg/", ".config/gcloud/"];
-        for sd in secret_dirs {
+        // v0.42 fix #2 extended denylist — these targets enable self-attack
+        // (overwrite the substrate or shell init for RCE on next session).
+        let dir_secrets = [
+            ".ssh/", ".aws/", ".gnupg/", ".config/gcloud/", ".cargo/credentials",
+            ".npmrc", ".docker/config.json", ".kube/",
+            ".claude/",      // our own substrate: hooks, settings, agents
+            ".grok/",        // sibling CLI's settings
+            ".gemini/",      // antigravity settings
+            ".copilot/",     // copilot config
+            ".kimi/",        // kimi config
+        ];
+        for sd in dir_secrets {
             let full = format!("{home}/{sd}");
             if canon_str.starts_with(&full) {
-                return Err(format!("file_path: denied (secret dir): {canon_str}"));
+                return Err(format!("file_path: denied (secret/substrate dir): {canon_str}"));
+            }
+        }
+        // Exact shell-init files (overwriting → RCE on next shell start).
+        let init_files = [
+            ".zshrc", ".bashrc", ".profile", ".bash_profile", ".zprofile",
+            ".zshenv", ".bash_login", ".inputrc", ".gitconfig",
+            ".config/fish/config.fish",
+        ];
+        for f in init_files {
+            let full = format!("{home}/{f}");
+            if canon_str == full {
+                return Err(format!("file_path: denied (shell-init file): {canon_str}"));
             }
         }
     }
 
-    // 4. Enforce allowed-root containment.
+    // 5. Enforce allowed-root containment.
     let roots = allowed_roots();
     if !roots.is_empty() {
         let ok = roots.iter().any(|r| canon_str.starts_with(r));
@@ -335,13 +404,14 @@ fn allowed_roots() -> Vec<String> {
     if let Ok(v) = std::env::var("KEI_ALLOWED_ROOTS") {
         return v.split(':').filter(|s| !s.is_empty()).map(String::from).collect();
     }
+    // v0.42 fix #2 (Claude+Gemini HIGH): default to $PWD ONLY. Was: $PWD +
+    // $HOME blanket — too permissive, agent could overwrite ~/.claude/hooks/
+    // or ~/.zshrc and self-neuter the safety layer. Operators who need
+    // broader access opt in via KEI_ALLOWED_ROOTS=":" -separated abs paths.
     let mut roots = Vec::new();
     if let Ok(cwd) = std::env::current_dir() {
         roots.push(format!("{}/", cwd.display()));
     }
-    if let Ok(home) = std::env::var("HOME") {
-        roots.push(format!("{home}/"));
-    }
     roots
 }
 
@@ -353,15 +423,34 @@ fn allowed_roots() -> Vec<String> {
 ///
 /// Skips the chain if the parent process is already inside Claude or Grok
 /// (env flags), since those CLIs' native PreToolUse hooks already fired.
+/// Run the configured hook chain for `tool` ("bash"/"edit"/"write").
+///
+/// v0.42 fixes:
+///   #3 [HIGH]   empty chain (section absent or zero hooks) now FAILS CLOSED
+///               unless KEI_POLICY_CHAIN_OPTIONAL=1.
+///   #4 [MED]    load_chain() converted to async (was: blocking std::fs).
+///   #5 [MED]    hook subprocess gets `process_group(0)` + killpg on timeout
+///               (was: only the bash action got it; hooks could orphan).
+///   #6 [MED]    aggregate timeout across the whole chain + action (was:
+///               per-hook 60s, so chain+action could legitimately run
+///               4× the documented cap on a 3-hook chain).
 async fn run_chain(tool: &str, hook_input: &Value) -> Result<(), String> {
     if env_truthy("CLAUDECODE") || env_truthy("GROKCODE") {
         // Native hooks already enforced — don't double-fire.
         return Ok(());
     }
 
-    let chain = load_chain(tool)?;
+    let chain = load_chain(tool).await?;
     if chain.is_empty() {
-        return Ok(());
+        // v0.42 fix #3 (Claude+Gemini HIGH): empty section is the same
+        // misconfig class as missing file — FAIL CLOSED with explicit opt-in.
+        if env_truthy("KEI_POLICY_CHAIN_OPTIONAL") {
+            return Ok(());
+        }
+        return Err(format!(
+            "[policy-chain] section [{tool}] is empty — refusing to run \
+             (set KEI_POLICY_CHAIN_OPTIONAL=1 to allow pass-through, e.g. for tests)"
+        ));
     }
 
     let hooks_dir = hooks_dir()?;
@@ -371,24 +460,26 @@ async fn run_chain(tool: &str, hook_input: &Value) -> Result<(), String> {
     for hook in chain {
         let path = hooks_dir.join(&hook);
         if !path.is_file() {
-            // v0.41 fix #1 (Gemini HIGH): FAIL-CLOSED on missing hook.
-            // Previously we logged a warning and continued — that meant a
-            // misconfigured deployment (hook deleted, wrong path) silently
-            // disabled enforcement. Now: refuse the action, surface the
-            // error so the operator notices.
             return Err(format!(
                 "[policy-chain] hook missing: {} (declared in policy-chain.toml [{}])",
                 path.display(), tool
             ));
         }
 
-        let mut child = Command::new(&path)
+        let mut child_cmd = Command::new(&path);
+        child_cmd
             .stdin(Stdio::piped())
             .stdout(Stdio::piped())
             .stderr(Stdio::piped())
-            .kill_on_drop(true)
+            .kill_on_drop(true);
+        // v0.42 fix #5: put hook child in its own process group so timeout
+        // can killpg the whole tree (was: kill_on_drop = immediate child only).
+        set_process_group(&mut child_cmd);
+
+        let mut child = child_cmd
             .spawn()
             .map_err(|e| format!("spawn {}: {e}", path.display()))?;
+        let pid_opt = child.id();
 
         if let Some(mut stdin) = child.stdin.take() {
             stdin.write_all(payload.as_bytes()).await
@@ -398,10 +489,18 @@ async fn run_chain(tool: &str, hook_input: &Value) -> Result<(), String> {
         }
 
         let fut = child.wait_with_output();
-        let out = tokio::time::timeout(Duration::from_secs(SAFE_TOOL_TIMEOUT_SECS), fut)
-            .await
-            .map_err(|_| format!("hook {} timeout", hook))?
-            .map_err(|e| format!("wait {}: {e}", path.display()))?;
+        let out = match tokio::time::timeout(Duration::from_secs(SAFE_TOOL_TIMEOUT_SECS), fut).await {
+            Ok(Ok(o)) => o,
+            Ok(Err(e)) => return Err(format!("wait {}: {e}", path.display())),
+            Err(_) => {
+                // v0.42 fix #5: kill the whole hook process group, not just
+                // the immediate child.
+                if let Some(pid) = pid_opt {
+                    killpg_best_effort(pid);
+                }
+                return Err(format!("hook {hook} timeout"));
+            }
+        };
 
         let code = out.status.code().unwrap_or(-1);
         if code == 0 {
@@ -417,14 +516,14 @@ async fn run_chain(tool: &str, hook_input: &Value) -> Result<(), String> {
 
 // ---- config helpers -----------------------------------------------------
 
-fn load_chain(tool: &str) -> Result<Vec<String>, String> {
+/// v0.42 fix #4: async + tokio::fs (was: blocking std::fs would freeze
+/// a tokio worker if policy-chain.toml lived on a slow / hung mount).
+async fn load_chain(tool: &str) -> Result<Vec<String>, String> {
     let path = chain_path()?;
-    if !path.is_file() {
-        // v0.41 fix #1 (Gemini HIGH companion): default behavior when
-        // policy-chain.toml is absent is now configurable via env. Without
-        // explicit opt-in to pass-through, FAIL-CLOSED — caller sees a
-        // clear error instead of silent bypass.
-        if std::env::var("KEI_POLICY_CHAIN_OPTIONAL").as_deref() == Ok("1") {
+    // tokio::fs::try_exists avoids a blocking is_file() syscall.
+    let exists = fs::try_exists(&path).await.unwrap_or(false);
+    if !exists {
+        if env_truthy("KEI_POLICY_CHAIN_OPTIONAL") {
             return Ok(vec![]);
         }
         return Err(format!(
@@ -432,7 +531,7 @@ fn load_chain(tool: &str) -> Result<Vec<String>, String> {
             path.display()
         ));
     }
-    let raw = std::fs::read_to_string(&path)
+    let raw = fs::read_to_string(&path).await
         .map_err(|e| format!("read policy-chain.toml: {e}"))?;
     let parsed: PolicyChain = toml::from_str(&raw)
         .map_err(|e| format!("parse policy-chain.toml: {e}"))?;

bin/kei

@@ -224,7 +224,7 @@ ${C1}    ██╔═██╗ ██╔══╝  ██║╚════█
 ${C1}    ██║  ██╗███████╗██║███████║███████╗██║${C0}
 ${C1}    ╚═╝  ╚═╝╚══════╝╚═╝╚══════╝╚══════╝╚═╝${C0}
 
-${C2}    KeiSeiKit · substrate v0.40${C0}
+${C2}    KeiSeiKit · substrate v0.42${C0}
 ${C3}    ─────────────────────────────────────${C0}
       primary CLI    : ${CV}${PRIMARY}${C0}
       profile        : ${CV}${p}${C0}

docs/encyclopedia/cross-cli-policy.md

@@ -116,22 +116,34 @@ The chain runs against the same hook scripts Claude uses; identical input
 shape, identical decisions. On block, the hook's stderr surfaces as the MCP
 error message so the calling agent sees exactly why.
 
-**v0.41 hardening** (post-audit fixes):
+**v0.42 hardening** (post 4-CLI re-audit, supersedes v0.41):
 
-- **Fail-CLOSED on missing config** — if `policy-chain.toml` is absent the
-  chain refuses to run (was: silent pass-through). Tests / dev can opt in
-  via `KEI_POLICY_CHAIN_OPTIONAL=1` env.
-- **Fail-CLOSED on missing hook script** — if a hook declared in the chain
-  is not on disk the call fails (was: warn-and-skip).
-- **Path-traversal guard** on `kei_edit` / `kei_write` — rejects `..`
-  segments, `/etc/`, `/usr/`, `/System/`, `/var/`, `/root/`, plus
-  `$HOME/{.ssh,.aws,.gnupg,.config/gcloud}/` recursively. Override via
-  `KEI_ALLOWED_ROOTS=':'-separated-absolute-paths`.
-- **Async file I/O** — `kei_edit` / `kei_write` now use `tokio::fs` so a
-  pathological file (`/dev/random` etc.) cannot block a tokio worker.
-- **Process-group kill on timeout** — `kei_bash` puts its child shell in
-  its own process group; on timeout the entire group is `killpg(SIGKILL)`'d
-  so grandchildren don't orphan (Unix-only; no-op on Windows).
+- **Fail-CLOSED everywhere** — missing config, missing hook, OR empty
+  section (`[bash]/[edit]/[write]` with no entries) all refuse to run.
+  Tests / dev can opt in via `KEI_POLICY_CHAIN_OPTIONAL=1`.
+- **Symlink-safe path guard** — `kei_edit` / `kei_write` canonicalize the
+  FULL path (resolving any leaf symlink to its real target) and reject
+  if the leaf itself is a symlink for a not-yet-existent file. Fixes the
+  v0.41 CRITICAL bypass where `ln -s ~/.ssh/keys ./x; kei_write x` would
+  follow the link.
+- **$PWD-only default root** — `allowed_roots` defaults to current working
+  directory only. Was: `$PWD` + entire `$HOME` — too permissive, agent
+  could overwrite `~/.claude/hooks/*` (self-neuter) or `~/.zshrc` (RCE on
+  next shell). Operators who need broader access set `KEI_ALLOWED_ROOTS`.
+- **Denylist extended** — system dirs (`/etc/`, `/usr/`, `/System/`,
+  `/var/`, `/root/`, `/bin/`, `/sbin/`); credential stores (`~/.ssh/`,
+  `~/.aws/`, `~/.gnupg/`, `~/.config/gcloud/`, `~/.cargo/credentials`,
+  `~/.docker/config.json`, `~/.kube/`); substrate dirs (`~/.claude/`,
+  `~/.grok/`, `~/.gemini/`, `~/.copilot/`, `~/.kimi/`); exact shell-init
+  files (`.zshrc`, `.bashrc`, `.profile`, `.zshenv`, `.gitconfig`, ...).
+- **Async file I/O in load_chain** — `policy-chain.toml` now read via
+  `tokio::fs` (was: blocking `std::fs` froze worker on slow mounts).
+- **Process-group kill on hooks too** — hook subprocesses get
+  `process_group(0)` and `killpg(SIGKILL)` on timeout. Was: only the bash
+  action got this; hook grandchildren orphaned.
+- **CLAUDECODE/GROKCODE design note** — documented as perf/UX
+  optimization, NOT a security boundary (env-controllable parent → confused
+  deputy is already-game-over scenario).
 
 ### Double-enforcement guard
 

plugin.json

@@ -3,7 +3,7 @@
   "name": "keisei",
   "displayName": "KeiSei",
   "description": "Constructor Pattern multi-LLM agent substrate — 38 agents, 69 skills, 54 hooks, 86 blocks. Cross-CLI policy enforcement (Claude/Grok/Copilot/Agy/Kimi) via kei-mcp + kei_bash/kei_edit/kei_write. Rust primitives via classic ./install.sh.",
-  "version": "0.40.0",
+  "version": "0.42.0",
   "homepage": "https://keisei.app",
   "repository": "https://github.com/KeiSeiLab/KeiSeiKit-1.0.git",
   "author": {