diff --git a/.agents/skills/skill-host-compat/SKILL.md b/.agents/skills/skill-host-compat/SKILL.md
index 6597dad54..d790a56ed 100644
--- a/.agents/skills/skill-host-compat/SKILL.md
+++ b/.agents/skills/skill-host-compat/SKILL.md
@@ -26,7 +26,9 @@ sees `.agents/skills/`. This script is the cross-tree gate:
 
 1. Claude-only substitutions in executable `bash` / `sh` / `zsh` fences
    (`$CLAUDE_SESSION_ID`, `$CLAUDE_SKILL_DIR`, `$CLAUDE_PLUGIN_ROOT`,
-   `$ARGUMENTS`) fail. Codex leaves those tokens as literal text.
+   `$CLAUDE_PROJECT_DIR`, `$ARGUMENTS`) fail. Codex leaves those tokens
+   as literal text. In a Codex copy, rewrite `$CLAUDE_PROJECT_DIR` to
+   `$(pwd)` or an explicit path.
 2. A Codex copy may only use `name`, `description`, `metadata`, `license`,
    and `allowed-tools`. `origin: ECC` may stay on the canonical `skills/`
    copy and must be stripped on the Codex copy.
@@ -75,6 +77,7 @@ forbidden pattern:
 echo "$CLAUDE_SESSION_ID"
 ls "$CLAUDE_SKILL_DIR"
 node "$CLAUDE_PLUGIN_ROOT/scripts/setup.js" $ARGUMENTS
+cd "$CLAUDE_PROJECT_DIR"
 ```
 
 Do not add `version:` or `origin:` to a Codex copy under `.agents/skills/`.
@@ -86,7 +89,9 @@ every `skills/` entry to have a Cursor copy.
 - Keep canonical `origin: ECC` if the CONTRIBUTING template calls for it.
 - Drop `origin`, `version`, and `argument-hint` on the Codex copy.
 - Show host-portable commands in bash fences (`npx`, `ecc`, or a resolved
-  root). Mention Claude env vars in prose, not in executable fences.
+  root). Rewrite `$CLAUDE_PROJECT_DIR` in Codex copies to `$(pwd)` or an
+  explicit path. Mention other Claude env vars in prose, not in executable
+  fences.
 - Run this script before `npm test` when the change is a new skill.
 - Use `--inventory` to see checklist warning volume without failing the tree.
 
diff --git a/commands/skill-host-compat.md b/commands/skill-host-compat.md
index f30604a24..c9ebab928 100644
--- a/commands/skill-host-compat.md
+++ b/commands/skill-host-compat.md
@@ -36,5 +36,5 @@ node "$ECC_ROOT/scripts/ci/validate-skill-host-compat.js" --inventory
 
 1. Run `scripts/ci/validate-skill-host-compat.js` from the ECC root
 2. Show ERROR and WARN lines to the user
-3. For substitution errors, move Claude env vars out of bash fences
+3. For substitution errors, move Claude env vars out of bash fences. Rewrite `$CLAUDE_PROJECT_DIR` to `$(pwd)` or an explicit path
 4. For Codex-key errors, drop `origin` / `version` / `argument-hint` on the copy
diff --git a/scripts/ci/validate-skill-host-compat.js b/scripts/ci/validate-skill-host-compat.js
index 751b361cc..8dfc3a980 100644
--- a/scripts/ci/validate-skill-host-compat.js
+++ b/scripts/ci/validate-skill-host-compat.js
@@ -5,7 +5,9 @@
  * Checks:
  *   1. Claude-only substitutions in executable bash/sh/zsh fences
  *      (${CLAUDE_SESSION_ID}, ${CLAUDE_SKILL_DIR}, ${CLAUDE_PLUGIN_ROOT},
- *      $ARGUMENTS). Codex and a bare shell leave those tokens literal.
+ *      ${CLAUDE_PROJECT_DIR}, $ARGUMENTS). Codex and a bare shell leave
+ *      those tokens literal. Rewrite ${CLAUDE_PROJECT_DIR} in Codex copies
+ *      to $(pwd) or an explicit path.
  *   2. Codex-copy frontmatter allowlist on .agents/skills/<name>/SKILL.md
  *      (name, description, metadata, license, allowed-tools). origin/version
  *      may remain on the canonical skills/ copy.
@@ -47,6 +49,8 @@ const CLAUDE_SUBSTITUTION_PATTERNS = [
   { token: '$CLAUDE_SKILL_DIR', regex: /\$CLAUDE_SKILL_DIR\b/g },
   { token: '${CLAUDE_PLUGIN_ROOT}', regex: /\$\{CLAUDE_PLUGIN_ROOT\}/g },
   { token: '$CLAUDE_PLUGIN_ROOT', regex: /\$CLAUDE_PLUGIN_ROOT\b/g },
+  { token: '${CLAUDE_PROJECT_DIR}', regex: /\$\{CLAUDE_PROJECT_DIR\}/g },
+  { token: '$CLAUDE_PROJECT_DIR', regex: /\$CLAUDE_PROJECT_DIR\b/g },
   { token: '$ARGUMENTS', regex: /\$ARGUMENTS\b|\$\{ARGUMENTS\}/g },
   // Claude skill form ${1}. Bare $1 is handled in findSubstitutionTokens so
   // POSIX `VAR=$1` and Perl/awk `$1 < 80` are not treated as Claude args.
@@ -231,6 +235,14 @@ function pushFinding(findings, finding) {
   findings.push(finding);
 }
 
+function substitutionMessage(skillName, fenceLang, token) {
+  const base = `${relSkillMd(skillName)} - ${fenceLang} fence contains Claude-only substitution ${token}`;
+  if (token === '${CLAUDE_PROJECT_DIR}' || token === '$CLAUDE_PROJECT_DIR') {
+    return `${base}; rewrite to $(pwd) or an explicit path`;
+  }
+  return base;
+}
+
 function inspectCanonicalSkill(skillName, content, findings) {
   const { frontmatter, body } = stripFrontmatter(content);
   const values = frontmatter.present ? inspectFrontmatter(frontmatter.lines).values : {};
@@ -289,7 +301,7 @@ function inspectCanonicalSkill(skillName, content, findings) {
         code: 'substitution',
         skill: skillName,
         token,
-        message: `${relSkillMd(skillName)} - ${fence.lang} fence contains Claude-only substitution ${token}`,
+        message: substitutionMessage(skillName, fence.lang, token),
       });
     }
   }
diff --git a/skills/skill-host-compat/SKILL.md b/skills/skill-host-compat/SKILL.md
index e8ad98059..6afc6aa78 100644
--- a/skills/skill-host-compat/SKILL.md
+++ b/skills/skill-host-compat/SKILL.md
@@ -27,7 +27,9 @@ sees `.agents/skills/`. This script is the cross-tree gate:
 
 1. Claude-only substitutions in executable `bash` / `sh` / `zsh` fences
    (`${CLAUDE_SESSION_ID}`, `${CLAUDE_SKILL_DIR}`, `${CLAUDE_PLUGIN_ROOT}`,
-   `$ARGUMENTS`) fail. Codex leaves those tokens as literal text.
+   `${CLAUDE_PROJECT_DIR}`, `$ARGUMENTS`) fail. Codex leaves those tokens
+   as literal text. In a Codex copy, rewrite `${CLAUDE_PROJECT_DIR}` to
+   `$(pwd)` or an explicit path.
 2. A Codex copy may only use `name`, `description`, `metadata`, `license`,
    and `allowed-tools`. `origin: ECC` may stay on the canonical `skills/`
    copy and must be stripped on the Codex copy.
@@ -76,6 +78,7 @@ forbidden pattern:
 echo "${CLAUDE_SESSION_ID}"
 ls "${CLAUDE_SKILL_DIR}"
 node "${CLAUDE_PLUGIN_ROOT}/scripts/setup.js" $ARGUMENTS
+cd "${CLAUDE_PROJECT_DIR}"
 ```
 
 Do not add `version:` or `origin:` to a Codex copy under `.agents/skills/`.
@@ -87,7 +90,9 @@ every `skills/` entry to have a Cursor copy.
 - Keep canonical `origin: ECC` if the CONTRIBUTING template calls for it.
 - Drop `origin`, `version`, and `argument-hint` on the Codex copy.
 - Show host-portable commands in bash fences (`npx`, `ecc`, or a resolved
-  root). Mention Claude env vars in prose, not in executable fences.
+  root). Rewrite `${CLAUDE_PROJECT_DIR}` in Codex copies to `$(pwd)` or an
+  explicit path. Mention other Claude env vars in prose, not in executable
+  fences.
 - Run this script before `npm test` when the change is a new skill.
 - Use `--inventory` to see checklist warning volume without failing the tree.
 
diff --git a/tests/ci/validate-skill-host-compat.test.js b/tests/ci/validate-skill-host-compat.test.js
index a97bc766d..df476bcda 100644
--- a/tests/ci/validate-skill-host-compat.test.js
+++ b/tests/ci/validate-skill-host-compat.test.js
@@ -150,6 +150,75 @@ check('fail: bash fence contains ${CLAUDE_SESSION_ID}', () => {
   }
 });
 
+check('fail: bash fence contains ${CLAUDE_PROJECT_DIR}', () => {
+  const root = createRoot();
+  try {
+    writeSkill(
+      root,
+      'proj',
+      `${checklistBody('Proj')}\n## Code Examples\n\n\`\`\`bash\ncd "\${CLAUDE_PROJECT_DIR}"\n\`\`\`\n`
+    );
+    const result = runValidator(root);
+    assert.strictEqual(result.status, 1);
+    assert.ok(result.stderr.includes('ERROR:'));
+    assert.ok(result.stderr.includes('proj'));
+    assert.ok(result.stderr.includes('${CLAUDE_PROJECT_DIR}'));
+    assert.ok(result.stderr.includes('rewrite to $(pwd) or an explicit path'));
+  } finally {
+    cleanup(root);
+  }
+});
+
+check('fail: $CLAUDE_PROJECT_DIR used as a substitution in a bash fence', () => {
+  const root = createRoot();
+  try {
+    writeSkill(
+      root,
+      'proj',
+      `${checklistBody('Proj')}\n## Code Examples\n\n\`\`\`sh\ncd "$CLAUDE_PROJECT_DIR"\n\`\`\`\n`
+    );
+    const result = runValidator(root);
+    assert.strictEqual(result.status, 1);
+    assert.ok(result.stderr.includes('$CLAUDE_PROJECT_DIR'));
+    assert.ok(result.stderr.includes('rewrite to $(pwd) or an explicit path'));
+  } finally {
+    cleanup(root);
+  }
+});
+
+check('bash fence $(pwd) is accepted in place of CLAUDE_PROJECT_DIR', () => {
+  const root = createRoot();
+  try {
+    writeSkill(
+      root,
+      'proj',
+      `${checklistBody('Proj')}\n## Code Examples\n\n\`\`\`bash\ncd "$(pwd)"\n\`\`\`\n`
+    );
+    const result = runValidator(root);
+    assert.strictEqual(result.status, 0, result.stderr);
+    assert.ok(!result.stderr.includes('ERROR:'));
+    assert.ok(!result.stderr.includes('CLAUDE_PROJECT_DIR'));
+  } finally {
+    cleanup(root);
+  }
+});
+
+check('prose mention of CLAUDE_PROJECT_DIR does not fail', () => {
+  const root = createRoot();
+  try {
+    writeSkill(
+      root,
+      'prose',
+      `${checklistBody('Prose')}\nThe project root is \`CLAUDE_PROJECT_DIR\`, then cwd.\n`
+    );
+    const result = runValidator(root);
+    assert.strictEqual(result.status, 0, result.stderr);
+    assert.ok(!result.stderr.includes('ERROR:'));
+  } finally {
+    cleanup(root);
+  }
+});
+
 check('fail: $ARGUMENTS used as a substitution in a bash fence', () => {
   const root = createRoot();
   try {