fix(scripts): stop wrap composition looping on a token in core content

scripts/bash/common.sh

@@ -902,12 +902,20 @@ except Exception as exc:
                     *'{CORE_TEMPLATE}'*) ;;
                     *) echo "Error: wrap strategy missing {CORE_TEMPLATE} placeholder" >&2; return 2 ;;
                 esac
-                while [[ "$layer_content" == *'{CORE_TEMPLATE}'* ]]; do
-                    local before="${layer_content%%\{CORE_TEMPLATE\}*}"
-                    local after="${layer_content#*\{CORE_TEMPLATE\}}"
-                    layer_content="${before}${content}${after}"
+                # Consume the wrapper left to right instead of rewriting it in
+                # place. Rewriting re-scanned the string just modified, so base
+                # content holding a literal {CORE_TEMPLATE} reintroduced the
+                # token every pass and the loop never terminated. Advancing over
+                # ``rest`` bounds the work by the tokens in the original wrapper
+                # and leaves inserted content untouched, matching the single-pass
+                # semantics of .Replace()/.replace() in the PowerShell and Python
+                # ports.
+                local wrapped="" rest="$layer_content"
+                while [[ "$rest" == *'{CORE_TEMPLATE}'* ]]; do
+                    wrapped="${wrapped}${rest%%\{CORE_TEMPLATE\}*}${content}"
+                    rest="${rest#*\{CORE_TEMPLATE\}}"
                 done
-                content="$layer_content"
+                content="${wrapped}${rest}"
                 ;;
             *) echo "Error: unknown strategy '$strat'" >&2; return 2 ;;
         esac

tests/parity_helpers.py

@@ -83,15 +83,25 @@ def clean_env() -> dict[str, str]:
 
 
 def run(
-    cmd: list[str], repo: Path, env: dict[str, str] | None = None
+    cmd: list[str],
+    repo: Path,
+    env: dict[str, str] | None = None,
+    timeout: float | None = None,
 ) -> subprocess.CompletedProcess[str]:
+    """Run a script variant.
+
+    ``timeout`` guards cases whose regression mode is a hang rather than a bad
+    value; without it such a failure would stall the suite instead of failing
+    it. ``subprocess.TimeoutExpired`` propagates so the test reports the hang.
+    """
     return subprocess.run(
         cmd,
         cwd=repo,
         capture_output=True,
         text=True,
         check=False,
         env=env if env is not None else clean_env(),
+        timeout=timeout,
     )
 
 

tests/test_resolve_template_python_parity.py

@@ -91,6 +91,40 @@ def test_all_variants_preserve_composition_parity(
     )
 
 
+@requires_bash
+def test_all_variants_treat_core_token_in_core_content_as_literal(
+    tmp_path: Path,
+) -> None:
+    """Core content holding a literal ``{CORE_TEMPLATE}`` must not be re-expanded.
+
+    The wrap strategy fills the placeholders present in the *wrapper*. A token
+    that arrives as part of the composed core content is data, not a slot, so it
+    survives into the output untouched. Rescanning the substituted string instead
+    reintroduces a token on every pass and never terminates, so the regression
+    mode here is a hang rather than a wrong value -- hence the timeout, without
+    which a reintroduced bug would stall the suite instead of failing it.
+    """
+    repo = make_repo(tmp_path)
+    install_scripts(repo, SCRIPT)
+    expected = install_composition_stack(repo, TEMPLATE, "# Core {CORE_TEMPLATE}\n")
+
+    results = [
+        run(bash_cmd(repo, SCRIPT, TEMPLATE, "--json"), repo, timeout=30),
+        run(py_cmd(repo, SCRIPT, TEMPLATE, "--json"), repo, timeout=30),
+    ]
+    if HAS_POWERSHELL:
+        results.append(run(ps_cmd(repo, SCRIPT, TEMPLATE, "-Json"), repo, timeout=30))
+
+    assert all(result.returncode == 0 for result in results)
+    assert all(result.stderr == "" for result in results)
+    # The wrapper contributes exactly one placeholder, so exactly one literal
+    # token -- the one carried in by the core content -- remains in the output.
+    assert expected.count("{CORE_TEMPLATE}") == 1
+    assert all(
+        json_stdout(result)["TEMPLATE_CONTENT"] == expected for result in results
+    )
+
+
 @requires_bash
 def test_all_variants_read_utf8_registry_under_ascii_locale(
     tmp_path: Path,