diff --git a/.gitignore b/.gitignore
index 05920d3..9d7ace8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -134,6 +134,7 @@ celerybeat.pid
 # Environments
 .env
 .venv
+.venv-analysis/
 env/
 venv/
 ENV/
diff --git a/docs/dependencies.md b/docs/dependencies.md
index 0fb1d0c..a5705f4 100644
--- a/docs/dependencies.md
+++ b/docs/dependencies.md
@@ -13,6 +13,25 @@ uv sync --locked --group automation --python 3.12
 
 The second command selects an automation environment; use a separate UV_PROJECT_ENVIRONMENT when keeping application and tool environments side by side. `code2llm` itself is excluded from the registry catalog when it is the local editable package.
 
+## Analysis environment (pfix / pipreqs)
+
+The analyzer toolchain (`clickmd` / `code2logic` → `pfix` → `pipreqs`) enters the
+locked dependency graph transitively. `pipreqs` 0.5.0 — the newest published
+release — declares `Requires-Python >=3.8.1,<3.13`, so analyzer runs must not
+use the application `.venv` on Python 3.13 (PLF-036 / issue #26). Until pipreqs
+or pfix publishes a 3.13-compatible release, materialize the pinned analysis
+environment instead:
+
+```sh
+scripts/analysis-env.sh          # create/sync .venv-analysis (Python 3.12, uv.lock)
+scripts/analysis-env.sh --check  # + uv pip check + pipreqs smoke test
+```
+
+The application `.venv` is preserved untouched until the dependency-lock
+review; `.venv-analysis` is disposable and rebuilds deterministically from
+`uv.lock`. Run analyzer entry points with `.venv-analysis/bin/python`.
+
+
 ## Daily updates and verification
 
 [Dependabot configuration](../.github/dependabot.yml) checks the explicit internal package allowlist daily, including weekends, and groups updates in one PR. It includes transitive dependencies and may widen a manifest constraint when needed. Local or Git sources require separate review.
diff --git a/scripts/analysis-env.sh b/scripts/analysis-env.sh
new file mode 100755
index 0000000..18c3cbe
--- /dev/null
+++ b/scripts/analysis-env.sh
@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+# Pinned analysis environment for the analyzer toolchain (pfix -> pipreqs).
+#
+# pipreqs 0.5.0 (the newest published release) declares
+# Requires-Python >=3.8.1,<3.13, so the analyzer chain must not run on the
+# application .venv (Python 3.13) until pipreqs or pfix publishes a
+# 3.13-compatible release. This script materializes a separate, locked
+# Python 3.12 environment (PLF-036 / issue #26).
+#
+# Usage:
+#   scripts/analysis-env.sh            # create/sync .venv-analysis
+#   scripts/analysis-env.sh --check    # sync + uv pip check + smoke test
+#
+# The application .venv is never touched. Remove .venv-analysis only with
+# `uv python dir` knowledge; it is disposable and rebuilds deterministically
+# from uv.lock.
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+ANALYSIS_PYTHON="${ANALYSIS_PYTHON:-3.12}"
+ANALYSIS_ENV="${ANALYSIS_ENV:-$ROOT/.venv-analysis}"
+
+cd "$ROOT"
+UV_PROJECT_ENVIRONMENT="$ANALYSIS_ENV" uv sync --locked --python "$ANALYSIS_PYTHON" --all-extras
+
+if [[ "${1:-}" == "--check" ]]; then
+  UV_PROJECT_ENVIRONMENT="$ANALYSIS_ENV" uv pip check --python "$ANALYSIS_ENV/bin/python"
+  # Analyzer smoke test: pipreqs resolves imports for a small sample project.
+  "$ANALYSIS_ENV/bin/python" - <<'PY'
+import tempfile
+from pathlib import Path
+
+from pipreqs import pipreqs
+
+with tempfile.TemporaryDirectory() as tmp:
+    sample = Path(tmp)
+    (sample / "sample.py").write_text(
+        "import json\nimport pathlib\nimport yaml\n\nprint(json, pathlib, yaml)\n",
+        encoding="utf-8",
+    )
+    imports = pipreqs.get_all_imports(str(sample))
+    # pipreqs filters stdlib/local imports: only third-party names remain.
+    assert "yaml" in imports, f"third-party import not resolved: {imports}"
+    assert "json" not in imports, f"stdlib import should be filtered: {imports}"
+    print(f"analysis-env smoke OK (pipreqs resolved {len(imports)} imports)")
+PY
+fi
diff --git a/tests/test_analysis_env.py b/tests/test_analysis_env.py
new file mode 100644
index 0000000..7f8a508
--- /dev/null
+++ b/tests/test_analysis_env.py
@@ -0,0 +1,46 @@
+"""Guardrails for the pinned Python 3.12 analysis environment (PLF-036 / #26).
+
+The analyzer chain clickmd/code2logic -> pfix -> pipreqs cannot run on the
+Python 3.13 application venv: pipreqs 0.5.0 declares Requires-Python
+>=3.8.1,<3.13 and no newer release exists. These tests keep the analysis
+environment script and its documentation discoverable and pinned.
+"""
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parents[1]
+SCRIPT = ROOT / "scripts" / "analysis-env.sh"
+DOCS = ROOT / "docs" / "dependencies.md"
+
+
+def test_analysis_env_script_exists_and_is_executable():
+    assert SCRIPT.is_file()
+    assert SCRIPT.stat().st_mode & 0o111, "analysis-env.sh must be executable"
+
+
+def test_analysis_env_script_pins_python_312_and_locked_sync():
+    content = SCRIPT.read_text(encoding="utf-8")
+    assert 'ANALYSIS_PYTHON="${ANALYSIS_PYTHON:-3.12}"' in content
+    assert "uv sync --locked" in content
+    # The application venv must never be the target of the sync.
+    assert "UV_PROJECT_ENVIRONMENT" in content
+    assert "--all-extras" in content
+
+
+@pytest.mark.parametrize(
+    ("fragment",),
+    [
+        ("pipreqs",),
+        (">=3.8.1,<3.13",),
+        ("scripts/analysis-env.sh",),
+        (".venv-analysis",),
+    ],
+)
+def test_dependency_docs_explain_the_analysis_environment(fragment):
+    assert fragment in DOCS.read_text(encoding="utf-8")
+
+
+def test_gitignore_covers_analysis_environment():
+    ignores = (ROOT / ".gitignore").read_text(encoding="utf-8").splitlines()
+    assert ".venv-analysis/" in ignores