diff --git a/static/workspace.js b/static/workspace.js
index e3a3da4c..4a2eefb4 100644
--- a/static/workspace.js
+++ b/static/workspace.js
@@ -170,6 +170,12 @@ function _normalizeArtifactPath(path){
   if(!path) return '';
   path = String(path).trim().replace(/[\`"'<>),.;:]+$/g,'').replace(/^[\`"'(<]+/g,'');
   if(!path || path.length > 240 || path.includes('://')) return '';
+  // Canonicalize workspace-relative prefixes so a file-tree open ("foo.md") and a
+  // tool arg recorded as "./foo.md" or "~/foo.md" compare equal for mutation
+  // tracking; otherwise an agent edit via a ./-prefixed path leaves the open
+  // preview stale (#3262 / pre-release regression-gate finding).
+  path = path.replace(/^~\//,'').replace(/^(?:\.\/)+/,'');
+  if(!path) return '';
   if(ARTIFACT_IGNORE_RE.test(path)) return '';
   if(!/[./]/.test(path)) return '';
   return path;
diff --git a/tests/test_issue3262_artifact_path_canonicalization.py b/tests/test_issue3262_artifact_path_canonicalization.py
new file mode 100644
index 00000000..76c81305
--- /dev/null
+++ b/tests/test_issue3262_artifact_path_canonicalization.py
@@ -0,0 +1,87 @@
+"""Regression: _normalizeArtifactPath() canonicalizes ./ and ~/ prefixes (#3262).
+
+The workspace preview reload-on-mutation tracking (#3262) compares the open
+preview path against the set of paths the agent's tools touched during the
+turn. File-tree opens record a bare workspace-relative path ("foo.md"), but a
+tool argument can arrive as "./foo.md" or "~/foo.md". Before the fix,
+_normalizeArtifactPath() did not strip those prefixes, so "./foo.md" != "foo.md"
+in _turnMutatedPreviewPaths and an agent edit via a ./-prefixed path left the
+open preview stale (pre-release Codex regression-gate finding).
+
+This drives the ACTUAL _normalizeArtifactPath() from static/workspace.js via
+node so it can't drift from a Python mirror.
+"""
+
+import json
+import re
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+REPO = Path(__file__).resolve().parent.parent
+WORKSPACE_JS = (REPO / "static" / "workspace.js").read_text(encoding="utf-8")
+NODE = shutil.which("node")
+
+pytestmark = pytest.mark.skipif(NODE is None, reason="node not on PATH")
+
+
+def _extract(decl_regex: str) -> str:
+    m = re.search(decl_regex, WORKSPACE_JS)
+    assert m, f"definition not found: {decl_regex}"
+    return m.group(0)
+
+
+def _normalize_via_node(paths):
+    ignore_re = _extract(r"const ARTIFACT_IGNORE_RE = /.*?/;")
+    # Extract the full function body by brace-matching.
+    start = WORKSPACE_JS.index("function _normalizeArtifactPath(")
+    brace = WORKSPACE_JS.index("{", start)
+    depth = 0
+    end = None
+    for i in range(brace, len(WORKSPACE_JS)):
+        c = WORKSPACE_JS[i]
+        if c == "{":
+            depth += 1
+        elif c == "}":
+            depth -= 1
+            if depth == 0:
+                end = i + 1
+                break
+    fn = WORKSPACE_JS[start:end]
+    driver = (
+        ignore_re + "\n" + fn + "\n"
+        + "const out = JSON.parse(process.argv[1]).map(_normalizeArtifactPath);\n"
+        + "process.stdout.write(JSON.stringify(out));\n"
+    )
+    r = subprocess.run(
+        [NODE, "-e", driver, json.dumps(paths)],
+        capture_output=True, text=True, timeout=15,
+    )
+    assert r.returncode == 0, f"node failed: {r.stderr}"
+    return json.loads(r.stdout)
+
+
+def test_dot_slash_and_tilde_prefixes_canonicalize_to_bare_path():
+    out = _normalize_via_node(["foo.md", "./foo.md", "~/foo.md", "././foo.md"])
+    assert out == ["foo.md", "foo.md", "foo.md", "foo.md"], (
+        f"./ and ~/ prefixes must canonicalize to the bare workspace-relative "
+        f"path so mutation tracking matches a file-tree open (#3262); got {out}"
+    )
+
+
+def test_nested_relative_path_prefix_canonicalizes():
+    out = _normalize_via_node(["sub/dir/x.py", "./sub/dir/x.py", "~/sub/dir/x.py"])
+    assert out == ["sub/dir/x.py", "sub/dir/x.py", "sub/dir/x.py"], (
+        f"prefix canonicalization must apply to nested paths too (#3262); got {out}"
+    )
+
+
+def test_canonicalization_preserves_ignore_and_url_rejection():
+    # Canonicalization must not weaken the existing rejections.
+    out = _normalize_via_node(["./node_modules/x.js", "https://e.com/a", "./"])
+    assert out == ["", "", ""], (
+        f"ignore-dir, URL, and empty-after-strip rejections must still hold "
+        f"after prefix canonicalization (#3262); got {out}"
+    )