@@ -400,7 +400,7 @@ jobs:
         # SHA pin resolved from `gh api repos/actions/setup-go/git/refs/tags/v6.4.0`.
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0
         with:
-          go-version: '1.24'
+          go-version: '1.24.13' # exact: bump deliberately (#1645)
           cache: false
 
       - name: Restore vexctl (macOS)
@@ -617,7 +617,7 @@ jobs:
         # This job is the Linux leg of `test` (see there): same Go pin.
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0
         with:
-          go-version: '1.24'
+          go-version: '1.24.13' # exact: bump deliberately (#1645)
           cache: false
 
       - name: Install vexctl
@@ -1419,13 +1419,13 @@ jobs:
         if: matrix.suite == 'e2e_redirect_pnpm_build'
         uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
         with:
-          node-version: '24.x'
+          node-version: '24.21.0' # exact: bump deliberately (#1645)
 
       - name: Setup Python
         if: matrix.suite == 'e2e_pypi' || matrix.uv != '' || matrix.poetry != '' || matrix.pdm != '' || matrix.hatch != ''
         uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
         with:
-          python-version: '3.12.x'
+          python-version: '3.12.10' # exact: last 3.12 with Windows+macOS builds; bump deliberately (#1645)
 
       - name: Setup uv (uv legs)
         if: matrix.uv != ''
@@ -2238,7 +2238,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
         with:
-          node-version: '24.x'
+          node-version: '24.21.0' # exact: bump deliberately (#1645)
       - name: Manifest-less VEX over every real yarn classic flow
         # The script exports SOCKET_PATCH_YARN_E2E_REQUIRED=1 and
         # SOCKET_PATCH_YARN_CLASSIC_E2E_VERSION itself.
@@ -2632,9 +2632,9 @@ jobs:
           # `node:sqlite` for its store index, which does not exist before
           # Node 22 (and is only stable in 24) — on 20 every `pnpm install`
           # dies with ERR_UNKNOWN_BUILTIN_MODULE. This suite drives real,
-          # current package managers against production, so it tracks what
-          # users actually run rather than the pin the offline suites need.
-          node-version: '24.x'
+          # current package managers against production, so it runs the Node
+          # line users run rather than the 20.x pin the offline suites need.
+          node-version: '24.21.0' # exact: bump deliberately (#1645)
 
       - name: Setup npm-family package managers
         if: steps.gate.outputs.run == 'true'
@@ -2679,7 +2679,7 @@ jobs:
         if: steps.gate.outputs.run == 'true'
         uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
         with:
-          python-version: '3.12.x'
+          python-version: '3.12.10' # exact: last 3.12 with Windows+macOS builds; bump deliberately (#1645)
 
       - name: Install uv
         if: steps.gate.outputs.run == 'true'
@@ -2699,7 +2699,7 @@ jobs:
         if: steps.gate.outputs.run == 'true'
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0
         with:
-          go-version: '1.24'
+          go-version: '1.24.13' # exact: bump deliberately (#1645)
           cache: false
 
       - name: Run hosted-mode production e2e
 
@@ -0,0 +1,250 @@
+#!/usr/bin/env python3
+"""Fail when a workflow installs an oracle toolchain at a floating version.
+
+`pin-check.yml` makes every `uses:` reference an immutable SHA, but the
+*tool* a setup action installs can still float: `node-version: '24.x'`,
+`python-version: '3.12.x'`, `go-version: '1.24'`, or `astral-sh/setup-uv`
+with no `version:` at all. Any upstream release then changes what CI runs
+while main stays the same. On 2026-10-20 uv 0.13.2 did exactly that, failed
+a Pipenv leg on every merge-queue entry and stalled the queue for 2.7 h
+(#1645).
+
+Rules, per step:
+  * `astral-sh/setup-uv` must set `with.version`.
+  * `with.version` of setup-uv, and `with.node-version`, `python-version`
+    and `go-version` of any step, must be an exact `X.Y.Z` release.
+  * A `${{ ... }}` expression may read only `matrix.*`. Every quoted value
+    it can yield (comparison operands aside) must be exact, and so must
+    every value the job's matrix gives a key it reads. A matrix built with
+    `fromJSON` can't be resolved statically and is left to review.
+
+The workflow is scanned as text with the standard library only, the same
+way scripts/tests reads ci.yml, so the lint runs on any python3. It relies
+on the block style ci.yml uses: steps as `- ` items, `with:` inputs one
+per line, matrix rows as `{key: value, ...}` or `key: [a, b]`. A step
+shared through a YAML anchor is checked once, against the matrix of the
+job that defines it.
+
+Repo gate: scripts/tests/test_check_tool_pins.py runs this on ci.yml in
+the lean `lint-ecosystems` job.
+
+Usage: check-tool-pins.py WORKFLOW.yml [...]   (exit 1 on any violation)
+"""
+
+import re
+import sys
+
+EXACT = re.compile(r"^\d+\.\d+\.\d+$")
+VERSION_KEYS = ("node-version", "python-version", "go-version")
+UV_ACTION = "astral-sh/setup-uv"
+LITERAL = re.compile(r"'([^']*)'")
+CONTEXT_REF = re.compile(r"\b([A-Za-z_][A-Za-z0-9_]*)\.([A-Za-z0-9_-]+)")
+COMPARED = re.compile(r"(==|!=)\s*$")
+COMPARES = re.compile(r"^\s*(==|!=)")
+JOB = re.compile(r"^  ([A-Za-z0-9_-]+):\s*(#.*)?$")
+KEY_VALUE = re.compile(r"^(\s*)(-\s+)?([A-Za-z0-9_-]+):\s*(.*)$")
+
+
+def indent(line):
+    return len(line) - len(line.lstrip(" "))
+
+
+def strip_comment(value):
+    """Drop a trailing ` # ...` comment that sits outside quotes."""
+    quote = None
+    for i, ch in enumerate(value):
+        if quote:
+            if ch == quote:
+                quote = None
+        elif ch in "'\"":
+            quote = ch
+        elif ch == "#" and (i == 0 or value[i - 1].isspace()):
+            return value[:i].rstrip()
+    return value.strip()
+
+
+def unquote(value):
+    value = value.strip()
+    if len(value) >= 2 and value[0] == value[-1] and value[0] in "'\"":
+        return value[1:-1]
+    return value
+
+
+def is_content(line):
+    stripped = line.strip()
+    return stripped != "" and not stripped.startswith("#")
+
+
+def job_spans(lines):
+    """(name, start, end) for every job under the top-level `jobs:` key."""
+    try:
+        top = next(i for i, l in enumerate(lines) if re.match(r"^jobs:\s*(#.*)?$", l))
+    except StopIteration:
+        return []
+    starts = []
+    for i in range(top + 1, len(lines)):
+        line = lines[i]
+        if is_content(line) and indent(line) == 0:
+            break
+        m = JOB.match(line)
+        if m:
+            starts.append((m.group(1), i))
+    end_of_jobs = next(
+        (i for i in range(top + 1, len(lines)) if is_content(lines[i]) and indent(lines[i]) == 0),
+        len(lines),
+    )
+    return [
+        (name, start, starts[n + 1][1] if n + 1 < len(starts) else end_of_jobs)
+        for n, (name, start) in enumerate(starts)
+    ]
+
+
+def matrix_values(lines, start, end, key):
+    """Every value the job's matrix gives `key`, or None if unresolvable."""
+    matrix_at = None
+    for i in range(start, end):
+        m = KEY_VALUE.match(lines[i])
+        if m and m.group(3) == "matrix" and not m.group(2):
+            matrix_at = i
+            break
+    if matrix_at is None:
+        return []
+    m = KEY_VALUE.match(lines[matrix_at])
+    if "${{" in m.group(4):
+        return None
+    base = indent(lines[matrix_at])
+    block_end = matrix_at + 1
+    while block_end < end and (not is_content(lines[block_end]) or indent(lines[block_end]) > base):
+        block_end += 1
+    values = []
+    flow = re.compile(r"[{,]\s*" + re.escape(key) + r"""\s*:\s*('[^']*'|"[^"]*"|[^,}]+)""")
+    for i in range(matrix_at + 1, block_end):
+        line = strip_comment(lines[i])
+        for v in flow.findall(line):
+            values.append(unquote(v))
+        kv = KEY_VALUE.match(line)
+        if kv and kv.group(3) == key and not kv.group(2):
+            rest = kv.group(4).strip()
+            if rest.startswith("${{"):
+                return None
+            if rest.startswith("["):
+                values.extend(unquote(v) for v in rest.strip("[]").split(",") if v.strip())
+            elif rest:
+                values.append(unquote(rest))
+            else:
+                j = i + 1
+                while j < block_end and (not is_content(lines[j]) or indent(lines[j]) > indent(lines[i])):
+                    item = re.match(r"^\s*-\s+(.*)$", strip_comment(lines[j]))
+                    if item:
+                        values.append(unquote(item.group(1)))
+                    j += 1
+    return values
+
+
+def yielded_literals(expr):
+    """Quoted literals an expression can evaluate to (not compared against)."""
+    out = []
+    for m in LITERAL.finditer(expr):
+        before, after = expr[: m.start()], expr[m.end() :]
+        if COMPARED.search(before) or COMPARES.match(after):
+            continue
+        out.append(m.group(1))
+    return out
+
+
+def check_value(lines, span, value):
+    """Return reasons `value` is not an exact pin (empty if it is)."""
+    text = unquote(strip_comment(value))
+    if "${{" not in text:
+        return [] if EXACT.match(text) else [f"{text!r} is not an exact X.Y.Z"]
+    reasons = []
+    body = LITERAL.sub("''", text)
+    for ctx, key in CONTEXT_REF.findall(body):
+        if ctx != "matrix":
+            reasons.append(f"reads `{ctx}.{key}`, which can't be checked; use a literal or matrix value")
+            continue
+        values = matrix_values(lines, span[1], span[2], key) if span else None
+        for v in values or []:
+            if not EXACT.match(v):
+                reasons.append(f"matrix.{key} value {v!r} is not an exact X.Y.Z")
+    for literal in yielded_literals(text):
+        if not EXACT.match(literal):
+            reasons.append(f"value {literal!r} in the expression is not an exact X.Y.Z")
+    return reasons
+
+
+def steps(lines):
+    """Yield (line_no, uses, {input: (line_no, value)}) for every `- ` item."""
+    for i, line in enumerate(lines):
+        m = re.match(r"^(\s*)-\s+(.*)$", line)
+        if not m or m.group(2).startswith("{") or m.group(2).startswith("#"):
+            continue
+        dash = len(m.group(1))
+        item = dash + 2
+        uses, inputs, with_at = None, {}, None
+        j = i
+        while j < len(lines):
+            cur = lines[j]
+            if j > i and is_content(cur) and indent(cur) <= dash:
+                break
+            text = cur if j > i else " " * item + m.group(2)
+            kv = KEY_VALUE.match(text)
+            if kv and not kv.group(2):
+                level = len(kv.group(1))
+                if level == item:
+                    with_at = j if kv.group(3) == "with" else None
+                    if kv.group(3) == "uses":
+                        uses = unquote(strip_comment(kv.group(4)))
+                elif with_at is not None and level == item + 2:
+                    inputs[kv.group(3)] = (j, kv.group(4))
+            j += 1
+        if uses is not None or inputs:
+            yield i, uses, inputs
+
+
+def check_text(path, text):
+    lines = text.splitlines()
+    spans = job_spans(lines)
+    violations = []
+    for line_no, uses, inputs in steps(lines):
+        span = next((s for s in spans if s[1] <= line_no < s[2]), None)
+        where = f"{path}:{line_no + 1}" + (f": job {span[0]!r}" if span else "")
+        if uses and uses.split("@")[0].lower() == UV_ACTION:
+            if "version" not in inputs:
+                violations.append(f"{where}: {UV_ACTION} without `version:`")
+            else:
+                at, value = inputs["version"]
+                for r in check_value(lines, span, value):
+                    violations.append(f"{path}:{at + 1}: setup-uv version {r}")
+        for key in VERSION_KEYS:
+            if key in inputs:
+                at, value = inputs[key]
+                for r in check_value(lines, span, value):
+                    violations.append(f"{path}:{at + 1}: {key} {r}")
+    return violations
+
+
+def check_workflow(path):
+    with open(path, encoding="utf-8") as f:
+        return check_text(path, f.read())
+
+
+def main(argv):
+    if not argv:
+        print(__doc__.strip().splitlines()[-1], file=sys.stderr)
+        return 2
+    violations = [v for path in argv for v in check_workflow(path)]
+    for v in violations:
+        print(f"::error::{v}")
+    if violations:
+        print(
+            f"{len(violations)} floating toolchain version(s). Pin each to an "
+            "exact release and bump it deliberately in its own PR."
+        )
+        return 1
+    print("All toolchain versions are pinned to exact releases.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))