diff --git a/.dev/tools/check-cookbook-snippets.py b/.dev/tools/check-cookbook-snippets.py
index ca173a0..59924be 100755
--- a/.dev/tools/check-cookbook-snippets.py
+++ b/.dev/tools/check-cookbook-snippets.py
@@ -126,6 +126,12 @@
 from dp_python_lib.client import data_frame_conversions as dfc
 
 client: MldpClient = MldpClient()
+# client.annotation and client.query are typed `X | None`, which is honest: they are None when MldpClient is given
+# only an ingestion channel (connecting.md, "Sub-clients can be None").  A client built from configuration, as every
+# recipe's is, always has both, so narrow once here rather than in every recipe.  Do NOT instead disable union-attr:
+# on an `X | None` receiver that code also carries the "no such attribute on X" error, so the self-test canary stops
+# firing and every misspelled name under client.annotation passes.
+assert client.annotation is not None and client.query is not None
 begin: datetime = datetime(2024, 1, 1, tzinfo=timezone.utc)
 end: datetime = datetime(2024, 1, 2, tzinfo=timezone.utc)
 
@@ -266,9 +272,9 @@ def check_types(snippets: list[Snippet], verbose: bool) -> list[str]:
             *MYPY_CMD,
             # The generated gRPC stubs are untyped; without this every `import ..._pb2` is an error.
             "--ignore-missing-imports",
-            # Type-check the snippets but NOT the library itself.  dp_python_lib currently has
-            # ~145 of its own mypy errors (mostly untyped protobuf stubs); those are not this
-            # tool's business and would bury real snippet errors.
+            # Type-check the snippets but NOT the library itself.  The library is checked by
+            # `mypy src/` in CI's quality job; re-reporting its errors here would bury real
+            # snippet errors.  (The [tool.mypy] config in pyproject.toml applies here too.)
             "--follow-imports=silent",
             # Snippets are illustrative; unreachable/redundant warnings are noise here.
             "--no-warn-unused-ignores",
diff --git a/.dev/tools/check-release-notes.py b/.dev/tools/check-release-notes.py
new file mode 100755
index 0000000..9b4991f
--- /dev/null
+++ b/.dev/tools/check-release-notes.py
@@ -0,0 +1,226 @@
+#!/usr/bin/env python3
+"""Verify that every doc/release-notes/rel-X.Y.Z.md carries a correct verification section and changelog link.
+
+The notes file is published verbatim as the GitHub release body (release.yml; plan/tickets/56/plan.md D1), so
+the artifact verification instructions and the changelog link exist only if the file contains them.  This checks,
+per file:
+
+  - the file name is rel-X.Y.Z.md (release.yml derives the name from the tag, so nothing else is ever published);
+  - there is a `## Verifying these artifacts` heading;
+  - there is at least one `sigstore verify identity` command, each naming the wheel, the sdist, and SHA256SUMS,
+    and every `--cert-identity` in the file is exactly this repository's release.yml at *this file's* tag, with
+    the GitHub Actions OIDC issuer;
+  - there is a `**Full Changelog**:` compare link ending at this file's tag and starting at an earlier one.
+
+The identity check is the one that earns its keep.  The section is hand-written per release, usually by copying
+the previous one, and a stale tag in the identity makes `sigstore verify` reject every genuine artifact of the
+release ("Certificate's SANs do not match").  Readers would reasonably conclude the release is forged.  The
+changelog link is copied the same way and goes stale the same way, though less dangerously.  Only the `<this>`
+end can be checked: which release came before is not knowable from one file, so `<prev>` is checked only for
+being earlier.
+
+Runs in CI's quality job over every notes file, so a mistake fails the notes PR rather than the tag push; and in
+release.yml on the tagged file, as a backstop.  Each run starts with a self-test that feeds the rules known-bad
+notes and fails if any is accepted, so a rule that has quietly stopped matching cannot pass as clean notes.
+
+Usage:
+    python .dev/tools/check-release-notes.py [FILE ...]
+
+With no arguments, checks every doc/release-notes/rel-*.md.  Stdlib only.  Exits 0 if all pass, 1 otherwise.
+"""
+
+from __future__ import annotations
+
+import re
+import sys
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+NOTES_DIR = REPO_ROOT / "doc" / "release-notes"
+
+REPOSITORY = "osprey-dcs/dp-python-lib"
+OIDC_ISSUER = "https://token.actions.githubusercontent.com"
+
+STEM_RE = re.compile(r"^rel-(\d+)\.(\d+)\.(\d+)$")
+HEADING_RE = re.compile(r"^## Verifying these artifacts\s*$", re.MULTILINE)
+# The whole command, backslash continuations included, up to the first line that does not continue.
+VERIFY_RE = re.compile(r"\bsigstore\s+verify\s+identity\b(?:[^\n]*\\\n)*[^\n]*")
+IDENTITY_RE = re.compile(r"--cert-identity[ =]\"?([^\"\s]+)\"?")
+ISSUER_RE = re.compile(r"--cert-oidc-issuer[ =]\"?([^\"\s]+)\"?")
+CHANGELOG_RE = re.compile(r"^\*\*Full Changelog\*\*:\s*(\S+)\s*$", re.MULTILINE)
+COMPARE_RE = re.compile(
+    rf"^https://github\.com/{re.escape(REPOSITORY)}/compare/(rel-\d+\.\d+\.\d+)\.\.\.(rel-\d+\.\d+\.\d+)$"
+)
+
+# What each `sigstore verify identity` must name, as (description, predicate over its file operands).  Every
+# release signs all three, and verifying only the wheel was exactly the shape rel-1.16.0's page first shipped with.
+REQUIRED_OPERANDS = [
+    ("the wheel", lambda arg: arg.endswith(".whl")),
+    ("the sdist", lambda arg: arg.endswith(".tar.gz")),
+    ("SHA256SUMS", lambda arg: arg == "SHA256SUMS"),
+]
+
+
+def expected_identity(tag: str) -> str:
+    return f"https://github.com/{REPOSITORY}/.github/workflows/release.yml@refs/tags/{tag}"
+
+
+def version_of(tag: str) -> tuple[int, ...]:
+    match = STEM_RE.match(tag)
+    assert match is not None
+    return tuple(int(part) for part in match.groups())
+
+
+def verify_operands(command: str) -> list[str]:
+    """The file operands of one `sigstore verify identity` command: every token that is not an option or its value."""
+    tokens = command.replace("\\\n", " ").split()[3:]
+    operands: list[str] = []
+    skip_value = False
+    for token in tokens:
+        if skip_value:
+            skip_value = False
+        elif token.startswith("--"):
+            skip_value = "=" not in token
+        else:
+            operands.append(token)
+    return operands
+
+
+def check_text(name: str, tag: str, text: str) -> list[str]:
+    """Returns one message per problem found in the notes `text` for `tag`; empty when it passes."""
+    problems: list[str] = []
+
+    if not HEADING_RE.search(text):
+        problems.append(f"{name}: missing a '## Verifying these artifacts' section")
+
+    commands = VERIFY_RE.findall(text)
+    if not commands:
+        problems.append(f"{name}: missing a 'sigstore verify identity' command")
+    for command in commands:
+        operands = verify_operands(command)
+        for description, matches in REQUIRED_OPERANDS:
+            if not any(matches(arg) for arg in operands):
+                problems.append(f"{name}: 'sigstore verify identity' does not verify {description}")
+
+    identities = IDENTITY_RE.findall(text)
+    if not identities:
+        problems.append(f"{name}: missing --cert-identity")
+    want = expected_identity(tag)
+    for identity in identities:
+        if identity != want:
+            problems.append(f"{name}: --cert-identity is\n      {identity}\n    expected\n      {want}")
+
+    issuers = ISSUER_RE.findall(text)
+    if not issuers:
+        problems.append(f"{name}: missing --cert-oidc-issuer")
+    for issuer in issuers:
+        if issuer != OIDC_ISSUER:
+            problems.append(f"{name}: --cert-oidc-issuer is {issuer}, expected {OIDC_ISSUER}")
+
+    changelogs = CHANGELOG_RE.findall(text)
+    if not changelogs:
+        problems.append(f"{name}: missing a '**Full Changelog**: .../compare/rel-<prev>...{tag}' line")
+    for url in changelogs:
+        compare = COMPARE_RE.match(url)
+        if compare is None:
+            problems.append(
+                f"{name}: Full Changelog link is\n      {url}\n    expected"
+                f"\n      https://github.com/{REPOSITORY}/compare/rel-<prev>...{tag}"
+            )
+            continue
+        prev, this = compare.groups()
+        if this != tag:
+            problems.append(f"{name}: Full Changelog link ends at {this}, expected {tag}")
+        elif version_of(prev) >= version_of(tag):
+            problems.append(f"{name}: Full Changelog link starts at {prev}, which is not earlier than {tag}")
+
+    return problems
+
+
+def check_file(path: Path) -> list[str]:
+    """Returns one message per problem found in `path`; empty when it passes."""
+    tag = path.stem
+    if path.suffix != ".md" or not STEM_RE.match(tag):
+        return [f"{path}: name must be rel-X.Y.Z.md (release.yml looks the notes up by tag)"]
+    return check_text(str(path), tag, path.read_text(encoding="utf-8"))
+
+
+def _sample(
+    identity_tag: str = "rel-2.1.0",
+    files: str = "dp_python_lib-*.whl dp_python_lib-*.tar.gz SHA256SUMS",
+    changelog: str | None = "rel-2.0.0...rel-2.1.0",
+) -> str:
+    notes = f"""# dp-python-lib rel-2.1.0
+
+## Verifying these artifacts
+
+```bash
+sigstore verify identity \\
+  --cert-identity "{expected_identity(identity_tag)}" \\
+  --cert-oidc-issuer "{OIDC_ISSUER}" \\
+  {files}
+```
+"""
+    if changelog is not None:
+        notes += f"\n**Full Changelog**: https://github.com/{REPOSITORY}/compare/{changelog}\n"
+    return notes
+
+
+def self_test() -> list[str]:
+    """Confirms a correct sample passes and each known-bad variant is rejected; returns a message per failure."""
+    failures: list[str] = []
+    good = check_text("<good>", "rel-2.1.0", _sample())
+    if good:
+        failures.append("a correct sample was rejected:\n      " + "\n      ".join(good))
+
+    bad_cases = {
+        "a stale --cert-identity tag": _sample(identity_tag="rel-2.0.0"),
+        "a verify of the wheel only": _sample(files="dp_python_lib-*.whl"),
+        "a verify missing SHA256SUMS": _sample(files="dp_python_lib-*.whl dp_python_lib-*.tar.gz"),
+        "a verify missing the sdist": _sample(files="dp_python_lib-*.whl SHA256SUMS"),
+        "no Full Changelog line": _sample(changelog=None),
+        "a Full Changelog link ending at a stale tag": _sample(changelog="rel-1.9.0...rel-2.0.0"),
+        "a Full Changelog link starting at a later tag": _sample(changelog="rel-2.2.0...rel-2.1.0"),
+        "a Full Changelog link to another repository": _sample().replace(
+            f"{REPOSITORY}/compare", "someone-else/dp-python-lib/compare"
+        ),
+        "no verification heading": _sample().replace("## Verifying these artifacts", "## Verification"),
+    }
+    for description, notes in bad_cases.items():
+        if not check_text(f"<{description}>", "rel-2.1.0", notes):
+            failures.append(f"{description} was accepted")
+    return failures
+
+
+def main(argv: list[str]) -> int:
+    canary_failures = self_test()
+    if canary_failures:
+        print("FAIL: checker self-test failed; its rules no longer catch what they are meant to\n")
+        for failure in canary_failures:
+            print(f"  {failure}")
+        return 1
+
+    paths = [Path(arg) for arg in argv] if argv else sorted(NOTES_DIR.glob("rel-*.md"))
+    if not paths:
+        print(f"FAIL: no release notes found under {NOTES_DIR}")
+        return 1
+
+    problems: list[str] = []
+    for path in paths:
+        if not path.is_file():
+            problems.append(f"{path}: not found")
+            continue
+        problems.extend(check_file(path))
+
+    if problems:
+        print(f"FAIL: {len(problems)} problem(s) in {len(paths)} release notes file(s)\n")
+        for problem in problems:
+            print(f"  {problem}")
+        return 1
+
+    print(f"OK: {len(paths)} release notes file(s)")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 40bcb18..914c721 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -57,7 +57,7 @@ jobs:
         run: pytest tests/unit -v -m "not integration"
 
   quality:
-    name: Lint, format, and docs
+    name: Lint, type-check, and docs
     runs-on: ubuntu-latest
     # These checks are interpreter-independent, so they run once rather than on all four
     # matrix legs -- no added signal, 4x the runtime.
@@ -85,11 +85,22 @@ jobs:
       - name: Ruff format check
         run: ruff format --check .
 
+      - name: Type check
+        # Config under [tool.mypy] in pyproject.toml.  The generated gRPC package is excluded
+        # until it ships typed stubs (osprey-dcs/dp-grpc#158); everything hand-written is checked.
+        run: mypy src/
+
       - name: Check cookbook snippets
         # Type-checks every Python example in doc/cookbook against this package, so a recipe
         # referencing a renamed attribute or method fails here rather than in a user's hands.
         run: python .dev/tools/check-cookbook-snippets.py
 
+      - name: Check release notes
+        # Each doc/release-notes/rel-X.Y.Z.md is published verbatim as its release body, so it
+        # must carry a verification section whose signing identity names its own tag.  Checked
+        # here so a mistake fails the notes PR, not the tag push.
+        run: python .dev/tools/check-release-notes.py
+
   build:
     name: Build distributions
     runs-on: ubuntu-latest
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index b9e7208..bd7782f 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -73,13 +73,17 @@ jobs:
             echo "Manual dispatch; version comes from setuptools-scm."
           fi
 
-      - name: Verify release notes exist
+      - name: Verify release notes
         id: notes
         # Checked here, before the build, rather than left to action-gh-release: that action
         # fails on a missing body_path only after everything has been built, signed, and
         # uploaded, which reads as a late and unrelated failure.  A rehearsal (workflow_dispatch)
         # has no rel- tag and so no notes to look for, hence the push-only guard.
         # Every release from 1.16.0 on ships notes; see CLAUDE.md "Cutting a release".
+        #
+        # The notes file is the entire release body, so it must carry its own verification
+        # section with this tag's signing identity.  CI's quality job runs the same checker
+        # on every notes file at PR time; this is the backstop for a tag pushed anyway.
         if: github.event_name == 'push'
         run: |
           set -euo pipefail
@@ -89,6 +93,7 @@ jobs:
             echo "::error::Add the notes for ${{ steps.version.outputs.version }} and retag once they are on the tagged commit."
             exit 1
           fi
+          python .dev/tools/check-release-notes.py "$NOTES"
           echo "notes=$NOTES" >> "$GITHUB_OUTPUT"
 
       - name: Build wheel and sdist
@@ -144,48 +149,19 @@ jobs:
         with:
           inputs: ./dist/*.whl ./dist/*.tar.gz ./dist/SHA256SUMS
 
-      - name: Assemble the release body
-        # The publish job downloads artifacts but never checks out the repo, so the notes
-        # have to travel with the dist/ upload.  They are concatenated with the verification
-        # and install instructions here rather than passed to action-gh-release as `body`,
-        # because `body_path` takes precedence over `body` outright (it is a fallback, not a
-        # companion) -- setting both would silently drop these instructions from the release.
-        # action-gh-release appends its generated commit list after whatever body it resolves,
-        # so generate_release_notes still composes on top of this.
+      - name: Stage the release notes
+        # The notes file is the release body, verbatim -- nothing is added to it here.  That is
+        # what makes `gh release edit <tag> --notes-file doc/release-notes/<tag>.md` a lossless
+        # republish: anything a workflow appended would be exactly what such an edit drops, which
+        # is how rel-1.16.0's page lost its verification instructions (#56).  The verification
+        # section is therefore hand-written in each notes file and checked above.
+        #
+        # The publish job downloads artifacts but never checks out the repo, so the notes travel
+        # with the dist/ upload.  Staged after signing, so they are not signed as an artifact.
         if: github.event_name == 'push'
         env:
           NOTES: ${{ steps.notes.outputs.notes }}
-        run: |
-          set -euo pipefail
-          {
-            cat "$NOTES"
-            cat <<'BODY'
-
-          ## Verifying these artifacts
-
-          Checksums:
-
-          ```bash
-          sha256sum -c SHA256SUMS
-          ```
-
-          Signatures (keyless Sigstore; `pip install sigstore`):
-
-          ```bash
-          sigstore verify identity \
-            --cert-identity "https://github.com/${{ github.repository }}/.github/workflows/release.yml@${{ github.ref }}" \
-            --cert-oidc-issuer "https://token.actions.githubusercontent.com" \
-            dp_python_lib-*.whl
-          ```
-
-          ## Installing
-
-          ```bash
-          pip install dp_python_lib-*.whl
-          ```
-          BODY
-          } > dist/RELEASE_BODY.md
-          cat dist/RELEASE_BODY.md
+        run: cp "$NOTES" dist/RELEASE_NOTES.md
 
       - name: Upload build outputs
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
@@ -222,13 +198,35 @@ jobs:
             dist/*.tar.gz
             dist/SHA256SUMS
             dist/*.sigstore.json
-          generate_release_notes: true
           fail_on_unmatched_files: true
-          # Assembled in the build job: the hand-written doc/release-notes/rel-X.Y.Z.md
-          # followed by the verification and install instructions.  RELEASE_BODY.md is
-          # deliberately absent from `files` above -- it is the release body, not an
-          # artifact to download.
-          body_path: dist/RELEASE_BODY.md
+          # doc/release-notes/<tag>.md, verbatim.  RELEASE_NOTES.md is deliberately absent
+          # from `files` above -- it is the release body, not an artifact to download.
+          #
+          # generate_release_notes is deliberately NOT set: GitHub's commit list would be the
+          # one part of the body not in the file, and so the part a republish from the file
+          # silently drops.  The notes carry a hand-written Full Changelog link instead.
+          body_path: dist/RELEASE_NOTES.md
+
+      - name: Verify the published body matches the notes
+        # Closes the loop for the one path this workflow controls: if the action ever resolves
+        # a different body (a changed default, a pre-existing release it declines to update),
+        # the release is flagged here instead of being noticed by a reader.  Later hand edits of
+        # the page are out of reach of any workflow; CLAUDE.md forbids them instead.
+        env:
+          GH_TOKEN: ${{ github.token }}
+          GH_REPO: ${{ github.repository }}
+          TAG: ${{ github.ref_name }}
+        run: |
+          set -euo pipefail
+          gh release view "$TAG" --json body --jq .body > published.md
+          # GitHub does not preserve the file's trailing newline, so both sides go through
+          # "$(cat ...)", which strips trailing newlines; CRLF line ends are normalized too.
+          if ! diff -u --strip-trailing-cr <(printf '%s\n' "$(cat dist/RELEASE_NOTES.md)") \
+                                           <(printf '%s\n' "$(cat published.md)"); then
+            echo "::error::The published release body differs from doc/release-notes/${TAG}.md."
+            exit 1
+          fi
+          echo "Published body matches doc/release-notes/${TAG}.md."
 
   # ---------------------------------------------------------------------------------------
   # PyPI publishing -- WIRED UP BUT INTENTIONALLY DISABLED.
@@ -264,9 +262,9 @@ jobs:
           path: dist
 
       - name: Remove non-distribution files
-        # Only sdists and wheels may be uploaded; the checksums file, the assembled release
-        # body, and the Sigstore bundles would all be rejected.
-        run: rm -f dist/SHA256SUMS dist/RELEASE_BODY.md dist/*.sigstore.json
+        # Only sdists and wheels may be uploaded; the checksums file, the release notes, and
+        # the Sigstore bundles would all be rejected.
+        run: rm -f dist/SHA256SUMS dist/RELEASE_NOTES.md dist/*.sigstore.json
 
       - name: Publish to PyPI
         uses: pypa/gh-action-pypi-publish@dc37677b2e1c63e2034f94d8a5b11f265b73ba33 # v1.14.2
diff --git a/CLAUDE.md b/CLAUDE.md
index fb52c25..4c7abaa 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -49,12 +49,30 @@ a comment saying why, rather than reshaping correct code to satisfy the linter.
 examples: the naive-datetime test inputs (`DTZ001`) that exist precisely to assert a
 `ValueError`, and the numpy import that doubles as the `[analysis]` availability probe (`F401`).
 
+### Type Checking
+```bash
+mypy src/                 # what CI runs; must report "Success"
+```
+Configured under `[tool.mypy]` in `pyproject.toml`.  The generated `src/dp_python_lib/grpc/`
+package has no type information, so it is excluded and its imports resolve to `Any` -- both an
+`exclude` and a `follow_imports = "skip"` override are needed, and the comment there says why.
+They go once dp-grpc ships typed stubs (osprey-dcs/dp-grpc#158), at which point a `py.typed`
+marker becomes worth adding.  There is deliberately no `python_version`: numpy's stubs use 3.12
+syntax, and pinning 3.10 stops mypy checking anything.  Two consequences worth knowing:
+
+- An alias whose union includes a proto type needs an explicit `TypeAlias` annotation
+  (`TimestampInput: TypeAlias = ...`); with the proto resolving to `Any`, mypy no longer infers it.
+- `client.annotation` / `client.query` are typed `X | None`, because they are.  The cookbook
+  checker's preamble narrows them once; do **not** switch the checker to
+  `--disable-error-code=union-attr` instead, which also hides misspelled names reached through
+  them (the checker's self-test fails if you try).
+
 ### Continuous Integration and Releases
 GitHub Actions workflows live in `.github/workflows/`:
 
 - **`ci.yml`** — runs on PRs targeting `main` and on pushes to `main`.  Three jobs:
   unit tests across Python 3.10–3.13; a single-interpreter quality job (ruff lint,
-  ruff format check, cookbook snippet checker); and a build job that produces the
+  ruff format check, `mypy src/`, cookbook snippet checker, release-notes checker); and a build job that produces the
   wheel/sdist, runs `twine check --strict`, and verifies the wheel imports in a
   clean venv.  Integration tests are deselected with `-m "not integration"`.
 - **`release.yml`** — runs on `rel-X.Y.Z` tag pushes.  Builds the wheel and sdist,
@@ -91,12 +109,32 @@ a note by issue ticket rather than by PR, since a ticket often spans several PRs
 a breaking release with an "Upgrading from <previous>" checklist that separates silent
 behavior changes from outright errors.
 
-`release.yml` publishes the document as the GitHub release body: the build job concatenates
-it with the artifact verification and install instructions into `dist/RELEASE_BODY.md`,
-which the publish job passes as `body_path` (that job never checks out the repo, so the
-notes travel with the `dist/` upload).  Note `body_path` *overrides* `body` rather than
-complementing it, so those instructions belong in the assembled file, not in a `body:` input.
-GitHub's own generated commit list is appended after all of it.
+**The notes file is the release body, verbatim** (#56; `plan/tickets/56/plan.md`), the same
+arrangement as the Java repos.  `release.yml` copies it to `dist/RELEASE_NOTES.md` (the publish job
+never checks out the repo, so it travels with the `dist/` upload) and passes that as `body_path`;
+nothing is appended, and `generate_release_notes` is deliberately off.  A step after publishing
+diffs the live body against the file.  So each notes file must carry, by hand:
+
+- a `## Verifying these artifacts` section: `sha256sum -c SHA256SUMS`, then
+  `sigstore verify identity` over the wheel, sdist, and `SHA256SUMS`, with `--cert-identity`
+  exactly `https://github.com/osprey-dcs/dp-python-lib/.github/workflows/release.yml@refs/tags/<this tag>`,
+  plus a pointer to `README.env`, the full verification reference;
+- a `**Full Changelog**: https://github.com/osprey-dcs/dp-python-lib/compare/rel-<prev>...rel-<this>` line,
+  standing in for GitHub's generated commit list.
+
+`.dev/tools/check-release-notes.py` enforces both, and above all the tag in the identity: the
+section is usually copied from the previous release, and a stale tag makes `sigstore verify`
+reject every genuine artifact.  It also requires each verify command to name all three files (the
+backported rel-1.16.0 section first verified the wheel only), and the changelog link to end at
+this file's tag and start at an earlier one; which release came before is not knowable from one
+file, so `<prev>` is checked only for being earlier.  Each run starts with a self-test that feeds
+the rules known-bad notes, so a rule that stops matching fails loudly instead of passing everything.
+It runs in CI's quality job and again at tag time.
+
+**Never edit a release page by hand.**  Fix the notes file by PR, then republish with
+`gh release edit rel-X.Y.Z --notes-file doc/release-notes/rel-X.Y.Z.md`.  With the file as the
+whole body that is lossless; when the workflow appended a verification section, exactly this
+command silently stripped it from rel-1.16.0's page (#56).
 
 The build job fails early — before building — if `doc/release-notes/<tag>.md` is missing on
 the tagged commit, so **write the notes and merge them before pushing the `rel-*` tag**.  A
@@ -112,7 +150,8 @@ Core dependencies are managed in `pyproject.toml`:
 
 Optional extras:
 - `[analysis]` - `pandas`, `numpy`, `openpyxl` for the query-result conversions
-- `[dev]` - `pytest`, `mypy`, `ruff`; install with `pip install -e ".[analysis,dev]"`
+- `[dev]` - `pytest`, `mypy` (with `types-PyYAML`, `types-protobuf`, `pandas-stubs`), `ruff`, `build`, `twine`;
+  install with `pip install -e ".[analysis,dev]"`
 
 ## Ticket Planning Workflow
 
diff --git a/README.env b/README.env
new file mode 100644
index 0000000..3d49ee8
--- /dev/null
+++ b/README.env
@@ -0,0 +1,123 @@
+dp-python-lib — Release Artifacts and Verification
+==================================================
+
+This repository publishes versioned dp-python-lib Python distributions via
+GitHub Releases.  Each release corresponds to a Git tag of the form:
+
+  rel-<version>
+
+Example:
+  rel-1.16.0
+
+------------------------------------------------------------
+Release Contents
+------------------------------------------------------------
+
+Each release contains:
+
+  dp_python_lib-<version>-py3-none-any.whl
+    The wheel.  This is what you install.
+
+  dp_python_lib-<version>.tar.gz
+    The source distribution.
+
+  SHA256SUMS
+    SHA-256 checksums for the two files above, in sha256sum format.
+
+  dp_python_lib-<version>-py3-none-any.whl.sigstore.json
+  dp_python_lib-<version>.tar.gz.sigstore.json
+  SHA256SUMS.sigstore.json
+    Keyless Sigstore signature bundles, one per file above.
+
+Releases before rel-1.16.0 may lack SHA256SUMS or the Sigstore bundles; the
+verification steps below do not apply to them.
+
+------------------------------------------------------------
+Download and Installation
+------------------------------------------------------------
+
+1. Download the artifacts from the GitHub Release page into a single directory,
+   with no subdirectories.  Both commands below expect to find the files side
+   by side.  With the GitHub CLI:
+
+     gh release download rel-<version> -R osprey-dcs/dp-python-lib
+
+2. Verify the checksums:
+
+     sha256sum -c SHA256SUMS
+
+   (On macOS without GNU coreutils: shasum -a 256 -c SHA256SUMS)
+
+   The output should indicate:
+
+     dp_python_lib-<version>-py3-none-any.whl: OK
+     dp_python_lib-<version>.tar.gz: OK
+
+   SHA256SUMS lists both distributions, so this fails if you downloaded only
+   the wheel.  To check the files you actually have and ignore the rest:
+
+     sha256sum --ignore-missing -c SHA256SUMS
+
+   Note that --ignore-missing succeeds if it checked nothing at all, so confirm
+   the file you care about is listed as OK rather than relying on the exit code.
+
+3. Verify the signatures.
+
+   The checksums establish integrity but not origin: they are published to the
+   same release page as the artifacts, so anyone able to replace a file could
+   replace its checksum alongside it.  The Sigstore signatures close that gap by
+   binding each file to the repository, workflow file, and tag that produced
+   it.  There is no public key to fetch or trust: the signing identity is a
+   short-lived certificate issued to the GitHub Actions run and recorded in the
+   public Rekor transparency log.
+
+   Install the Sigstore client:
+
+     pip install sigstore
+
+   Then, substituting the release's tag in both places:
+
+     sigstore verify identity \
+       --cert-identity "https://github.com/osprey-dcs/dp-python-lib/.github/workflows/release.yml@refs/tags/rel-<version>" \
+       --cert-oidc-issuer "https://token.actions.githubusercontent.com" \
+       dp_python_lib-*.whl dp_python_lib-*.tar.gz SHA256SUMS
+
+   Each file's bundle is found automatically as <file>.sigstore.json.  The
+   output should be one line per file:
+
+     OK: dp_python_lib-<version>-py3-none-any.whl
+     OK: dp_python_lib-<version>.tar.gz
+     OK: SHA256SUMS
+
+   The --cert-identity is an exact match, pinned to this repository, this
+   workflow file, and one tag.  A signature made by any other workflow, any
+   other repository, or the run for a different tag fails with
+   "Certificate's SANs do not match".  Do not loosen it to make a failure go
+   away; a mismatch is the check doing its job.
+
+4. Install the wheel:
+
+     pip install dp_python_lib-<version>-py3-none-any.whl
+
+   Optional extras are installed the usual way, e.g.:
+
+     pip install "dp_python_lib-<version>-py3-none-any.whl[analysis]"
+
+------------------------------------------------------------
+Release Notes
+------------------------------------------------------------
+
+The body of each GitHub Release is the version-controlled file
+doc/release-notes/rel-<version>.md, published verbatim.  Each carries a short
+"Verifying these artifacts" section with that release's exact identity; this
+file is the fuller reference it points to.
+
+------------------------------------------------------------
+Notes
+------------------------------------------------------------
+
+- dp-python-lib is a client library; it does not run as a standalone service.
+- It talks to the MLDP services implemented in dp-service, over the gRPC API
+  defined in dp-grpc.
+- Publishing to PyPI is not enabled yet; GitHub Releases are the distribution
+  channel.
diff --git a/README.md b/README.md
index e9a4b86..65ee8b6 100644
--- a/README.md
+++ b/README.md
@@ -129,8 +129,8 @@ older than your `dp_python_lib` will not implement everything listed here.  The
 **Project infrastructure**
 
 - Publishing to PyPI.  The release workflow has the job wired up but disabled; everything else —
-  unit tests across Python 3.10-3.13, lint and format checks, the cookbook snippet checker, and
-  signed release artifacts — runs in CI today.
+  unit tests across Python 3.10-3.13, lint, format, and type checks, the cookbook snippet checker,
+  and signed release artifacts — runs in CI today.
 
 ## Installation
 
@@ -143,10 +143,13 @@ pip install -e .
 # with pandas / NumPy / Excel conversions for query results
 pip install -e .[analysis]
 
-# development tooling (pytest, mypy for the cookbook snippet checker)
+# development tooling (pytest, ruff, mypy)
 pip install -e .[dev]
 ```
 
+Released wheels are also attached to each [GitHub release](https://github.com/osprey-dcs/dp-python-lib/releases),
+with checksums and Sigstore signatures; [`README.env`](README.env) says how to verify them.
+
 **Upgrading from 1.15.0 or earlier:** 1.16.0 raises the `grpcio` floor to 1.84.0, because the
 regenerated stubs require it.  `pip install` picks that up, but an existing editable install will
 not upgrade it on its own — the stubs then fail at import with a version mismatch naming the
diff --git a/doc/release-notes/rel-1.16.0.md b/doc/release-notes/rel-1.16.0.md
index dfda6ab..e26e2b9 100644
--- a/doc/release-notes/rel-1.16.0.md
+++ b/doc/release-notes/rel-1.16.0.md
@@ -407,3 +407,32 @@ in fact been a no-op since before `rel-1.15.0`.
 [plan-40]: https://github.com/osprey-dcs/dp-python-lib/blob/rel-1.16.0/plan/tickets/40/plan.md
 [plan-41]: https://github.com/osprey-dcs/dp-python-lib/blob/rel-1.16.0/plan/tickets/41/plan.md
 [plan-readme]: https://github.com/osprey-dcs/dp-python-lib/blob/rel-1.16.0/plan/README.md
+[readme-env]: https://github.com/osprey-dcs/dp-python-lib/blob/main/README.env
+
+## Verifying these artifacts
+
+Checksums:
+
+```bash
+sha256sum -c SHA256SUMS
+```
+
+Signatures (keyless Sigstore; `pip install sigstore`):
+
+```bash
+sigstore verify identity \
+  --cert-identity "https://github.com/osprey-dcs/dp-python-lib/.github/workflows/release.yml@refs/tags/rel-1.16.0" \
+  --cert-oidc-issuer "https://token.actions.githubusercontent.com" \
+  dp_python_lib-*.whl dp_python_lib-*.tar.gz SHA256SUMS
+```
+
+Each file's bundle (`<file>.sigstore.json`) is found automatically.  [`README.env`][readme-env] is the full
+verification reference.
+
+## Installing
+
+```bash
+pip install dp_python_lib-*.whl
+```
+
+**Full Changelog**: https://github.com/osprey-dcs/dp-python-lib/compare/rel-1.15.0...rel-1.16.0
diff --git a/plan/tickets/56/plan.md b/plan/tickets/56/plan.md
new file mode 100644
index 0000000..cef5443
--- /dev/null
+++ b/plan/tickets/56/plan.md
@@ -0,0 +1,265 @@
+# #56 + #30 — Release body as the notes file verbatim, and a mypy CI gate
+
+**Status:** decisions settled 2026-09-24; open questions resolved in place.
+
+## Overview
+
+One change closing two tickets, both about CI and release tooling:
+
+- **#56** — the rel-1.16.0 release page lost its artifact verification and install instructions,
+  and nothing noticed.  This makes the reviewed notes file the *entire* release body, the same
+  arrangement the three Java repos use (dp-grpc#137, plan D9), so no path to the release page can
+  drop content the file contains, and checks that the published page matches the file.
+- **#30** (near-term scope only) — makes `mypy src/` clean and enforces it in the CI `quality` job.
+  The typed-stub half moved to osprey-dcs/dp-grpc#158.
+
+For: release consumers (verification instructions that actually reach the page), and maintainers
+(a type-check gate on hand-written client logic).
+
+## Background / triage findings
+
+### #56: the ticket's root cause is wrong
+
+#56 attributes the missing content to the release **already existing** when the workflow ran,
+so that `action-gh-release` kept the old body.  Its evidence is a timeline: release "created"
+17:49:05Z, workflow started 18:02:17Z.  Both halves of that are contradicted:
+
+- **GitHub's release `created_at` is the date of the tagged commit**, not when the release object
+  was created (documented API behavior).  The rel-1.16.0 tag commit `17d2cdb` is dated
+  `2026-09-16T11:49:05-06:00` — 17:49:05Z exactly.  rel-1.15.0 shows the same 35-minute "gap"
+  and its body is correct.
+- **The workflow created the release.**  The publish step's log (run 35131880732) reads
+  `Creating new GitHub release for tag rel-1.16.0...`, and the release's author is
+  `github-actions[bot]`.  It received the full 27,145-byte `RELEASE_BODY.md` and passed it as
+  `body_path`.
+
+So the body was right when published and was **replaced afterwards**.  The replacement is the
+notes file alone: no verification section and no generated commit list, both of which only the
+workflow adds.  That fits `gh release edit rel-1.16.0 --notes-file doc/release-notes/rel-1.16.0.md`,
+run while fixing the dp-grpc link.  #56's own comment notes that the link was fixed on the page
+first and only backported later (aa994d5, PR #53).  **Confirmed (Q1):** a notes-file edit made
+in another session.
+
+The page has since been corrected in place and now carries the verification and install
+sections.  It does **not** carry the generated commit list (rel-1.15.0's does).
+
+What this changes: the ticket's options A (`append_body`) and B (don't pre-create the release)
+address something that didn't happen.  Its underlying concern still stands, and is sharper than
+it said: **the page and the file are two copies of the same content, and the obvious way to
+republish from the file loses whatever the workflow added.**  Option C removes the difference
+between them.
+
+The issue description gets a triage note saying this.
+
+### #30: re-measured, and a config that reaches zero
+
+Numbers and scope in #30 were updated 2026-09-24 (426 errors / 27 files).  Trialled locally:
+
+| Configuration | Result |
+|---|---|
+| none | 426 errors, 27 files |
+| + `types-PyYAML`, `types-protobuf`, `pandas-stubs`; `ignore_missing_imports` for `grpc` | import-untyped cleared |
+| + `follow_imports = "skip"` for `dp_python_lib.grpc.*` **alone** | still 391 — `src/` passes the generated files on the command line, so they are checked regardless |
+| + `exclude = ["^src/dp_python_lib/grpc/"]` | **7 errors, 3 files** |
+| + `TimestampInput: TypeAlias = ...` | **3 errors** — the real ones |
+
+The remaining 4 came from `TimestampInput`: once `common_pb2.Timestamp` resolves to `Any`, mypy
+can no longer infer the union as an alias.  An explicit `TypeAlias` annotation fixes it and is
+correct regardless.
+
+**None of the 3 "real" errors is a runtime defect** (#30 calls them genuine; they are genuine
+*type* errors):
+
+- `mldp_client.py:120,130` — `self.annotation` / `self.query` are legitimately `None`; the
+  annotations don't say so.
+- `data_frame_conversions.py:209` — `data_frame_image_descriptors()` iterates
+  `frame.imageColumns`, so `image_descriptor_dict()` can never return `None` there, but mypy can't
+  prove it from a `column: Any` parameter.
+
+Two constraints found in the trial:
+
+- **Do not set `python_version = "3.10"`.**  numpy's bundled stubs use the 3.12 `type` statement,
+  and mypy then refuses to check anything.  mypy checks against the running interpreter (3.12 in
+  the `quality` job).  The 3.10 unit-test leg and ruff's `target-version = "py310"` already guard
+  3.10 syntax.
+- **The cookbook checker reads `[tool.mypy]` too** (it runs mypy with `cwd=REPO_ROOT`).  Verified
+  with the config in `pyproject.toml`: `OK: 107 snippets in 8 files (5 skipped)`, unchanged.
+
+## Design decisions
+
+**D1 — The notes file is the release body, verbatim.**  `body_path` points at
+`doc/release-notes/<tag>.md`, carried through the `dist/` upload as `RELEASE_NOTES.md`.  The
+assembly step and its heredoc go.  Each release's notes carry a hand-written
+"Verifying these artifacts" section, reviewed in the notes PR.  Then the page equals the file, and
+`gh release edit --notes-file` is a lossless republish rather than a destructive one.
+*Rejected:* `append_body: true` (#56 option A), which fixes a pre-existing-release case that
+didn't occur and would duplicate the notes if it did; keeping assembly plus a post-publish check
+(the check would catch a bad publish, but not a later hand edit, which is what happened).
+
+**D2 — Add `README.env`, matching the Java repos.**  A version-controlled
+"Release Artifacts and Verification" reference: asset list, `sha256sum -c` (with the
+`--ignore-missing` caveat), and `sigstore verify identity`.  The per-release notes section stays
+short and points to it.  The name is odd for a Python repo, but dp-grpc D9 treats it as the
+convention across all three Java repos, and four repos agreeing is worth more than a better name.
+No Python convention competes with it: PyPA defines no file for release-verification
+instructions, and projects put them in their README or docs.  (Q3.)
+
+**D3 — Drop `generate_release_notes`.**  It's the one part of the body not in the file, so it's
+exactly what a republish from the file loses.  The notes are organized by ticket and link their
+PRs, and the Java repos don't set it.  A hand-written `**Full Changelog**: …/compare/rel-A...rel-B`
+line in the notes gives most of the value.  (Q2: agreed.)
+
+**D4 — Check the notes content at PR time, not only at tag time.**  A new
+`.dev/tools/check-release-notes.py` (sibling of the cookbook checker) runs in the `quality` job
+over every `doc/release-notes/rel-*.md`.  It asserts a `## Verifying these artifacts` heading and
+a `sigstore verify identity` command whose `--cert-identity` ends
+`release.yml@refs/tags/<file stem>`.  The last check matters: the identity is now hand-written per
+release, and a copy-pasted previous tag would verify nothing.  release.yml's existing
+"notes file must exist" step calls the same script on the tagged file.  *Rejected:* tag-time only,
+because by then the notes are merged and the tag is public, so a failure costs a re-tag.
+
+**D5 — After publishing, compare the page to the file.**  A step after `action-gh-release`
+fetches the body (`gh release view "$TAG" --json body`) and diffs it against `RELEASE_NOTES.md`,
+ignoring trailing whitespace.  With D3 the comparison is exact.  This is the "nothing compares
+assembled against published" gap #56 names, closed for the one path the workflow controls.
+Later hand edits are covered by D6.
+
+**D6 — Rule: release pages are never hand-edited.**  Fix the notes file by PR, then republish
+with `gh release edit <tag> --notes-file doc/release-notes/<tag>.md`.  Recorded in CLAUDE.md.
+Lossless under D1 + D3.
+
+**D7 — Backport the verification section into `rel-1.16.0.md`.**  The live page has it, and the
+file doesn't, so D4 would fail on it and D6's republish would strip it again.  After the backport,
+file and page match (apart from the trailing newline).
+
+**D8 — mypy config in `pyproject.toml`**, exactly as trialled:
+```toml
+[tool.mypy]
+exclude = ["^src/dp_python_lib/grpc/"]
+
+[[tool.mypy.overrides]]
+module = ["dp_python_lib.grpc.*"]
+follow_imports = "skip"
+
+[[tool.mypy.overrides]]
+module = ["grpc", "grpc.*"]
+ignore_missing_imports = true
+```
+Each part carries a comment giving its reason, and a pointer to dp-grpc#158 for when the generated
+package suppression can go.  No `python_version` (see Background).  *Rejected:* global
+`ignore_missing_imports`, which would also hide a genuinely missing dependency.
+
+**D9 — Fix `data_frame_conversions.py:209` by restructuring, not by casting.**  Split out a
+private `_image_descriptor(column) -> dict[str, Any]` that assumes an `ImageColumn`.
+`image_descriptor_dict()` keeps its `isinstance` guard and calls it, and
+`data_frame_image_descriptors()` calls it directly.  *Rejected:* `cast` or `# type: ignore`, which
+would hide the claim instead of making it true by construction.
+
+## Implementation tasks
+
+### #56
+
+- `.github/workflows/release.yml`
+  - Build job: replace "Assemble the release body" with copying the notes file to
+    `dist/RELEASE_NOTES.md`.  Run `check-release-notes.py` on the tag's file in the existing
+    notes-presence step.  Update the comment block that explains assembly and `body_path`
+    precedence.
+  - Publish job: `body_path: dist/RELEASE_NOTES.md`; remove `generate_release_notes` (D3); add
+    the D5 compare step (`GH_TOKEN: ${{ github.token }}`, `set -euo pipefail`).
+  - Sigstore signing: no change.
+- `.dev/tools/check-release-notes.py` — new (D4).  Stdlib only; exits non-zero with a message
+  naming the file and the missing or incorrect item.  Takes optional paths (default: all
+  `doc/release-notes/rel-*.md`).
+- `.github/workflows/ci.yml` — `quality` job: add a "Check release notes" step.
+- `README.env` — new (D2).  Assets: wheel, sdist, `SHA256SUMS`, and a `.sigstore.json` bundle for
+  each of the three.  Verify all three in one `sigstore verify identity` call, not only the wheel
+  as today's body does.
+- `doc/release-notes/rel-1.16.0.md` — append the verification and install sections exactly as on
+  the live page (D7).
+- `CLAUDE.md` — rewrite the "Release notes" paragraph (no assembly; `body_path` is the file; D6
+  rule; `README.env`).
+- `README.md` — check for any mention of the release body or verification and align it.
+
+### #30
+
+- `pyproject.toml` — D8 config; add `types-PyYAML`, `types-protobuf`, `pandas-stubs` to `[dev]`.
+- `src/dp_python_lib/client/time_conversions.py` — `TimestampInput: TypeAlias = ...`.
+- `src/dp_python_lib/client/mldp_client.py` — `AnnotationClient | None` / `QueryClient | None`
+  on the attribute declarations.
+- `src/dp_python_lib/client/data_frame_conversions.py` — D9.
+- `.github/workflows/ci.yml` — `quality` job: `mypy src/` step, after ruff.
+- `.dev/tools/check-cookbook-snippets.py` — update the stale "~145 of its own mypy errors"
+  comment.  `--follow-imports=silent` stays, since the snippets should not re-report library
+  errors either way.
+- `CLAUDE.md` — CI description (quality job now runs mypy; mention the release-notes check);
+  `[dev]` extra contents.
+
+### Verification
+
+- `mypy src/` → `Success`; cookbook checker unchanged; `pytest tests/unit` green; ruff clean.
+- `check-release-notes.py` passes on `rel-1.16.0.md` after D7, and fails on a copy with the tag in
+  the cert identity changed.
+- `workflow_dispatch` rehearsal of release.yml on the branch: build and sign succeed.  Publish and
+  the D5 compare are tag-gated, so they aren't exercised until rel-1.17.0.  The compare step can
+  be dry-checked locally against rel-1.16.0 after D7 (`gh release view rel-1.16.0 --json body`).
+
+## Out of scope
+
+- Typed protobuf stubs and removing the D8 suppression — osprey-dcs/dp-grpc#158.
+- `py.typed` marker — follow-up to dp-grpc#158 (typing the public surface is only useful once the
+  protos are typed).
+- Env-var vs YAML precedence bug — #19, independent.
+- Publishing to PyPI (the disabled job) — unchanged.
+
+## Dependencies and sequencing
+
+- **Must merge before the `rel-1.17.0` tag**, or that release publishes through the old assembly
+  path.
+- Not blocked by dp-grpc#158, and doesn't block it.
+- Not related to #19.
+- D7 (the 1.16.0 backport) must land in the same PR as D4, or the new CI check fails on `main`.
+
+## Open questions
+
+All resolved 2026-09-24.
+
+**Q1 — Was rel-1.16.0's body replaced with `gh release edit --notes-file` (or equivalent)?**
+*Resolved:* yes, confirmed by the maintainer.  It was done in another session while fixing the
+dp-grpc link.  The Background section and the #56 triage note state it as the cause.
+
+**Q2 — Drop the generated commit list (D3)?**  *Resolved:* drop it, and add a hand-written Full
+Changelog compare link to each release's notes.
+
+**Q3 — `README.env` name (D2)?**  *Resolved:* `README.env`.  A Python-specific name would have
+been fine, but none is conventional, so consistency with the Java repos wins.
+
+## Implementation notes
+
+Found while implementing, 2026-09-24:
+
+- **The `mldp_client.py` fix moved errors into the cookbook, not out of existence.**  Typing
+  `client.annotation` / `client.query` as `X | None` is correct (they are `None` when only an
+  ingestion channel is passed; `doc/cookbook/connecting.md`), but it made 83 cookbook snippets
+  fail `union-attr`.  The trial in Background measured the config, not this change.  Fixed with a
+  single narrowing `assert` in the checker's preamble.  `--disable-error-code=union-attr` was tried
+  first and rejected: on an `X | None` receiver that code also carries "no attribute on X", so it
+  hid misspelled names too, and the checker's self-test canary failed.  End users are unaffected
+  until a `py.typed` marker ships; at that point, revisit whether an unconfigured sub-client should
+  raise on access instead of being `None`.
+- **`timestamp_list()` now takes `Sequence[TimestampInput]`**, not `list[...]`.  With the explicit
+  alias, a `list[datetime]` argument failed on list invariance (2 cookbook errors).
+- **D5 diffs with `--strip-trailing-cr`**, not `--ignore-trailing-space`, which BSD `diff` lacks,
+  so the step can be dry-run on macOS.  Trailing newlines are normalized by `"$(cat …)"`.
+  Dry-run against rel-1.16.0: matches; a one-line change fails.
+- **The D4 rationale, corrected:** a stale tag in `--cert-identity` doesn't "verify nothing".
+  `sigstore verify` *rejects* every genuine artifact ("Certificate's SANs do not match"), which
+  readers would take as a forged release.  Confirmed against the rel-1.16.0 assets, which verify
+  with the correct identity (wheel, sdist, and `SHA256SUMS` in one call, as `README.env` shows).
+- **Review follow-up (PR #57): the checker covers the whole contract, not just the identity.**
+  The review found `rel-1.16.0.md` still lacked the Full Changelog line that Q2 promised, and its
+  backported verify command named the wheel only, although CLAUDE.md and `README.env` both say
+  wheel, sdist, and `SHA256SUMS`.  The checker had accepted both.  Fixed in the file (it also
+  gained the `README.env` pointer CLAUDE.md asks for), and the checker now requires every verify
+  command to name all three files and a Full Changelog compare link ending at the file's own tag
+  and starting at an earlier one.  Following the cookbook checker's canary, it self-tests on each
+  run against known-bad samples.  The rel-1.16.0 page is republished from the file after merge.
diff --git a/pyproject.toml b/pyproject.toml
index d4356fb..8740739 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -55,11 +55,17 @@ analysis = [
   "openpyxl",
 ]
 
-# Development tooling.  Not required to use the library.  mypy backs the cookbook snippet
-# checker (.dev/tools/check-cookbook-snippets.py), which type-checks every example in
-# doc/cookbook against this package to catch wrong attribute/method names in the docs.
+# Development tooling.  Not required to use the library.  mypy runs in CI as `mypy src/`
+# (config under [tool.mypy]) and also backs the cookbook snippet checker
+# (.dev/tools/check-cookbook-snippets.py), which type-checks every example in doc/cookbook
+# against this package to catch wrong attribute/method names in the docs.  The types-* and
+# pandas-stubs packages are the third-party stubs mypy needs to check against real
+# signatures rather than treating those imports as untyped.
 dev = [
   "mypy",
+  "types-PyYAML",
+  "types-protobuf",
+  "pandas-stubs",
   "pytest",
   "ruff",
   "build",
@@ -92,6 +98,27 @@ markers = [
   "integration: requires a live MLDP ecosystem on localhost:50051-50053 (deselect with '-m \"not integration\"')",
 ]
 
+[tool.mypy]
+# No python_version: numpy's bundled stubs use the 3.12 `type` statement, and pinning 3.10
+# makes mypy refuse to check anything.  mypy checks against the running interpreter (3.12 in
+# CI's quality job); the 3.10 unit-test leg and ruff's target-version guard 3.10 syntax.
+#
+# The generated gRPC package is untyped (no .pyi stubs; osprey-dcs/dp-grpc#158), so it is
+# excluded from checking and its imports are resolved to Any.  Both are needed: `exclude`
+# alone still follows imports into it, and `follow_imports = "skip"` alone does nothing for
+# files `mypy src/` names on the command line.  Remove both once typed stubs are synced.
+exclude = ["^src/dp_python_lib/grpc/"]
+
+[[tool.mypy.overrides]]
+module = ["dp_python_lib.grpc.*"]
+follow_imports = "skip"
+
+# grpcio ships no type information and there is no maintained stub package for it.  Scoped
+# to grpc rather than set globally, which would also hide a genuinely missing dependency.
+[[tool.mypy.overrides]]
+module = ["grpc", "grpc.*"]
+ignore_missing_imports = true
+
 [tool.ruff]
 # 120 matches the margin this codebase was already written to: at line-length 100 there were
 # 307 violations, nearly all docstrings and long string literals that the formatter will not
diff --git a/src/dp_python_lib/client/data_frame.py b/src/dp_python_lib/client/data_frame.py
index 9ffb87b..5d9ae7c 100644
--- a/src/dp_python_lib/client/data_frame.py
+++ b/src/dp_python_lib/client/data_frame.py
@@ -22,6 +22,7 @@
     the ones its builders return.
 """
 
+from collections.abc import Sequence
 from numbers import Integral, Real
 from typing import Any
 
@@ -110,7 +111,7 @@ def sampling_clock(
     return timestamps
 
 
-def timestamp_list(values: list[TimestampInput]) -> common_pb2.DataTimestamps:
+def timestamp_list(values: Sequence[TimestampInput]) -> common_pb2.DataTimestamps:
     """
     Builds a DataTimestamps with an explicit TimestampList time axis, the form for irregularly-spaced samples --
     and, for sample status, for sparse labeling that names only the samples being labeled.
diff --git a/src/dp_python_lib/client/data_frame_conversions.py b/src/dp_python_lib/client/data_frame_conversions.py
index e921a9f..50e875e 100644
--- a/src/dp_python_lib/client/data_frame_conversions.py
+++ b/src/dp_python_lib/client/data_frame_conversions.py
@@ -173,6 +173,16 @@ def image_descriptor_dict(column: Any) -> dict[str, Any] | None:
     """
     if not isinstance(column, common_pb2.ImageColumn):
         return None
+    return _image_descriptor(column)
+
+
+def _image_descriptor(column: common_pb2.ImageColumn) -> dict[str, Any]:
+    """
+    The descriptor dict for a column already known to be an ImageColumn.
+
+    Split out so data_frame_image_descriptors(), which iterates imageColumns and so never sees another kind, gets a
+    non-optional dict by construction rather than by a cast over image_descriptor_dict()'s None arm.
+    """
     descriptor = column.imageDescriptor
     return {
         "width": descriptor.width,
@@ -206,7 +216,7 @@ def data_frame_image_descriptors(frame: common_pb2.DataFrame) -> dict[str, dict[
     :param frame: The frame to inspect.
     :return: A dict of column name -> descriptor dict; empty when the frame has no image columns.
     """
-    return {column.name: image_descriptor_dict(column) for column in frame.imageColumns}
+    return {column.name: _image_descriptor(column) for column in frame.imageColumns}
 
 
 def data_frame_schema_ids(frame: common_pb2.DataFrame) -> dict[str, str]:
diff --git a/src/dp_python_lib/client/mldp_client.py b/src/dp_python_lib/client/mldp_client.py
index e10c2bc..fa00033 100644
--- a/src/dp_python_lib/client/mldp_client.py
+++ b/src/dp_python_lib/client/mldp_client.py
@@ -114,7 +114,7 @@ def __init__(
         # Annotation service facade (exposes .pv_metadata, etc.); only created if a channel is available
         if self._annotation_channel is not None:
             self.logger.info("Initializing annotation client")
-            self.annotation = AnnotationClient(self._annotation_channel)
+            self.annotation: AnnotationClient | None = AnnotationClient(self._annotation_channel)
         else:
             self.logger.debug("No annotation channel provided - annotation client will be None")
             self.annotation = None
@@ -124,7 +124,7 @@ def __init__(
         # the .annotation facade.
         if self._query_channel is not None:
             self.logger.info("Initializing query client")
-            self.query = QueryClient(self._query_channel)
+            self.query: QueryClient | None = QueryClient(self._query_channel)
         else:
             self.logger.debug("No query channel provided - query client will be None")
             self.query = None
diff --git a/src/dp_python_lib/client/time_conversions.py b/src/dp_python_lib/client/time_conversions.py
index 249ed75..32cfb64 100644
--- a/src/dp_python_lib/client/time_conversions.py
+++ b/src/dp_python_lib/client/time_conversions.py
@@ -20,12 +20,13 @@
 
 import math
 from datetime import datetime, timezone
+from typing import TypeAlias
 
 from dp_python_lib.grpc import common_pb2
 
 # Accepted input types for API parameters that map to a common.Timestamp:
 # a timezone-aware datetime, epoch seconds (int or float), or an already-built Timestamp.
-TimestampInput = datetime | int | float | common_pb2.Timestamp
+TimestampInput: TypeAlias = datetime | int | float | common_pb2.Timestamp
 
 
 NANOS_PER_SECOND = 1_000_000_000