Minipada · Minipada · Aug 17, 2026
@@ -35,5 +35,6 @@ This will automatically close the issue when this PR gets merged.
 - [ ] 📑 I documented correctly following our [guidelines](./CONTRIBUTING.md)
 - [ ] 💯 I tested locally and it is working
 - [ ] 🟢 My code does not fail neither code linting checks nor unit test.
+- [ ] ✍️ Every commit is signed off (`git commit -s`) — see the [DCO](../DCO)
 
 Thank you!
@@ -0,0 +1,37 @@
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+1 Letterman Drive
+Suite D4700
+San Francisco, CA, 94129
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+
+Developer's Certificate of Origin 1.1
+
+By making a contribution to this project, I certify that:
+
+(a) The contribution was created in whole or in part by me and I
+    have the right to submit it under the open source license
+    indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the best
+    of my knowledge, is covered under an appropriate open source
+    license and I have the right under that license to submit that
+    work with modifications, whether created in whole or in part
+    by me, under the same open source license (unless I am
+    permitted to submit under a different license), as indicated
+    in the file; or
+
+(c) The contribution was provided directly to me by some other
+    person who certified (a), (b) or (c) and I have not modified
+    it.
+
+(d) I understand and agree that this project and the contribution
+    are public and that a record of the contribution (including all
+    personal information I submit with it, including my sign-off) is
+    maintained indefinitely and may be redistributed consistent with
+    this project or the open source license(s) involved.
@@ -41,6 +41,43 @@ You can contribute to the source code with Pull Requests, for example:
   * Make sure to add documentation if it's relevant.
 
 
+### Signing off your commits
+
+Every commit in a pull request must carry a `Signed-off-by` trailer. It certifies that you
+wrote the patch, or otherwise have the right to submit it under this project's license — the
+full text is the [Developer Certificate of Origin](https://github.com/Minipada/ros2_data_collection/blob/jazzy/DCO)
+at the repository root. There is no agreement to sign and nothing to send: the trailer *is* the
+certification.
+
+`-s` adds it from your `user.name` and `user.email`, which is also the identity the trailer has
+to match:
+
+```bash
+git commit -s -m "fix(dc_group): drop partial Records on timeout"
+```
+
+If you forgot it, sign off the last commit:
+
+```bash
+git commit --amend -s --no-edit
+```
+
+…or a whole branch at once, then force-push:
+
+```bash
+git rebase --signoff origin/jazzy
+git push --force-with-lease
+```
+
+The `DCO` check on your pull request looks at every commit the pull request adds — history
+before it is left alone — and names each commit that is missing or mismatching the trailer. It
+is required on `jazzy`, so an unsigned commit blocks the merge. To see where your branch stands
+before you push — an empty right-hand side is a commit with no sign-off:
+
+```bash
+git log --no-merges --format='%h %s → %(trailers:key=Signed-off-by,valueonly,separator=%x2C%x20)' origin/jazzy..HEAD
+```
+
 ### Setup environment
 #### ROS
 Follow the steps to build your workspace and install dependencies in the [setup section](./setup.md)

@@ -6748,3 +6748,68 @@ either way.
 .github/ISSUE_TEMPLATE/config.yml --skip build-doc` passes (codespell, yaml syntax,
 end-of-file/whitespace fixers). Private vulnerability reporting confirmed enabled through the
 API, not just assumed.
+
+## #303 - Add a DCO check to pull requests
+
+**The repo already had the check, and nobody could tell.** The issue was written on the premise
+that nothing recorded a contributor's right to submit what they submit. Half true: the probot
+[DCO app](https://github.com/apps/dco) has been installed on this repo the whole time and posts
+a `DCO` check run on every pull request (green on #353, so it predates this work). It already
+covered three of the four acceptance criteria — fails an unsigned PR, names the offending
+commits, only looks at the PR's own commits. What was missing was everything *in the tree* — no
+DCO text, no `git commit -s` in the contributing guide — and, as it turned out, enforcement.
+
+So nothing here is a new checker, and two attempts at writing one were deleted along the way:
+
+1. `.github/workflows/dco.yaml` running an in-repo script over `base.sha..head.sha`. Verified
+   green on real CI (job "Sign-off" on #355) before being removed. Two identical gates on every
+   PR is noise, and it was the weaker of the two — it only required a well-formed trailer to be
+   present, where the app requires it to *match the commit author*.
+2. `tools/ci/dco_check.sh`, kept for a while as the local half after the workflow went. Also
+   deleted: with no CI job running it, it was a hand-reimplementation of a rule it could never
+   be verified against, and its failure mode is the bad one — drift toward leniency means it
+   passes locally while the app fails, which is worse than having no local check. Its `tools/ci/`
+   path also oversold it, since nothing in CI ran it.
+
+What actually shipped:
+
+- **`DCO`** at the repo root — the verbatim v1.1 text from developercertificate.org. The
+  sign-off now points at a file in the tree rather than a URL that can change under the
+  project, and the app's invisibility stops being the whole problem.
+- **Docs** — `doc/src/dc/contributing.md` gains "Signing off your commits" before the setup
+  instructions: what the trailer certifies, that it has to match `user.name`/`user.email`,
+  `git commit -s`, `git commit --amend -s --no-edit`, `git rebase --signoff origin/jazzy` +
+  `--force-with-lease`. In place of a script, a documented one-liner for a pre-push eyeball —
+  `git log --no-merges --format='%h %s → %(trailers:key=Signed-off-by,valueonly,separator=%x2C%x20)' origin/jazzy..HEAD`,
+  where an empty right-hand side is an unsigned commit. `separator` matters: without it every
+  commit's line is followed by a blank one. Matching item on the PR template checklist.
+- **Enforcement** — `jazzy` had no branch protection and no rulesets at all, so the app's check
+  reported an unsigned PR and the merge went through regardless; AC 1 ("a CI check *fails* a
+  pull request") was only half-met however many checkers were wired up. `jazzy` now requires
+  `DCO` as its one status check (pinned to the app, `app_id` 1861), with `enforce_admins: false`
+  so the maintainer can still push straight to the branch, and force-pushes/deletions off.
+
+Two traps from the deleted script, recorded because any future in-repo git-message check walks
+into both:
+
+- `git show -s --format=%B "$sha" | grep -Eiq …` is wrong under `set -o pipefail`. `grep -q`
+  exits at the first match, `git` takes SIGPIPE, the pipeline reports 141, and a *signed* commit
+  reads as unsigned — intermittently, and only for long messages. Feed the message in through a
+  herestring instead.
+- `while read … < <(git rev-list "$RANGE")` swallows an unresolvable range and then cheerfully
+  reports "every commit is signed off" over a list it never read. Capture first, check the exit
+  status, then iterate.
+
+Matching the app's rule, in case it is ever reimplemented: the trailer has to equal the commit
+author's `Name <email>` (the committer's also passes, which is what makes an `am`/rebase of
+someone else's signed patch legal), compared case-insensitively, and merge commits are exempt —
+those come from GitHub's "Update branch" button and the contributor can't sign them.
+
+**Verified**: the deleted script was tested against throwaway repos with `core.hooksPath`
+pointed at nothing, so the sign-off wasn't added behind the test's back — this machine's global
+`prepare-commit-msg` hook signs every commit, which silently made the first two attempts at that
+test pass for the wrong reason. Worth knowing for any future test of commit-message tooling here.
+The one-liner that replaced it was run against the same repo: unsigned, wrong-identity and
+correctly-signed commits are all distinguishable at a glance. On #355 itself the required `DCO`
+check is green, along with `Format`, `build`, `build-workspace`, `build-e2e-image`, `e2e`, `sim`
+and codecov; `prek run --all-files --skip build-doc` is green.