ci: require DCO sign-off on every pull request (#153)

Adds a Developer Certificate of Origin check. Every non-merge commit in a
PR must carry a Signed-off-by line matching its author, which is what
git commit -s produces.

Chose DCO over a CLA deliberately. A CLA means collecting and storing
contributor names and email addresses, which is personal data this project
would then be responsible for - a heavy obligation for a repo where most
contributions are a single table row. DCO makes the same assertion, that
the contributor has the right to submit the work, with nothing stored
beyond the commit itself.

Implemented with actions/github-script rather than a third-party action so
there is no external dependency in the merge path. Merge commits are
skipped since GitHub generates them.

On failure the check writes a job summary naming the offending commits and
the exact rebase command to fix them.

Signed-off-by: ashishpatel26 <3095771+ashishpatel26@users.noreply.github.com>
Co-authored-by: ashishpatel26 <3095771+ashishpatel26@users.noreply.github.com>

.github/workflows/dco.yml

@@ -0,0 +1,68 @@
+name: DCO
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: read
+  pull-requests: read
+
+jobs:
+  DCO:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check every commit is signed off
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const commits = await github.paginate(
+              github.rest.pulls.listCommits,
+              { ...context.repo, pull_number: context.payload.pull_request.number }
+            );
+
+            const unsigned = [];
+            for (const c of commits) {
+              // Merge commits are generated by GitHub, not authored by the contributor.
+              if (c.parents && c.parents.length > 1) continue;
+
+              const author = c.commit.author;
+              const expected = `Signed-off-by: ${author.name} <${author.email}>`;
+              const hasSignoff = c.commit.message
+                .split('\n')
+                .some(line => line.trim().toLowerCase() === expected.toLowerCase());
+
+              if (!hasSignoff) {
+                unsigned.push(`${c.sha.slice(0, 7)}  ${c.commit.message.split('\n')[0]}`);
+              }
+            }
+
+            if (unsigned.length === 0) {
+              core.info(`All ${commits.length} commit(s) signed off.`);
+              return;
+            }
+
+            core.summary.addHeading('DCO check failed', 2);
+            core.summary.addRaw(
+              'These commits are missing a `Signed-off-by` line matching their author:'
+            );
+            core.summary.addCodeBlock(unsigned.join('\n'));
+            core.summary.addRaw([
+              '',
+              'Sign off your existing commits and force-push:',
+              '',
+              '```bash',
+              'git rebase --signoff origin/main',
+              'git push --force-with-lease',
+              '```',
+              '',
+              'For future commits, `git commit -s` adds the line automatically.',
+              '',
+              'The sign-off certifies you wrote the contribution or have the right to',
+              'submit it under the repository\'s MIT licence. Full text: https://developercertificate.org/'
+            ].join('\n'));
+            await core.summary.write();
+
+            core.setFailed(
+              `${unsigned.length} of ${commits.length} commit(s) missing a valid Signed-off-by line.`
+            );

CONTRIBUTION.md

@@ -107,12 +107,42 @@ requirements: requirements.txt
 ## PR process and checklist
 Before opening a PR:
 - [ ] Fork and create a branch: feat/<short-desc> or fix/<short-desc>
+- [ ] Sign off every commit with `git commit -s` (see below)
 - [ ] Update README and metadata
 - [ ] Paste real sample output from a run into your agent's README
 - [ ] Ensure no secrets or private data are included
 - [ ] Rebase onto current `main` — README moves fast and stale branches conflict
 - [ ] Confirm license compatibility for added assets
 
+### Sign your commits (DCO)
+
+Every commit needs a `Signed-off-by` line. Use `-s` and git adds it for you:
+
+```bash
+git commit -s -m "add my agent"
+```
+
+Which appends:
+
+```
+Signed-off-by: Your Name <you@example.com>
+```
+
+Forgot on commits you already pushed? Fix them all at once:
+
+```bash
+git rebase --signoff origin/main
+git push --force-with-lease
+```
+
+Set `git config user.name` and `git config user.email` first, since the sign-off must
+match the commit author. A CI check enforces this on every PR.
+
+This is the [Developer Certificate of Origin](https://developercertificate.org/) — by
+signing off you're stating that you wrote the contribution, or otherwise have the right
+to submit it under this repository's MIT licence. There's no separate form to fill in
+and nothing is stored beyond the commit itself.
+
 PR description should include:
 - What changed and why
 - How to run the example(s) and tests