diff --git a/.github/scripts/check-changeset-coverage.mjs b/.github/scripts/check-changeset-coverage.mjs
new file mode 100644
index 0000000..ee68f38
--- /dev/null
+++ b/.github/scripts/check-changeset-coverage.mjs
@@ -0,0 +1,176 @@
+#!/usr/bin/env node
+// Reusable changeset-hygiene check, called from PostHog/.github/.github/workflows/changeset-hygiene.yml.
+//
+// Compares packages modified in a PR against packages declared in any changeset
+// added/modified in that PR, and surfaces issues as a sticky comment. Always
+// exits 0 — output is purely informational, the caller workflow does not gate
+// the PR.
+
+import { execSync } from 'node:child_process';
+import { existsSync, readFileSync } from 'node:fs';
+
+const baseRef = process.env.BASE_REF || 'main';
+
+const sh = (cmd) => execSync(cmd, { encoding: 'utf8' }).trim();
+
+// 1. Workspace package directories → package names. Use pnpm itself as the
+//    source of truth so we handle globs, exclusions, and the catalog correctly.
+const cwd = process.cwd();
+const workspaceListing = JSON.parse(sh('pnpm m ls --json --depth=-1'));
+const dirToName = {};
+for (const entry of workspaceListing) {
+    if (!entry.name) continue; // workspace root has no name field
+    if (entry.path === cwd) continue;
+    const relPath = entry.path.startsWith(cwd + '/')
+        ? entry.path.slice(cwd.length + 1)
+        : entry.path;
+    dirToName[relPath] = entry.name;
+}
+const knownNames = new Set(Object.values(dirToName));
+
+// 2. Diff vs base.
+const mergeBase = sh(`git merge-base origin/${baseRef} HEAD`);
+const changedFiles = sh(`git diff --name-only ${mergeBase}...HEAD`).split('\n').filter(Boolean);
+
+// 3. Map changed files → affected packages.
+const ignoreSuffixes = ['/CHANGELOG.md', '/package.json'];
+const affected = new Set();
+for (const file of changedFiles) {
+    if (file.startsWith('.changeset/')) continue;
+    if (ignoreSuffixes.some((s) => file.endsWith(s))) continue;
+    for (const [dir, name] of Object.entries(dirToName)) {
+        if (file === dir || file.startsWith(dir + '/')) {
+            affected.add(name);
+            break;
+        }
+    }
+}
+
+// 4. Find changeset files added or modified in this PR.
+const changesetFiles = sh(
+    `git diff --name-only --diff-filter=AM ${mergeBase}...HEAD -- .changeset/`,
+)
+    .split('\n')
+    .filter((f) => f.endsWith('.md') && !f.endsWith('README.md'));
+
+const writeOutput = (body) => {
+    if (!body) {
+        process.stdout.write('body=\n');
+    } else {
+        process.stdout.write(`body<<CHANGESET_HYGIENE_EOF\n${body}\nCHANGESET_HYGIENE_EOF\n`);
+    }
+};
+
+// 5. Parse frontmatter from each changeset file.
+const declared = new Map();
+for (const file of changesetFiles) {
+    if (!existsSync(file)) continue;
+    const content = readFileSync(file, 'utf8');
+    const fm = content.match(/^---\r?\n([\s\S]*?)\r?\n---/);
+    if (!fm) continue;
+    for (const line of fm[1].split(/\r?\n/)) {
+        const m = line.match(/^\s*["']?([^"'\s:]+)["']?\s*:\s*(patch|minor|major)\s*$/);
+        if (m) declared.set(m[1], m[2]);
+    }
+}
+
+// 6. Compare.
+const missing = [...affected].filter((n) => !declared.has(n)).sort();
+const extra = [...declared.keys()].filter((n) => !affected.has(n) && knownNames.has(n)).sort();
+const unknownDeclared = [...declared.keys()].filter((n) => !knownNames.has(n)).sort();
+const noChangesetButPackagesModified = changesetFiles.length === 0 && affected.size > 0;
+
+const hasIssue =
+    missing.length > 0 ||
+    extra.length > 0 ||
+    unknownDeclared.length > 0 ||
+    noChangesetButPackagesModified;
+
+if (!hasIssue) {
+    writeOutput('');
+    process.exit(0);
+}
+
+const declaredList = [...declared]
+    .sort(([a], [b]) => a.localeCompare(b))
+    .map(([n, b]) => `- \`${n}\` — ${b}`)
+    .join('\n');
+
+const summary = (() => {
+    if (noChangesetButPackagesModified) {
+        const arr = [...affected].sort();
+        return arr.length === 1
+            ? `\`${arr[0]}\` is modified but this PR has no changeset`
+            : `${arr.length} packages modified but this PR has no changeset`;
+    }
+    const issues = [];
+    if (missing.length) issues.push(`${missing.length} undeclared`);
+    if (unknownDeclared.length) issues.push(`${unknownDeclared.length} unknown`);
+    if (extra.length) issues.push(`${extra.length} extra`);
+    if (unknownDeclared.length === 1 && !missing.length && !extra.length) {
+        return `Changeset declares \`${unknownDeclared[0]}\` which isn't a known workspace package`;
+    }
+    if (missing.length === 1 && !extra.length && !unknownDeclared.length) {
+        return `\`${missing[0]}\` is modified but not declared in any changeset`;
+    }
+    if (extra.length === 1 && !missing.length && !unknownDeclared.length) {
+        return `Changeset declares \`${extra[0]}\` but no source files in that package changed`;
+    }
+    return `Possible changeset mismatch — ${issues.join(', ')}`;
+})();
+
+const inner = [];
+inner.push(
+    'This is informational — the PR is not blocked. Click the triangle above to collapse, or push a fix and this comment will auto-delete.',
+);
+inner.push('');
+
+if (noChangesetButPackagesModified) {
+    inner.push('**Modified in this PR but no changeset added:**');
+    for (const n of [...affected].sort()) inner.push(`- \`${n}\``);
+    inner.push('');
+    inner.push('If this change should ship, run `pnpm changeset` and select a bump level.');
+    inner.push(
+        "If it isn't user-facing (refactor with no behavior change, internal tooling, generated files), no action needed.",
+    );
+} else {
+    if (missing.length > 0) {
+        inner.push('**Modified in this PR but not in any changeset:**');
+        for (const n of missing) inner.push(`- \`${n}\``);
+        inner.push('');
+        inner.push('If this package should ship the change, add it to the changeset frontmatter:');
+        inner.push('');
+        inner.push('```');
+        inner.push('---');
+        for (const n of missing) inner.push(`"${n}": patch`);
+        inner.push('---');
+        inner.push('```');
+        inner.push('');
+    }
+    if (unknownDeclared.length > 0) {
+        inner.push('**Declared in a changeset but not a known workspace package (typo?):**');
+        for (const n of unknownDeclared) inner.push(`- \`${n}\``);
+        inner.push('');
+        const sample = [...knownNames].sort().slice(0, 5);
+        inner.push(
+            `Valid workspace package names: \`${sample.join('`, `')}\`${knownNames.size > 5 ? ', …' : ''}`,
+        );
+        inner.push('');
+    }
+    if (extra.length > 0) {
+        inner.push('**Declared in a changeset but no source files modified:**');
+        for (const n of extra) inner.push(`- \`${n}\``);
+        inner.push('');
+        inner.push(
+            'Double-check this is intentional — for example, releasing a previously-merged change.',
+        );
+        inner.push('');
+    }
+    if (declared.size > 0) {
+        inner.push('**Changesets in this PR:**');
+        inner.push(declaredList || '_(none)_');
+    }
+}
+
+const body = `<!-- changeset-hygiene -->\n<details open>\n<summary>⚠️ ${summary}</summary>\n\n${inner.join('\n')}\n\n</details>`;
+writeOutput(body);
diff --git a/.github/workflows/changeset-hygiene.yml b/.github/workflows/changeset-hygiene.yml
new file mode 100644
index 0000000..9695c0b
--- /dev/null
+++ b/.github/workflows/changeset-hygiene.yml
@@ -0,0 +1,95 @@
+name: 'Changeset hygiene'
+
+on:
+    workflow_call:
+        inputs:
+            script-ref:
+                description: 'Ref of PostHog/.github to fetch the script from. Pin only for testing.'
+                required: false
+                type: string
+                default: 'main'
+
+permissions:
+    contents: read
+    pull-requests: write
+
+jobs:
+    check:
+        name: Check changeset hygiene
+        runs-on: ubuntu-latest
+        steps:
+            - name: Checkout caller repository
+              uses: actions/checkout@v6
+              with:
+                  ref: ${{ github.event.pull_request.head.sha }}
+                  fetch-depth: 0
+
+            - name: Checkout PostHog/.github (for the script)
+              uses: actions/checkout@v6
+              with:
+                  repository: PostHog/.github
+                  ref: ${{ inputs.script-ref }}
+                  path: _shared
+
+            - name: Install pnpm
+              uses: pnpm/action-setup@41ff72655975bd51cab0327fa583b6e92b6d3061 # pin v4.2.0
+
+            - name: Setup Node
+              uses: actions/setup-node@v6
+              with:
+                  node-version: '22'
+
+            - name: Compute hygiene report
+              id: hygiene
+              env:
+                  BASE_REF: ${{ github.event.pull_request.base.ref }}
+              run: node _shared/.github/scripts/check-changeset-coverage.mjs >> "$GITHUB_OUTPUT"
+
+            - name: Upsert or delete sticky PR comment
+              uses: actions/github-script@v7
+              env:
+                  COMMENT_BODY: ${{ steps.hygiene.outputs.body }}
+              with:
+                  github-token: ${{ secrets.GITHUB_TOKEN }}
+                  script: |
+                      const marker = '<!-- changeset-hygiene -->';
+                      const body = process.env.COMMENT_BODY || '';
+
+                      const { data: comments } = await github.rest.issues.listComments({
+                          owner: context.repo.owner,
+                          repo: context.repo.repo,
+                          issue_number: context.issue.number,
+                      });
+                      const existing = comments.find(
+                          (c) => c.user.type === 'Bot' && c.body.includes(marker),
+                      );
+
+                      if (!body) {
+                          if (existing) {
+                              await github.rest.issues.deleteComment({
+                                  owner: context.repo.owner,
+                                  repo: context.repo.repo,
+                                  comment_id: existing.id,
+                              });
+                              console.log('Deleted stale changeset-hygiene comment');
+                          }
+                          return;
+                      }
+
+                      if (existing) {
+                          await github.rest.issues.updateComment({
+                              owner: context.repo.owner,
+                              repo: context.repo.repo,
+                              comment_id: existing.id,
+                              body,
+                          });
+                          console.log('Updated existing changeset-hygiene comment');
+                      } else {
+                          await github.rest.issues.createComment({
+                              owner: context.repo.owner,
+                              repo: context.repo.repo,
+                              issue_number: context.issue.number,
+                              body,
+                          });
+                          console.log('Created changeset-hygiene comment');
+                      }