diff --git a/09-frontend-dep-changes.md b/09-frontend-dep-changes.md
new file mode 100644
index 0000000..fd9dfcc
--- /dev/null
+++ b/09-frontend-dep-changes.md
@@ -0,0 +1,100 @@
+# 09 — Frontend dependency changes
+
+When your work touches `frontend/package.json` or `frontend/package-lock.json` (e.g. a `bot-eligible` Dependabot bump like #45), the lockfile is the artifact that matters most. The rest of this rule is about producing a lockfile that's *reproducible under strict install* — not just one that happens to work on the autobox.
+
+## Why this rule exists
+
+The autobox runs npm 9.2.0. Newer npm majors (10+) enforce stricter listing of transitive deps in `package-lock.json` than npm 9 does. A lockfile generated by `npm install <pkg>` under npm 9 can be silently missing entries that npm 10's `npm ci` then refuses (16+ "Missing: <pkg> from lock file" errors).
+
+The autobox's own `npm test` and `npm run build` reuse the bot's pre-populated `node_modules` and never re-resolve, so this defect is invisible locally but blocks any reviewer with a newer npm — and blocks reproducible CI/CD installs in general.
+
+This was the failure mode of the PR-#55 vite bump (caught at review time on 2026-05-06, after a clean rebase + green local tests).
+
+## The mandatory workflow for frontend dep changes
+
+### Step 1: Regenerate the lockfile from scratch
+
+Don't surgically edit `package-lock.json`. Don't trust `npm install <pkg>` to keep the rest of the lockfile honest. Always do a full delete + regenerate:
+
+```bash
+cd /home/bot/work/meshcore-planner/frontend
+rm -rf node_modules package-lock.json
+npm install --no-audit --no-fund
+```
+
+If the bump requires a coupled-tooling jump (e.g. vite 5→6 forces vitest 1→3 because vitest 1 bundles vite 5 internally), edit `package.json` to bump BOTH versions FIRST, then run the regenerate above. The single regenerate produces a self-consistent lockfile.
+
+### Step 2: Verify strict reproducibility
+
+```bash
+rm -rf node_modules
+npm ci --no-audit --no-fund
+```
+
+`npm ci` is strict: every entry in `node_modules` must be in the lockfile and vice versa. If this fails, the lockfile is incomplete — go back to Step 1 and check that `package.json` is sane.
+
+If `npm ci` passes under npm 9 but you suspect npm-major-skew issues (the PR-#55 failure mode), additionally validate against a newer npm:
+
+```bash
+# Only if the autobox provisioner has a newer node available; otherwise skip
+# and rely on Step 1's full-regenerate to be sufficient.
+node20 --version 2>/dev/null && {
+  rm -rf node_modules
+  npx --package=npm@10 -- npm ci --no-audit --no-fund
+}
+```
+
+If a newer npm isn't available on the autobox, document that in the PR body's audit block: "verified `npm ci` under npm 9.2.0; reviewer should re-verify under their own npm version before merging."
+
+### Step 3: Run build + tests
+
+```bash
+npm run build  # capture full output, not just exit code
+npm test       # capture full output, not just exit code
+```
+
+Both must succeed end-to-end. Capture the output verbatim for the PR body — see Step 5.
+
+### Step 4: Commit BOTH files together
+
+```bash
+git add package.json package-lock.json
+git commit -m "deps(frontend): bump <pkg> <old> → <new> (<reason>)"
+```
+
+Never commit one without the other. A `package.json` change without a corresponding lockfile update — or vice versa — produces an inconsistent state that fails `npm ci` for everyone.
+
+### Step 5: PR body requirements
+
+In addition to the standard Q1-Q5 audit (per `12-pre-pr-review.md`), the PR body MUST include:
+
+- **`npm ci` output** (literal capture, last 5-10 lines showing "added N packages" with no "Missing:" errors). This is the reproducibility proof; it stands in for "tests pass" for the lockfile-correctness dimension.
+- **`npm run build` output** (last 5-10 lines including the "✓ built in Xs" line).
+- **`npm test` output** (full pass/fail summary including the actual test count — verify this matches reality; don't reuse a stale count from a prior iteration).
+- **Breaking-change matrix** for any major-version bump, citing the upstream migration guide and confirming each breaking change does or doesn't affect this codebase.
+
+### Step 6: Pre-PR audit subagent — additional check for frontend dep diffs
+
+When you dispatch the Phase 3 review subagent (per `12-pre-pr-review.md`), include this extra question for any diff touching `frontend/package*.json`:
+
+> Q6: Does the lockfile diff *only* contain entries that are direct or transitive consequences of the `package.json` change, OR are there orphan removals/additions suggesting a partial regenerate? If you see lockfile churn that doesn't trace back to a package.json delta, flag it as ⚠ revise.
+
+The subagent should grep the lockfile diff for added/removed top-level packages and confirm each one is reachable from a `package.json` dependency.
+
+## Anti-patterns (each one is a ❌ block)
+
+- Editing `package-lock.json` by hand to "fix" something
+- Running `npm install <pkg>` and committing without regenerating from scratch when the bump is non-trivial (major version, peer-dep cascade, etc.)
+- Reusing test-count or build-time numbers from an earlier audit block without re-running and re-capturing
+- Claiming "build passes" without `npm ci` having succeeded first
+- Shipping a `package.json` change with no `package-lock.json` change, or vice versa
+
+## When to block instead of ship
+
+`bot-blocked-need-decision` if:
+
+- The bump introduces a peer-dep version conflict you can't resolve without picking a winner across multiple packages
+- The breaking-change migration guide says "manual code changes required" and the changes touch protected paths (anything under `app/` requires CODEOWNERS review per `02-meshcore-invariants.md`)
+- `npm audit` post-bump reveals a NEW high/critical advisory introduced by the bump itself (vs. a pre-existing one on main)
+
+Pre-existing audit hits on main are NOT a reason to block this PR — file a separate `bot-eligible` issue for them.
diff --git a/11-work-phase.md b/11-work-phase.md
index a033f9c..f116b39 100644
--- a/11-work-phase.md
+++ b/11-work-phase.md
@@ -55,6 +55,15 @@ Commit messages: conventional-commits style, footer `refs #N`.
   If you're adding an ingest path, see `backend/app/provenance.py` and
   don't merge without it.
 
+## Frontend dependency changes
+
+If your work touches `frontend/package.json` or `frontend/package-lock.json`,
+the lockfile-correctness rules in `09-frontend-dep-changes.md` apply.
+TL;DR: full regenerate (delete `node_modules` + lockfile, `npm install`),
+verify `npm ci` succeeds, capture build + test output verbatim. Don't
+trust `npm install <pkg>` to keep the lockfile honest under newer npm
+versions than the autobox's npm 9.
+
 ## State file updates — REQUIRED, not optional
 
 You MUST write `/home/bot/.bot-state.md` BEFORE the iteration ends.
diff --git a/README.md b/README.md
index 7a64e17..e1c807e 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,7 @@ start of every Ralph loop iteration before any work begins.
 | 06-feasibility-check.md | Pre-flight: data / hardware / decision |
 | 07-no-secrets.md | Never write secret values to any file or message |
 | 08-rebase-and-retest.md | When main has moved under your PR (label `bot-rebase` or `@meshomatic please rebase` comment) |
+| 09-frontend-dep-changes.md | Lockfile-correct workflow for `frontend/package*.json` bumps (regenerate, `npm ci` verify, capture output) |
 | 10-inbox-phase.md | Phase 1 of each iteration: find work |
 | 11-work-phase.md | Phase 2: TDD on the chosen issue |
 | 12-pre-pr-review.md | Phase 3: fresh-context subagent audit |