diff --git a/.github/scripts/detect-code-changes.sh b/.github/scripts/detect-code-changes.sh
index b27fcae6b..ac3e56974 100644
--- a/.github/scripts/detect-code-changes.sh
+++ b/.github/scripts/detect-code-changes.sh
@@ -5,13 +5,20 @@ event_name=${1:?usage: detect-code-changes.sh <event-name> <repository> [pull-re
 repository=${2:?usage: detect-code-changes.sh <event-name> <repository> [pull-request-number]}
 pull_request_number=${3:-}
 
-set_code_output() {
-  printf 'code=%s\n' "$1" >>"$GITHUB_OUTPUT"
-  printf 'Non-docs changes: %s\n' "$1"
+# code: anything outside docs, so the Unit legs and static checks run.
+# e2e:  anything the Playwright suite can observe. The suite boots the web
+#       dev server (packages/web, which imports only packages/core) against
+#       stubbed routes; packages/backend, packages/sync, and packages/scripts
+#       are never loaded, so a PR that touches only those skips the e2e
+#       shards. merge_group and push runs always run everything, so nothing
+#       reaches main untested.
+set_outputs() {
+  printf 'code=%s\ne2e=%s\n' "$1" "$2" >>"$GITHUB_OUTPUT"
+  printf 'Non-docs changes: %s\nE2E-reachable changes: %s\n' "$1" "$2"
 }
 
 if [ "$event_name" != "pull_request" ]; then
-  set_code_output true
+  set_outputs true true
   exit 0
 fi
 
@@ -21,7 +28,7 @@ if ! files=$(gh api --paginate \
   "repos/${repository}/pulls/${pull_request_number}/files" \
   --jq '.[].filename'); then
   echo "Could not read pull request files; running checks." >&2
-  set_code_output true
+  set_outputs true true
   exit 0
 fi
 
@@ -29,10 +36,17 @@ fi
 # printf's SIGPIPE as a failure on large pull requests.
 code_files=$(printf '%s\n' "$files" |
   grep -vE '(\.md$|^docs/|^\.gitignore$)' || true)
+e2e_files=$(printf '%s\n' "$code_files" |
+  grep -vE '^packages/(backend|sync|scripts)/' || true)
 
 # An empty response is unverified, so run the checks.
-if [ -z "$files" ] || [ -n "$code_files" ]; then
-  set_code_output true
-else
-  set_code_output false
+if [ -z "$files" ]; then
+  set_outputs true true
+  exit 0
 fi
+
+code=false
+e2e=false
+[ -n "$code_files" ] && code=true
+[ -n "$e2e_files" ] && e2e=true
+set_outputs "$code" "$e2e"
diff --git a/.github/workflows/test-e2e.yml b/.github/workflows/test-e2e.yml
index 9475c80e1..c7f797dbc 100644
--- a/.github/workflows/test-e2e.yml
+++ b/.github/workflows/test-e2e.yml
@@ -35,11 +35,16 @@ jobs:
   # does report, and reports Success. So for pull_request the filter lives
   # here, as a job gate, not in `on:`. The push trigger keeps its
   # paths-ignore: push runs block nothing.
+  # The `e2e` output is false when a PR touches only packages/backend,
+  # packages/sync, or packages/scripts (plus docs): the suite boots the web
+  # dev server against stubbed routes and never loads those packages. 22% of
+  # PR e2e runs in the 2026-09 audit were such PRs. merge_group and push runs
+  # always report true, so main is still tested end to end.
   changes:
     runs-on: ubuntu-latest
     timeout-minutes: 2
     outputs:
-      code: ${{ steps.filter.outputs.code }}
+      e2e: ${{ steps.filter.outputs.e2e }}
     steps:
       - name: Check out repository
         uses: actions/checkout@v7
@@ -64,7 +69,7 @@ jobs:
   # would show the unexpanded ${{ matrix.shard }} expression.
   e2e-shard:
     needs: changes
-    if: needs.changes.outputs.code == 'true'
+    if: needs.changes.outputs.e2e == 'true'
     runs-on: ubuntu-latest
     timeout-minutes: 12
     strategy:
@@ -117,7 +122,7 @@ jobs:
         run: bunx playwright test --shard=${{ matrix.shard }}/4
 
   # The one required status check. Reports success when every shard passed
-  # or when the docs-only gate skipped them all, and fails on a shard
+  # or when the `changes` gate skipped them all, and fails on a shard
   # failure. A cancelled run (a newer push superseded it) is not a failure;
   # `!cancelled()` leaves it cancelled instead of painting the old head red.
   e2e:
diff --git a/docs/CI-CD/workflows.md b/docs/CI-CD/workflows.md
index 6b3ac69ea..4a87c8855 100644
--- a/docs/CI-CD/workflows.md
+++ b/docs/CI-CD/workflows.md
@@ -5,7 +5,7 @@ Compass uses GitHub Actions for continuous integration, Docker Hub for image dis
 | Workflow | Trigger | Purpose |
 |---|---|---|
 | Unit (`test-unit.yml`) | Push / PR / merge_group to `main` | Runs `static` (lint, knip, type-check) and unit tests |
-| E2E (`test-e2e.yml`) | Push / PR / merge_group to `main` | Playwright e2e in four shards behind one required `e2e` gate (docs-only diffs skipped) |
+| E2E (`test-e2e.yml`) | Push / PR / merge_group to `main` | Playwright e2e in four shards behind one required `e2e` gate (PRs that touch only docs, or only `packages/backend`, `packages/sync`, `packages/scripts`, skip the shards; merge queue and `main` always run them) |
 | CodeQL | Push / PR to `main` | Static security analysis |
 | Performance budget | Push to `main` (web/core/lock/budget), nightly schedule, `workflow_dispatch`; PR only when `.github/perf/**` or the workflow file changes | Lighthouse budget (not a required merge check) |
 | Error autofix (`error-autofix.yml`) | `posthog[bot]` issue / `workflow_dispatch` | Governed Routine: triage or fix PostHog error issues |
diff --git a/packages/scripts/src/testing/detect-code-changes.test.ts b/packages/scripts/src/testing/detect-code-changes.test.ts
index 9e1041240..be49fd7ad 100644
--- a/packages/scripts/src/testing/detect-code-changes.test.ts
+++ b/packages/scripts/src/testing/detect-code-changes.test.ts
@@ -74,6 +74,17 @@ describe("detect-code-changes", () => {
     }
   });
 
+  it("gates the e2e shards on the e2e output and the unit legs on code", () => {
+    const unit = readFileSync(".github/workflows/test-unit.yml", "utf8");
+    const e2e = readFileSync(".github/workflows/test-e2e.yml", "utf8");
+
+    expect(e2e).toContain("e2e: ${{ steps.filter.outputs.e2e }}");
+    expect(e2e).toContain("if: needs.changes.outputs.e2e == 'true'");
+    expect(e2e).not.toContain("needs.changes.outputs.code");
+    expect(unit).toContain("code: ${{ steps.filter.outputs.code }}");
+    expect(unit).not.toContain("outputs.e2e");
+  });
+
   it("runs Unit once per PR push and names Unit vs E2E", () => {
     const unit = readFileSync(".github/workflows/test-unit.yml", "utf8");
     const e2e = readFileSync(".github/workflows/test-e2e.yml", "utf8");
@@ -105,7 +116,7 @@ describe("detect-code-changes", () => {
       const result = runDetector(eventName);
 
       expect(result.status, result.stderr).toBe(0);
-      expect(result.output).toBe("code=true\n");
+      expect(result.output).toBe("code=true\ne2e=true\n");
       expect(result.command).toBe("");
     }
   });
@@ -117,7 +128,36 @@ describe("detect-code-changes", () => {
     );
 
     expect(result.status, result.stderr).toBe(0);
-    expect(result.output).toBe("code=false\n");
+    expect(result.output).toBe("code=false\ne2e=false\n");
+  });
+
+  it("skips only e2e for backend, sync, and scripts pull requests", () => {
+    const result = runDetector(
+      "pull_request",
+      "packages/backend/src/app.ts\npackages/sync/src/jobs.ts\npackages/scripts/src/cli.ts\ndocs/sync.md",
+    );
+
+    expect(result.status, result.stderr).toBe(0);
+    expect(result.output).toBe("code=true\ne2e=false\n");
+  });
+
+  it("runs e2e when a backend pull request also touches anything else", () => {
+    for (const other of [
+      "packages/core/src/types.ts",
+      "packages/web/src/app.tsx",
+      "e2e/timed/event-smoke.spec.ts",
+      "playwright.config.ts",
+      "bun.lock",
+      ".github/workflows/test-e2e.yml",
+    ]) {
+      const result = runDetector(
+        "pull_request",
+        `packages/backend/src/app.ts\n${other}`,
+      );
+
+      expect(result.status, result.stderr).toBe(0);
+      expect(result.output, other).toBe("code=true\ne2e=true\n");
+    }
   });
 
   it("runs checks for pull requests containing code", () => {
@@ -127,7 +167,7 @@ describe("detect-code-changes", () => {
     );
 
     expect(result.status, result.stderr).toBe(0);
-    expect(result.output).toBe("code=true\n");
+    expect(result.output).toBe("code=true\ne2e=true\n");
     expect(result.command).toContain(
       "api --paginate repos/example/compass/pulls/42/files --jq .[].filename",
     );
@@ -141,7 +181,7 @@ describe("detect-code-changes", () => {
       const result = runDetector("pull_request", files, ghStatus);
 
       expect(result.status, result.stderr).toBe(0);
-      expect(result.output).toBe("code=true\n");
+      expect(result.output).toBe("code=true\ne2e=true\n");
     }
   });
 });