diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 09c970a..f891482 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -24,6 +24,28 @@ env:
   RUST_BACKTRACE: 1
   SOURCE_DATE_EPOCH: 0  # overridden per-step after checkout
 
+# ─────────────────────────────────────────────────────────────────────────────
+# CI parity invariant
+#
+# This GitHub integration matrix and the local default suite set
+# (testing/ci-local.sh) MUST run the same integration suites, EXCEPT for the
+# deliberate local-only entries below. Adding a suite to one runner without
+# the other means "local green" and "GitHub green" stop being equivalent.
+# testing/check-ci-parity.sh enforces this and fails on unexpected drift.
+#
+# Deliberate local-only (NOT on the GitHub gate), with reason:
+#   tor-socks5     — requires live Tor network; opt-in via --with-tor,
+#                    unreliable on GitHub-hosted runners.
+#   tor-directory  — same; live Tor dependency.
+#
+# Granularity-only differences (same coverage, different matrix shape —
+# NOT a divergence):
+#   deb-install    — split here into per-distro legs (debian12/ubuntu24/
+#                    ubuntu26) for parallelism; local runs all distros in one
+#                    suite.
+#   dns-resolver   — single leg here; runs all scenarios (same as local).
+# ─────────────────────────────────────────────────────────────────────────────
+
 # ─────────────────────────────────────────────────────────────────────────────
 # Job 1 – Build matrix
 #
@@ -35,9 +57,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           components: rustfmt
+          cache: false
+          rustflags: ''
       - run: cargo fmt --check
 
   clippy:
@@ -47,9 +71,11 @@ jobs:
       - uses: actions/checkout@v4
       - name: Install system dependencies
         run: sudo apt-get update && sudo apt-get install -y libdbus-1-dev
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           components: clippy
+          cache: false
+          rustflags: ''
       - name: Cache Cargo registry + build
         uses: actions/cache@v4
         with:
@@ -98,7 +124,10 @@ jobs:
         run: sudo nft -c -f packaging/common/fips.nft
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          cache: false
+          rustflags: ''
 
       - name: Cache Cargo registry + build
         uses: actions/cache@v4
@@ -160,7 +189,10 @@ jobs:
         run: sudo apt-get update && sudo apt-get install -y libdbus-1-dev
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          cache: false
+          rustflags: ''
 
       - name: Cache Cargo registry + build
         uses: actions/cache@v4
@@ -210,7 +242,10 @@ jobs:
         run: echo "SOURCE_DATE_EPOCH=$(git log -1 --format=%ct)" >> "$GITHUB_ENV"
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          cache: false
+          rustflags: ''
 
       - name: Cache Cargo registry + build
         uses: actions/cache@v4
@@ -239,7 +274,10 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          cache: false
+          rustflags: ''
 
       - name: Cache Cargo registry + build
         uses: actions/cache@v4
@@ -323,6 +361,10 @@ jobs:
           - suite: rekey-outbound-only
             type: rekey-outbound-only
             topology: rekey-outbound-only
+          # ── Inbound max_peers admission-cap test ───────────────────────
+          - suite: admission-cap
+            type: admission-cap
+            topology: mesh
           - suite: acl-allowlist
             type: acl-allowlist
           # ── Mixed-profile node-role integration test ─────────────────
@@ -755,6 +797,42 @@ jobs:
           docker compose -f testing/static/docker-compose.yml \
             --profile gateway down --volumes --remove-orphans
 
+      # ── Inbound max_peers admission-cap integration test ────────────────
+      # Lowers node.max_peers on one mesh node and asserts the inbound cap
+      # holds under sustained retry pressure: denied peers keep retrying but
+      # are never promoted to an active session. The admission-cap-test.sh
+      # assertions are tailored per link-layer handshake variant; the leg
+      # itself is uniform. Static-style harness on the shared mesh profile.
+      - name: Generate configs (admission-cap)
+        if: matrix.type == 'admission-cap'
+        run: bash testing/static/scripts/generate-configs.sh mesh
+
+      - name: Inject admission-cap config (admission-cap)
+        if: matrix.type == 'admission-cap'
+        run: bash testing/static/scripts/admission-cap-test.sh inject-config
+
+      - name: Start containers (admission-cap)
+        if: matrix.type == 'admission-cap'
+        run: |
+          docker compose -f testing/static/docker-compose.yml \
+            --profile mesh up -d
+
+      - name: Run admission-cap test
+        if: matrix.type == 'admission-cap'
+        run: bash testing/static/scripts/admission-cap-test.sh
+
+      - name: Collect logs on failure (admission-cap)
+        if: matrix.type == 'admission-cap' && failure()
+        run: |
+          docker compose -f testing/static/docker-compose.yml \
+            --profile mesh logs --no-color | tail -300
+
+      - name: Stop containers (admission-cap)
+        if: matrix.type == 'admission-cap' && always()
+        run: |
+          docker compose -f testing/static/docker-compose.yml \
+            --profile mesh down --volumes --remove-orphans
+
       # ── Real-deb install integration ────────────────────────────────────
       # The deb-install harness builds its own .deb from source in a
       # cargo-deb builder image; the pre-built Linux binary from the
diff --git a/.github/workflows/package-linux.yml b/.github/workflows/package-linux.yml
index f51047e..f2d4d49 100644
--- a/.github/workflows/package-linux.yml
+++ b/.github/workflows/package-linux.yml
@@ -72,7 +72,10 @@ jobs:
         run: sudo apt-get update && sudo apt-get install -y --no-install-recommends libdbus-1-dev llvm
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          cache: false
+          rustflags: ''
 
       - name: Cache Cargo registry + build
         if: ${{ env.ACT != 'true' }}
diff --git a/.github/workflows/package-macos.yml b/.github/workflows/package-macos.yml
index f5bb05f..712be11 100644
--- a/.github/workflows/package-macos.yml
+++ b/.github/workflows/package-macos.yml
@@ -69,10 +69,11 @@ jobs:
         run: echo "SOURCE_DATE_EPOCH=$(git log -1 --format=%ct)" >> "$GITHUB_ENV"
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
-
-      - name: Add cross-compile target
-        run: rustup target add ${{ matrix.target }}
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          target: ${{ matrix.target }}
+          cache: false
+          rustflags: ''
 
       - name: Cache Cargo registry + build
         uses: actions/cache@v4
diff --git a/.github/workflows/package-openwrt.yml b/.github/workflows/package-openwrt.yml
index 76a31f9..511d3e2 100644
--- a/.github/workflows/package-openwrt.yml
+++ b/.github/workflows/package-openwrt.yml
@@ -110,9 +110,11 @@ jobs:
 
       - name: Install Rust toolchain (stable)
         if: matrix.rust_channel == 'stable'
-        uses: dtolnay/rust-toolchain@stable
+        uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
-          targets: ${{ matrix.rust_target }}
+          target: ${{ matrix.rust_target }}
+          cache: false
+          rustflags: ''
 
       - name: Install Rust toolchain (nightly, Tier 3)
         if: matrix.rust_channel == 'nightly'
diff --git a/.github/workflows/package-windows.yml b/.github/workflows/package-windows.yml
index 5b98792..09e4424 100644
--- a/.github/workflows/package-windows.yml
+++ b/.github/workflows/package-windows.yml
@@ -63,7 +63,10 @@ jobs:
           echo "SOURCE_DATE_EPOCH=$epoch" >> $env:GITHUB_ENV
 
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          cache: false
+          rustflags: ''
 
       - name: Cache Cargo registry + build
         uses: actions/cache@v4
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ca9f57a..8d6af7c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -154,6 +154,16 @@ with v0.3.x peers.
   requests" and "Further reading". Running the checklist before
   opening surfaces problems that would otherwise come back as review
   comments, saving a round trip.
+- [`docs/how-to/tune-file-descriptors.md`](docs/how-to/tune-file-descriptors.md)
+  — an operator how-to for raising `RLIMIT_NOFILE`. A busy node opens
+  roughly three file descriptors per established UDP peer (a
+  `connect()`-ed socket plus a 2-FD drain self-pipe), so the default
+  1024 soft limit is exhausted near 320 peers, after which further
+  admission, handshakes, and discovery fail with `EMFILE`. The guide
+  documents the per-peer FD budget and symptom, the systemd
+  (`LimitNOFILE` drop-in) and OpenWrt (procd `nofile`) procedures to
+  raise the limit, and how to verify the per-peer ratio stays bounded.
+  Linked from the how-to index.
 
 ### Changed
 
@@ -290,6 +300,39 @@ with v0.3.x peers.
   RTT +0.11–0.19 ms from the worker queue handoff. Windows
   continues on the existing tokio-based send/recv path.
 
+- The Debian package no longer ships `/etc/fips/fips.yaml` as a dpkg
+  conf-file. The default configuration is installed as an example at
+  `/usr/share/fips/fips.yaml.example`, and `postinst` seeds
+  `/etc/fips/fips.yaml` (mode 600) from it only when the file does not
+  already exist — so a configuration-management-rendered or
+  operator-edited config is never prompted for or clobbered on
+  upgrade, removing the need for a `dpkg-divert` workaround.
+  `fips.service` gains `ConditionPathExists=/etc/fips/fips.yaml`. The
+  example is placed under `/usr/share/fips`, deliberately outside
+  `/usr/share/doc`, which minimal and container installs path-exclude
+  (so the install-time seed source is never dropped).
+- Local and GitHub CI integration coverage brought into parity, and
+  the Rust toolchain selection given a single source of truth:
+  - The `admission-cap` integration suite, previously run only by
+    `ci-local.sh`, now also runs as a GitHub `ci.yml` matrix leg, so a
+    regression in it turns the GitHub gate red rather than depending on
+    a developer remembering to run local CI. A new
+    `testing/check-ci-parity.sh` (wired as `ci-local.sh
+    --check-parity`) diffs the two runners' integration-suite sets and
+    fails on unexpected drift; the deliberate local-only (live-Tor)
+    and granularity-only differences are documented in a comment block
+    atop both runners.
+  - CI and packaging jobs now select the toolchain with
+    `actions-rust-lang/setup-rust-toolchain` (which reads
+    `rust-toolchain.toml`) instead of `dtolnay/rust-toolchain@stable`.
+    The pinned channel already overrode the installed stable, so each
+    job downloaded an unused toolchain and logged a misleading `rustc`
+    version; the single-source action removes the waste and the
+    confusion. Existing cache steps are kept (`cache: false` on the
+    new action) and `RUSTFLAGS` is left untouched so no global
+    `-D warnings` is newly imposed. The OpenWrt nightly Tier-3 leg
+    keeps `@nightly`.
+
 ### Fixed
 
 - Inbound connections that arrive while a node is already at its
@@ -323,6 +366,56 @@ with v0.3.x peers.
   Previously the old session could linger after the peer came back
   with a new startup epoch, leaving the session-layer map out of sync
   with the freshly promoted peer.
+
+- Two nodes that each `auto_connect` to the other no longer stall their
+  Nostr-mediated NAT-traversal handshake. Each side ran both an
+  initiator and a responder traversal session, binding a separate UDP
+  socket per session, and adopted only the first `Established` event; if
+  the two sides adopted mismatched sessions, each sent its Noise msg1 to
+  a peer port the peer had already stopped draining and both handshakes
+  hung until the adoption budget expired. The responder now elects a
+  single session deterministically — it declines an incoming offer only
+  when it also has an in-flight outbound initiator for the same peer and
+  its own NodeAddr is smaller — so one matching socket pair survives on
+  both ends and the peer's redundant initiator times out harmlessly.
+  One-sided (asymmetric) `auto_connect` has no co-active initiator and is
+  never suppressed, so connectivity is preserved. (Distinct from the
+  cross-init adoption tie-breaker below, which dedups two simultaneous
+  punches but does not stop each node from running redundant
+  initiator + responder sessions.)
+- FMP link-layer rekey is now reliable under packet loss, bringing it up
+  to the FSP session layer's rekey discipline:
+  - The rekey msg1 retransmission driver was uncapped and never
+    abandoned, so a rekey that never completed resent msg1 forever. It
+    now uses a bounded retransmission budget (`handshake_max_resends`
+    with exponential backoff) and abandons the rekey cycle cleanly once
+    the budget is exhausted, mirroring the FSP rekey msg3 driver. With
+    the cap in place the link-dead heartbeat is rekey-aware:
+    `check_link_heartbeats` no longer reaps a link that is still
+    actively carrying rekey-handshake traffic, while a genuinely dead
+    link is still reaped once the budget abandons.
+  - At the K-bit cutover the receiver now authenticates an inbound frame
+    against the pending session before promoting it, instead of
+    promoting on the bare header K-bit. Under jitter a node could
+    otherwise promote a stale pending session, leaving the two endpoints
+    on different keys and silently dropping traffic until the link died
+    — the same failure class already closed on FSP, now closed on FMP.
+- Node-level multi-node tests no longer flake under parallel CPU load.
+  They previously delivered handshake packets over real localhost UDP,
+  whose kernel receive buffer could overflow and drop a packet when many
+  tests ran concurrently, panicking the large-network convergence tests.
+  A `cfg(test)`-only loopback `TransportHandle` variant now delivers
+  packets directly between nodes over an unbounded in-process channel, so
+  there is no socket buffer to overflow, and the previously-quarantined
+  large-network tests run in the default suite again. The shipping daemon
+  build is unaffected (the variant is test-gated).
+- Integration suites that wait for the mesh to converge no longer
+  false-fail under concurrent CI load. The rekey, static-mesh, and
+  sidecar suites replace a fixed wall-clock baseline timeout (and a blind
+  sleep) with a progress-aware wait that polls the suite's own pairwise
+  pings, returns as soon as every pair is reachable, extends its deadline
+  while the reachable-pair count is still climbing, and gives up only
+  when progress stalls.
 - TCP and Tor `max_inbound_connections` admission cap is now compared
   against the per-direction inbound count (`pool_inbound`) rather than
   the combined pool size. Outbound connect-on-send connections share
diff --git a/Cargo.toml b/Cargo.toml
index e0cee59..64f4153 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -74,7 +74,7 @@ assets = [
     ["target/release/fips", "/usr/bin/", "755"],
     ["target/release/fipsctl", "/usr/bin/", "755"],
     ["target/release/fipstop", "/usr/bin/", "755"],
-    ["packaging/common/fips.yaml", "/etc/fips/fips.yaml", "600"],
+    ["packaging/common/fips.yaml", "/usr/share/fips/fips.yaml.example", "644"],
     ["packaging/common/hosts", "/etc/fips/hosts", "644"],
     ["packaging/common/fips.nft", "/etc/fips/fips.nft", "644"],
     ["packaging/debian/fips.service", "/lib/systemd/system/fips.service", "644"],
@@ -87,7 +87,7 @@ assets = [
     ["packaging/debian/fips-gateway.service", "/lib/systemd/system/fips-gateway.service", "644"],
     ["docs/design/fips-security.md", "/usr/share/doc/fips/fips-security.md", "644"],
 ]
-conf-files = ["/etc/fips/fips.yaml", "/etc/fips/hosts", "/etc/fips/fips.nft"]
+conf-files = ["/etc/fips/hosts", "/etc/fips/fips.nft"]
 
 [dev-dependencies]
 tempfile = "3.15"
diff --git a/docs/how-to/README.md b/docs/how-to/README.md
index cbfa300..ab2ac4f 100644
--- a/docs/how-to/README.md
+++ b/docs/how-to/README.md
@@ -18,6 +18,7 @@ X" to "X is done".
 | [enable-nostr-discovery.md](enable-nostr-discovery.md) | Turn on Nostr-mediated discovery (3 capabilities — resolve, advertise, open — across 5 scenarios) |
 | [deploy-tor-onion.md](deploy-tor-onion.md) | Run a Tor onion service for inbound FIPS connections |
 | [tune-udp-buffers.md](tune-udp-buffers.md) | Set host sysctls so FIPS UDP sockets don't get clamped |
+| [tune-file-descriptors.md](tune-file-descriptors.md) | Raise `RLIMIT_NOFILE` so a busy node doesn't exhaust file descriptors (`EMFILE`) as peer count grows |
 | [run-as-unprivileged-user.md](run-as-unprivileged-user.md) | Run the daemon under a dedicated unprivileged service account (drops the default-root posture) |
 | [deploy-gateway.md](deploy-gateway.md) | Manually deploy `fips-gateway` on a non-OpenWrt Linux host (LAN-to-mesh outbound + mesh-to-LAN inbound port-forwards). For the OpenWrt path, see the gateway tutorial. |
 | [troubleshoot-gateway.md](troubleshoot-gateway.md) | Diagnostic recipes for the gateway, organised by half (outbound, inbound, common) |
diff --git a/docs/how-to/tune-file-descriptors.md b/docs/how-to/tune-file-descriptors.md
new file mode 100644
index 0000000..92963f1
--- /dev/null
+++ b/docs/how-to/tune-file-descriptors.md
@@ -0,0 +1,144 @@
+# Tune the File-Descriptor Limit for FIPS
+
+A busy FIPS node opens many file descriptors, and the count grows with
+the number of peers it serves. On most systemd distributions the daemon
+inherits a soft `RLIMIT_NOFILE` of 1024, which a well-connected node can
+exhaust — at which point peer admission, handshakes, and discovery start
+failing with `EMFILE` ("Too many open files").
+
+This guide explains the FD budget, shows how to raise the limit on
+systemd and on OpenWrt, and how to verify the result.
+
+## Why FIPS is FD-hungry
+
+Unlike a service that multiplexes all traffic over one socket, the FIPS
+data plane allocates descriptors **per peer**. The dominant term is:
+
+```text
+fds ≈ 3·P + fixed overhead (~30)
+```
+
+where `P` is the number of established UDP peers. Each such peer consumes
+**3 file descriptors**:
+
+- one `connect()`-ed UDP socket dedicated to that peer, plus
+- a 2-FD self-pipe owned by that peer's receive-drain worker (used to
+  wake and stop the worker cleanly).
+
+The remaining consumers are bounded and do not scale with peer count:
+
+- the TUN device (one descriptor, process-lifetime),
+- the wildcard UDP listen socket(s) (one per bound UDP transport),
+- TCP and Tor transport listeners and the Tor control socket,
+- Nostr relay websockets (one per configured discovery relay),
+- the control socket (one `UnixListener`, plus short-lived per-request
+  client connections for `fipsctl` / `fipstop`),
+- and base runtime descriptors (epoll, eventfd, logs).
+
+Together these add a roughly flat overhead of about 30 descriptors. The
+per-peer term is what drives the daemon toward the FD ceiling.
+
+## The symptom
+
+The systemd and distro default **soft** `RLIMIT_NOFILE` is **1024**.
+With the `3·P` budget above, that ceiling is reached near **~320 peers**
+(3 × 320 ≈ 960, plus the fixed overhead). Once the process is out of
+descriptors, every syscall that allocates one — `socket()`, `accept()`,
+`open()`, `pipe()` — fails with `EMFILE`, which surfaces as:
+
+- failed peer admission (new peers cannot be accepted),
+- failed handshakes (the daemon cannot open the per-peer socket), and
+- dropped discovery (relay or probe sockets cannot be created).
+
+These symptoms appear only under load, once the node has accumulated
+enough peers to cross the ceiling, so they can be easy to misattribute.
+
+## Raise the limit on systemd
+
+Create a drop-in override for the service:
+
+```sh
+sudo systemctl edit fips.service
+```
+
+Add:
+
+```ini
+[Service]
+LimitNOFILE=65535
+```
+
+A single `LimitNOFILE=` value sets **both** the soft and the hard limit,
+so no separate soft/hard syntax is needed here.
+
+Reload systemd and restart the daemon so the new limit takes effect:
+
+```sh
+sudo systemctl daemon-reload
+sudo systemctl restart fips
+```
+
+`65535` (2¹⁶ − 1) is the conventional headroom value for network
+daemons. With the `3·P` budget, it supports roughly **~21,800 peers**
+before the FD ceiling binds — well beyond any plausible single-node FIPS
+mesh degree. Past that point other limits (threads, memory, CPU) bind
+first, so raising `LimitNOFILE` higher buys nothing.
+
+## Raise the limit on OpenWrt
+
+OpenWrt uses procd, not systemd, so `LimitNOFILE` does not apply.
+Set the equivalent limit in the init script at `/etc/init.d/fips`,
+inside the block that starts the service:
+
+```sh
+procd_set_param limits nofile="65535 65535"
+```
+
+The two values are the soft and hard limits respectively; setting them
+equal mirrors the single-value systemd behaviour above.
+
+Restart the service to apply:
+
+```sh
+/etc/init.d/fips restart
+```
+
+## Verify
+
+Compare the live descriptor count against the established peer count:
+
+```sh
+ls /proc/$(pidof fips)/fd | wc -l
+fipsctl show peers | wc -l
+```
+
+At steady state, expect a stable ratio of about **3 descriptors per
+peer** plus the flat ~30-descriptor overhead. A ratio that holds steady
+as peers come and go confirms healthy, bounded scaling.
+
+If the descriptor count climbs steadily while the peer count stays flat,
+that would indicate a descriptor leak rather than legitimate scaling —
+the limit bump would only delay the wall. The current data plane has
+been audited as leak-free (every per-peer descriptor has a guaranteed
+close on every teardown path), so a climbing ratio at fixed peer count
+would be a regression worth investigating.
+
+## A note on deployment lines
+
+The per-peer connected-UDP socket — the amplifier behind the
+`3·P` term — is present on the master and next data planes. It is **not
+yet present on the maintenance line**. On maintenance-only deployments
+the 3-descriptor-per-peer term does not apply, and FD pressure comes
+only from the fixed consumers listed above. Raising `LimitNOFILE` there
+is still worthwhile as forward-looking headroom, and harmless where the
+amplifier is absent.
+
+## See also
+
+- [tune-udp-buffers.md](tune-udp-buffers.md) — host sysctls so FIPS UDP
+  sockets don't get clamped
+- [run-as-unprivileged-user.md](run-as-unprivileged-user.md) — run the
+  daemon under a dedicated service account
+- [../reference/configuration.md](../reference/configuration.md) —
+  transport and discovery configuration that influences the fixed FD
+  overhead
diff --git a/packaging/README.md b/packaging/README.md
index 161207c..7147728 100644
--- a/packaging/README.md
+++ b/packaging/README.md
@@ -33,10 +33,20 @@ packaging/
 ### Debian/Ubuntu (`.deb`)
 
 Built with [cargo-deb](https://github.com/kornelski/cargo-deb). Installs
-`fips`, `fipsctl`, and `fipstop` to `/usr/bin/`, places config at
-`/etc/fips/fips.yaml` (preserved on upgrade), and enables the systemd
+`fips`, `fipsctl`, and `fipstop` to `/usr/bin/`, and enables the systemd
 service.
 
+The default configuration ships as an example at
+`/usr/share/fips/fips.yaml.example` and is **not** a dpkg conf-file.
+(It is deliberately **not** under `/usr/share/doc`, which minimal and
+container installs path-exclude, since the postinst reads it at install
+time.)
+On install, `postinst` seeds `/etc/fips/fips.yaml` (mode 600) from the
+example **only if it does not already exist**, so a configuration that
+was rendered by configuration management or edited by an operator is
+never prompted for or clobbered on upgrade. To reset to defaults, remove
+`/etc/fips/fips.yaml` and reinstall, or copy the example back manually.
+
 ```sh
 # Build
 make deb
diff --git a/packaging/debian/fips.service b/packaging/debian/fips.service
index 4460eaa..d1b5616 100644
--- a/packaging/debian/fips.service
+++ b/packaging/debian/fips.service
@@ -3,6 +3,11 @@ Description=FIPS Mesh Network Daemon
 After=network-online.target
 Wants=network-online.target
 
+# The config file is no longer a packaged conf-file; postinst seeds it
+# if absent. Skip the unit (inactive, not failed) rather than crash-loop
+# if it is ever missing.
+ConditionPathExists=/etc/fips/fips.yaml
+
 [Service]
 Type=simple
 ExecStart=/usr/bin/fips --config /etc/fips/fips.yaml
diff --git a/packaging/debian/postinst b/packaging/debian/postinst
index 3e2c200..5c4bf4c 100755
--- a/packaging/debian/postinst
+++ b/packaging/debian/postinst
@@ -9,6 +9,16 @@ case "$1" in
             groupadd --system fips
         fi
 
+        # Seed /etc/fips/fips.yaml from the shipped example only if it
+        # does not already exist. The live config is no longer a dpkg
+        # conf-file; this copy-if-absent yields to any operator- or
+        # configuration-management-rendered file and never clobbers it.
+        if [ ! -e /etc/fips/fips.yaml ]; then
+            install -m 600 -o root -g root \
+                /usr/share/fips/fips.yaml.example \
+                /etc/fips/fips.yaml
+        fi
+
         # Drop-in directory for operator nftables rules included by
         # /etc/fips/fips.nft. Empty by default; the include glob matches
         # nothing cleanly out of the box.
diff --git a/testing/check-ci-parity.sh b/testing/check-ci-parity.sh
new file mode 100755
index 0000000..cb5ac7e
--- /dev/null
+++ b/testing/check-ci-parity.sh
@@ -0,0 +1,144 @@
+#!/bin/bash
+# ── CI parity invariant guard ───────────────────────────────────────────────
+# The GitHub integration matrix (.github/workflows/ci.yml) and the local
+# default suite set (ci-local.sh) MUST run the same integration suites,
+# EXCEPT for the deliberate local-only entries listed below. Adding a suite
+# to one runner without the other means "local green" and "GitHub green" stop
+# being equivalent claims.
+#
+# Deliberate local-only (NOT on the GitHub gate), with reason:
+#   tor-socks5     — requires live Tor network; opt-in via --with-tor,
+#                    unreliable on GitHub-hosted runners.
+#   tor-directory  — same; live Tor dependency.
+#
+# Granularity-only differences folded before comparison (same coverage,
+# different matrix shape — NOT a divergence):
+#   deb-install    — GitHub splits into per-distro legs
+#                    (deb-install-debian12/ubuntu24/ubuntu26); local runs all
+#                    distros in one suite. Folded to "deb-install".
+#   chaos-*        — GitHub fans each chaos scenario into its own matrix leg
+#                    (type: chaos); local runs them all via the one CHAOS_SUITES
+#                    path. The individual scenario names also differ cosmetically
+#                    between runners (e.g. chaos-smoke-10 vs churn-mixed-10).
+#                    Folded to a single "chaos" token on both sides.
+#   dns-resolver   — single leg / single suite both sides; runs all scenarios.
+#
+# Exit 0 = parity clean. Exit 1 = unexpected divergence (suite names printed).
+# ─────────────────────────────────────────────────────────────────────────────
+set -uo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+PROJECT_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+CI_LOCAL="$SCRIPT_DIR/ci-local.sh"
+CI_YML="$PROJECT_ROOT/.github/workflows/ci.yml"
+
+# Deliberate local-only allowlist (suites intentionally absent from GitHub).
+ALLOWLIST="tor-socks5 tor-directory"
+
+for f in "$CI_LOCAL" "$CI_YML"; do
+    if [[ ! -f "$f" ]]; then
+        echo "check-ci-parity: missing file: $f" >&2
+        exit 2
+    fi
+done
+
+# Extract and normalize both suite sets in Python (robust YAML parse of the
+# matrix; regex extraction of the bash suite arrays). Folding rules above are
+# applied identically to both sides so only genuine divergence surfaces.
+python3 - "$CI_LOCAL" "$CI_YML" "$ALLOWLIST" <<'PY'
+import re
+import sys
+
+ci_local_path, ci_yml_path, allowlist_raw = sys.argv[1], sys.argv[2], sys.argv[3]
+allowlist = set(allowlist_raw.split())
+
+
+def fold(name):
+    """Collapse granularity-only matrix shape into canonical suite identity."""
+    if name.startswith("chaos-") or name == "chaos":
+        return "chaos"
+    if name.startswith("deb-install"):
+        return "deb-install"
+    return name
+
+
+# ── Local: parse the suite arrays from ci-local.sh ───────────────────────────
+with open(ci_local_path, encoding="utf-8") as fh:
+    local_src = fh.read()
+
+
+def bash_array(var):
+    m = re.search(rf"^{var}=\((.*?)\)", local_src, re.MULTILINE | re.DOTALL)
+    if not m:
+        return []
+    body = m.group(1)
+    # Quoted entries (chaos uses "display scenario flags"): first token is name.
+    quoted = re.findall(r'"([^"]*)"', body)
+    if quoted:
+        return [entry.split()[0] for entry in quoted if entry.strip()]
+    return [tok for tok in body.split() if tok.strip()]
+
+
+local = set()
+# Static, rekey, gateway, sidecar, acl, firewall, nostr, stun, dns, deb.
+for var in ("STATIC_SUITES", "REKEY_SUITES", "ADMISSION_SUITES",
+            "GATEWAY_SUITES", "SIDECAR_SUITES", "ACL_SUITES",
+            "FIREWALL_SUITES", "NOSTR_RELAY_SUITES", "STUN_FAULTS_SUITES",
+            "DNS_RESOLVER_SUITES", "DEB_INSTALL_SUITES"):
+    local.update(bash_array(var))
+# Chaos display names → fold to "chaos".
+for _ in bash_array("CHAOS_SUITES"):
+    local.add("chaos")
+# NAT scenarios are stored bare (cone/symmetric/lan) and prefixed nat- at use.
+for scen in bash_array("NAT_SUITES"):
+    local.add(f"nat-{scen}")
+# TOR_SUITES is the deliberate local-only set — excluded from the default path.
+
+local = {fold(n) for n in local}
+
+# ── GitHub: parse the integration matrix suite: values from ci.yml ───────────
+import yaml  # noqa: E402
+
+with open(ci_yml_path, encoding="utf-8") as fh:
+    doc = yaml.safe_load(fh)
+
+include = doc["jobs"]["integration"]["strategy"]["matrix"]["include"]
+github = set()
+for leg in include:
+    if "suite" not in leg:
+        continue
+    # Chaos legs carry inconsistent suite: names (chaos-smoke-10 vs
+    # churn-mixed-10) but a uniform type: chaos — fold via type, not name.
+    if str(leg.get("type", "")) == "chaos":
+        github.add("chaos")
+    else:
+        github.add(fold(str(leg["suite"])))
+
+# ── Diff (subtract allowlist from local before comparison) ───────────────────
+local_cmp = {n for n in local if n not in allowlist}
+
+local_only = sorted(local_cmp - github)
+github_only = sorted(github - local_cmp)
+
+if local_only or github_only:
+    print("CI parity FAILED: integration suite sets diverge.\n")
+    if local_only:
+        print("  Local-only (in ci-local.sh, missing from ci.yml, "
+              "not in deliberate allowlist):")
+        for n in local_only:
+            print(f"    - {n}")
+    if github_only:
+        print("  GitHub-only (in ci.yml, missing from local default path):")
+        for n in github_only:
+            print(f"    - {n}")
+    print("\n  Resolve by adding the suite to the other runner, or by adding "
+          "it\n  to the deliberate local-only allowlist in "
+          "check-ci-parity.sh with a\n  stated reason.")
+    sys.exit(1)
+
+print("CI parity OK: integration suite sets match "
+      "(allowlist: " + ", ".join(sorted(allowlist)) + ").")
+print(f"  {len(github)} canonical suites compared on each side.")
+sys.exit(0)
+PY
diff --git a/testing/ci-local.sh b/testing/ci-local.sh
index 6e57486..7630bcb 100755
--- a/testing/ci-local.sh
+++ b/testing/ci-local.sh
@@ -12,6 +12,8 @@
 #   --only <suite>       Run a single integration suite
 #   -j, --jobs <N>       Max parallel chaos scenarios (default: 4)
 #   --list               List available integration suites
+#   --check-parity       Verify this suite set matches ci.yml's integration
+#                        matrix (see testing/check-ci-parity.sh), then exit
 #   -h, --help           Show this help
 #
 # Integration suites (default coverage):
@@ -32,6 +34,25 @@
 # Exit codes:
 #   0 — all stages passed
 #   1 — one or more stages failed
+#
+# ── CI parity invariant ─────────────────────────────────────────────────────
+# This local default suite set and the GitHub integration matrix
+# (.github/workflows/ci.yml) MUST run the same integration suites, EXCEPT for
+# the deliberate local-only entries below. Adding a suite to one runner
+# without the other means "local green" and "GitHub green" stop being
+# equivalent. testing/check-ci-parity.sh enforces this and fails on drift.
+#
+# Deliberate local-only (NOT on the GitHub gate), with reason:
+#   tor-socks5     — requires live Tor network; opt-in via --with-tor,
+#                    unreliable on GitHub-hosted runners.
+#   tor-directory  — same; live Tor dependency.
+#
+# Granularity-only differences (same coverage, different matrix shape —
+# NOT a divergence):
+#   deb-install    — local runs all distros sequentially in one suite; GitHub
+#                    splits into per-distro legs (debian12/ubuntu24/ubuntu26).
+#   dns-resolver   — single suite both sides; runs all scenarios.
+# ─────────────────────────────────────────────────────────────────────────────
 set -uo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
@@ -170,6 +191,7 @@ while [[ $# -gt 0 ]]; do
         --only)             ONLY_SUITE="$2"; shift 2 ;;
         -j|--jobs)          PARALLEL_JOBS="$2"; shift 2 ;;
         --list)             list_suites ;;
+        --check-parity)     exec "$SCRIPT_DIR/check-ci-parity.sh" ;;
         -h|--help)          usage ;;
         *)                  echo "Unknown option: $1"; usage ;;
     esac