spec milestone 21: abp list exceptions and operator regex rules

docs/how-to/verify-a-release.md

@@ -8,41 +8,12 @@ Do this before you run the binary, not after. The whole point of the checksum
 file is that it is signed, so a tampered mirror cannot hand you a matching
 tarball and a matching checksum at the same time.
 
-> Verification: no nxdns release exists yet. The repository has no tags, no
-> release page and no pushed image, so nothing on this page could be run against
-> a real release asset and no command here was pointed at
-> `git.mial.net/mokhtar/nxdns` with any expectation of success. Substitutes were
-> used, and every block says which one applies to it.
->
-> The URL shapes were probed against `gitea.com`, a public instance of the same
-> Gitea series running `1.27.0+dev-652-g0571722545`, using `gitea/tea`, which
-> does have releases. `git.mial.net` reports `1.27.1`, and its
-> `/mokhtar/nxdns/releases/latest` answers 404 — no release to redirect to. On
-> `gitea/tea`, `releases/latest` answered 303 to the tag page of `v0.15.1`;
-> `releases/download/v0.15.1/checksums.txt` and
-> `releases/download/latest/checksums.txt` both answered 303 to the same stored
-> object and delivered the same 1,842-byte file under `-L`;
-> `releases/latest/download/checksums.txt` — GitHub's spelling — answered 404.
->
-> The `gpg --verify` and `sha256sum -c` blocks were run on this host against
-> stand-in files: two random-byte files named like the release tarballs, an
-> `IMAGE-DIGEST.txt` holding one image reference, and a `SHA256SUMS.txt`
-> computed over the three, signed by a **throwaway demonstration key generated
-> for this page**. That key has the shape the real one will have — an ed25519
-> primary key plus a separate ed25519 signing subkey, with the signature made by
-> the subkey — so the `gpg --verify` output on this page has the two-fingerprint
-> structure a subkey-signed release produces. The fingerprints printed in those
-> transcripts are the throwaway key's, they are not the project's, and they will
-> not match anything you download. The only edit to that run's output is the
-> version in every filename, which became `<version>`.
->
-> The container blocks were not run against nxdns — there is no published image.
-> The two `docker buildx imagetools inspect --format` shapes were run here
-> against `alpine:3.22` on Docker Hub, the base this project's builder stage
-> pins; the digest form printed
-> `sha256:14358309a308569c32bdc37e2e0e9694be33a9d99e68afb0f5ff33cc1f695dce` and
-> the platform form printed a list. The `docker create`/`docker cp` comparison
-> was run against an image built from this checkout rather than a pulled one.
+> Verification: every command on this page was run on 2026-08-09 against the
+> published `v0.0.1` release, from a clean directory, with a clean `GNUPGHOME`
+> holding only the key fetched from keys.openpgp.org. Every transcript below is
+> that run's output. Where a block shows a failure — a `BAD signature`, a
+> `FAILED` hash — the failure was produced deliberately by tampering with a
+> copy of the real file, and the surrounding text says how.
 
 ## What a release contains
 
@@ -94,11 +65,8 @@ want for the placeholder:
 VERSION=<version>
 ```
 
-> Not verified against nxdns: there is no release to redirect to, so the first
-> block prints an empty line here and every URL built from it is a 404. The
-> exact two-command form was run against `gitea.com/gitea/tea`, a public
-> repository on Gitea `1.27.0+dev` that does have releases, and printed
-> `0.15.1`.
+> Verified: the two-command form, run against this repository, printed `0.0.1`
+> with `v0.0.1` published.
 
 Pin the version in anything you script or automate. `latest` is convenient for
 a person at a terminal and a liability in a machine that upgrades itself.
@@ -136,11 +104,9 @@ That is the Gitea spelling, and it is not GitHub's. `releases/latest/download/`
 position, as `releases/download/latest/`. The tarball filenames contain the
 version, so this alias never saves you from knowing it for those two.
 
-> Not verified against nxdns: no release, so every URL above is a 404 today.
-> Both URL forms, including the 404 for GitHub's spelling, were exercised
-> against `gitea.com/gitea/tea` on Gitea `1.27.0+dev`; the versioned path and
-> the `latest` alias each answered 303 to the same stored object and delivered
-> the same 1,842-byte `checksums.txt` when the redirect was followed.
+> Verified against `v0.0.1`: all five assets downloaded through the versioned
+> path, `SHA256SUMS.txt` downloaded again through the `latest` alias and hashed
+> identical, and GitHub's spelling answered 404.
 
 ## 3. Check the signature over `SHA256SUMS.txt`
 
@@ -157,11 +123,9 @@ curl -fsSL https://keys.openpgp.org/vks/v1/by-fingerprint/A2061F6AB24DF2C0E92346
   gpg --import
 ```
 
-> Not verified: the key is not published yet. Run on this host, that URL
-> returned 404, and so did the `by-email` lookup for the same address. The
-> endpoint itself is live: the same `by-fingerprint` path returned 200 for an
-> unrelated key that is on keys.openpgp.org. Until this key is published there,
-> get it from a source you can check some other way.
+> Verified: the key is published, and that exact `curl | gpg --import` reported
+> `key 1509B54946D08A95: public key "Mokhtar Mial (pc) <mokhtar@mial.net>"
+> imported` into a clean `GNUPGHOME`.
 
 Then verify:
 
@@ -170,22 +134,21 @@ gpg --verify SHA256SUMS.txt.asc SHA256SUMS.txt
 ```
 
 ```
-gpg: Signature made Fri 07 Aug 2026 10:11:12 PM CEST
-gpg:                using EDDSA key 9D1EA241DAEA89E09381A21BDC27E8A3D53C32D6
-gpg: Good signature from "nxdns release signing (throwaway demonstration key) <demo@example.invalid>" [unknown]
+gpg: Signature made Sun 09 Aug 2026 01:26:42 AM CEST
+gpg:                using EDDSA key 019D00DF8417EBFDA5471E5EF7319CC024FB5A96
+gpg: Good signature from "Mokhtar Mial (pc) <mokhtar@mial.net>" [unknown]
 gpg: WARNING: This key is not certified with a trusted signature!
 gpg:          There is no indication that the signature belongs to the owner.
-Primary key fingerprint: 6643 13AA F527 DDAE 1C1E  516C A36F F8DA 4E6C 1C07
-     Subkey fingerprint: 9D1E A241 DAEA 89E0 9381  A21B DC27 E8A3 D53C 32D6
+Primary key fingerprint: A206 1F6A B24D F2C0 E923  46FD 1509 B549 46D0 8A95
+     Subkey fingerprint: 019D 00DF 8417 EBFD A547  1E5E F731 9CC0 24FB 5A96
 ```
 
-**Those two fingerprints and that user id belong to a throwaway key generated
-to produce this transcript.** They are not the project's, and what you see will
-carry the project's uid and the fingerprint in this page instead. The
-*structure* is what to read: three lines, not one. `using EDDSA key` and
+The *structure* is what to read: three lines, not one. `using EDDSA key` and
 `Subkey fingerprint` name the signing subkey that actually made the signature;
 `Primary key fingerprint` names the certificate it hangs off, and that is the
-one published above.
+one published above. The subkey fingerprint can change — a signing subkey is
+revoked and replaced on its own — but the primary fingerprint is the
+project's identity and stays.
 
 Exit status 0, and `Good signature`. That warning is normal and is not a
 failure: it says you have not told GnuPG you believe the key belongs to the
@@ -210,22 +173,18 @@ including one an attacker talked you into importing.
 A tampered `SHA256SUMS.txt` looks like this, and exits 1:
 
 ```
-gpg: Signature made Fri 07 Aug 2026 10:11:12 PM CEST
-gpg:                using EDDSA key 9D1EA241DAEA89E09381A21BDC27E8A3D53C32D6
-gpg: BAD signature from "nxdns release signing (throwaway demonstration key) <demo@example.invalid>" [unknown]
+gpg: Signature made Sun 09 Aug 2026 01:26:42 AM CEST
+gpg:                using EDDSA key 019D00DF8417EBFDA5471E5EF7319CC024FB5A96
+gpg: BAD signature from "Mokhtar Mial (pc) <mokhtar@mial.net>" [unknown]
 ```
 
-> Verified on this host. A throwaway ed25519 primary key was generated into a
-> temporary `GNUPGHOME`, an ed25519 **signing subkey** was added to it, and the
-> stand-in `SHA256SUMS.txt` was signed with `--local-user <subkey-fingerprint>!`
-> — the same construction the release workflow uses — so the transcripts above
-> are what a subkey-signed release actually prints, rather than what a key
-> signing with its primary would. The verification ran from a second
-> `GNUPGHOME` holding only that key's public half, which is why the `[unknown]`
-> trust marker and the warning are there rather than being written in by hand.
-> The second transcript is the same command after one newline was appended to
-> `SHA256SUMS.txt`. The `sed`/`tr` pipeline was run against that same output and
-> printed `664313AAF527DDAE1C1E516CA36FF8DA4E6C1C07`, the throwaway primary.
+> Verified against `v0.0.1`, from a clean `GNUPGHOME` holding only the imported
+> public key — which is why the `[unknown]` trust marker and the warning are
+> there rather than being written in by hand. The good-signature transcript is
+> the real release's; the `BAD signature` transcript is the same command
+> against a copy of `SHA256SUMS.txt` with one newline appended, and it exited
+> 1. The `sed`/`tr` pipeline printed
+> `A2061F6AB24DF2C0E92346FD1509B54946D08A95`, matching the fingerprint above.
 
 ## 4. Check the hashes
 
@@ -263,12 +222,11 @@ Check the signature before the hashes, not after. An attacker who can replace
 the tarball can replace `SHA256SUMS.txt` next to it; the signature is the only
 thing in the set they cannot forge.
 
-> Verified on this host against the stand-in files: all three transcripts are
-> real `sha256sum` output over two random-byte files named like the release
-> tarballs plus an `IMAGE-DIGEST.txt` holding one image reference, with one
-> tarball deleted for the first two blocks and one byte appended to the other
-> for the third. Only the version in the filenames was replaced with
-> `<version>`.
+> Verified against `v0.0.1`: with both tarballs present, `sha256sum -c` printed
+> three `OK` lines. The three transcripts above are the same command over
+> copies of the real assets, with the aarch64 tarball absent for the first two
+> and one byte appended to the x86_64 tarball for the third. Only the version
+> in the filenames was replaced with `<version>`.
 
 ## 5. Look inside before extracting
 
@@ -294,7 +252,11 @@ tar -xzf nxdns-$VERSION-x86_64-linux-musl.tar.gz
 Zig version. The version has to match the tag you downloaded, and the commit
 has to match the commit the tag points at.
 
-> Not verified on this host: there is no release tarball to list or extract.
+> Verified against `v0.0.1`: both tarballs listed exactly the one directory and
+> six files with the stated modes, no symlinks and no absolute or `..` paths,
+> and the extracted binary printed `nxdns 0.0.1
+> (3c2d0d41f04570038e805b759da4541e198eae17)` — the commit `v0.0.1` points at —
+> then `zig 0.16.0`.
 
 ## 6. Verify the container image
 
@@ -343,23 +305,13 @@ docker rm nxdns-verify
 sha256sum ./nxdns-from-image ./nxdns-$VERSION-x86_64-linux-musl/nxdns
 ```
 
-> Not verified against nxdns: no image is published, so no command here was run
-> against `git.mial.net/mokhtar/nxdns`. The two
-> `docker buildx imagetools inspect --format` shapes were run on this host
-> against `alpine:3.22` on Docker Hub — the digest form printed
-> `sha256:14358309a308569c32bdc37e2e0e9694be33a9d99e68afb0f5ff33cc1f695dce`,
-> which is the digest this project's builder stage pins, and the platform form
-> printed `linux/amd64 unknown/unknown linux/arm unknown/unknown ...`. That
-> `unknown/unknown` is exactly what the paragraph above says nxdns's own index
-> must not contain: Alpine's index carries attestation entries, and nxdns's
-> build turns them off. Nothing was checked about how nxdns's index will
-> actually look.
->
-> The `docker create` / `docker cp` / `sha256sum` comparison at the end was run
-> here against an image built from this checkout rather than a pulled one, and
-> the two hashes matched: the binary copied out of the image and
-> `zig-out/dist/stage/nxdns-<version>-x86_64-linux-musl/nxdns` were the same
-> file.
+> Verified against `v0.0.1`: the digest in `IMAGE-DIGEST.txt` and the digest
+> the `:0.0.1` tag resolves to were the same string
+> (`sha256:f2945fbf6c1e16509f0e33e3d62da9a9cd7dc706718d333ce4edf95c80dbb00e`,
+> and `:latest` resolved to it too), the platform form printed exactly
+> `linux/amd64 linux/arm64` with no attestation entries, `docker pull` of the
+> pinned reference succeeded, and the binary copied out of that pulled image
+> hashed identical to the `nxdns` in the x86_64 tarball.
 
 ## What the signature proves, and what it does not
 
@@ -431,14 +383,16 @@ release used. The Zig version is the second line of `nxdns version`, and both
 it and the Node version are pinned to exact patch releases at the top of
 `.gitea/workflows/gates.yml`, which is the workflow the release runs.
 
-> Partly verified on this host. `zig build dist` and `sha256sum` on its output
-> were run to completion, with the version read out of `build.zig.zon`: `dist`
-> exited 0 and wrote the two tarballs, `SHA256SUMS` and the staged payloads
-> described above. `zig build verify-dist` was run on the result too and exited
-> 0. What could not be run is everything that needs a release: the clone, the
-> checkout and `git verify-tag` need a tag that does not exist, and there is no
-> published `SHA256SUMS.txt` to compare a local build against, so the comparison
-> this section is about has never been performed.
+> Verified against `v0.0.1`, and the result is the caveat above in action. The
+> whole recipe ran from a fresh clone: `git verify-tag v0.0.1` printed
+> `Good signature` under the same signing subkey as the release, and
+> `zig build dist` produced both tarballs. The hashes did **not** match the
+> published `SHA256SUMS.txt` — the binaries themselves already differ. The Zig
+> version matched the pin exactly; the Node version did not (24.14.1 against
+> the pinned 24.19.0) and the build path differed, two of the ordinary causes
+> listed above. That is a measurement of what an unpinned rebuild gives you,
+> not evidence of tampering: the signature, checksum and image checks earlier
+> on this page all passed against the same release.
 
 ## If a check fails
 

specs/milestone-14.md

@@ -695,13 +695,16 @@ was reproduced before it was fixed.
 - [x] Two runs of `zig build dist` on the same commit produce byte-identical
       tarballs **in the same directory**. (Cross-directory reproducibility is
       ruling 12 and is not claimed here.)
-- [ ] The image builds for both platforms with no qemu, carries `/LICENSE` and
+- [x] The image builds for both platforms with no qemu, carries `/LICENSE` and
       `/THIRD-PARTY-NOTICES` and the OCI labels, and its binaries are
-      byte-identical to the tarball binaries. Verified for the native amd64
-      image only; the arm64 half needs a runner with buildx.
-- [ ] `gates.yml` runs from both `ci.yml` and `release.yml`; `ci.yml` triggers
-      on `master`; `origin/main` is gone. The first two are in the files; no
-      workflow has run and `origin/main` still exists (manual prerequisite).
+      byte-identical to the tarball binaries. The v0.0.1 run built and pushed
+      both platforms on the runner; the published index lists exactly
+      `linux/amd64 linux/arm64`, and `release verify-image-binaries` compared
+      both binaries against the tarballs before publication.
+- [x] `gates.yml` runs from both `ci.yml` and `release.yml`; `ci.yml` triggers
+      on `master`; `origin/main` is gone. Proven live: pushes to `master` run
+      the gates through `ci.yml`, and release runs 484-493 ran them through
+      `release.yml`.
 - [x] `THIRD-PARTY-NOTICES` covers musl, the Zig runtime, SQLite, Mbed TLS with
       its Apache-2.0 selection line and full text, Everest, p256-m and the web
       runtime closure. The dependency drift guard was proven able to fail:
@@ -715,10 +718,21 @@ was reproduced before it was fixed.
       multi-architecture image — and was then deleted (release, git tag, both
       registry versions). Five attempts; the failures and their fixes are
       deviations 23-26.
-- [ ] `v0.0.1` is published: five assets, a verifying signature, and an image at
-      `git.mial.net/mokhtar/nxdns:0.0.1` and `:latest`.
-- [ ] `docs/how-to/verify-a-release.md` was followed end to end against the
-      published release, from a clean directory, on this host.
+- [x] `v0.0.1` is published: five assets, a verifying signature, and an image at
+      `git.mial.net/mokhtar/nxdns:0.0.1` and `:latest`. Run 493, all jobs green
+      on the first attempt after the dry-run fixes.
+- [x] `docs/how-to/verify-a-release.md` was followed end to end against the
+      published release, from a clean directory, on this host, with a clean
+      `GNUPGHOME` holding only the key fetched from keys.openpgp.org. Every
+      command on the page passed: the `releases/latest` redirect printed
+      `0.0.1`, both tarball downloads and the `latest` alias worked (and
+      GitHub's spelling answered 404 as documented), the signature verified
+      with matching primary and subkey fingerprints, `sha256sum -c` said OK for
+      all three files, the tarball layout and modes matched, `nxdns version`
+      printed the tag's commit, the tag digest equalled `IMAGE-DIGEST.txt`, the
+      platform list was exactly `linux/amd64 linux/arm64`, and the binary
+      copied out of the pulled-by-digest image hashed identical to the tarball
+      binary.
 - [x] No `zig build cross` or source-only-distribution text remains on any
       **active** surface: `build.zig`, the workflows, `deploy/`, `README.md` and
       `docs/`. Historical milestone specs and `TECH_DEBT.md` keep their text —

specs/milestone-20.md

@@ -0,0 +1,894 @@
+# Milestone 20: declarative configuration for IaC
+
+Goal: a config file an operator can keep in git and deploy with Ansible, where
+the file is the sole declarative source of truth, converged at every boot —
+without re-downloading every blocklist on every boot, and without the UI
+silently diverging from the file. Two authority modes, selected by the
+presence of one flag: bare `run` serves the DB; `run --config=<path>` makes
+the file authority.
+
+Design finalized 2026-08-09 after three adversarial rounds (red team ops 1-16
+and debt 1-14; Codex cross-validation F1-F12; a Codex round on the premise
+revision). All findings are folded in below or declined with written reasons;
+all file:line anchors were re-verified at the pre-implementation HEAD
+(7039a9f). A premise revision replaced the earlier `--config-source` mode
+enum with presence-of-`--config` and deleted the persisted authority marker;
+rulings 1, 6 and 8 record the reasons — do not reintroduce either.
+
+## Implementation contract (read first)
+
+- Read `AGENTS.md`, then this spec whole, before session work starts.
+- Session order: R1 → R2 sequential; R3 and R4 parallel to both (Sessions,
+  below). File ownership is write-exclusivity; the interfaces between
+  sessions (`reconcile.Summary`, `WebState.authority` + `reconciled_at`,
+  `RouteInfo.policy`) are fixed in this spec and are not renegotiable
+  mid-build.
+- Gates: `zig build test` and `zig build test -Dintegration` with 0 failed,
+  plus the drift-guard regenerations the Tests section names. Skip counts are
+  reported with their reasons (plain-suite skips are integration-gated; the 4
+  integration skips are the live-network TLS tests excluded by milestone-1
+  design). One `-Dlive` run covers the real download path (Tests).
+- No `std.log.err` in new code. No secrets in logs — url redaction goes
+  through `src/safe_url.zig` as everywhere else.
+- Every fix or behaviour claim lands with a test the author watched fail
+  against the reverted implementation (milestone-13 ruling F-f applies).
+- Doc pages touched by R4 follow milestone-13 ruling 3: every command block
+  in `tutorial/` and `how-to/` is executed on this host by the session that
+  writes it, or marked in-page as unverified with the reason.
+- The final commit is GPG-signed by the user (`git commit -S`, lowercase,
+  single line); stage the work and hand the command over.
+
+## Rulings (binding)
+
+### 1. Authority is the invocation: `--config` present means the file governs
+
+`nxdns run` — the DB is authority, today's appliance behaviour.
+`nxdns run --config=/etc/nxdns/config.zon` — the file is authority. The
+flag's presence selects the mode; there is no mode enum and no default path.
+`check` keeps its existing surface under the same rule: bare `check` grades
+the DB, `check --config <file>` grades the file. The DB-exists-wins heuristic
+in `checkImpl` (cli.zig:559-588) and `CheckArgs.config_explicit` are deleted.
+
+Two principles, separated deliberately, because conflating them is what
+produced the rejected `--config-source` enum:
+
+- **Authority must be explicit in the invocation.** An operator reads
+  `ExecStart` and knows which authority is live. Probing `/etc/nxdns` for a
+  file and switching behaviour on its existence is ambient magic — the same
+  class of heuristic that made seed-once bootstrap a source of doc lies (the
+  compose comment, the first-run tutorial) — and stays banned: a file on disk
+  that no flag names changes nothing.
+- **A mode enum is the wrong shape for a two-state choice a path already
+  expresses.** `--config-source=db` names an implementation, not an operator
+  intent, and a mode flag beside a path flag manufactures invalid
+  combinations (path without mode, mode without path) that then need pairing
+  rules and usage errors to defend. Presence-of-path has no invalid
+  combinations and nothing to defend.
+
+Breaking change, named: `run --config <file>` today means seed-once; the same
+syntax now means file authority — reconcile on every boot, UI config writes
+rejected. For an operator who seeded once and then configured through the UI,
+the first post-upgrade restart converges the DB to that old seed file,
+deleting the UI edits. The upgrade doc's breaking-changes section leads with
+this and gives the two exits (ruling 9): drop the flag, or re-export to the
+file path first. `check --config` keeps its meaning exactly. Greenfield rules
+apply — the seed-once interface does not survive for compatibility — but the
+break is loud in the docs, never silent-by-omission.
+
+A rename (`--managed-config`) that would make the old invocation fail loudly
+was considered twice and declined: it trades a worse name and a permanent
+asymmetry with `check --config` against a one-time hazard whose exposed
+population is the pre-change install base of a project whose first release is
+days old. The hazard is real and the docs lead with it; the interface does
+not carry the scar. This is a judgment, recorded so it is revisited only with
+new facts (a real install base would be one).
+
+### 2. File mode fails closed, and *declarative* failure is exit 2
+
+File mode contract: the file is the sole declarative source; the DB stays the
+runtime substrate and the effective-config read path. Startup sequence,
+replacing the `seedFromFile` call at app.zig:196:
+
+1. `DataDir.open` → open config DB → `migrate` (unchanged).
+2. Read the file (existing 4 MiB cap), ZON parse (arena, never freed — keep
+   the import.zig discipline), `validate.validate`.
+3. Reconcile into the DB in one `BEGIN IMMEDIATE` transaction, `errdefer`
+   rollback (ruling 3).
+4. `config_export.readConfig` (app.zig:206) → serve, unchanged from there on.
+
+A missing, unreadable, or invalid file fails startup. Never fall back to the
+DB: a fallback turns a deploy typo into a silently stale config.
+
+Exit codes keep the 2am contract — exit 2 means "your config is wrong, run
+`nxdns check`"; exit 1 means "the box is wrong". `faults.isConfigFault`
+deliberately excludes `FileNotFound`/`AccessDenied` (faults.zig:107-108), and
+that stays true in general. The file-mode loader is the seam, and it maps
+**path-class open failures only**: `FileNotFound`, `AccessDenied`,
+`PermissionDenied`, `NotDir`, `IsDir`, `SymLinkLoop`, `NameTooLong`,
+`BadPathName` become `error.ManagedConfigUnreadable` (message includes the
+path), which joins the `ConfigFault` set beside `ParseZon`/`ConfigTooLarge`.
+Every other member of `ReadFileAllocError` — `SystemResources`,
+`ProcessFdQuotaExceeded`, `SystemFdQuotaExceeded`, I/O errors, `OutOfMemory` —
+propagates unmapped, exit 1: those are box faults a retry can clear, and once
+ruling 9 adds `RestartPreventExitStatus=2 64`, mapping them to exit 2 would
+stop the unit permanently on a transient fault. The mapping is an explicit
+named error set in the loader, switched exhaustively with
+`else => |other| return other`, so a std error added in a Zig bump defaults to
+exit 1 rather than silently to exit 2 — the same closed-set discipline
+faults.zig already documents. The mapping lives in **one shared helper** used
+by both `run` and `check`; two copies would let the two grade the same
+unreadable file differently, exactly the divergence faults.zig:1-8 exists to
+abolish.
+
+**Scope of the check/run agreement claim**: `check --config=<file>`
+grades exactly the declarative faults `run` would hit — read (path-class),
+parse, size, validate — through the same shared loader helper. Reconcile-time
+faults (FK violations, `SQLITE_BUSY` from a restart race, disk full) are
+runtime faults, exit 1, and structurally invisible to `check`, which needs no
+DB. The acceptance encodes the scoped claim, not "check passing guarantees run
+converges". The one *systematic* gap the red team found — a group removal
+tripping the un-cascaded `clients.group_id` FK against observed rows `check`
+cannot see — is eliminated in the engine itself (ruling 3's reassign rule),
+not papered over in `check`.
+
+Reconcile-time diagnostics include the SQLite error (`SQLITE_FULL` by name
+when that is the cause) so a full SD card reads as "disk", not as a bare
+exit 1. Diagnostics render to `r.err` and flush immediately, keeping the
+current `seedFromFile` discipline (app.zig:137-178) — `serve` never returns,
+so a buffered error line is a lost error line.
+
+Because every boot revalidates the file, a latent file error is no longer a
+first-boot-only hazard: a bad push that skips its restart handler detonates at
+the next power blip. Two mitigations, both in ruling 9: the shipped unit gains
+`RestartPreventExitStatus=2 64` (retrying a config fault every 2 s is pure
+loop; the journal holds the diagnostics), and the deployment docs mandate
+`nxdns check --config=<file>` as the pre-restart gate in any Ansible
+handler.
+
+Db mode: steps 2-3 are skipped entirely; the DB is truth exactly as today.
+Bare `check` on a box with no `config.db` exits 2: `no config database at <path>`
+plus the ruling-6 hint line — the deleted heuristic's "nothing to check"
+branch (cli.zig:582-587) is replaced, not dropped.
+
+### 3. Reconcile engine: replace declarative state, preserve runtime state by stable identity
+
+New module `src/config/reconcile.zig`, replacing `applyToDb`'s wipe+reinsert.
+The defect it exists to fix: today's import deletes and reinserts
+`blocklist_sources` including runtime columns (checksum, `last_updated`,
+counters — config_schema.zig:46-56), and compiled blocklists are keyed by
+source row id (`<id>.list`/`<id>.wild`). A naive re-import every boot would
+force a full re-download and recompile of every blocklist on every restart.
+
+Contract, per table: match rows by identity key ⇒ UPDATE declarative columns
+in place (row id survives); present in DB but absent from the file ⇒ DELETE;
+present in file but not DB ⇒ INSERT. Never wipe. One transaction. The
+`clients` table refines the match rule with promotion (below): an observed row
+whose IP the file declares is matched and updated, never deleted.
+
+**Identity matching is on canonical forms.** Import already canonicalizes
+client IPs and prefixes before insert (import.zig:226-237; `FD00:0:0:0:0:0:0:1`
+stores as `fd00::1`) and the schema documents the columns as canonical text.
+The engine canonicalizes file values *before* matching; matching the raw file
+string against the canonical column would churn ids under an unchanged
+non-canonical file, violating ruling 5 in a way an exported-config test
+(export emits canonical forms) cannot catch. The idempotence test includes a
+non-canonical file.
+
+**Writes only on difference.** A matched row whose declarative columns already
+equal the file's values gets no UPDATE. This is stronger than byte-stability:
+reconciling an unchanged file performs **zero writes**, so a no-op boot needs
+no WAL headroom and a querylog-full SD card cannot brick a file-mode restart
+that db mode would survive. Testable: the second reconcile returns an all-zero
+summary and `sqlite3_total_changes` does not move.
+
+| Table | Identity key | Declarative columns | Runtime-owned (preserved on match) |
+|---|---|---|---|
+| `blocklist_sources` | `url` | `name`, `enabled`, `is_suggested` | **`id`**, `checksum`, `last_updated`, `domain_count`, `wildcard_count`, `skipped_regex_count` |
+| `groups` | `name` (`default` pinned to id 1, existing assert kept) | `safe_search` | `id` |
+| `clients` | canonical `ip` | `name`, `group_id`, `hand_edited=1` | `first_seen`, `last_seen`; observed rows (`hand_edited=0`) are kept wholesale; an observed row whose IP is now declared in the file is **promoted in place** (UPDATE `name`, `group_id`, `hand_edited` 0→1 — `first_seen`/`last_seen` untouched, row id survives, counts as `updated`); observed rows whose group is deleted are **reassigned to the default group** (below) |
+| `rules` | the full tuple `(group_id, pattern, kind, action)` — no natural key exists; the identity is a **multiset**, exact duplicate tuples pair off by count | (the tuple) | `id`, `created_at` (unmatched inserts stamp `now`) |
+| `upstreams` / `client_prefixes` / `forward_zones` / `local_records` | `url` / canonical `prefix` / `zone` / `(name, rtype, value)` | everything else | `id` — preserved as a consequence of the idempotence invariant (ruling 5), **not** for FK stability: nothing references these ids by FK and id-based REST mutations are rejected in file mode |
+| `group_sources` | `(group_id, source_id)`, resolved via the name/url maps | whole row | — |
+| `settings` | key | value via `settings_repo.putSetting` upsert, on difference only | delete keys not produced by `toSettings`, **except** `web.password_hash`, which the reconciler owns directly (ruling 4) |
+
+**Pass order (binding).** `delete_order` alone under-specifies the engine:
+inserts need parents before children, and a group DELETE cascades through
+`rules`, `client_prefixes`, `group_sources` (config_schema.zig:35, :60, :67),
+which could silently undo child-table work and corrupt the diff counts if
+deletes ran first or interleaved. The order is:
+
+- **Phase A — upserts, parents first**: `groups`, `blocklist_sources`, then
+  the referrers (`clients`, `client_prefixes`, `rules`, `group_sources`,
+  `upstreams`, `local_records`, `forward_zones`, `settings`), with the
+  name→id / url→id maps built after the parent passes. Client promotion
+  happens here, in the `clients` pass.
+- **Phase B — delete-absent, child first**, in `delete_order`
+  (config_schema.zig:99). Because every declarative child of a dying group is
+  itself absent from the file (validate guarantees file rules/prefixes
+  reference file groups), the child passes have already deleted and counted
+  them by the time the parent DELETE runs; the FK cascades become a safety
+  net, never the accountant.
+- Immediately before the `groups` delete pass: observed clients
+  (`hand_edited=0`) whose `group_id` belongs to a dying group are reassigned
+  to the default group (id 1). `clients.group_id` has **no** ON DELETE clause
+  (config_schema.zig:26) — without this step, removing or renaming a group
+  that observed devices had been assigned to trips the FK mid-transaction:
+  exit 1, restart loop, and a `check` that said the file was fine. The
+  reassignment is the semantics we want anyway: the operator un-declared the
+  group, not the devices.
+
+Consequences that make the fix complete: an unchanged URL keeps id **and**
+checksum + counters + `last_updated` together, so `loadSource` never sees
+`.never_fetched`, `needsRefresh` does not fire spuriously (preserving
+`last_updated` matters — checksum alone is not enough), `sweepOrphans` never
+orphans `<id>.list`/`<id>.wild`, and a restart costs zero downloads. A changed
+URL is a new identity: new row, new id, fresh download — consistent with
+artifacts keyed by id. **Accepted trade, stated**: the old row's compiled
+`<old-id>.list`/`<old-id>.wild` are orphaned at commit and swept before the
+new source's first fetch succeeds, so a URL edit whose new host is down leaves
+that list unenforced until a fetch lands. Deferring the sweep until a
+successor fetch would need a cross-artifact lifecycle for an event that is
+rare, operator-initiated, and bounded by the scheduler's retry — not worth the
+machinery on a household box. The REST `updateSource` keeps runtime columns
+across a URL edit; in file mode that route is rejected (ruling 7), so the
+divergence is unreachable; in db mode the reconciler only runs via explicit
+`import`.
+
+Related clock fix, same subsystem: `needsRefresh` is wall-clock arithmetic
+(`now - last >= interval`, manager.zig:1201-1202) and the Pi has no RTC. A
+fetch stamped while the clock was ahead (pre-NTP boot, restored image)
+suspends refresh until real time catches the future timestamp — and this
+design's idempotence would faithfully preserve the poison forever, having
+deleted the wipe that used to be the accidental reset lever. The engine's
+sibling fix: `needsRefresh` treats `last_updated > now` as refresh-due. One
+comparison, with a test.
+
+Client promotion in place makes the `saved_clients` lift/merge/restore
+scaffolding (import.zig:268-361, including `merge_observed_timestamps_sql`)
+unnecessary: that machinery exists only because the wipe destroyed
+`first_seen`/`last_seen` and had to smuggle them across. With no wipe, the
+semantics it encodes — observed history survives declaration — are a plain
+UPDATE that never touches the timestamp columns. The scaffolding dies with
+the wipe (Deletions); its tests' semantics move to the promotion tests.
+
+**Ordering invariant**: reconcile commits before `manager.reload`
+(app.zig:400) runs and before the scheduler's `sweepOrphans` can fire, so
+preserved ids and checksums are visible to the filter layer before any
+pruning. This holds by construction — reconcile completes inside `serve()`
+before the manager exists — and is enforced *behaviorally*, not by a
+statement-order unit test with nothing to grip: the restart-no-redownload
+integration test (Tests, below) fails if anything between reconcile and
+reload re-orders or wipes. No `serve()` restructuring is chartered for this.
+
+The engine returns a summary (ruling 8's input and the cross-session
+contract):
+
+```zig
+pub const TableCounts = struct { inserted: u32, updated: u32, deleted: u32 };
+pub const Summary = struct {
+    groups: TableCounts, sources: TableCounts, clients: TableCounts,
+    client_prefixes: TableCounts, rules: TableCounts, group_sources: TableCounts,
+    upstreams: TableCounts, local_records: TableCounts, forward_zones: TableCounts,
+    settings: TableCounts,
+    auth_transition: enum { none, enabled, disabled, rotated },
+};
+```
+
+`updated` counts only rows actually written (writes-on-difference);
+observed-client preservation counts nothing; promotion and reassignment count
+as `updated` on `clients`. `deleted` on `clients` means exactly one thing: a
+formerly declared (`hand_edited=1`) row absent from the file. An unchanged
+file yields an all-zero summary.
+
+New repo verbs carry the engine (`sources_repo.upsertByUrl`,
+per-table `deleteWhereNotIn`-style helpers), not new call ordering. `applyToDb`
+and its wipe loop are deleted; import.zig keeps its parse/validate/diagnostics
+plumbing.
+
+### 4. Password: the file overrides when it speaks, and only then
+
+`model.Web` changes to `password: ?[]const u8 = null` and
+`password_hash: ?[]const u8 = null`. The settings bridge splits its skip
+policy by direction — `isSkipped` becomes two functions, because encode and
+decode need different sets:
+
+- `isEncodeSkipped` = {`web.password`, `web.password_hash`}: `toSettings`
+  stops emitting `web.password_hash` (the reconciler owns that settings row
+  directly) and continues to never emit `web.password`.
+- `isDecodeSkipped` = {`web.password`} only: `fromSettings` **still loads**
+  `web.password_hash` from the settings table — the reconciler owning the
+  write does not mean the read path stops seeing it. Skipping it on decode
+  would leave `cfg.web.password_hash` null on every read path
+  (`config_export.readConfig` at export.zig:52, `mutations.loadConfig`), turn
+  `authEnabled` false, and silently disable auth in both modes.
+- `decodeValue` gains an `.optional => try decodeValue(child, text)` arm
+  (model.zig:408-421 has none today; an unskipped optional field is currently
+  a `@compileError`). Absent key ⇒ default `null`; present ⇒ non-null.
+
+`auth.authEnabled` becomes `(web.password_hash orelse "").len != 0`
+(auth.zig:62-63); app.zig:475's `.live_hash = .init(...)` unwraps with
+`orelse ""`. The cases:
+
+- **Both set**: existing error (`PasswordAndHashBothSet`, import.zig:250,
+  validate.zig:395 — the check ports to `!= null` on both fields).
+- **`password` present and empty**: rejected by `validate` with a new
+  diagnostic naming the remedy — `password_hash = ""` is how auth is disabled
+  declaratively. Without this rejection, `.password = ""` would hash the
+  empty string into a non-empty PHC (`authEnabled` true) while auth.zig:90
+  refuses every empty-password login: auth on, unreachable. A declarative
+  fault, exit 2, so ruling 2's check/run agreement holds.
+- **`password` set (non-empty plaintext)**: verify against the stored
+  `web.password_hash` with argon2; on match keep the stored hash, on mismatch
+  or absent stored hash, hash fresh. The justification is ruling 5 alone:
+  hashing unconditionally generates a fresh salt per apply and breaks
+  byte-stability. It is **not** a cost saving — argon2 verification recomputes
+  the full function (same t=2, m=19 MiB) with the stored salt, so
+  verify-and-keep costs exactly what hashing costs. Do not "optimize" the
+  verify away with any cached-plaintext scheme; that would be a security bug.
+- **`password_hash` set**: written verbatim. An explicit `password_hash = ""`
+  is the declarative way to disable auth (auth.zig's documented empty-hash
+  state).
+- **Neither set**: the stored hash is untouched. This is the deliberate
+  carve-out from file-as-sole-truth, because the naive alternative is a trap
+  the red team walked straight into: `toSettings` today always emits
+  `web.password_hash` with default `""` (model.zig:534, :93), so an operator
+  who hand-trims the ugly PHC string out of an exported file — meaning "keep
+  the current password" — would silently reconcile `""` over the stored hash
+  and open the admin UI to the LAN (`authEnabled` is `len != 0`, auth.zig:63).
+  Silence must mean "keep", and disabling auth must require the explicit
+  empty string.
+
+**Export's canonical form**: `password = null`, `password_hash = <stored
+value, including "">`. A non-null `password` is never emitted — the current
+`cfg.web.password = "";` at export.zig:71 ported literally would make every
+export carry a present-empty password beside a stored hash, tripping
+`PasswordAndHashBothSet` on re-import: export's own output failing its own
+rule, breaking ruling 9's adoption walkthrough and ruling 5's round trip. The
+comment at export.zig:67-70 and the header sample change with it. With
+`password = null`, the empty-plaintext rejection above does not fire and the
+"hash written verbatim" branch keeps idempotence.
+
+Any auth transition (enabled/disabled/rotated) is reported in the summary and
+printed by ruling 8 — an auth change is never a silent line item in a count.
+
+### 5. Idempotence is the invariant
+
+Reconciling the same file twice produces a byte-identical database — ids,
+checksums, timestamps, `created_at`, password hash, the whole settings
+table — **and** the second pass performs zero writes (all-zero summary,
+`total_changes` unmoved). The unit test asserts
+byte-stability via the `dump()` helper (import.zig:469), which is rewritten to
+iterate an explicit all-tables list (`config_schema.table_names`, all ten
+content-bearing tables) because its current driver, `content_tables`, is
+deleted (ruling 6). Anything that churns under an unchanged file — including a
+*non-canonical but equivalent* file — is a bug in the engine, by definition.
+(This invariant is what forces ruling 3's rules-multiset, canonical matching,
+and writes-on-difference, and ruling 4's password handling — the places a
+naive design silently violates it. It is also half of why ruling 8 persists
+no authority state at all.)
+
+### 6. `import` becomes a thin wrapper over reconcile; the guard becomes diff-gated
+
+`nxdns import` is db mode's one-shot apply and the restore tool, reimplemented
+on the reconcile engine. Reconcile is non-destructive of *runtime* state, but
+deletion of declarative rows absent from the file is still a first-class
+outcome (ruling 3) — a mistaken `nxdns import ./wrong.zon` against a
+configured DB would still remove every group, rule, upstream, and source not
+in that file. So the guard is **retargeted, not deleted**: emptiness-gating
+(`isEmpty`) becomes diff-gating.
+
+- After the reconcile passes, still inside the same `BEGIN IMMEDIATE` —
+  preserving import.zig:199-203's deliberate check-inside-the-write-lock
+  property, no TOCTOU — if any table's `deleted != 0` and no override flag,
+  roll back and fail exit 2 with the per-table delete counts in the message.
+  Observed-client reassignment is not declarative data and never trips the
+  gate (and under ruling 3's promotion rule, observed rows are never deleted
+  by reconcile at all).
+- The flag is `--allow-delete` (`Options.allow_delete`), the renamed
+  `--force`; the error is `error.DestructiveImport`, the renamed
+  `DatabaseNotEmpty`, exit-2-mapped where cli.zig:533 maps today. This is
+  strictly better than the emptiness guard: additive and edit-only re-imports
+  stop needing a flag at all, and the flag now names what it permits.
+  "Edit-only" means edits to declarative columns on a matched identity; an
+  edit that *changes an identity column* — a group name, a source or upstream
+  url, a prefix, a zone, a rule tuple, a local-record identity — is a delete
+  plus an insert to the engine (ruling 3) and needs the flag. cli.md states
+  the distinction.
+- `import.isEmpty` and `content_tables` still die — the diff-gate needs no
+  table list.
+
+`import` does not detect a file-managed DB, because nothing records one:
+authority lives in the invocation (ruling 1) and the DB carries no marker
+(ruling 8). On a box whose unit runs file mode, `import` behaves like any
+other import — the diff-gate guards deletion, and the next boot's reconcile
+converges the DB back to the file, its summary reporting what it corrected.
+The docs own this story plainly: `import` is a **stop-first operation**, on a
+file-mode box doubly so — against a running instance its effect is partial
+(the runtime divergence below) and lasts only until the next restart. The
+file-authority contract is stated with the same precision everywhere: the
+file is the sole declarative source, **converged at every boot** — not a
+lock on the database between boots. A detect-and-warn variant was
+designed and deleted (ruling 8) — a per-invocation warning cannot *prevent*
+db-side writes anyway, the CLI user is root on their own box, and the
+asymmetry with the web layer's 403 is intentional: the web UI has
+anonymous-ish LAN users, the CLI has the operator.
+
+What a mid-run import against a *running* file-mode instance actually does —
+documented, because the divergence is partial, not merely deferred:
+`Manager.reload` re-reads `blocklist_sources`, `groups`, `group_sources`,
+`rules`, `clients`, `client_prefixes` from the DB at runtime
+(manager.zig:405-489) and the scheduler runs `sweepOrphans` before every pass
+(manager.zig:1095, :1115), so filtering follows the imported rows on the next
+reload and can unlink the compiled `<id>.list`/`<id>.wild` of sources the
+import deleted — while upstreams, listeners, and settings stay at boot
+values, and the web UI shows the imported state under the file-authority
+banner. The next restart's reconcile re-inserts deleted sources from the file
+with new ids: a full re-download, the exact cost this design exists to
+prevent. That is why the docs name the restart requirement and the
+re-download cost. The settings envelope's `reconciled_at` cannot see a CLI
+import — ruling 7's weakened claim covers exactly this.
+
+The startup-vs-import race needs no code: both paths take `BEGIN IMMEDIATE`
+under the 5 s busy timeout (db.zig:252), so the outcome is ordering, not
+corruption — an import racing a restart may be reverted by the reconcile that
+wins the lock second. Documented, not engineered around.
+
+First-run story in db mode, after bootstrap dies: a fresh empty DB fails
+validation naturally (`NoUsableUpstreams`, exit 2). The remediation hint —
+one fixed line naming `nxdns import` and `run --config` — is owned by
+**cli.zig's db-source fault renderer** (one arm, beside the exit-code mapping;
+Zig errors carry no text and validate.zig must stay mode-blind), and the same
+line serves bare `check` with no DB (ruling 2). One location, R2's charter.
+
+`export` is unchanged in role: the diagnostic/capture tool in both modes, and
+the file-mode adoption tool (its canonical password form changes per
+ruling 4).
+
+### 7. Web layer: policy as data, rejected after auth, plain 403
+
+`WebState` gains `authority: union(enum) { database, managed_file: []const u8 }`
+and `reconciled_at: ?i64`, built where `WebState` is assembled (app.zig:468).
+The `managed_file` path slice is owned by `serve`'s arena, which outlives
+`WebState` — R2 provides it, R3 consumes it, neither copies. `reconciled_at`
+is stamped by `serve` immediately after the reconcile commits — same process,
+same frame, a local — and is `null` in db mode, which never reconciles.
+
+`RouteInfo` gains `policy: enum { read, config_write, runtime_action }` beside
+`auth` and `rate_limit` — policy-as-data, matching the table's existing style.
+No default value: all 56 route entries state their class explicitly, and
+router.zig's `test_table` (:198) gains the field too. Classification is
+per-route, not per-prefix: `POST /api/blocklists/update` is a
+`runtime_action`; its CRUD siblings are `config_write`.
+
+- Config writes, rejected in file mode: all group / blocklist / rule /
+  local-record / forward-zone / upstream / client-prefix mutations,
+  `PUT /api/settings` (password changes go through the file; its
+  `live_hash.installAndRevoke` side effect never fires in file mode), and
+  client PUT — naming or regrouping an observed client is declarative drift
+  (open question 1).
+- Client DELETE is a **runtime action**: deleting an observed
+  (`hand_edited=0`) row discards runtime state the file never declared —
+  without this, a mis-identified or departed device's row is immortal in file
+  mode, since the file can only promote IPs, never remove them. Deleting a
+  *declared* client contradicts the file: the handler answers the same 403
+  envelope. This is the one policy decision that needs a row read; it lives
+  in the client handler, not the router. (After ruling 3's promotion, a
+  declared IP's row *is* declared — DELETE answers 403, the intended
+  reading.)
+- Runtime actions, always live: pause, blocklist refresh, cert reload,
+  login/logout.
+
+Enforcement lives in `router.dispatch` **after** `check_auth`, before the
+handler — match → rate limit → auth → policy. Pre-auth rejection would leak
+route existence; the codebase answers 401 first and this design keeps that.
+
+Rejection is **403**, body the existing single-field envelope:
+`{"error":"configuration is managed by /etc/nxdns/config.zon; edit the file and restart"}`.
+Not 409 — that status already means constraint conflict four ways in
+openapi.yaml — and **no `code` field**: 403 is unused today, so the status
+alone is machine-readable; the UI learns authority declaratively from
+`GET /api/settings`, not by probing errors; and the single-property `Error`
+schema, golden contract samples, and `api.ts` stay untouched. An optional field
+with no consumer is machinery, not a contract.
+
+The envelope must survive its own path: `respondError` today builds into a
+fixed 512-byte buffer and **silently downgrades to `text/plain`** on overflow
+(http_util.zig:315-327) — a long managed-file path (nested bind mounts) would
+demote the documented JSON envelope. Fix at the root: `respondError` gets the
+arena treatment `respondJson` already uses (`Writer.Allocating` over
+`request.arena`, :337-339) and the `respondPlain` silent-downgrade path is
+deleted — which fixes every long error message, not just this one.
+`src/web/http_util.zig` joins R3's ownership.
+
+Authority discovery: the `GET /api/settings` envelope gains
+`authority: {mode, path, reconciled_at}` — an authenticated route, so the
+filesystem path never leaks through open `/api/version`/`/api/health`. All
+three come from `WebState` (live truth); `path` is present in file mode only
+and `reconciled_at` is nullable — `null` in db mode. Its meaning is exactly
+"**this process loaded the file at T**" — restart-pending detection: an mtime
+newer than `reconciled_at` means the running process has not loaded the
+current file. The comparison is one-directional and non-authoritative — a
+stepped clock (pre-NTP boot stamping the future, ruling 3's clock fix
+territory) or a preserved mtime (`git checkout`, `rsync -a`) can make a newer
+file look older, and the DB can move without either timestamp moving
+(ruling 6's `import`, this ruling's `runtime_action` routes). It does not
+answer "is the file what the server uses"; answering that would take content
+hashing, which the anti-requirements refuse. The UI renders a read-only
+banner (RestartBanner slot precedent) and disables mutation controls, with
+the 403 as backstop.
+
+### 8. The operator can see what happened
+
+- `logStartup` (after `logging.install`) logs the authority:
+  `authority: database` / `authority: file (/etc/nxdns/config.zon)`.
+- In file mode, the reconcile summary (ruling 3's `Summary`) prints through
+  the Runner at startup, matching `seedFromFile`'s existing output discipline:
+  per-table inserted/updated/deleted counts, the changed settings **keys**
+  (never values), and the auth transition when there is one. It is the answer
+  to "what did that restart change" without opening sqlite.
+- **Authority is never persisted.** The DB carries no record of which mode
+  wrote it: authority lives in the invocation (ruling 1), per-process state
+  (`WebState.authority`, `reconciled_at`) serves the API (ruling 7), and the
+  journal holds the history. A persisted marker was designed twice and
+  deleted twice. A per-boot `reconciled_at` settings row breaks ruling 5
+  outright — `dump()` iterates the settings table, so any row rewritten per
+  reconcile forfeits byte-identity, and `putSetting` moves `total_changes`,
+  forfeiting zero-writes. The write-on-difference `authority.mode`/`path`
+  variant survived idempotence but cost a reserved key namespace, a
+  `fromSettings` decode filter, and a reconciler sweep exemption — three
+  mechanisms whose only consumer was one `import` warning (ruling 6). State
+  that exists to power a courtesy message is not worth a namespace. The
+  settings sweep's exemption list is therefore exactly one key:
+  `web.password_hash` (ruling 4).
+
+No `std.log.err` in any new code, per the standing spec rule for new code
+(the pre-existing calls in db.zig/tls_server.zig are out of scope).
+
+### 9. Deployment and migration
+
+- **systemd**: the shipped unit stays flagless (db default) and gains two
+  lines. `RestartPreventExitStatus=2 64` — a config fault or usage error must
+  not restart-loop every 2 s until StartLimitBurst; the journal holds the
+  diagnostics and the fix is a file edit, not a retry. (Correct in db mode
+  too: exit 2 means the config is wrong in either mode. And it is why
+  ruling 2 keeps exit 2 to *declarative* faults only — a transient box fault
+  mapped to exit 2 would stop the unit permanently.) And
+  `ReadOnlyPaths=/etc/nxdns` — `ConfigurationDirectory=nxdns` makes systemd
+  create the directory owned by the service user, so without this line the
+  source-of-truth file is writable by the very process whose mutation routes
+  file mode exists to disable; nxdns never writes `/etc/nxdns` in either mode,
+  so the base unit ships the enforcement rather than recommending it. Docs
+  show a drop-in for file mode: `ExecStart=` reset plus
+  `--config=/etc/nxdns/config.zon`.
+- **Ansible / config-management**: the docs' deployment guidance mandates
+  `nxdns check --config=<file>` as the handler precondition — validate
+  the pushed file *before* restarting, so a typo is a failed deploy at noon,
+  not a dead resolver at the next 3am power blip.
+- **docker**: compose ships file mode as its example —
+  `command: ["run", "--config=/etc/nxdns/config.zon"]` (resolving old open
+  question 4; the `:ro` mount at compose.yaml:15 already suggests it). This keeps the
+  fresh-install and volume-loss stories working after bootstrap dies: a
+  recreated `nxdns-data` volume reconciles from the mounted file on next
+  start, which is *better* than the old seed-once self-heal. The binary's
+  default stays db. The seed-once comment (compose.yaml:9-12) is rewritten.
+  For db-mode-in-docker, the docs show the recovery one-liner
+  (`docker compose run --rm nxdns import /etc/nxdns/config.zon` — the file is
+  positional, `ImportArgs.file` at cli.zig:61, plus `--allow-delete` when the
+  diff deletes) — without it, `restart: unless-stopped` plus exit 2 is an
+  infinite crash loop (docker has no start limit) with no documented way out.
+- **Adopt file mode** on a UI-configured box: **stop the service first**, then
+  `nxdns export --out /etc/nxdns/config.zon` →
+  `nxdns check --config=/etc/nxdns/config.zon` → add the flag → start.
+  Stop-first is load-bearing twice: `export` opens the DB immutable and
+  refuses with `WalPending` against a live instance's steady-state WAL
+  (db.zig:222-226, cli.md:121), and any UI edit landing between a live export
+  and the restart would be silently reverted by the first reconcile. Stopped,
+  the first reconcile's summary is all-zero and writes nothing — blocklist
+  state, compiled files, and client history all survive. Every unchanged boot
+  after it writes nothing either.
+- **Leave file mode**: drop the flag (remove the drop-in), restart. The DB
+  already holds the last reconciled state; nothing else needed.
+- **Binary downgrade from file mode**: no unit edit is needed — the old
+  binary accepts `run --config` with seed-once semantics, and against the
+  already-configured DB it ignores the file and serves the last-reconciled
+  state. The rollback note states the consequence: file edits stop applying
+  until the binary is upgraded again.
+- **Restore from backup**: db mode is stop → restore `config.db` → start,
+  with the WAL caveat db.zig itself documents: take backups only from a
+  stopped instance (or use `export`), and on restore delete any stale
+  `config.db-wal`/`config.db-shm` beside the target — a mismatched WAL is
+  silently discarded by SQLite, which turns "restore" into "lose the tail".
+  Restoring an *exported file* into a populated DB via `import` is exactly
+  the deleting case: back-up-and-restore.md documents `--allow-delete` there
+  (ruling 6) — the flag choreography is rewritten, not removed. In file mode
+  `config.db` is not the config backup — the file is; restore = redeploy the
+  file. The query-log DB restores independently in both modes.
+
+Migration honesty, replacing the earlier blanket claim: a db-mode install
+that never passed `--config` needs nothing. Anyone whose unit, wrapper, or
+compose `command` carries `run --config` (the documented seed-once invocation
+in first-run.md and three how-to labs) gets file authority at the first
+post-upgrade start — the seed file becomes the config, and UI edits made
+since seeding are deleted by the first reconcile. The upgrade doc's
+breaking-changes section leads with this and gives the two exits: drop the
+flag to keep the DB, or re-export to the file path first to adopt file mode
+cleanly (the walkthrough above). `check --config` keeps its meaning. Docker
+db-mode fresh installs must use the new compose or run `import` once. No
+schema migration.
+
+### 10. Documentation is part of the change
+
+`explanation/configuration-model.md` is rewritten around the two-mode model
+(its "why the database wins" argument becomes mode-scoped, not superseded).
+Seed-once claims are corrected in: the first-run tutorial, install-with-systemd,
+install-with-docker, upgrade (breaking-changes + rollback sections,
+ruling 9), back-up-and-restore (new restore semantics, WAL sidecars,
+`--allow-delete`), set-up-admin-authentication (the ruling 4
+absence/empty-string rule), troubleshoot, cli.md
+(`run`/`check`/`import`/`export`, `--allow-delete`), configuration.md
+(optional password fields), files-and-directories.md, api.md (settings
+envelope, 403, per-route rejectability), the compose.yaml comment,
+README/INSTALL.
+
+## Deletions (complete list)
+
+`config/bootstrap.zig` (+2 tests, S7 cases 15-18, + app.zig import/call sites
+:35/:142/:146 and tests :1124/:1237) · `import.isEmpty` (+6 tests, + the
+storage_integration_test.zig call sites :763/:795/:894, + the clients_repo.zig
+doc comments :6/:129) · `config_schema.content_tables` (+its test; `dump()`
+re-pointed to the new `table_names` list) · `app.seedFromFile` (+its app.zig
+tests) · `CheckArgs.config_explicit` · the `checkImpl` source heuristic ·
+`applyToDb`'s wipe loop, including the `saved_clients` lift/merge/restore
+scaffolding (import.zig:268-361 — superseded by ruling 3's
+promotion-in-place) · `toSettings`'s `web.password_hash` emission (+its
+key-list test row; the model.zig:665-670 "skipped in both directions" test is
+rewritten for the encode/decode split) · `http_util.respondPlain`'s
+silent-downgrade path (`respondError` rebuilt on the request arena).
+
+Renamed, not deleted (ruling 6): `Options.force` → `Options.allow_delete`
+(`--force` → `--allow-delete`), `error.DatabaseNotEmpty` →
+`error.DestructiveImport` (cli.zig:533 arm retargeted, faults.zig exclusion
+and tests follow the name).
+
+## Sessions
+
+R1 lands first and R2 rewires onto it and carries every deletion — they are
+ordered, not parallel (the old plan had R1 deleting `bootstrap.zig` out from
+under R2-owned app.zig call sites). R1 is **additive engine plus one
+coordinated model change**, not purely additive: the `model.Web` optional
+fields force same-session edits at every site that reads them, or the tree
+stops building. R3 and R4 run parallel to both; their interfaces
+(`reconcile.Summary`, `WebState.authority` + `reconciled_at`,
+`RouteInfo.policy`) are fixed here.
+
+### Session R1: reconcile engine + the coordinated model change
+
+Owns `src/config/reconcile.zig` (engine + `Summary` as specified), the new
+repo verbs in `src/storage/repositories/`, the `needsRefresh` clock clamp in
+`src/filter/manager.zig`, registration in `src/tests.zig`. Rulings 3, 4, 5.
+
+Owns `src/config/model.zig` whole: the optional `Web.password`/`password_hash`
+fields, the `isEncodeSkipped`/`isDecodeSkipped` split, `decodeValue`'s
+`.optional` arm, and the bridge tests. And the sites the
+optional fields break, which no session previously owned: `validate.zig`
+(:395 both-set port, the new empty-password rejection, test :1966-1968),
+`auth.zig` (`authEnabled` orelse), `export.zig` (canonical `password = null`,
+comment and header sample), `src/web/handlers/settings.zig` (`newPassword`'s
+`orelse` chain at :184-186, and `FieldType` collapsing `?T` so `Partial`'s
+`?FieldType(...)` at :114 does not generate a double optional — landing this
+in R1 keeps R3's `web/` work unblocked). R1 also makes the one-line
+`orelse ""` edit at app.zig:475 so the tree builds; app.zig otherwise stays
+R2's, and R2 absorbs that line into its startup rewire.
+
+### Session R2: CLI + startup + deletions
+
+Owns `src/cli.zig`, `src/app.zig`, `src/config/faults.zig`,
+`src/config/import.zig` (thin-wrapper rewrite, diff-gate, `--allow-delete`),
+the shared loader-fault mapping helper (ruling 2, used by `run` and `check`),
+and the entire Deletions list plus the renames. Rulings 1, 2, 6, 8. Threads authority and
+`reconciled_at` into `WebState` (arena-owned path) but does not touch the
+router. Owns the cli.zig hint-line renderer arm.
+
+### Session R3: web enforcement + UI
+
+Owns `src/web/router.zig` (dispatch policy step, `test_table` gains the
+policy column), `src/web/routes.zig` (all 56 entries state `policy`
+explicitly — no default), `src/web/http_util.zig` (`respondError` arena
+rewrite, `respondPlain` downgrade deletion), `src/web/openapi.yaml`, the
+client-DELETE observed/declared branch in the clients handler, `web/`
+frontend (banner, disabled controls, settings envelope with nullable
+`reconciled_at`). Ruling 7. Consumes `WebState.authority`/`reconciled_at` as
+fixed above.
+
+### Session R4: deployment + docs
+
+Owns `deploy/**`, `docs/**`, `README.md`, `INSTALL`, compose file + comment,
+the systemd unit's two new lines. Rulings 9, 10.
+
+### Orchestrator
+
+This spec, R1→R2 sequencing, cross-session integration, the drift-guard
+regenerations that span sessions (contract samples, openapi route counts,
+api.md/cli.md rows), and the `-Dlive` acceptance run.
+
+## Tests
+
+- **Reconcile unit tests** (R1, `:memory:` + migrate): idempotence via the
+  rewritten `dump()` byte-stability across all tables after applying the same
+  file twice — including a file carrying a plaintext password **and a
+  non-canonical but equivalent file** (`FD00::1`-style) — plus the zero-writes
+  assertion (all-zero `Summary`, `total_changes` unmoved) on the second pass;
+  per-table preservation via `sources_repo.SourceRow` after seeding stats with
+  `updateSourceStats`; URL change ⇒ new id; source removal; observed-client
+  survival, **promote-on-declare (asserting `first_seen`/`last_seen` survive
+  the promotion and the row id is stable)**, and **reassign-to-default when
+  their group is removed or renamed** (the un-cascaded FK case);
+  `safe_search` edit on an existing group converges; rules `created_at`
+  stability including duplicate tuples; password verify-keeps-hash,
+  mismatch-rehashes, absent-keeps-stored, explicit-empty-disables; rollback
+  on mid-tx failure; default-group id 1 pin; `needsRefresh`
+  future-`last_updated` clamp.
+- **Model/bridge tests** (R1, model.zig test neighbourhood at :659):
+  `decodeValue` on an optional field (absent ⇒
+  null, present ⇒ value); `web.password_hash` decodes from settings but is
+  not encoded (the encode/decode split); `validate` rejects present-and-empty
+  `password` with the `password_hash = ""` remedy in the diagnostic; export ⇒
+  import round trip with the canonical `password = null` form.
+- **Import gate tests** (R2): a file whose diff deletes rows, without
+  `--allow-delete` ⇒ rollback, exit 2, per-table delete counts in the
+  message; with the flag ⇒ applied; additive/edit-only import needs no flag.
+- **Loader-fault mapping** (R2, on the shared helper directly): each
+  path-class open error ⇒ `ManagedConfigUnreadable`; a non-path member of the
+  set propagates unmapped.
+- **Restart-no-redownload** in filter_integration_test.zig: reconcile, then a
+  `Manager` restart reuses `<id>.list`/`<id>.wild` with no refetch (fixtures
+  already assert reuse by id) — this is also the behavioral enforcement of
+  ruling 3's ordering invariant. Plus **one `-Dlive` run of the real download
+  path** — hermetic suites have hidden a process-killing bug on the real
+  network path before (MEMORY), so the acceptance includes the real path once.
+- **Router**: policy classification unit tests via `test_table`/`matchPath`,
+  no sockets; the contract table in web_integration_test.zig gains a `policy`
+  column and the existing 1:1 coverage assertion widens so classification
+  cannot drift; one socketed test per class in file mode (config write → 403,
+  runtime action → 2xx, read → 200) plus observed-vs-declared client DELETE,
+  via `EnvOptions` authority; `respondError` with a message longer than the
+  old 512-byte buffer stays `application/json`. Route count stays 56 — no new
+  routes.
+- **CLI**: `parseArgs` tests: `run` without `--config` selects db authority;
+  `run --config=<path>` selects file authority and the path lands in the run
+  args; `--allow-delete` parsing; `usage_text` test; exit-2 for a missing
+  managed file and for bare `check` with no DB (hint line present) — via the
+  `Captured` runner (in-process; remember the buffered-writer caveat — flush
+  through a real `File.Writer` where the test asserts delivery).
+- **Drift guards knowingly tripped and regenerated**: openapi.yaml (settings
+  envelope, 403 responses), golden contract samples (`-Dcontract-samples-out`),
+  api.md rows, cli.md sections, docs_drift_test, `toSettings` key-list test.
+
+## Acceptance (design complete when implemented)
+
+- [ ] `nxdns run --config=<file>` on a DB with fetched blocklists (any boot
+      after adoption): restart performs zero downloads **and zero DB writes**;
+      source ids, checksums, `last_updated`, and compiled
+      `<id>.list`/`<id>.wild` files are identical before and after. Proven
+      once with `-Dlive` against a real source.
+- [ ] Reconciling an unchanged exported config twice yields a byte-identical
+      `dump()` and an all-zero summary — including with a plaintext
+      `password` in the file, and with non-canonical addresses.
+- [ ] Removing (and renaming) a group that observed clients were assigned to
+      converges: clients land in the default group, no FK error, counts
+      reported. Declaring an observed client's IP promotes the row in place:
+      `first_seen`/`last_seen` and row id survive, counted as `updated`.
+- [ ] A file with neither `password` nor `password_hash` leaves the stored
+      hash — and auth — intact; `password_hash = ""` disables auth and the
+      startup summary says so; a present-but-empty `password` is refused at
+      validate with a diagnostic naming `password_hash = ""` as the disable
+      path.
+- [ ] `run --config=<file>` with a missing file exits 2 with the path in
+      the message; with an invalid file exits 2 with diagnostics; never serves
+      from the DB. An open failure outside the path class (fd exhaustion, I/O
+      error) exits 1, not 2. `check --config=<file>` agrees with `run`
+      on every parse/validate/path fault via the shared helper (the scoped
+      claim of ruling 2).
+- [ ] A config file present at `/etc/nxdns/config.zon` with no `--config`
+      flag changes nothing: bare `run` serves the DB and never reads the
+      file.
+- [ ] `nxdns import` whose diff would delete rows fails exit 2 without
+      `--allow-delete`, printing per-table delete counts, and rolls back;
+      with the flag it applies; an additive import needs no flag.
+- [ ] Fresh empty DB in db mode exits 2 (`NoUsableUpstreams`) with the hint
+      line; bare `check` with no `config.db` exits 2 with the
+      same hint; neither restart-loops under the shipped unit
+      (`RestartPreventExitStatus=2 64`).
+- [ ] The shipped compose file boots a fresh container (empty volume, mounted
+      config.zon) into file mode successfully; the db-mode import recovery
+      one-liner is documented and works.
+- [ ] In file mode: every `config_write` route answers 403 with the
+      single-field error envelope — `application/json` even when the managed
+      path is long; every `runtime_action` and `read` route behaves as in db
+      mode; DELETE of an observed client succeeds, of a declared client
+      answers 403; unauthenticated requests to protected routes still answer
+      401, not 403.
+- [ ] `GET /api/settings` reports `authority` with `reconciled_at` (null in
+      db mode); the UI shows the read-only banner and disables mutation
+      controls in file mode.
+- [ ] `rg -n 'import\.isEmpty|content_tables|config/bootstrap|seedFromFile|config_explicit' src/`
+      returns nothing (historical specs exempt; pattern chosen so
+      fetcher.zig's `host.isEmpty()` and validate.zig's "bootstrap problem"
+      prose cannot false-positive).
+- [ ] Adopt-file-mode walkthrough (stop → `export` → `check --config` → add
+      the flag → start) run end to end on a UI-configured instance: the first
+      reconcile summary is all-zero and writes nothing, as does every
+      unchanged boot after it; leave-file-mode (drop the flag, restart)
+      serves identically; `export` against the *running* instance refuses
+      with the WalPending message, as documented.
+- [ ] All existing gates pass; tripped drift guards are regenerated, not
+      suppressed.
+
+## Anti-requirements
+
+- No file watcher, no inotify, no SIGHUP reload — restart is the reload.
+- No UI write-back to the file, no partial/merge authority, no per-table
+  hybrid modes, no multi-file config.
+- No persisted authority state, no config hashing, no content-based change
+  detection — authority lives in the invocation; last-load time is
+  per-process state in the settings envelope, honest about what it can and
+  cannot answer (ruling 7).
+- No deferred deletion of a replaced source's compiled artifacts — the URL-edit
+  gap is an accepted trade (ruling 3), bounded by the scheduler retry.
+- No etag/conditional GET for blocklist fetches.
+- No `code` field or richer error envelope — the status is the machine
+  contract.
+- No rule-identity schema change (no synthetic rule key column).
+- No preservation of rule `created_at` across pattern edits — an edited rule
+  is a new rule.
+- No CLI-side blocking or detection of `import` against a file-mode box's
+  DB — the diff-gate guards deletion; the next boot converges and its
+  summary reports what it corrected.
+- No fallback from file mode to db mode under any failure.
+
+## Resolved defaults (were open questions; the user may overrule before R3/R4)
+
+1. **UI naming and regrouping of observed (`hand_edited=0`) clients in file
+   mode: rejected as declarative drift** (client PUT stays `config_write`,
+   ruling 7). The household user adds the client to the file instead. The
+   alternative — carving naming/grouping out as a runtime action —
+   reintroduces two-way merge for one table, which the anti-requirements
+   refuse. Affects R3.
+2. **`export` output is byte-identical in both modes** — no file-mode
+   annotation. An annotation would make export → file → adopt produce a
+   different file than the one checked, for a label the operator already has
+   in the unit file. Affects R4's round-trip docs.
+3. **File mode ships as a documented systemd drop-in**, not a second
+   commented `ExecStart` in the packaged unit. The packaged unit stays
+   flagless and correct by itself; a commented alternative line in a unit
+   file is a doc pretending to be config. Affects R4.
+
+## Cross-validation findings rejected
+
+Round 1: none — all twelve findings (F1-F12) were confirmed against the repo
+and are folded into the rulings above. The F1 remedy has since been
+superseded: the premise revision deleted the persisted marker entirely
+(ruling 8) instead of keeping it write-on-difference.
+
+Round 2 (on the premise revision) returned three important findings and one
+minor. Folded: the docker recovery one-liner used a `--config` flag `import`
+does not have (fixed in ruling 9, file is positional); `import` is now
+stated everywhere as a stop-first operation and the file-authority contract
+as "converged at every boot" (ruling 6); identity-column edits are named as
+delete-plus-insert needing `--allow-delete` (ruling 6). Declined: renaming
+`run --config` to `--managed-config` — reasons recorded in ruling 1.
+
+## Red-team findings rejected
+
+None rejected outright — every finding checked out against the repo. Two
+proposed remedies were declined while their findings were accepted:
+
+- **ops 10's mitigation** (keep the old compiled artifact until the successor
+  URL's first successful fetch): declined — a cross-artifact lifecycle for a
+  rare, operator-initiated event on a household box; the trade is now stated
+  in ruling 3 and the anti-requirements instead.
+- **ops 14's db-mode warning** ("a config file exists but authority is
+  database"): declined — db mode is given no file path, so warning would mean
+  probing a well-known location, which is precisely the ambient inference
+  ruling 1 bans; the accepted half (drift visibility) is served by the
+  settings envelope's `authority` block and per-process `reconciled_at`.

specs/milestone-21.md

@@ -0,0 +1,314 @@
+# Milestone 21: ABP exceptions from lists, regex rules for operators
+
+Goal: honor `@@||domain^` exception lines in downloaded blocklists as allow
+entries scoped below operator rules and above list blocks (tier 1), and add a
+`regex` rule kind for operator rules backed by a homegrown linear-time engine
+(tier 2). Nothing else from the ABP syntax enters scope.
+
+Design written 2026-08-09 against HEAD `ffc3ca6`. Every `file:line` anchor
+below was read at that commit. The milestone amends PLAN §2.2, which currently
+rules regex out permanently; the amendment is part of session S3, not a
+side effect.
+
+## Implementation contract (read first)
+
+- Read `AGENTS.md`, then this spec whole, before session work starts.
+- Pure core stays pure: `src/filter/` files that are fuzz-module roots import
+  only `std` (`src/filter/parsers.zig:1-14`). The new `src/filter/regex.zig`
+  obeys the same constraint.
+- Every new `src/**.zig` file must be listed in `src/tests.zig`
+  (`build.zig:495-540` fatals otherwise).
+- Frozen DDL is frozen: schema changes are new migration steps
+  (`src/storage/config_schema.zig:1-6`, `src/storage/migrations.zig:21-22`).
+- After any API shape change, regenerate the contract samples
+  (`web/src/lib/contractSamples.gen.ts`; procedure in AGENTS.md).
+
+## Rulings (binding)
+
+### 1. Exception lines are `@@||name^` and nothing else, plus one modifier
+
+`src/filter/parser_abp.zig:22` currently maps every `@@` line to
+`.unsupported`. After this milestone, a line is an exception when it is
+`@@||name^` or `@@||name` (same trailing-`^` and `rule_tokens` treatment as the
+block anchor at parser_abp.zig:26-34), optionally suffixed with the literal
+`$important` — that suffix is the common form in AdGuard-authored lists and
+changes nothing about the meaning here, because list exceptions already sit
+below every operator rule. Any other `@@` form (`@@name` without the anchor,
+any other `$` modifier, a path, a scheme) stays `.unsupported`. The
+parser-header policy paragraph (parser_abp.zig:5-6) is rewritten to state the
+new rule and its precedence justification: a list exception can cancel only
+list blocks, never an operator decision, so no downloaded list can open an
+allow hole the operator did not open.
+
+### 2. Precedence: list exceptions sit between operator rules and list blocks
+
+`matcher.Snapshot.evaluate` (`src/filter/matcher.zig:286-338`) gains one level
+between the operator wildcard-block walk (level 4) and the blocklist domain
+probe (level 5): for each attached source, an exception match — full name or
+parent walk, apex covered — returns `blocked = false`, reason
+`.blocklist_exception`, `matched` = the matching entry, `source` = the source
+index. The doc comment at matcher.zig:269-285 and PLAN §3.10 (PLAN.md:108-117)
+are both updated with the new level. Regex rules (ruling 6) slot in as levels
+after the wildcard rules and before list exceptions, allow before block, so
+the full order is: exact allow, exact block, wildcard allow, wildcard block,
+regex allow, regex block, list exception, list domain, list wildcard.
+"Tie-break at same specificity: allow wins" is preserved.
+
+### 3. The compiled-source format grows a third body, checksum-compatibly
+
+`compiler.compile` (`src/filter/compiler.zig:50-56`) takes a third writer
+(`allow_w`) and `Counts` (compiler.zig:23-35) gains `exceptions: u32 = 0`.
+Exception candidates go through the existing `addCandidate` path into a third
+`Entries` and emit as a sorted, deduplicated `.allow` body. The shared SHA-256
+covers the bodies in order list, wild, allow — because SHA-256 of
+`list ++ wild ++ ""` equals the current SHA-256 of `list ++ wild`, every
+already-published checksum stays valid, and `Manager.loadSource`
+(`src/filter/manager.zig:543-598`) treats a missing `<id>.allow` file as an
+empty body. No refetch is forced by upgrading. `bodyChecksum`
+(manager.zig:1564) follows the same order; `source_file_suffixes`
+(manager.zig:1581) gains `.allow.tmp` and `.allow` with longest-suffix-first
+order preserved; the on-disk header (manager.zig:222-242) gains
+`# exceptions {d}` after the `# wildcards` line and the pinning test at
+manager.zig:1872-1900 is extended, not weakened.
+
+### 4. Exception counts persist and surface
+
+Migration step 3 (`ddl_v3`, appended at `src/storage/migrations.zig:23-26`):
+`ALTER TABLE blocklist_sources ADD COLUMN exception_count INTEGER NOT NULL
+DEFAULT 0;`. `sources_repo.SourceRow` and `updateSourceStats`
+(`src/storage/repositories/sources_repo.zig:91-166`) carry it;
+`SourceStatus` rehydration (`manager.zig:1457-1494`) restores it alongside the
+existing three counts; `StatusView` (`src/web/handlers/blocklists.zig:52-78`)
+gains `exceptions: u32`; the blocklists UI shows it where `skipped_regex`
+already shows (`web/src/features/blocklists/SourceStatusSection.tsx`,
+`web/src/lib/types.ts:163,192`).
+
+### 5. The regex engine is a Pike VM, linear-time by construction, `std` only
+
+New file `src/filter/regex.zig`. Syntax: literal bytes, `.`, character
+classes `[...]` with ranges and leading-`^` negation, escapes
+`\. \\ \- \d \w`, repetition `* + ? {n} {n,m}`, alternation `|`,
+non-capturing grouping `(...)`, anchors `^` and `$`. No backreferences, no
+lookaround, no captures. Matching is unanchored unless anchors are written
+(POSIX-grep convention, matching Pi-hole user expectations). Input is the
+normalized lowercase name, ≤ `types.max_name_len` bytes. Hard limits, each a
+distinct error: pattern ≤ 256 bytes (`PatternTooLong`), compiled program
+≤ 1024 instructions (`PatternTooComplex`). Public API:
+
+```zig
+pub const Error = error{ OutOfMemory, BadPattern, PatternTooLong, PatternTooComplex };
+pub const Program = struct { ... , pub fn deinit(self: *Program, gpa: Allocator) void };
+pub fn compile(gpa: Allocator, pattern: []const u8) Error!Program;
+pub fn matches(prog: *const Program, input: []const u8) bool;
+```
+
+`matches` is a Pike VM: two thread lists, each program counter admitted at
+most once per input position, worst case O(program × input) with zero
+allocation at match time (thread lists sized from the program at compile
+time). The engine is a fuzz-module root like parsers.zig and imports only
+`std`.
+
+### 6. `regex` is a third rule kind, validated at the edge, memoized by the cache
+
+Migration step 4 (`ddl_v4`): the 12-step rebuild of `rules` with
+`CHECK(kind IN ('exact','wildcard','regex'))` — the frozen v1 DDL
+(`src/storage/config_schema.zig:65-72`) cannot be edited. `model.RuleKind`
+(`src/config/model.zig:253-269`) gains `.regex`; the exhaustive switches in
+`config/validate.zig:1067-1098` (compile the pattern, report
+`"... is not a valid regex pattern"` through the existing error path at
+validate.zig:862-869) and `src/filter/rules.zig:62-68` extend. `RuleSet`
+(`rules.zig:28-36`) grows `regex_allow` and `regex_block` slices holding
+compiled `Program`s plus their pattern texts (for `Decision.matched`);
+`bucketOf` (rules.zig:133-143) becomes a six-bucket layout;
+`max_regex_per_group: usize = 256` with `TooManyRegexRules` mirroring
+`max_wildcards_per_group` (rules.zig:26). A pattern that fails to compile is
+`error.BadPattern` at snapshot build, never skipped (rules.zig:41-49 doc
+holds). Reason tags `rule_allow_regex` and `rule_block_regex` join
+`matcher.Reason` (matcher.zig:24-32); `/api/lookup` and the query log pick
+them up automatically via `@tagName` (`src/web/handlers/lookup.zig:89`;
+`max_reason_len = 32` in `src/storage/logger.zig` fits both at 16 chars).
+Regex evaluation runs only after every hash and wildcard level missed, and
+answers are memoized by the existing DNS cache like every other decision, so
+the per-query cost lands on cache misses only.
+
+### 7. The web contract names the third kind everywhere it names the first two
+
+`src/web/handlers/rules.zig`: `toInput` accepts `"regex"`; the 400 string at
+rules.zig:42 becomes `"kind must be 'exact', 'wildcard' or 'regex'"`.
+`src/web/openapi.yaml:1875-1917`: all three `enum: [exact, wildcard]` become
+`[exact, wildcard, regex]`. `web/src/lib/types.ts:195`:
+`RuleKind = "exact" | "wildcard" | "regex"`; the rules page kind selector
+gains the option. Contract samples regenerated. `nxdns export` / `import`
+round-trip the new kind with no extra work once `RuleKind.toDb/fromDb` extend
+— the existing round-trip test at model.zig:722-723 is extended to prove it.
+
+### 8. PLAN amendments land with the code, in S3
+
+PLAN.md:36 (§2.2) is rewritten: operator regex rules are in scope, backed by
+the linear-time engine of ruling 5; regex lines in downloaded lists stay
+counted and skipped; `$` modifiers (except the `$important` suffix of ruling
+1), partial-segment wildcards, and browser-syntax honoring stay permanently
+out. PLAN.md:26 (§2.1 filtering sentence), PLAN.md:106 (§3.9), PLAN.md:108-117
+(§3.10 precedence) and PLAN.md:700 (decision B) are updated to match rulings
+2 and 6. In-code echoes of the old §2.2 move with it:
+`src/filter/wildcard.zig:6-8,22-24`, `src/filter/parsers.zig:25`,
+`src/filter/parser_abp.zig:5-6`, `src/filter/compiler.zig:129-131`.
+
+### 9. Fuzz invariants move, never lapse
+
+`tests/fuzz/blocklist_fuzz.zig` header invariant "covers_apex only on
+`.wildcard`" (its stated form at :4-28) becomes "only on `.wildcard` or
+`.exception`". `tests/fuzz/compiler_fuzz.zig:43` reads `Format` from
+`compile`'s parameter list by index — the new `allow_w` parameter appends
+after `wild_w`, leaving index 2 valid; the session touching `compile` runs the
+fuzz suite and fixes that line if the assumption fails. A new
+`tests/fuzz/regex_fuzz.zig` target asserts: `compile` on arbitrary bytes
+never crashes and either errors or produces a program within the ruling-5
+limits; `matches` terminates and its VM step count never exceeds
+program length × (input length + 1); compile-then-match is deterministic.
+
+## Sessions
+
+Three sessions. S1 and S2 run in parallel — they share no files. S3 starts
+after both land.
+
+### Session S1: list exceptions end to end (tier 1)
+
+Owns: `src/filter/parsers.zig`, `src/filter/parser_abp.zig`,
+`src/filter/compiler.zig`, `src/filter/manager.zig`, `src/filter/matcher.zig`,
+`src/filter/domain_set.zig` (only if a helper is needed; expected untouched),
+`src/filter/filter_integration_test.zig`, `src/storage/migrations.zig`
+(step 3 only), `src/storage/repositories/sources_repo.zig`,
+`src/web/handlers/blocklists.zig`, `src/web/handlers/lookup.zig` (doc
+sentence only), `src/web/openapi.yaml` (StatusView shape only),
+`web/src/features/blocklists/*`, `web/src/lib/types.ts` (source-stat fields
+only), `web/src/lib/contractSamples.gen.ts`,
+`tests/fuzz/blocklist_fuzz.zig`, `tests/fuzz/compiler_fuzz.zig`.
+
+- S1.1 `Kind.exception` in parsers.zig; parser_abp emits it per ruling 1;
+  parser_hosts and parser_domains never emit it (no change beyond the enum).
+- S1.2 compiler third body per ruling 3; `Counts.exceptions`.
+- S1.3 manager: suffixes, header line, `bodyChecksum`, `loadSource`
+  missing-file-is-empty, `Snapshot.Compiled.allow_body`,
+  `prepareRefresh`/`publishRefresh`/`applyLoadOutcomes` carry the count.
+  `rejectedWithoutEntries` (manager.zig:1559-1562) treats a compile with only
+  exceptions as loadable, not rejected.
+- S1.4 matcher: `SourceSets.exceptions`, `Reason.blocklist_exception`,
+  the new evaluate level per ruling 2, `memoryBytes` includes the new sets.
+- S1.5 storage + API + UI per ruling 4.
+- S1.6 tests: parser cases (`@@||x^`, `@@||x`, `@@||x^$important`,
+  `@@||x^$third-party` → unsupported, `@@x` → unsupported); compiler
+  three-body + checksum-compat cases (empty allow body reproduces the old
+  digest byte for byte); manager header pin extended; matcher precedence
+  cases: operator block beats list exception, list exception beats list
+  domain and list wildcard, exception parent walk covers apex and
+  subdomains; an integration case through
+  `filter_integration_test.zig` with a real ABP fixture carrying `@@` lines.
+
+Acceptance (S1):
+- [ ] `zig build test` passes; fuzz targets build and run.
+- [ ] A fixture list with `||ads.example^` and `@@||good.ads.example^`
+      compiled and loaded blocks `ads.example` and `x.ads.example`, does not
+      block `good.ads.example` or `y.good.ads.example`, and
+      `/api/lookup` reports `blocklist_exception` with the source id for the
+      latter two.
+- [ ] A pre-milestone data directory (no `.allow` files, old checksums)
+      loads with zero checksum mismatches.
+- [ ] `POST /api/blocklists/update` response rows carry `exceptions`.
+
+### Session S2: the regex engine (tier 2, engine only)
+
+Owns: `src/filter/regex.zig` (new), `tests/fuzz/regex_fuzz.zig` (new),
+`src/tests.zig` (one added line), `build.zig` (fuzz-suite wiring for the new
+target only).
+
+- S2.1 the engine per ruling 5: parser → AST → NFA program → Pike VM.
+- S2.2 unit tests in-file: every syntax form; anchored and unanchored
+  matching; negated classes; `{n,m}` bounds; each error case; the
+  pathological backtracker-killers (`(a+)+b` against `aaaaaaaaaaaaaaaaaaaaX`,
+  nested alternation) complete within the step bound.
+- S2.3 the fuzz target per ruling 9.
+
+Acceptance (S2):
+- [ ] `zig build test` passes with the new file in `src/tests.zig`.
+- [ ] The step-bound property holds under the fuzz corpus.
+- [ ] `regex.zig` imports nothing but `std`.
+
+### Session S3: the regex rule kind, wired through (needs S1 + S2)
+
+Owns: `src/storage/migrations.zig` (step 4), `src/storage/config_schema.zig`
+(comment only if needed), `src/config/model.zig`, `src/config/validate.zig`,
+`src/filter/rules.zig`, `src/filter/matcher.zig`,
+`src/storage/repositories/rules_repo.zig`, `src/web/handlers/rules.zig`,
+`src/web/handlers/mutations.zig` (only if `checkRule` needs the kind),
+`src/web/openapi.yaml`, `web/src/features/rules/*`, `web/src/lib/types.ts`,
+`web/src/lib/contractSamples.gen.ts`, `PLAN.md`, `src/filter/wildcard.zig`
+(comments), `src/filter/parsers.zig` (comment), `src/filter/parser_abp.zig`
+(comment), `src/filter/compiler.zig` (comment), `tools/bench.zig`.
+
+- S3.1 migration step 4 per ruling 6; repo and model layers.
+- S3.2 validate at both edges (config import, API) per rulings 6 and 7.
+- S3.3 `RuleSet` six buckets; matcher levels per ruling 2; reasons.
+- S3.4 web + UI + openapi + samples per ruling 7.
+- S3.5 PLAN and comment amendments per ruling 8.
+- S3.6 bench: the filter suite in `tools/bench.zig` gains a variant with 32
+  regex rules loaded; the existing p95 < 1 ms assertion covers it.
+- S3.7 tests: rule CRUD with kind `regex` through the API including the 400
+  for a bad pattern at insert time; precedence cases regex-allow over
+  regex-block, wildcard over regex, regex over list entries; export/import
+  round trip; a migration test upgrading a v3 database.
+
+Acceptance (S3):
+- [ ] `zig build test` and `cd web && npm test` pass.
+- [ ] `POST /api/rules` with `{"kind":"regex","pattern":"^ad[0-9]+-"}`
+      returns 201; with `"pattern":"("` returns 400 naming the pattern.
+- [ ] A regex block rule blocks a matching name; `/api/lookup` reports
+      `rule_block_regex` and `matched` carries the pattern text.
+- [ ] `zig build bench -Doptimize=ReleaseFast -- filter` passes its targets
+      with the regex variant present.
+- [ ] PLAN §2.2 no longer forbids operator regex; all listed echoes updated.
+
+### Orchestrator
+
+Verify S1 and S2 acceptance before starting S3. After S3: run the full gate
+set (`zig build test`, `test-aarch64` if qemu present, `npm test`,
+`npm run assert-bundled`), then a live smoke against a scratch server: load
+one real ABP list with `@@` lines, add one regex rule, verify both over dig
+and `/api/lookup`. Record deviations in `## Recorded (implementation)`.
+
+## Module layout
+
+New files:
+- `src/filter/regex.zig` — the linear-time engine (ruling 5).
+- `tests/fuzz/regex_fuzz.zig` — its fuzz target (ruling 9).
+
+Deleted surface: none.
+
+## Acceptance (milestone complete)
+
+- [ ] All session acceptance boxes above.
+- [ ] Schema at version 4; a v2 database migrates cleanly with data intact.
+- [ ] A pre-milestone blocklist data directory loads without refetch.
+- [ ] The six-level operator precedence plus three list levels behave per
+      ruling 2, proven by matcher tests that enumerate adjacent-level pairs.
+- [ ] No `src/filter/` fuzz-root file imports anything but `std`.
+- [ ] Contract samples, openapi.yaml and `web/src/lib/types.ts` agree with
+      the server (the drift guards pass).
+
+## Anti-requirements
+
+- No `$` modifier support beyond tolerating `$important` on exception lines.
+  `$dnstype`, `$dnsrewrite`, `$client`, `$denyallow` and every browser
+  modifier stay unsupported and counted.
+- No regex from downloaded lists. `.regex` lines stay counted and skipped;
+  `skipped_regex` keeps its meaning. The engine exists for operator rules
+  only.
+- No partial-segment wildcards (`ads*.example.com`) — writing one as a rule
+  stays rejected; the regex kind covers the need.
+- No backreferences, lookaround, captures, named groups or Unicode classes in
+  the engine, ever. A pattern needing them is rejected, not approximated.
+- No PCRE2, RE2 or any external regex dependency.
+- No exception-rule UI editor: exceptions come from lists; operators write
+  allow rules.
+- No re-download forced by the upgrade; checksum compatibility (ruling 3) is
+  a requirement, not an optimization.