ADR 0175: the found front end is uninstalled once a machine is converged; design 08 note

02-DECISIONS/0168-a-converged-machine-is-filtered-by-the-mesh-alone.md

@@ -113,6 +113,22 @@ That is a difference a take shows, not a fault, and is decided when it bites.
 | `node show` lists filters with owners; `status` names a converged machine something else filters and is not well; the preview lists filters and fates | controller tests over a fixture report |
 | Live | the home server's record names the predecessor's chain in the runtime's user chain as *other*; `status` names the machine; after the operator removes the chain, the next report drops it and `status` is well |
 
+## Built and proven live, 2026-10-02
+
+> **Progressive insight — 2026-10-02.** The decision stands; these are the facts of its building.
+
+Built in mesh-host 67 (every refusing table and legacy chain classified with an owner, reported with
+every apply; the found firewall retired on every converged apply, *found inactive* kept apart from
+*disabled by the mesh*, a skipped step said) and mesh-controller 211 (kept per node, shown on `node
+show`, named by `status` and not well, previewed with fates). The live row was read at 10:10Z: the home
+server's record named the predecessor's chain in the legacy filter's user chain as *other*, beside two
+chains a retired front end left in the IPv6 legacy filter; the control node's record named the same two
+leftovers; the laptop and the workstation read *the mesh alone*; `status` named both machines. The five
+rule sets were removed at 12:46Z through the packet filter seat's `remove` verb
+([ADR 0170](0170-the-firewall-seat-serves-its-verbs.md)), and the next report read *the mesh alone* on
+all four machines. The control node's record still says the mesh retired its front end, which issue 143
+records as a hand's work: the host trusts its record, and from this build on the distinction is kept.
+
 ## References
 
 - [ADR 0100](0100-a-node-in-use-is-adopted-before-it-is-converged.md), [ADR 0103](0103-what-an-adopted-node-holds-and-what-its-guard-refuses.md), [ADR 0140](0140-the-filter-constrains-what-arrives-from-outside.md), [ADR 0102](0102-the-mesh-writes-into-a-shared-file-never-over-it.md), [ADR 0163](0163-taking-a-module-over-is-a-comparison.md)

02-DECISIONS/0175-the-found-front-end-is-uninstalled-once-a-machine-is-converged.md

@@ -0,0 +1,66 @@
+---
+topic: the mesh
+status: accepted
+date: 2026-10-02
+deciders: jochen
+reconstructed: false
+extends: 02-DECISIONS/0168-a-converged-machine-is-filtered-by-the-mesh-alone.md
+---
+
+# 175. The found front end is uninstalled once a machine is converged
+
+## Context
+
+[ADR 0100](0100-a-node-in-use-is-adopted-before-it-is-converged.md) retires the firewall a machine
+was found with by disabling it, never flushing it, and keeps its configuration on disk so that
+returning the node to adopted can enable it again. [ADR 0168](0168-a-converged-machine-is-filtered-by-the-mesh-alone.md)
+made the host keep it retired and say so. Both machines of this mesh that had a front end have been
+converged for days; neither is going back. What remained of the front end on each — its package,
+its unit enabled for boot on one, its empty chains still wired into the kernel's hooks, a chain of
+its container integration still dropping traffic on the IPv6 path until the day before this record
+— was not a rollback path. It was software nobody runs, left where a reader finds it and asks
+whether the machine has two firewalls.
+
+The operator asked on 2026-10-02 that it be disabled and uninstalled. Disabled it already was. For
+uninstalled, the host had no word: a package could be declared present and not absent.
+
+## Decision
+
+**1. A package may be declared absent.** `absent: true` on a package resource has the host remove
+the package when it is installed and leave alone a machine that never had it, through the machine's
+own package manager, dependencies untouched. A declaration that stops saying a package is absent
+installs nothing: there is nothing to undo.
+
+**2. The module that holds the packet filter seat declares the front end it replaced absent**, after
+its own filter is loaded, so the mesh's table is in force before the front end's package goes. On a
+converged machine the front end is therefore gone, not merely off; on an adopted machine nothing of
+this runs, because the filter module is assigned by the flip and not before.
+
+**3. Returning such a machine to adopted enables nothing.** A machine with no firewall needs no
+openings ([ADR 0100](0100-a-node-in-use-is-adopted-before-it-is-converged.md)); the host records the
+front end as *removed*, says so once, and asks nothing of a command that is not there. What
+ADR 0100 kept on disk for a return is kept only as far as the package manager keeps a changed
+configuration file; the rollback path it described is given up on purpose.
+
+## Consequences
+
+- The host's vocabulary grows by `absent` on a package; an older host refuses a declaration
+  carrying it, so the host rolls before the module.
+- The nftables module's declaration gains one resource; on the two machines of this mesh that were
+  found with ufw, the next push removes it.
+- `node show` reads *found firewall: ufw, removed* on those machines from then on.
+- ADR 0100's sentence about a return to adopted restoring the found firewall holds only while the
+  front end is installed, which after this record it is not on a converged machine.
+
+## How this is checked
+
+| Rule | Checked by |
+|---|---|
+| An absent package is removed when present, left when not, and read back | host tests over a fake package manager |
+| An uninstalled front end is recorded as removed and nothing is asked of it | a host test with ufw missing on a converged apply |
+| Live | the two machines report ufw gone: `pacman -Q ufw` has no answer, `node show` says removed, `status` is well |
+
+## References
+
+- [ADR 0100](0100-a-node-in-use-is-adopted-before-it-is-converged.md), [ADR 0168](0168-a-converged-machine-is-filtered-by-the-mesh-alone.md), [ADR 0170](0170-the-firewall-seat-serves-its-verbs.md)
+- [Design 08 — Connectivity](../03-DESIGN/01-to-be/08-connectivity.md)

02-DECISIONS/README.md

@@ -182,6 +182,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0169** — [A machine joins through the tunnel, and the bus is never public](0169-a-machine-joins-through-the-tunnel-and-the-bus-is-never-public.md)
 - **0170** — [The firewall seat serves its verbs, and a foreign rule set is removed through one of them](0170-the-firewall-seat-serves-its-verbs.md)
 - **0172** — [The lab is a module, and runs a bed when the mesh asks](0172-the-lab-is-a-module-and-runs-a-bed-when-the-mesh-asks.md)
+- **0175** — [The found front end is uninstalled once a machine is converged](0175-the-found-front-end-is-uninstalled-once-a-machine-is-converged.md)
 
 ### Its tiers, from the bottom up
 

03-DESIGN/01-to-be/08-connectivity.md

@@ -9,6 +9,7 @@ code:
   - mesh-host internal/apply (the service that reflects a rule set)
 updated: 2026-10-02
 decisions:
+  - 02-DECISIONS/0175-the-found-front-end-is-uninstalled-once-a-machine-is-converged.md
   - 02-DECISIONS/0170-the-firewall-seat-serves-its-verbs.md
   - 02-DECISIONS/0169-a-machine-joins-through-the-tunnel-and-the-bus-is-never-public.md
   - 02-DECISIONS/0168-a-converged-machine-is-filtered-by-the-mesh-alone.md
@@ -772,6 +773,11 @@ the host reports as *other* is reached through the packet filter seat's `remove`
 by name on the bus; the seat also serves `rules` and `reload`, and its holder's runtime declares the
 `NET_ADMIN` capability on the machine's network. See design 33.
 
+*2026-10-02, [ADR 0175](../../02-DECISIONS/0175-the-found-front-end-is-uninstalled-once-a-machine-is-converged.md):*
+once a machine is converged, the front end it was found with is uninstalled, not merely disabled — the
+packet filter's holder declares its package absent after the mesh's filter is loaded, and a return to
+adopted then enables nothing. The rollback path ADR 0100 kept on disk is given up on purpose.
+
 ## 5 — Certificates
 
 **Two authorities, kept separate on purpose.**