The mesh runs its own registry, certifies its own names, and computes its own filtering

Issue 003 is answered in both halves: manifests are parsed strictly, and a
module says what it listens on and from where rather than carrying a key
nothing reads. The design records what was built and how each part is checked.

Issue 013 is new, found by reading while writing the first module that has
both a computed file and a service that needs it. The file arrived second.
It failed, then the next reconcile fixed it, which is why nothing caught it.

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

@@ -1,8 +1,10 @@
 ---
 layer: to-be
 status: designed
-code: []
-updated: 2026-08-29
+code:
+  - mesh-control internal/catalogue/filtering.go
+  - mesh-host internal/apply (the service that reflects it)
+updated: 2026-08-31
 decisions:
   - 02-DECISIONS/0005-the-node-host.md
   - 02-DECISIONS/0004-a-node-and-how-it-joins.md
@@ -275,6 +277,50 @@ from a wrong one, and costs more, because people believe it.*
 ([ADR 0005](../../02-DECISIONS/0005-the-node-host.md)), and
 the one manifests lack. `scope:` survived because nothing rejected it.
 
+### What was built
+
+*2026-08-31. Everything above was the intention; this is what exists, and how each part is
+checked. [04-ISSUES/003](../../04-ISSUES/003-firewall-scope-is-read-by-no-code/00-report.md) is
+resolved by it.*
+
+**A module says what it listens on**, as a port, a protocol and a source — `mesh`, `anywhere`, or
+`machine`. The source is required and there is no default, which is the whole of *a rule names its
+source*: a manifest that omitted it would read as a restriction and be none. *Checked by a manifest
+with a port and no source being refused, and by one naming a source the mesh cannot render being
+refused as well — the second is what stops a source becoming a comment.*
+
+**The set is derived per node**, from every module assigned to it, not from the module asking for
+it. Where two modules want the same port, the wider source wins and both are still named, because
+removing one of them must not read as a reason to close a port the other needs. *Checked by
+rendering a node whose firewall module has no ports of its own and asserting another module's port
+is in the result; and by giving one port two modules and one source each, and asserting the
+narrower rule disappears while both names survive.*
+
+**What is not declared is closed.** The rule set drops by default. *Checked by naming the input
+chain in the assertion rather than the policy alone — the first version of that test passed while
+input accepted everything, because another chain in the same file also said `policy drop`.*
+
+**From the mesh means the machines the mesh has**, as their addresses on the private network, not
+as a subnet. A subnet is a guess that stays wrong quietly; the address set shrinks when a node
+leaves and nobody edits anything. A machine that asks for `mesh` where the mesh knows no addresses
+is **closed and told so in the file** — widening it would open a port nobody asked to open, and
+dropping it silently would close one somebody did.
+
+**Three things it deliberately does not do**, each of which looked right and would have broken
+something:
+
+| | why not |
+|---|---|
+| decide what the machine **forwards** | the container runtime writes its own forwarding rules and a second policy is consulted alongside them, so a drop here stops every container on the node — the control plane included. Nothing in a manifest says what a machine routes, so there is nothing to derive it from either |
+| **flush the ruleset** when loading | that empties every table on the machine, the runtime's among them. Only the mesh's own table is replaced, and it is declared empty first so the replacement works on a machine loading one for the first time |
+| carry a **command to load itself** | the link may not carry an action ([ADR 0005](../../02-DECISIONS/0005-the-node-host.md)). A service is declared to reflect the file instead, so replacing it restarts what loads it — the shape that rule leaves, used here for the first time for its real purpose |
+
+**And it is enforced, which is what separates this from `scope:`.** Proven on two real machines:
+two ports opened, one declared, and from the other machine the declared one answers and the
+undeclared one does not — then the module is removed and the port closes with nobody editing a
+rule. *A rule set that is written but never loaded passes every check that reads the file, which
+is why the check reads packets.*
+
 ## 5 — Certificates
 
 **Two authorities, kept separate on purpose.**