Seats are a closed set, a seat's holder answers for what it delivers, and a build source may live on the git seat

Implements novox/hq ADR 0110 and 0111.

The seat set lives in internal/catalogue/seats.go: fourteen seats, each with a scope, what occupying
it delivers, and the record that made it one. A test asserts the count and a decision per entry, so
changing the set means finding the argument, as the host's vocabulary test does. The first set is
every seat already claimed — including the-private-network, which the network module claims from a
manifest composed in this repository's code, not from any module.json — plus npm-package-registry
(ADR 0109) and git (ADR 0111). A test parses every catalogue manifest and this repository's own and
fails on any refused claim, so closing the set refuses nothing in use.

ParseManifest now refuses a claim on a seat the mesh does not define, a seat claimed at another
scope, and a delivering seat claimed by a module that does not provide what it delivers. A
malformed claim is refused once, for being malformed.

Resolution: among several providers of a mesh provision, a pin still wins; then the holder of the
seat that delivers it; then the only provider; otherwise refused as before. ADR 0009's "never
guessed" holds — the seat is the choice made once, mesh-wide, rather than a pin per consumer node.
A provider now carries the module it came from, because a provider is a (node, module) pair and the
pair is what tells a holder from a neighbour on the same machine.

The planner's second pass is now given the first pass's holdings. Without them, a node consuming a
seat-delivered provision was refused there, and a refused node's own claims dropped out of what the
mesh holds — letting a second holder of one of its seats pass unrefused.

`seats [--json]` lists every seat, what it delivers, and each holder, derived from assignments
every time and never stored. Unheld seats are listed. A stored claim outside the set — possible
for a manifest registered before the set closed, since stored manifests are not re-validated — is
shown rather than hidden.

`build --self <owner>/<repo>` builds from a repository on the git seat's holder. The clone URL is
composed at build time from the holder's node and what it serves for git; the recorded source is the
path and the seat (migration 0032), never an address, so a moved forge changes nothing recorded.
Nobody holding the seat refuses self-hosted builds and says so; external URLs are unchanged. An
address passed with --self is refused rather than recorded as a path.

Replaces three foundation tests that defended the builder's carried package binding. The catalogue
removed that binding when the builder began requiring the registry through a real grant, so the
tests were already failing on main; they now assert the builder requires what the npm seat delivers
and carries no copy of its own, and that the forge holds the npm and git seats.

Verified: go vet clean; the whole suite passes against a throwaway Postgres (make postgres), the new
inventory tests included; gofmt clean apart from cmd/mesh-builder/stdout_test.go, which fails on
main too.

cmd/mesh-controller/build.go

@@ -46,25 +46,35 @@ func buildCommand(ctx context.Context, args []string) error {
 	// retype each repository is asking them to be the loop. Naming a repository and asking which
 	// ones need building are different requests, so they are not combined.
 	behind := set.Bool("behind", false, "every module the mesh holds older than its source has")
+	// A repository on the mesh's own forge, named by its path there (novox/hq ADR 0111). Without it
+	// the repository is external, cloned exactly as given — see source.go.
+	self := set.Bool("self", false, "the repository is a path on the forge holding the git seat")
 	positionals, err := parseAround(set, args)
 	if err != nil {
 		return err
 	}
 	if *behind {
-		if len(positionals) != 0 {
+		if len(positionals) != 0 || *self {
 			return errors.New("build <repository> or build --behind, not both: one names a " +
 				"repository and the other asks which need building")
 		}
 		return buildBehind(ctx, *wait)
 	}
 	if len(positionals) != 1 {
-		return errors.New("build <repository> [--ref R] [--wait D] [--dry-run]")
+		return errors.New("build <repository> [--self] [--path P] [--ref R] [--wait D] [--dry-run]")
+	}
+	source := buildSource{Repository: positionals[0]}
+	if *self {
+		if err := onASeat(source.Repository); err != nil {
+			return err
+		}
+		source.Seat = gitSeat
 	}
 
 	if *dryRun {
-		return buildAndShow(ctx, positionals[0], *path, *ref, *wait)
+		return buildAndShow(ctx, source, *path, *ref, *wait)
 	}
-	return buildOne(ctx, positionals[0], *path, *ref, *wait)
+	return buildOne(ctx, source, *path, *ref, *wait)
 }
 
 // buildFrom turns what a builder said into what the mesh keeps.
@@ -325,7 +335,8 @@ func buildBehind(ctx context.Context, wait time.Duration) error {
 		// Its own recorded ref, not its head commit: a module tracking a branch should be built
 		// from that branch, and pinning to the commit the mesh happened to notice would quietly
 		// turn a tracked branch into a pin.
-		if err := buildOne(ctx, e.Source.Repository, e.Source.Path, e.Source.Ref, wait); err != nil {
+		source := buildSource{Repository: e.Source.Repository, Seat: e.Source.Seat}
+		if err := buildOne(ctx, source, e.Source.Path, e.Source.Ref, wait); err != nil {
 			fmt.Printf("  %v\n", err)
 			failed = append(failed, e.Manifest.Module)
 		}
@@ -343,7 +354,14 @@ func buildBehind(ctx context.Context, wait time.Duration) error {
 // buildOne asks a build machine for one repository and records everything that came back.
 //
 // Separated from the command so `--behind` can walk a list without a second path to the same act.
-func buildOne(ctx context.Context, repository, path, ref string, wait time.Duration) error {
+func buildOne(ctx context.Context, source buildSource, path, ref string, wait time.Duration) error {
+	// Before anything is asked of a builder: a source on a seat nobody holds is refused here, with
+	// the reason, rather than sent to a machine to fail at `git clone`.
+	repository, err := cloneFrom(ctx, source)
+	if err != nil {
+		return err
+	}
+
 	ident, err := openIdentity(ctx)
 	if err != nil {
 		return err
@@ -365,7 +383,10 @@ func buildOne(ctx context.Context, repository, path, ref string, wait time.Durat
 		Ref:        ref,
 		Held:       heldBy(ctx),
 	}
-	fmt.Printf("asked for %s", request.Repository)
+	fmt.Printf("asked for %s", source)
+	if source.Seat != "" {
+		fmt.Printf(" (%s)", repository)
+	}
 	if path != "" {
 		fmt.Printf(" at %s", path)
 	}
@@ -414,11 +435,18 @@ func buildOne(ctx context.Context, repository, path, ref string, wait time.Durat
 	}
 
 	// Recorded with where it came from, so "is this current?" is answerable without building it
-	// again (novox/hq ADR 0009).
-	if err := inv.RegisterModule(ctx, manifest, inventory.Source{
+	// again (novox/hq ADR 0009). **For a source on a seat, as the path and the seat, never the URL
+	// just cloned** (ADR 0111): the URL is where the forge runs today, and recording it would put
+	// the forge's address back into every module built from it. The build log above keeps the URL,
+	// because that is what was cloned.
+	recorded := inventory.Source{
 		Repository: result.Repository, Path: result.Path, Ref: result.Ref,
 		BuiltFrom: result.Commit, Head: result.Commit,
-	}); err != nil {
+	}
+	if source.Seat != "" {
+		recorded.Repository, recorded.Seat = source.Repository, source.Seat
+	}
+	if err := inv.RegisterModule(ctx, manifest, recorded); err != nil {
 		return err
 	}
 	fmt.Printf("\n%s %s, built on %s from %s\n",
@@ -428,7 +456,11 @@ func buildOne(ctx context.Context, repository, path, ref string, wait time.Durat
 }
 
 // buildAndShow builds and prints the manifest without recording anything.
-func buildAndShow(ctx context.Context, repository, path, ref string, wait time.Duration) error {
+func buildAndShow(ctx context.Context, source buildSource, path, ref string, wait time.Duration) error {
+	repository, err := cloneFrom(ctx, source)
+	if err != nil {
+		return err
+	}
 	ident, err := openIdentity(ctx)
 	if err != nil {
 		return err

cmd/mesh-controller/main.go

@@ -114,6 +114,8 @@ func run() error {
 		return planCommand(ctx, args[1:])
 	case "push":
 		return pushCommand(ctx, args[1:])
+	case "seats":
+		return seatsCommand(ctx, args[1:])
 	case "status":
 		return statusCommand(ctx, args[1:])
 	case "version":
@@ -157,6 +159,7 @@ func usage() {
   upgrade <name> roll-out [--together]   ...send it to the machines running it
   upgrade <name> record          ...record that they are behind, and send nothing
   status [--json]                what is wrong, what is quiet, and what is out of date
+  seats [--json]                 every seat this mesh defines, what it delivers, and who holds it
   board [--listen ADDR]          the same three questions, as a page that holds nothing
   api --issuer URL [--listen A]  assign and unassign over http, for a surface that is not here
   assign <node> <module>         put a module on a node

cmd/mesh-controller/plan.go

@@ -217,6 +217,7 @@ func theRestOfTheMesh(ctx context.Context, inv *inventory.Inventory,
 	}
 
 	offered := map[string][]catalogue.Provider{}
+	var firstHeld []catalogue.Held
 	for _, o := range others {
 		got, err := catalogue.Resolve(shelf, o.assigned, o.node, catalogue.World{Unchecked: true})
 		if err != nil {
@@ -224,6 +225,7 @@ func theRestOfTheMesh(ctx context.Context, inv *inventory.Inventory,
 			// report, and nothing of theirs is running, so it offers nothing.
 			continue
 		}
+		firstHeld = append(firstHeld, got.Claims...)
 		for _, m := range got.Modules {
 			for _, name := range m.OffersAt(catalogue.ScopeMesh) {
 				// What that module says a consumer needs to know, with that node's settings on
@@ -234,7 +236,7 @@ func theRestOfTheMesh(ctx context.Context, inv *inventory.Inventory,
 					return catalogue.World{}, err
 				}
 				offered[name] = append(offered[name], catalogue.Provider{
-					Node: o.node.Name, At: o.node.At, Serves: serves})
+					Node: o.node.Name, At: o.node.At, Serves: serves, Module: m.Module})
 			}
 		}
 	}
@@ -244,14 +246,20 @@ func theRestOfTheMesh(ctx context.Context, inv *inventory.Inventory,
 		})
 	}
 
-	world := catalogue.World{Offered: offered}
+	// **The second pass is given the first pass's holdings.** A seat's holder answers a requirement
+	// with several providers (novox/hq ADR 0110), so a node consuming one resolves only once the
+	// holder is known. Without them its set is refused here, and a refused node's own claims drop
+	// out of what the mesh holds — so a second holder of one of its seats would pass unrefused.
+	world := catalogue.World{Offered: offered, Held: firstHeld}
+	var held []catalogue.Held
 	for _, o := range others {
 		got, err := catalogue.Resolve(shelf, o.assigned, o.node, world)
 		if err != nil {
 			continue
 		}
-		world.Held = append(world.Held, got.Claims...)
+		held = append(held, got.Claims...)
 	}
+	world.Held = held
 	return world, nil
 }
 

cmd/mesh-controller/seats.go

@@ -0,0 +1,150 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+	"text/tabwriter"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+)
+
+// What this mesh can have one of, and who fills each (novox/hq ADR 0110).
+//
+// **Derived every time, never stored.** A seat is held by a module assignment, so the answer is
+// computed from assignments by the same resolution that decides what every machine runs. A table
+// of holders kept beside the assignments would be a second copy of one fact, and the first thing
+// to be wrong about it.
+
+// seatHolder is one assignment holding a seat.
+type seatHolder struct {
+	Node   string `json:"node"`
+	Module string `json:"module"`
+}
+
+// seatRow is one seat and who holds it. Unheld is an answer — "this mesh has no X" — not a fault.
+type seatRow struct {
+	Seat     string       `json:"seat"`
+	Scope    string       `json:"scope"`
+	Delivers string       `json:"delivers,omitempty"`
+	Decision string       `json:"decision"`
+	Holders  []seatHolder `json:"holders"`
+}
+
+// seatsHeld is every seat the mesh defines with its holders, and every claim held that names no
+// seat in the set.
+//
+// **The second list is not empty by construction.** Manifests are held to the set when they are
+// registered, and a mesh can hold one registered before the set closed. Leaving its claim out of the
+// overview would make the one thing the overview is for — what does this mesh have — quietly
+// incomplete.
+func seatsHeld(seats []catalogue.Seat, held []catalogue.Held) ([]seatRow, []catalogue.Held) {
+	defined := map[string]bool{}
+	rows := make([]seatRow, 0, len(seats))
+	for _, s := range seats {
+		defined[s.Name] = true
+		row := seatRow{Seat: s.Name, Scope: s.Scope, Delivers: s.Delivers, Decision: s.Decision,
+			Holders: []seatHolder{}}
+		seen := map[seatHolder]bool{}
+		for _, h := range held {
+			if h.Claim != s.Name || h.Scope != s.Scope {
+				continue
+			}
+			holder := seatHolder{Node: h.Node, Module: h.Module}
+			if !seen[holder] {
+				seen[holder] = true
+				row.Holders = append(row.Holders, holder)
+			}
+		}
+		sort.Slice(row.Holders, func(i, j int) bool {
+			if row.Holders[i].Node != row.Holders[j].Node {
+				return row.Holders[i].Node < row.Holders[j].Node
+			}
+			return row.Holders[i].Module < row.Holders[j].Module
+		})
+		rows = append(rows, row)
+	}
+	var outside []catalogue.Held
+	for _, h := range held {
+		if !defined[h.Claim] {
+			outside = append(outside, h)
+		}
+	}
+	sort.Slice(outside, func(i, j int) bool {
+		if outside[i].Claim != outside[j].Claim {
+			return outside[i].Claim < outside[j].Claim
+		}
+		return outside[i].Node < outside[j].Node
+	})
+	return rows, outside
+}
+
+func seatsCommand(ctx context.Context, args []string) error {
+	set := flag.NewFlagSet("seats", flag.ContinueOnError)
+	asJSON := set.Bool("json", false, "the same, as JSON")
+	if err := set.Parse(args); err != nil {
+		return err
+	}
+
+	open, err := openStores(ctx)
+	if err != nil {
+		return err
+	}
+	defer open.Close()
+	inv := open.inventory
+	shelf, err := inv.Catalogue(ctx)
+	if err != nil {
+		return err
+	}
+	// Every node, none excluded: the same view of what each machine holds that planning uses.
+	world, err := theRestOfTheMesh(ctx, inv, shelf, "")
+	if err != nil {
+		return err
+	}
+	rows, outside := seatsHeld(catalogue.Seats(), world.Held)
+
+	if *asJSON {
+		out := struct {
+			Seats   []seatRow        `json:"seats"`
+			Outside []catalogue.Held `json:"outside,omitempty"`
+		}{rows, outside}
+		body, err := json.MarshalIndent(out, "", "  ")
+		if err != nil {
+			return err
+		}
+		fmt.Println(string(body))
+		return nil
+	}
+
+	w := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
+	fmt.Fprintln(w, "SEAT\tSCOPE\tDELIVERS\tHELD BY")
+	for _, r := range rows {
+		delivers := r.Delivers
+		if delivers == "" {
+			delivers = "—"
+		}
+		holders := "unheld"
+		if len(r.Holders) > 0 {
+			parts := make([]string, 0, len(r.Holders))
+			for _, h := range r.Holders {
+				parts = append(parts, h.Module+" on "+h.Node)
+			}
+			holders = strings.Join(parts, ", ")
+		}
+		fmt.Fprintf(w, "%s\t%s\t%s\t%s\n", r.Seat, r.Scope, delivers, holders)
+	}
+	if err := w.Flush(); err != nil {
+		return err
+	}
+	if len(outside) > 0 {
+		fmt.Println("\nheld, and not a seat this mesh defines (registered before the set closed — novox/hq ADR 0110):")
+		for _, h := range outside {
+			fmt.Printf("  %s  %s on %s\n", h.Claim, h.Module, h.Node)
+		}
+	}
+	return nil
+}

cmd/mesh-controller/seats_test.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+)
+
+// The overview of what a mesh has (novox/hq ADR 0110).
+
+func TestEverySeatIsListedIncludingTheOnesNobodyHolds(t *testing.T) {
+	// An unheld seat is an answer — "this mesh has no forge" — so it is listed rather than omitted.
+	rows, _ := seatsHeld(catalogue.Seats(), []catalogue.Held{
+		{Claim: "mesh-store", Scope: catalogue.ScopeMesh, Node: "anchor", Module: "postgres"},
+	})
+	if len(rows) != len(catalogue.Seats()) {
+		t.Fatalf("%d seats listed of %d", len(rows), len(catalogue.Seats()))
+	}
+	for _, r := range rows {
+		switch r.Seat {
+		case "mesh-store":
+			if len(r.Holders) != 1 || r.Holders[0].Module != "postgres" || r.Holders[0].Node != "anchor" {
+				t.Errorf("mesh-store is held by %+v", r.Holders)
+			}
+			if r.Delivers != "postgres-database" {
+				t.Errorf("mesh-store does not say what it delivers: %q", r.Delivers)
+			}
+		case "git":
+			if len(r.Holders) != 0 {
+				t.Errorf("git is held by %+v in a mesh with no forge", r.Holders)
+			}
+		}
+	}
+}
+
+func TestANodeSeatListsEveryMachineHoldingIt(t *testing.T) {
+	rows, _ := seatsHeld(catalogue.Seats(), []catalogue.Held{
+		{Claim: "the-packet-filter", Scope: catalogue.ScopeNode, Node: "node2", Module: "nftables"},
+		{Claim: "the-packet-filter", Scope: catalogue.ScopeNode, Node: "anchor", Module: "nftables"},
+		// Resolved twice, reported once: a machine is one holder however many passes saw it.
+		{Claim: "the-packet-filter", Scope: catalogue.ScopeNode, Node: "anchor", Module: "nftables"},
+	})
+	for _, r := range rows {
+		if r.Seat != "the-packet-filter" {
+			continue
+		}
+		if len(r.Holders) != 2 || r.Holders[0].Node != "anchor" || r.Holders[1].Node != "node2" {
+			t.Fatalf("the packet filter is held by %+v", r.Holders)
+		}
+		return
+	}
+	t.Fatal("the packet filter is not listed")
+}
+
+func TestAClaimOutsideTheSetIsShownNotHidden(t *testing.T) {
+	// A manifest registered before the set closed can still hold one. Leaving it out would make
+	// the overview quietly incomplete, which is the one thing it may not be.
+	_, outside := seatsHeld(catalogue.Seats(), []catalogue.Held{
+		{Claim: "the-controller", Scope: catalogue.ScopeMesh, Node: "anchor", Module: "mesh-controller"},
+	})
+	if len(outside) != 1 || outside[0].Claim != "the-controller" {
+		t.Fatalf("a claim outside the set was not shown: %+v", outside)
+	}
+}

cmd/mesh-controller/source.go

@@ -0,0 +1,136 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+)
+
+// where a build's repository is (novox/hq ADR 0111).
+//
+// A repository is on the mesh's own forge, or it is anywhere else. The first is recorded as its path
+// on the forge holding the git seat, and cloned from wherever that forge runs at the moment of
+// building; the second is a URL, recorded and cloned exactly as given. The build machine is not told
+// the difference — it is handed a URL either way — because only the control plane knows where the
+// seat's holder runs.
+
+// gitSeat is the seat a self-hosted repository lives on.
+const gitSeat = "git"
+
+// buildSource is where a build's repository is: a URL, or a path on a seat's holder.
+type buildSource struct {
+	Repository string
+	Seat       string
+}
+
+// String is the source as a person reads it, which for one on a seat is not the URL: the URL is a
+// fact about where the forge happens to run today.
+func (s buildSource) String() string {
+	if s.Seat == "" {
+		return s.Repository
+	}
+	return fmt.Sprintf("%s on the %s seat", s.Repository, s.Seat)
+}
+
+// onASeat refuses an address given as a path on the forge.
+//
+// **A URL here would be recorded as a path**, and then composed onto the forge's address as one —
+// cloning `http://forge:3000/https://github.com/…`. Refused by what an address plainly looks like,
+// not repaired: `--self` promises a path, and something that is not one is a mistake to name.
+func onASeat(repository string) error {
+	if strings.Contains(repository, ":") || strings.HasPrefix(repository, "/") ||
+		strings.Trim(repository, "/") == "" {
+		return fmt.Errorf("--self takes the repository's path on the forge, such as novox/mesh-catalog, "+
+			"and %q is not one — without --self it is built from exactly what is given", repository)
+	}
+	return nil
+}
+
+// cloneFrom is the URL a build machine clones for a source.
+//
+// A URL is itself. A path on a seat is composed from the seat's holder as the mesh sees it now —
+// the same view planning takes of every machine, so the forge a build clones from is the forge the
+// mesh says holds the seat.
+func cloneFrom(ctx context.Context, source buildSource) (string, error) {
+	if source.Seat == "" {
+		return source.Repository, nil
+	}
+	open, err := openStores(ctx)
+	if err != nil {
+		return "", err
+	}
+	defer open.Close()
+	shelf, err := open.inventory.Catalogue(ctx)
+	if err != nil {
+		return "", err
+	}
+	world, err := theRestOfTheMesh(ctx, open.inventory, shelf, "")
+	if err != nil {
+		return "", err
+	}
+	return clonedFromSeat(world, source.Seat, source.Repository)
+}
+
+// clonedFromSeat composes the clone URL for a repository on a seat's holder.
+//
+// **Refused, never defaulted, at every step that has no answer.** Nobody holding the seat is a mesh
+// without a forge of its own: it builds from external repositories and must say so rather than fail
+// to clone. A holder off the private network cannot be reached by any build machine. A holder that
+// serves no scheme or port has nothing to compose from — a default port here would be the forge's
+// address guessed, which is the thing this exists to stop.
+func clonedFromSeat(world catalogue.World, seatName, repository string) (string, error) {
+	seat, known := catalogue.SeatNamed(seatName)
+	if !known || seat.Delivers == "" {
+		return "", fmt.Errorf("%q is not a seat a repository can live on", seatName)
+	}
+	var holder *catalogue.Held
+	for i, h := range world.Held {
+		if h.Claim == seat.Name && h.Scope == seat.Scope {
+			holder = &world.Held[i]
+			break
+		}
+	}
+	if holder == nil {
+		return "", fmt.Errorf("nobody holds the %s seat, so %s cannot be cloned from this mesh's "+
+			"forge — assign a module that claims it, or build from the repository's URL without --self",
+			seat.Name, repository)
+	}
+	var provider *catalogue.Provider
+	for i, p := range world.Offered[seat.Delivers] {
+		if p.Node == holder.Node && p.Module == holder.Module {
+			provider = &world.Offered[seat.Delivers][i]
+		}
+	}
+	if provider == nil {
+		return "", fmt.Errorf("%s on %s holds the %s seat and offers no %q to clone from",
+			holder.Module, holder.Node, seat.Name, seat.Delivers)
+	}
+	if provider.At == "" {
+		return "", fmt.Errorf("%s on %s holds the %s seat and is not on the private network, so no "+
+			"build machine can reach it", holder.Module, holder.Node, seat.Name)
+	}
+	scheme, _ := provider.Serves["scheme"].(string)
+	port := servedPort(provider.Serves["port"])
+	if scheme == "" || port == "" {
+		return "", fmt.Errorf("%s on %s holds the %s seat and does not serve a scheme and a port for %q",
+			holder.Module, holder.Node, seat.Name, seat.Delivers)
+	}
+	path := strings.TrimSuffix(strings.Trim(repository, "/"), ".git")
+	return fmt.Sprintf("%s://%s:%s/%s.git", scheme, provider.At, port, path), nil
+}
+
+// servedPort is a served port as text, however the manifest and the node's settings carried it.
+func servedPort(v any) string {
+	switch p := v.(type) {
+	case float64:
+		return strconv.Itoa(int(p))
+	case int:
+		return strconv.Itoa(p)
+	case string:
+		return p
+	}
+	return ""
+}

cmd/mesh-controller/source_test.go

@@ -0,0 +1,108 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+)
+
+// Defends novox/hq ADR 0111: a build source is on the git seat, or it is external.
+
+func forgeHolding(port any) catalogue.World {
+	return catalogue.World{
+		Held: []catalogue.Held{{Claim: "git", Scope: catalogue.ScopeMesh, Node: "anchor", Module: "gitea"}},
+		Offered: map[string][]catalogue.Provider{"git": {
+			// A second forge that does not hold the seat, so taking the first one found would be wrong.
+			{Node: "archive", At: "archive.internal", Module: "gitea-mirror",
+				Serves: map[string]any{"scheme": "http", "port": float64(3000)}},
+			{Node: "anchor", At: "anchor.internal", Module: "gitea",
+				Serves: map[string]any{"scheme": "http", "port": port}},
+		}},
+	}
+}
+
+func TestARepositoryOnTheSeatIsClonedFromItsHolder(t *testing.T) {
+	got, err := clonedFromSeat(forgeHolding(float64(3000)), "git", "novox/mesh-catalog")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != "http://anchor.internal:3000/novox/mesh-catalog.git" {
+		t.Fatalf("cloned from %s", got)
+	}
+}
+
+func TestAMovedForgeIsFollowedWithoutRewritingAnything(t *testing.T) {
+	// The whole point: the node gave the forge another port, and the same recorded path clones
+	// from the new one. Nothing recorded contained the old one to be wrong.
+	got, err := clonedFromSeat(forgeHolding(float64(3100)), "git", "novox/mesh-catalog")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(got, ":3100/") {
+		t.Fatalf("the moved port was not followed: %s", got)
+	}
+}
+
+func TestWithNobodyHoldingTheSeatASelfHostedBuildIsRefusedAndSaysWhy(t *testing.T) {
+	_, err := clonedFromSeat(catalogue.World{}, "git", "novox/mesh-catalog")
+	if err == nil {
+		t.Fatal("a repository was cloned from a forge the mesh does not have")
+	}
+	for _, want := range []string{"nobody holds the git seat", "without --self"} {
+		if !strings.Contains(err.Error(), want) {
+			t.Fatalf("the refusal does not say %q: %v", want, err)
+		}
+	}
+}
+
+func TestAnExternalRepositoryIsClonedExactlyAsGiven(t *testing.T) {
+	// Unaffected by the seat, held or not: GitHub and GitLab are the ordinary cases.
+	given := "https://github.com/someone/something.git"
+	got, err := cloneFrom(t.Context(), buildSource{Repository: given})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != given {
+		t.Fatalf("an external repository became %s", got)
+	}
+}
+
+func TestAHolderOffThePrivateNetworkIsRefused(t *testing.T) {
+	world := forgeHolding(float64(3000))
+	world.Offered["git"][1].At = ""
+	if _, err := clonedFromSeat(world, "git", "novox/mesh-catalog"); err == nil ||
+		!strings.Contains(err.Error(), "private network") {
+		t.Fatalf("a forge nothing can reach was cloned from: %v", err)
+	}
+}
+
+func TestAHolderServingNoPortIsRefusedRatherThanGuessed(t *testing.T) {
+	// A default port would be the forge's address guessed, which is what this exists to stop.
+	if _, err := clonedFromSeat(forgeHolding(nil), "git", "novox/mesh-catalog"); err == nil {
+		t.Fatal("a port was guessed for a forge that serves none")
+	}
+}
+
+func TestAnAddressGivenAsAPathOnTheForgeIsRefused(t *testing.T) {
+	for _, bad := range []string{
+		"https://github.com/someone/something.git",
+		"git@anchor:novox/mesh-catalog.git",
+		"/srv/git/mesh-catalog",
+		"",
+	} {
+		if err := onASeat(bad); err == nil {
+			t.Errorf("--self accepted %q as a path on the forge", bad)
+		}
+	}
+	if err := onASeat("novox/mesh-catalog"); err != nil {
+		t.Errorf("a path on the forge was refused: %v", err)
+	}
+}
+
+func TestASourceOnTheSeatReadsAsAPathNotAnAddress(t *testing.T) {
+	s := buildSource{Repository: "novox/mesh-catalog", Seat: "git"}
+	if got := s.String(); got != "novox/mesh-catalog on the git seat" {
+		t.Fatalf("read as %q", got)
+	}
+}